Difference between revisions of "Detailed Fire Modeling (Task 11)"

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[[File:EnclosureDynamics.png|800px||right]]
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[[File:EnclosureDynamics.png|700px||right]] __TOC__
 
==Task Overview==
 
==Task Overview==
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+
 
===Background===
 
===Background===
−
This task describes the method to examine the consequences of a fire. This includes consideration of scenarios involving single compartments, multiple fire compartments, and the main control room. Factors considered include initial fire characteristics, fire growth in a fire compartment or across fire compartments, detection and suppression, electrical raceway fire barrier systems, and damage from heat and smoke. Special consideration is given to turbine generator (T/G) fires, hydrogen fires, high-energy arcing faults, cable fires, and main control board (MCB) fires. There are considerable improvements in the method for this task over the [https://www.epri.com/#/pages/product/TR-100370/ EPRI FIVE] and EPRI's Fire PRA Implementation Guide (TR-105928, no longer available on epri.com) in nearly all technical areas.
+
This task describes the method to examine the consequences of a fire. This includes consideration of scenarios involving single compartments, multiple fire compartments, and the main control room. Factors considered include initial fire characteristics, fire growth in a fire compartment or across fire compartments, detection and suppression, electrical raceway fire barrier systems, and damage from heat and smoke. Special consideration is given to turbine generator (T/G) fires, hydrogen fires, high-energy arcing faults, cable fires, and main control board (MCB) fires. There are considerable improvements in the method for this task over the [https://www.epri.com/#/pages/product/TR-100370/ EPRI FIVE] and EPRI's Fire PRA Implementation Guide (TR‑105928, no longer available on epri.com) in nearly all technical areas.
  
 
===Purpose===
 
===Purpose===
−
In the preceding tasks, the analyses were organized around compartments, assuming that a fire would have widespread impact within the compartment. In Task 11, for those compartments found to be potentially risk-significant (i.e., unscreened compartments), a detailed analysis approach is provided. As part of the detailed analysis, fire growth and propagation is modeled and possibility of fire suppression before damage to a specific target set is analyzed.  
+
In the preceding tasks, the analyses were organized around compartments, assuming that a fire would have widespread impact within the compartment. In Task 11, for those compartments found to be potentially risk-significant (i.e., unscreened compartments), a detailed analysis approach is provided. As part of the detailed analysis, fire growth and propagation is modeled and possibility of fire suppression before damage to a specific target set is analyzed.  
  
−
The detailed fire modeling process generally follows a common step structure, but the details of the analyses often vary depending on the specifics of the postulated fire scenario. This task provides separate procedures for three general categories of fire scenarios: fires affecting target sets located inside one compartment (discussed in Section 11.5.1); fires affecting the main control room (MCR; Section 11.5.2); and fires affecting target sets located in more than one fire compartment (multicompartment fire analysis; Section 11.5.3).  
+
The detailed fire modeling process generally follows a common step structure, but the details of the analyses often vary depending on the specifics of the postulated fire scenario. This task provides separate procedures for three general categories of fire scenarios: fires affecting target sets located inside one compartment (discussed in Section 11.5.1); fires affecting the main control room (MCR; Section 11.5.2); and fires affecting target sets located in more than one fire compartment (multicompartment fire analysis; Section 11.5.3).  
  
−
Task 11 provides final estimates for the frequency of occurrence of fire scenarios involving a specific fire ignition source failing a predefined target set before fire protection succeeds in protecting the target set. This result is combined in the final quantification steps that follow this task, with the CCDP/CLERP given failure of the target set to estimate the CDF/LERF contribution for each fire scenario. The CCDP/CLERP may include modified human error probabilities based on fire scenario specifics.
+
Task 11 provides final estimates for the frequency of occurrence of fire scenarios involving a specific fire ignition source failing a predefined target set before fire protection succeeds in protecting the target set. This result is combined in the final quantification steps that follow this task, with the CCDP/CLERP given failure of the target set to estimate the CDF/LERF contribution for each fire scenario. The CCDP/CLERP may include modified human error probabilities based on fire scenario specifics.
  
 
===Scope===
 
===Scope===
 
Detailed fire modeling encompasses an analysis of the physical fire behavior (i.e., fire growth and propagation analysis), equipment damage, fire detection, and fire suppression. The fire scenarios to analyze as part of this detailed analysis task are divided into three categories:  
 
Detailed fire modeling encompasses an analysis of the physical fire behavior (i.e., fire growth and propagation analysis), equipment damage, fire detection, and fire suppression. The fire scenarios to analyze as part of this detailed analysis task are divided into three categories:  
  
−
* ''General single compartment fire scenarios''. This general category covers fire scenarios damaging target sets located within the same compartment, exclusive of those scenarios within or impacting the MCR. In general, in this category, the fire ignition source is in the same compartment as the target set. The majority of fire scenarios analyzed generally falls into this category. The procedures applicable to the analysis of these fire scenarios are presented in Section 11.5.1.  
+
* ''General single compartment fire scenarios''. This general category covers fire scenarios damaging target sets located within the same compartment, exclusive of those scenarios within or impacting the MCR. In general, in this category, the fire ignition source is in the same compartment as the target set. The majority of fire scenarios analyzed generally falls into this category. The procedures applicable to the analysis of these fire scenarios are presented in Section 11.5.1.  
−
* ''MCR fire scenarios''. This general category covers all fires that occur within the MCR. This category also covers scenarios involving fires in compartments other than the MCR that may force MCR abandonment. The MCR analysis procedures are presented in Section 11.5.2.  
+
* ''MCR fire scenarios''. This general category covers all fires that occur within the MCR. This category also covers scenarios involving fires in compartments other than the MCR that may force MCR abandonment. The MCR analysis procedures are presented in Section 11.5.2.  
−
* ''Multicompartment fire scenarios'': This general category covers all fire scenarios where it is postulated that a fire may spread from one compartment to another and damage target elements in multiple compartments. In this category of scenarios, damaging effects of a fire (e.g., heat) are assumed to spread beyond the compartment of fire origin. The multicompartment fire analysis procedures are presented in Section 11.5.3.  
+
* ''Multicompartment fire scenarios'': This general category covers all fire scenarios where it is postulated that a fire may spread from one compartment to another and damage target elements in multiple compartments. In this category of scenarios, damaging effects of a fire (e.g., heat) are assumed to spread beyond the compartment of fire origin. The multicompartment fire analysis procedures are presented in Section 11.5.3.  
  
−
A detailed fire modeling analysis is performed for each fire scenario in each unscreened fire compartment. For many compartments, it may be appropriate to develop several fire scenarios to appropriately represent the range of unscreened fire ignition sources (i.e., scenarios that would not screen out in Task 8) that might contribute to the fire risk. Detailed fire modeling may utilize a range of tools to assess fire growth and damage behavior, and the fire detection and suppression response, for specific fire scenarios.  
+
A detailed fire modeling analysis is performed for each fire scenario in each unscreened fire compartment. For many compartments, it may be appropriate to develop several fire scenarios to appropriately represent the range of unscreened fire ignition sources (i.e., scenarios that would not screen out in Task 8) that might contribute to the fire risk. Detailed fire modeling may utilize a range of tools to assess fire growth and damage behavior, and the fire detection and suppression response, for specific fire scenarios.  
  
 
[[File:ScreeningDetailed.png|900px||center]]
 
[[File:ScreeningDetailed.png|900px||center]]
  
−
The ultimate output of Task 11 is a set of fire scenarios, frequency of occurrence of those scenarios, and a list of target sets (in terms of fire PRA components) associated with the scenarios. For scenarios involving the MCR, the possibility of forced abandonment is also  noted. Note that a fire scenario represents a specific chain of events starting with ignition of a fire ignition source, propagation of the fire effects to other items, and possibility of damaging a set of items identified as target set before successful fire suppression.
+
The ultimate output of Task 11 is a set of fire scenarios, frequency of occurrence of those scenarios, and a list of target sets (in terms of fire PRA components) associated with the scenarios. For scenarios involving the MCR, the possibility of forced abandonment is also  noted. Note that a fire scenario represents a specific chain of events starting with ignition of a fire ignition source, propagation of the fire effects to other items, and possibility of damaging a set of items identified as a target set before successful fire suppression.
  
 
==Related Element of ASME/ANS PRA Standard==
 
==Related Element of ASME/ANS PRA Standard==
 
Fire Scenario Selection (FSS)
 
Fire Scenario Selection (FSS)
  
−
==Related EPRI 1011989 NUREG/CR-6850 Appendices==
+
==Related EPRI 1011989 NUREG/CR‑6850 Appendices==
−
Appendix E, Appendix for Chapters 8 and 11, Severity Factors
+
Appendix E, Appendix for Chapters 8 and 11, Severity Factors
  
−
Appendix F, Appendix for Chapter 8, Walkdown Forms
+
Appendix F, Appendix for Chapter 8, Walkdown Forms
  
−
Appendix G, Appendix for Chapters 8 and 11, Heat Release Rates
+
Appendix G, Appendix for Chapters 8 and 11, Heat Release Rates
  
−
Appendix H, Appendix for Chapters 8 and 11, Damage Criteria
+
Appendix H, Appendix for Chapters 8 and 11, Damage Criteria
  
−
Appendix L, Appendix for Chapter 11, Main Control Board Fires
+
Appendix L, Appendix for Chapter 11, Main Control Board Fires
  
−
Appendix M, Appendix for Chapter 11, High Energy Arcing Faults
+
Appendix M, Appendix for Chapter 11, High Energy Arcing Faults
  
−
Appendix N, Appendix for Chapter 11, Hydrogen Fires
+
Appendix N, Appendix for Chapter 11, Hydrogen Fires
  
−
Appendix O, Appendix for Chapter 11, Turbine Generator Fires
+
Appendix O, Appendix for Chapter 11, Turbine Generator Fires
  
−
Appendix P, Appendix for Chapter 11, Detection And Suppression Analysis
+
Appendix P, Appendix for Chapter 11, Detection and Suppression Analysis
  
−
Appendix Q, Appendix for Chapter 11, Passive Fire Protection Features
+
Appendix Q, Appendix for Chapter 11, Passive Fire Protection Features
  
−
Appendix R, Appendix for Chapter 11, Cable Fires
+
Appendix R, Appendix for Chapter 11, Cable Fires
  
−
Appendix S, Appendix for Chapter 11, Fire Propagation To Adjacent Cabinets
+
Appendix S, Appendix for Chapter 11, Fire Propagation to Adjacent Cabinets
  
−
Appendix T, Appendix for Chapter 11, Smoke Damage
+
Appendix T, Appendix for Chapter 11, Smoke Damage
  
 
==Fire Modeling Tools==
 
==Fire Modeling Tools==
  
−
Fire modeling tools include a range of complexity, from Excel-based tools which rely on physics-based algebraic relationships such as EPRI FIVE and the NRC FDTs, to moderately complex tools such as CFAST's two-zone computational model, up to the most complex (and computationally-demanding) finite element analysis tools such as FDS.
+
Fire modeling tools include a range of complexity, from Excel-based tools which rely on physics-based algebraic relationships such as EPRI FIVE and the NRC FDT<sup>s</sup>, to moderately complex tools such as CFAST's two-zone computational model, up to the most complex (and computationally-demanding) finite element analysis tools such as FDS.
  
 
===Fire Model Verification and Validation===
 
===Fire Model Verification and Validation===
  
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1824/ NUREG-1824 EPRI 1011999] documents the verification and validation (V&V) of five fire models that are commonly used in NPP applications. The models in the V&V report include:
+
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1824/ NUREG&#8209;1824 EPRI&nbsp;1011999] documents the verification and validation (V&V) of five fire models that are commonly used in NPP applications. The models in the V&V report include:
−
*NRC's NUREG-1805 Revision 1
+
*NRC's NUREG&#8209;1805 Revision&nbsp;1
−
*EPRI's Fire-Induced Vulnerability Evaluation Revision 1 (FIVE-REV 1)
+
*EPRI's Fire-Induced Vulnerability Evaluation Revision&nbsp;1 (FIVE-REV 1)
 
*National Institute of Standards and Technology's (NIST) Consolidated Model of Fire Growth and Smoke Transport (CFAST) Version 5
 
*National Institute of Standards and Technology's (NIST) Consolidated Model of Fire Growth and Smoke Transport (CFAST) Version 5
 
*NIST's Fire Dynamics Simulator (FDS) Version 4
 
*NIST's Fire Dynamics Simulator (FDS) Version 4
 
*Electricite de France's (EdF) MAGIC Version 4.1.1
 
*Electricite de France's (EdF) MAGIC Version 4.1.1
  
−
[https://www.epri.com/#/pages/product/000000003002002182/?lang=en-US NUREG-1824 Supplement 1 EPRI 3002002182] updates the original NUREG-1824 / EPRI 1011999 report with additional experiments and uses the latest versions of the fire modeling software available at the time of publication. The models in the V&V report include:
+
[https://www.epri.com/#/pages/product/000000003002002182/?lang=en-US NUREG&#8209;1824 Supplement&nbsp;1 EPRI&nbsp;3002002182] updates the original NUREG&#8209;1824 / EPRI&nbsp;1011999 report with additional experiments and uses the latest versions of the fire modeling software available at the time of publication. The models in the V&V report include:
−
*NRC's Fire Dynamics Tools (FDTs Version 1805.1)
+
*NRC's Fire Dynamics Tools (FDT<sup>s</sup> Version 1805.1)
−
*EPRI's Fire-Induced Vulnerability Evaluation (FIVE Rev. 2)
+
*EPRI's Fire-Induced Vulnerability Evaluation (FIVE Revision&nbsp;2)
 
*NIST's CFAST Version 7.0.0
 
*NIST's CFAST Version 7.0.0
 
*EdF's MAGIC Version 4.1.3
 
*EdF's MAGIC Version 4.1.3
Line 76: Line 76:
  
 
===Fire Models Included in V&V Guidance===
 
===Fire Models Included in V&V Guidance===
−
[https://www.epri.com/#/pages/product/000000003002000830/?lang=en-US EPRI FIVE]
+
EPRI FIVE
  
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1805/ NRC Fire Dynamics Tools - NUREG-1805]
+
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1805/ NRC Fire Dynamics Tools - NUREG&#8209;1805]
  
 
[https://www.nist.gov/el/fire-research-division-73300/product-services/consolidated-fire-and-smoke-transport-model-cfast NIST CFAST]
 
[https://www.nist.gov/el/fire-research-division-73300/product-services/consolidated-fire-and-smoke-transport-model-cfast NIST CFAST]
Line 88: Line 88:
 
===Fire Model User's Guide===
 
===Fire Model User's Guide===
  
−
[https://www.epri.com/#/pages/product/000000000001023259/?lang=en-US NUREG-1934 EPRI 1023259] provides guidance on the proper application of fire models to nuclear power plant fire scenarios. Eight (8) different example fire scenarios are developed and discussed in this report.
+
[https://www.epri.com/#/pages/product/000000000001023259/?lang=en-US NUREG&#8209;1934 EPRI&nbsp;1023259] provides guidance on the proper application of fire models to nuclear power plant fire scenarios. Eight (8) different example fire scenarios are developed and discussed in this report.
  
 
==Ignition Source Specific Fire Modeling Guidance==
 
==Ignition Source Specific Fire Modeling Guidance==
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| Battery Room
 
| Battery Room
 
| Batteries
 
| Batteries
−
| Use HRR distribution for Electric Motors (Case 7 of Table G-1)
+
| Use HRR distribution for Motors (Distribution 7 of Table G-1)
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 2
 
| 2
 
| Containment (PWR)
 
| Containment (PWR)
−
| Reactor Coolant Pump
+
| Reactor Coolant Pumps
−
| For electrical fires: Pumps (electrical fires) HRR distributions and fire durations are provided in Chapter 5 of NUREG-2178, Vol. 2 / EPRI 3002016052.
+
| Reactor coolant pump fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR&#8209;6850 (0.14 electrical / 0.86 oil).
−
For oil fires: See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. 
 
−
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
 
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 
  
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
'''Electrical (motor) fires: ''' HRR distributions and fire durations are provided in Chapter&nbsp;5 of NUREG&#8209;2178, Volume&nbsp;2 / EPRI&nbsp;3002016052. The pump HRR in NUREG/CR&#8209;6850 is bounding compared with the updated values, and is therefore still valid.
 +
 
 +
'''Oil fire split fractions:''' The oil spill size fractions recommended in NUREG/CR&#8209;6850 Appendix E.3 should be applied.
 +
 
 +
'''Oil fire HRR:''' See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. 
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 +
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
 
 +
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 3
 
| 3
 
| Containment (PWR)
 
| Containment (PWR)
 
| Transients and Hotwork
 
| Transients and Hotwork
−
| ''Prior Guidance''
+
| <div id="FMBin3"></div>NUREG&#8209;2233 / EPRI&nbsp;3002018231 provides updated HRR distributions and zones of influence for generic transient fires and also transient combustible control locations (TCCLs). These HRRs are based upon the laboratory testing conducted by EPRI and the NRC on relevant transient ignition sources expected in nuclear power plants (see EPRI&nbsp;3002015997 / NUREG&#8209;2232). The HRR distribution (Distribution&nbsp;8 of Table&nbsp;G&#8209;1 in NUREG/CR&#8209;6850) is bounding compared with the updated generic HRR distribution, and is therefore still valid.
−
For HRR: Transient Combustible HRR Distribution (Case 8 of Table G-1)
 
−
 
 
−
While NUREG/CR-6850 (EPRI 1011989) provides a value for a default transient fire heat release rate (HRR) distribution and guidance for addressing plant specific locations not bounded by the default HRR, it does not provide guidance on the use of a lower HRR for plant specific locations where the lower HRR can be justified. See the methods panel links for additional information on using HRRs other than the one prescribed in NUREG/CR-6850 Table G-1.
 
−
 
 
−
For transient growth rates: See Section 17 of Supplement 1 (FAQ 08-0052)
 
−
 
 
−
 
 
−
 
 
−
''New Guidance (2019/2020)''
 
  
−
EPRI 3002015997 provides the data and results from an experimental program (based on laboratory testing) to obtain more relevant data for expected nuclear power plant transient fire events.
+
NUREG&#8209;2233 / EPRI&nbsp;3002018231 also recommends fire modeling parameters including fire growth and decay parameters,  yields of minor products of combustion, heat of combustion, and the physical size and effective elevation of the fire.
  
−
The results from the testing effort served as a primary input to develop more realistic data to analyze transient fire risk. NUREG-2233 / EPRI 3002018231 develops new distributions of peak heat release rate, total energy release, and zones of influence for transient fires. Additionally, NUREG-2233 / EPRI 3002018231 recommends input values for the detailed fire modeling of transient fires that include fire growth and decay parameters, yields of minor products of combustion, heat of combustion, and the physical size and effective elevation of the fire.
+
| [https://www.epri.com/#/pages/product/3002018231/ NUREG&#8209;2233 / EPRI&nbsp;3002018231]
  
−
| [https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6850/s1/cr6850s1.pdf EPRI 1011989 / NUREG/CR-6850]
+
[https://www.epri.com/#/pages/product/3002015997/ NUREG&#8209;2232 / EPRI&nbsp;3002015997]
  
−
[https://www.nrc.gov/docs/ML1217/ML12171A583.pdf Methods Panel Review Decisions]
+
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6850/s1/cr6850s1.pdf NUREG/CR&#8209;6850 / EPRI&nbsp;1011989]
−
 
 
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6850/s1/cr6850s1.pdf FAQ 08-0052, Section 17 of Supplement 1]
 
−
 
 
−
[https://epri.box.com/s/ni3hxahnm13m0j29whf3bcixl7310s1v Description of Treatment for Transient Fires (NRC Recent Fire PRA Methods Review Panel Decisions - Attachment 1)]
 
−
 
 
−
[https://epri.box.com/s/f9n4opxd69xfgopbkt4fcf44rlqupdux Fire PRA Methods Review Panel Membership (NRC Recent Fire PRA Methods Review Panel Decisions - Attachment 2)]
 
−
 
 
−
[https://epri.box.com/s/nt808eiznbw7c4a5lzye1v4yw1f2wwtt Panel Decision (NRC Recent Fire PRA Methods Review Panel Decisions - Attachment 3)]
 
−
 
 
−
[https://www.epri.com/#/pages/product/3002015997/ EPRI 3002015997]
 
−
 
 
−
[https://www.epri.com/#/pages/product/3002016054/ NUREG-2233 / EPRI 3002018231]
 
  
 
|-
 
|-
Line 154: Line 138:
 
| Control Room
 
| Control Room
 
| Main Control Board
 
| Main Control Board
−
| '''Target damage:''' Appendix L of NUREG/CR-6850 provides a statistical model for estimating the conditional probability of damage to a set of target items inside the main control board.*
+
| '''Target damage:''' Appendix&nbsp;L of NUREG/CR&#8209;6850 provides a statistical model for estimating the conditional probability of damage to a set of target items inside the main control board.<sup>&nbsp;&sect;</sup>
  
−
'''Target damage:''' NUREG-2178 Volume 2 / EPRI 3002016052 Section 7 provides an alternative to the method described in Appendix L of NUREG/CR-6850 for evaluating the risk of fire events originating in the MCB, whereby MCB fire scenarios are modeled as a progression of damage states using an event tree model.* In this formulation, each damage state requires the definition of a target set, which consists of one or more MCB functions that can be damaged by fire. The functions within the scope of this analysis are those that are represented with basic events in the plant response model and supported with cables routed within the MCB. The alternative model described in this guidance explicitly incorporates two characteristics of MCB fires observed in operating experience—relatively small fires in low-voltage panels and the ability for prompt detection and suppression by control room operators. Operating experience suggests that the majority of fires in the MCB are limited to a single subcomponent or group of subcomponents near the point of ignition. In addition, these fires are promptly detected and suppressed by control room operators. Therefore, the event tree model explicitly accounts for the operator’s ability to quickly detect and suppress the fire before growth and/or propagation.
+
'''Target damage:''' NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 Section&nbsp;7 provides an alternative to the method described in Appendix&nbsp;L of NUREG/CR&#8209;6850 for evaluating the risk of fire events originating in the MCB, whereby MCB fire scenarios are modeled as a progression of damage states using an event tree model.<sup>&nbsp;&sect;</sup> In this formulation, each damage state requires the definition of a target set, which consists of one or more MCB functions that can be damaged by fire. The functions within the scope of this analysis are those that are represented with basic events in the plant response model and supported with cables routed within the MCB. The alternative model described in this guidance explicitly incorporates two characteristics of MCB fires observed in operating experience—relatively small fires in low-voltage panels and the ability for prompt detection and suppression by control room operators. Operating experience suggests that the majority of fires in the MCB are limited to a single subcomponent or group of subcomponents near the point of ignition. In addition, these fires are promptly detected and suppressed by control room operators. Therefore, the event tree model explicitly accounts for the operator’s ability to quickly detect and suppress the fire before growth and/or propagation.
−
* ''The original NUREG/CR-6850 Appendix L method and also NUREG-2178 Vol. 2 event tree method BOTH remain viable as methods for assessing MCB fires.''
+
<div style="font-size:88%; margin-right: 3em; margin-left: 4em; text-indent: -1em;">&sect;&nbsp;''The original NUREG/CR&#8209;6850 Appendix&nbsp;L method and NUREG&#8209;2178 Volume&nbsp;2 event tree method BOTH remain viable as methods for assessing MCB fires.''</div>
  
−
'''HRR distributions:''' NUREG-2178 Volume 1 / EPRI 3002005578 provides updated HRR distributions for the main control board based on control cabinet size (either Function Group 4a (Large Enclosures) or Group 4b (Medium Enclosures).
+
'''HRR distributions:''' NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578 provides updated HRR distributions for the main control board based on control cabinet size (either Function Group 4a (Large Enclosures) or Group 4b (Medium Enclosures)).
  
−
'''Propagation to adjacent:'''  NUREG-2178 Volume 2 / EPRI 3002016052 Section 4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.
+
'''Propagation to adjacent cabinet:'''  NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 Section&nbsp;4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.
−
| [https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG-2178 Vol 1 / EPRI 3002005578]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
[https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578]
  
−
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 
|-
 
|-
 
| 5
 
| 5
 
| Control/Aux/Reactor Building
 
| Control/Aux/Reactor Building
 
| Cable fires caused by welding and cutting
 
| Cable fires caused by welding and cutting
−
| FAQ 13-0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR-6850. However, the current method of evaluating cable fire risk in NUREG/CR-6850 remains an acceptable approach.  
+
| FAQ&nbsp;13&#8209;0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section&nbsp;R.1 of NUREG/CR&#8209;6850. However, the current method of evaluating cable fire risk in NUREG/CR&#8209;6850 remains an acceptable approach.  
−
|[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
|[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ 13-0005]
+
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ&nbsp;13&#8209;0005]
 
|-
 
|-
 
| 6
 
| 6
 
| Control/Aux/Reactor Building
 
| Control/Aux/Reactor Building
 
| Transient fires caused by welding and cutting
 
| Transient fires caused by welding and cutting
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|-
 
|-
 
| 7
 
| 7
 
| Control/Aux/Reactor Building
 
| Control/Aux/Reactor Building
 
| Transients
 
| Transients
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|-
 
|-
 
| 8
 
| 8
 
| Diesel Generator Room
 
| Diesel Generator Room
 
| Diesel Generators
 
| Diesel Generators
−
| For electrical fires: Use HRR distribution for Electric Motors (Case 7 of Table G-1)
+
| There is limited guidance on modeling diesel generator fires in NUREG/CR-6850:
−
For oil fires: See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.  
+
* Diesel generator fires have an electrical (motor) component and an oil component.  The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.16 electrical / 0.84 oil).
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
* Section&nbsp;G.4 of NUREG/CR&#8209;6850 provides guidance on flammable liquid (oil) fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 9
 
| 9
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Air Compressors
 
| Air Compressors
−
| For electrical fires: HRR distributions and fire durations are provided in Chapter 5 of NUREG-2178, Vol. 2 / EPRI 3002016052.
+
| Air compressor fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR&#8209;6850 (0.83 electrical / 0.17 oil).
−
For oil fires: See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.
+
 
−
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
'''Electrical (motor) fires: ''' HRR distributions and fire durations are provided in Chapter&nbsp;5 of NUREG&#8209;2178, Volume&nbsp;2 / EPRI&nbsp;3002016052.
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 
  
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
'''Oil fire split fractions:''' The oil spill size fractions recommended in NUREG/CR&#8209;6850 Appendix E.3 should be applied.
 +
 
 +
'''Oil fire HRR:''' See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. 
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 +
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
 
 +
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 10
 
| 10
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Battery Chargers
 
| Battery Chargers
−
| HRR Distribution for Classification Group 2, MCCs and Battery Chargers
+
| Table&nbsp;7&#8209;1 of NUREG&#8209;2178 Volume&nbsp;1 provides HRR distributions for Group 2 electrical enclosures, including battery chargers.
−
| [https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG-2178 Vol 1 / EPRI 3002005578]
+
| [https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578]
 
|-
 
|-
 
| 11
 
| 11
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Cable fires caused by welding and cutting
 
| Cable fires caused by welding and cutting
−
| FAQ 13-0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR-6850. However, the current method of evaluating cable fire risk in NUREG/CR-6850 remains an acceptable approach.  
+
| FAQ&nbsp;13&#8209;0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section&nbsp;R.1 of NUREG/CR&#8209;6850. However, the current method of evaluating cable fire risk in NUREG/CR&#8209;6850 remains an acceptable approach.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ 13-0005]
+
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ&nbsp;13&#8209;0005]
 
|-
 
|-
 
| 12
 
| 12
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Cable Run (self-ignited cable fires)
 
| Cable Run (self-ignited cable fires)
−
| FAQ 13-0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR-6850. However, the current method of evaluating cable fire risk in NUREG/CR-6850 remains an acceptable approach.  
+
| FAQ&nbsp;13&#8209;0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section&nbsp;R.1 of NUREG/CR&#8209;6850. However, the current method of evaluating cable fire risk in NUREG/CR&#8209;6850 remains an acceptable approach.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ 13-0005]
+
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ&nbsp;13&#8209;0005]
 
|-
 
|-
 
| 13
 
| 13
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Dryers
 
| Dryers
−
| Transient Combustible HRR Distribution (Case 8 of Table G-1)
+
| The transient HRR is recommended for Bin&nbsp;13 dryer fires (refer to Table&nbsp;11&#8209;1 of NUREG/CR&#8209;6850). NUREG&#8209;2233 / EPRI&nbsp;3002018231 provides updated HRR distribution and zones of influence for generic transient fires (see also [[#FMBin3|Bin&nbsp;3]]).
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
 
 +
| [https://www.epri.com/#/pages/product/3002018231/ NUREG&#8209;2233 / EPRI&nbsp;3002018231]
 +
 
 +
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6850/s1/cr6850s1.pdf NUREG/CR&#8209;6850 / EPRI&nbsp;1011989]
 
|-
 
|-
 
| 14
 
| 14
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Electric Motors
 
| Electric Motors
−
| NUREG-2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG-6850 Table G-1) by horsepower, as well as growth and decay timing.
+
| <div id="FMBin14"></div>Chapter&nbsp;5 of NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG/CR&#8209;6850 Table G-1). To improve realism, the HRRs in NUREG&#8209;2178 Volume&nbsp;2 are characterized by horsepower, and NUREG&#8209;2178 Volume&nbsp;2 also provides growth and decay timing.
−
|  [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
|  [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 
|-
 
|-
 
| 15
 
| 15
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Electrical Cabinets
 
| Electrical Cabinets
−
| '''Propagation from electrical cabinets: ''' FAQ 08-0042 (Section 8 of Supplement 1) clarifies the treatment of fire spread beyond the ignition source for electrical cabinets considering conditions such as the presence of ventilation, robust door construction, and seal penetration. This clarification was needed due to conflicting language in Chapters 6 and 11 and Appendix G of NUREG/CR-6850FAQ 08-0042 states that the wording in Chapter 11 is correct.
+
| <div id="FmBin15">'''Propagation from electrical cabinets: ''' FAQ&nbsp;08&#8209;0042 (Section&nbsp;8 of Supplement&nbsp;1) clarifies the treatment of fire spread beyond the ignition source for electrical cabinets considering conditions such as the presence of ventilation, robust door construction, and seal penetration. This clarification was needed due to conflicting language in Chapters 6 and 11 and Appendix&nbsp;G of NUREG/CR&#8209;6850. FAQ&nbsp;08&#8209;0042 states that the wording in Chapter&nbsp;11 is correct.
  
−
'''Propagation to adjacent: ''' NUREG-2178 Volume 2 / EPRI 3002016052 Section 4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.
+
'''Propagation to adjacent cabinet: ''' NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 Section&nbsp;4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.
  
−
'''Propagation for Well-Sealed MCCs Greater Than 440V:''' FAQ 14-0009 provides clarification for the treatment of fire propagation from well-sealed MCCs operating at greater than 440V.
+
'''Propagation for Well-Sealed MCCs Greater Than 440V:''' FAQ&nbsp;14&#8209;0009 provides clarification for the treatment of fire propagation from well-sealed MCCs operating at greater than 440V.
  
−
'''Heat Release Rates: ''' NUREG-2178 Volume 1 / EPRI 3002005578 provides updated heat release distributions for electrical enclosures. The analyst should review the equipment function or size to determine an appropriate heat release rate distribution provided in Table 7-1. Heat release rates for electrical cabinets are also found in Table G-1 of EPRI 1011989 / NUREG/CR-6850.
+
'''Heat Release Rates: ''' NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578 provides updated heat release distributions for electrical enclosures. The analyst should review the equipment function or size to determine an appropriate heat release rate distribution provided in Table 7-1. Heat release rates for electrical cabinets are also found in Table G-1 of EPRI&nbsp;1011989 / NUREG/CR&#8209;6850.
  
−
'''Fire location: ''' FAQ 08-0043 clarifies the treatment of fire location in electrical cabinets.  
+
'''Fire location: ''' FAQ&nbsp;08&#8209;0043 clarifies the treatment of fire location in electrical cabinets.  
  
−
'''Fire diameter: ''' NUREG-2178 Volume 1 / EPRI 3002005578 Section 4.2 provides guidance on the selection of an appropriate fire diameter.  
+
'''Fire diameter: ''' NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578 Section&nbsp;4.2 provides guidance on the selection of an appropriate fire diameter.  
  
−
'''Obstructed plume model: ''' NUREG-2178 Volume 1 / EPRI 3002005578 Section 6 provides a method to account for the impact of the enclosure on the vertical thermal zone of influence above the enclosure during a fire. A summary of the obstructed plume methodology and the results can be found [https://firepra.epri.com/index.php?title=Obstructed_Plume here].
+
'''Obstructed plume model: ''' NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578 Section&nbsp;6 provides a method to account for the impact of the enclosure on the vertical thermal zone of influence above the enclosure during a fire. A summary of the obstructed plume methodology and the results can be found [https://firepra.epri.com/index.php?title=Obstructed_Plume here].
  
−
'''Obstructed radiation model: ''' NUREG-2178 Volume 2 / EPRI 3002016052 Section 3 provides a method to account for the impact of the enclosure on the horizontal (radial) zone of influence surrounding the enclosure during a fire. This report establishes values for the ZOI measured from the cabinet face
+
'''Obstructed radiation model: ''' NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 Section&nbsp;3 provides a method to account for the impact of the enclosure on the horizontal (radial) zone of influence surrounding the enclosure during a fire. This report establishes values for the ZOI measured from the cabinet face
 
as a function of the cabinet type, cable type, fuel loading, and fire size.
 
as a function of the cabinet type, cable type, fuel loading, and fire size.
  
−
'''Growth and suppression: ''' NUREG-2230 / EPRI 3002016051 significantly improves the realism of modeling electrical cabinet fires, presenting a revised set of parameters that addresses both the fire growth and the suppression response. The set of electrical cabinet fire events was classified into either a growing or interruptible fire categorization. Interruptible fires are those that have observed ignition but no significant growth for a period of time. Growing fires, on the other hand, experience growth immediately after ignition. Furthermore, the detection-suppression event tree has been updated to better allow for early plant personnel suppression actions. Additional manual non-suppression bins have been added to better reflect the scenario characteristics.
+
'''Growth and suppression: ''' NUREG&#8209;2230 / EPRI&nbsp;3002016051 includes the following updates:
 +
:1) Updated fire ignition frequency ([[Fire Ignition Frequency (Task 6)#IgnBin15|Task&nbsp;6]])
 +
:2) Classification of electrical cabinet fires into one of two profiles:
 +
::::{| class="wikitable" style="line-height:110%"
 +
|-
 +
| Interruptible fires
 +
| 0.723
 +
|-
 +
| Growing fires
 +
| 0.277
 +
|}
 +
:3) HRR timing for interruptible and growing fires:
 +
:::<p style="line-height:110%; margin-left: 2em; text-indent:-2em">Interruptible fires – Option&nbsp;1:</p>
 +
::::{| class="wikitable"
 +
| Pre-growth (negligible HRR)
 +
| 9 minutes
 +
|-
 +
| Growth
 +
| 7 minutes
 +
|-
 +
| Steady state
 +
| 5 minutes
 +
|-
 +
| Decay
 +
| 13 minutes
 +
|}
 +
:::<p style="line-height:110%; margin-left: 2em; text-indent:-2em">Interruptible fires – Option&nbsp;2:<br>(NUREG/CR&#8209;6850 timing profile supplemented with pre-growth period)</p>
 +
::::{| class="wikitable"
 +
| Pre-growth (negligible HRR)
 +
| 4 minutes
 +
|-
 +
| Growth
 +
| 12 minutes
 +
|-
 +
| Steady state
 +
| 8 minutes
 +
|-
 +
| Decay
 +
| 19 minutes
 +
|}
 +
:::<p style="line-height:110%; margin-left: 2em; text-indent:-2em">Growing fires:<br>&emsp;(unchanged from NUREG/CR&#8209;6850)</p>
 +
::::{| class="wikitable"
 +
| Growth
 +
| 12 minutes
 +
|-
 +
| Steady state
 +
| 8 minutes
 +
|-
 +
| Decay
 +
| 19 minutes
 +
|}
 +
:4) Changes to the detection-suppression event tree to better represent the operating experience.  
 +
:The detection-suppression event tree was revised to better represent the manual suppression outcomes observed in operating experience (including the development of two new manual suppression curves). See EPRI&nbsp;3002016051 / NUREG&#8209;2230 for full details.
  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
  
−
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 08-0042, Section 8 of Supplement 1]
+
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ&nbsp;08&#8209;0042, Section&nbsp;8 of Supplement&nbsp;1]
  
−
[https://www.nrc.gov/docs/ML1511/ML15119A176.html FAQ 14-0009]
+
[https://www.nrc.gov/docs/ML1511/ML15119A176.html FAQ&nbsp;14&#8209;0009]
  
−
[https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG-2178 Vol 1 / EPRI 3002005578]
+
[https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578]
  
−
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 08-0043, Section 12 of Supplement 1]
+
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ&nbsp;08&#8209;0043, Section&nbsp;12 of Supplement&nbsp;1]
  
−
[https://www.epri.com/#/pages/product/000000003002016051/ NUREG-2230 / EPRI 3002016051]
+
[https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230 / EPRI&nbsp;3002016051]
  
−
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
  
 
|-
 
|-
Line 276: Line 321:
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V)
 
| High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V)
−
| Appendix M (M.4.2) provides an empirical model for determination of the ZOI from HEAFsHigh Energy Arcing Faults (HEAFs).
+
| Appendix&nbsp;M (M.4.2) provides an empirical model for determination of the ZOI from High Energy Arcing Faults (HEAFs).
−
Additional research is on-going ([[#High Energy Arcing Fault (HEAF) Research|HEAF Research]]).
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 
 
|-
 
|-
 
| 16.b
 
| 16.b
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V)
 
| High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V)
−
| Appendix M (M.4.2) provides an empirical model for determination of the ZOI from HEAFs.
+
| Appendix&nbsp;M (M.4.2) provides an empirical model for determination of the ZOI from HEAFs.  
−
Additional research is on-going ([[#High Energy Arcing Fault (HEAF) Research|HEAF Research]]).
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 
 
|-
 
|-
 
| 16.1
 
| 16.1
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| HEAF for segmented bus ducts
 
| HEAF for segmented bus ducts
−
| Section 7.2.1.5 of Supplement 1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for segmented bus duct fires.
+
| Section&nbsp;7.2.1.5 of Supplement&nbsp;1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for segmented bus duct fires.  
−
Additional research is on-going ([[#High Energy Arcing Fault (HEAF) Research|HEAF Research]]).
+
| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section&nbsp;7 of Supplement&nbsp;1]
−
| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
 
 
|-
 
|-
 
| 16.2
 
| 16.2
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| HEAF for iso-phase bus ducts
 
| HEAF for iso-phase bus ducts
−
| Section 7.2.1.5 of Supplement 1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for iso-phase duct fires.
+
| Section&nbsp;7.2.1.5 of Supplement&nbsp;1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for iso-phase duct fires.  
−
Additional research is on-going ([[#High Energy Arcing Fault (HEAF) Research|HEAF Research]]).
+
| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section&nbsp;7 of Supplement&nbsp;1]
−
| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
 
 
|-
 
|-
 
| 17
 
| 17
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Hydrogen Tanks
 
| Hydrogen Tanks
−
| See Appendix N of NUREG/CR-6850
+
| See Appendix&nbsp;N of NUREG/CR&#8209;6850.
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 18
 
| 18
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Junction Boxes
 
| Junction Boxes
−
| FAQ 13-0006 provides a definition for junction boxes that allows the characterization and quantification of junction box fire scenarios in plant fire compartment requiring detailed Fire PRA/Fire Modeling analysis and (2) describe a process for quantifying the risk associated with junction box fire scenarios in such plant locations.
+
| FAQ&nbsp;13&#8209;0006 provides a definition for junction boxes that allows the characterization and quantification of these scenarios in fire compartments that require detailed fire modeling analysis.
−
|[https://www.nrc.gov/docs/ML1333/ML13331B213.pdf FAQ 13-0006]
+
|[https://www.nrc.gov/docs/ML1333/ML13331B213.pdf FAQ&nbsp;13&#8209;0006]
 
|-
 
|-
 
| 19
 
| 19
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Miscellaneous Hydrogen Fires
 
| Miscellaneous Hydrogen Fires
−
| See Appendix N of NUREG/CR-6850
+
| See Appendix&nbsp;N of NUREG/CR&#8209;6850.
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 20
 
| 20
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Off-gas/H<sub>2</sub> Recombiner (BWR)
 
| Off-gas/H<sub>2</sub> Recombiner (BWR)
−
| See Appendix N of NUREG/CR-6850
+
| See Appendix&nbsp;N of NUREG/CR&#8209;6850.
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 21
 
| 21
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Pumps and large hydraulic valves
 
| Pumps and large hydraulic valves
−
| Bin 21 fires can be classified as either electrical (motor) or oil. The split fraction between pump electrical and oil fires is updated in EPRI 3002002936 / NUREG-2169 (0.69 electrical / 0.31 oil)
+
| <span id="Bin21"></span>Pump fires are classified as either electrical (motor) or oil. The split fraction between pump electrical and oil fires is updated in EPRI&nbsp;3002002936 / NUREG&#8209;2169 (0.69 electrical / 0.31 oil).
  
−
'''Electrical fire HRR: ''' NUREG-2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG-6850 Table G-1) by horsepower, as well as growth and decay timing.
+
'''Electrical (motor) fires: ''' In NUREG/CR&#8209;6850, Bin 21 pump electrical fires were distinguished from non-pump motor fires. Research documented in NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 suggests that there is little or no difference between pump motor fires and non-pump motor fires, and so electric motors and motor-driven pumps have been consolidated into a single ignition source. To improve realism, the HRRs in NUREG&#8209;2178 Volume&nbsp;2 are characterized by horsepower, and NUREG&#8209;2178 Volume&nbsp;2 also provides growth and decay timing. The pump HRR in NUREG/CR&#8209;6850 is bounding compared with the updated values, and is therefore still valid.
  
−
'''Oil fire split fractions:''' The methods panel decision letter updates the likelihood and oil spill sizes for general pump oil fires ''other than'' large hydraulic valves. Specifically:  
+
'''Oil fire split fractions:''' The methods panel decision letter (ML12171A583) updates the likelihood and oil spill sizes for general pump oil fires ''other than'' large hydraulic valves. Specifically:  
 
* 88% of oil fires from pumps limit damage to the pump itself,
 
* 88% of oil fires from pumps limit damage to the pump itself,
 
* 7% of oil fires from pumps produce oil pools of 10% capacity, and
 
* 7% of oil fires from pumps produce oil pools of 10% capacity, and
 
* 5% of oil fires from pumps produce oil pools of 100% capacity.
 
* 5% of oil fires from pumps produce oil pools of 100% capacity.
−
For large hydraulic valves (which are included in Bin 21), the oil spill size fractions recommended in NUREG/CR-6850 should still be applied.  
+
For large hydraulic valves (which are included in Bin 21), the oil spill size fractions recommended in NUREG/CR&#8209;6850 Appendix E.3 should still be applied.
  
−
'''Oil fire HRR:''' See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.   
+
'''Oil fire HRR:''' See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.   
  
−
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US EPRI 3002002936 / NUREG-2169]
+
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US EPRI&nbsp;3002002936 / NUREG&#8209;2169]
  
−
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
  
−
[https://www.nrc.gov/docs/ML1217/ML12171A583.pdf Methods Panel Decision]
+
[https://www.nrc.gov/docs/ML1217/ML12171A583.pdf Methods Panel Decision, ML12171A583]
  
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
  
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 22
 
| 22
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| RPS MG Sets
 
| RPS MG Sets
−
| Use HRR distribution for Electric Motors (Case 7 of Table G-1)
+
| The motor HRR is recommended for Bin&nbsp;22 RPS MG Sets (refer to Table&nbsp;11&#8209;1 of NUREG/CR&#8209;6850). See [[#FMBin14|Bin&nbsp;14]].
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
 
 +
See [[#FMBin14|Bin&nbsp;14]]
 
|-
 
|-
 
| 23a
 
| 23a
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Transformers (oil filled)
 
| Transformers (oil filled)
−
| See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.  
+
| See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 23b
 
| 23b
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Transformers (dry)
 
| Transformers (dry)
−
| NUREG-2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for dry transformers (compared with the original distribution from NUREG-6850) based on power rating, as well as growth and decay timing.
+
| Chapter&nbsp;5 of NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052 provides updated HRR distributions for dry transformers (compared with the original distribution from NUREG&#8209;6850) based on power rating, as well as growth and decay timing.
−
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 
|-
 
|-
 
| 24
 
| 24
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Transient fires caused by welding and cutting
 
| Transient fires caused by welding and cutting
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|-
 
|-
 
| 25
 
| 25
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Transients
 
| Transients
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|-
 
|-
 
| 26
 
| 26
 
| Plant-Wide Components
 
| Plant-Wide Components
 
| Ventilation Subsystems
 
| Ventilation Subsystems
−
| For electrical (motor) fires: NUREG-2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG-6850 Table G-1) by horsepower, as well as growth and decay timing.
+
| Ventilation subsystem fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR&#8209;6850 (0.95 electrical / 0.05 oil).
−
For oil fires: See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. 
 
−
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
 
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 
  
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
'''Electrical (motor) fires: ''' HRR distributions and fire durations are provided in Chapter&nbsp;5 of NUREG&#8209;2178, Volume&nbsp;2 / EPRI&nbsp;3002016052.
 +
 
 +
'''Oil fire split fractions:''' The oil spill size fractions recommended in NUREG/CR&#8209;6850 Appendix E.3 should be applied.
 +
 
 +
'''Oil fire HRR:''' See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.   
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]
 +
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
 
 +
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
  
 
|-
 
|-
Line 395: Line 443:
 
| Transformer Yard
 
| Transformer Yard
 
| Transformer - Catastrophic
 
| Transformer - Catastrophic
−
| The catastrophic failure of a large transformer is defined as an energetic failures of the transformer that includes a rupture of the transformer tank, oil spill, and burning oil splattered a distance from the transformer. The analyst should use the frequency and 1.) determine availability of offsite power based on the function of the transformer(s) and 2.) consider propagation to adjacent (not nearby) buildings or components. A propagation path may be considered at the location of open or sealed penetrations, e.g., where a bus-duct enters from the Yard into the Turbine Building. Structural damage need only be considered only where appropriate shields are not present to protected structures and components against blast or debris.   
+
| The catastrophic failure of a large transformer is defined as an energetic failure of the transformer that includes a rupture of the transformer tank, oil spill, and burning oil splattered a distance from the transformer. The analyst should use the frequency and 1.) determine availability of offsite power based on the function of the transformer(s) and 2.) consider propagation to adjacent (not nearby) buildings or components. A propagation path may be considered at the location of open or sealed penetrations, e.g., where a bus-duct enters from the Yard into the Turbine Building. Structural damage need only be considered only where appropriate shields are not present to protected structures and components against blast or debris.   
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 28
 
| 28
Line 402: Line 450:
 
| Transformer - Non Catastrophic
 
| Transformer - Non Catastrophic
 
| In this failure, oil does not spill outside the transformer tank and the fire does not necessarily propagate beyond the fire source transformer. Analyst can use all the frequency and assume total loss of the "Transformer/ Switch Yard" or may split this frequency equally among the large transformers of the area and assume loss of each transformer separately. Loss of offsite power should be determined based on the function of the affected transformer(s).   
 
| In this failure, oil does not spill outside the transformer tank and the fire does not necessarily propagate beyond the fire source transformer. Analyst can use all the frequency and assume total loss of the "Transformer/ Switch Yard" or may split this frequency equally among the large transformers of the area and assume loss of each transformer separately. Loss of offsite power should be determined based on the function of the affected transformer(s).   
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 29
 
| 29
Line 408: Line 456:
 
| Yard Transformers (Others)
 
| Yard Transformers (Others)
 
| In the screening phase of the project, the analyst may conservatively assign the same frequency to all of the items in this group. If the scenario would not screen out, the frequency may then be divided among the various items in this group. A relative ranking scheme may be used for this purpose. The ranking may be based on the relative characteristics of the item and the analysts' judgment.  
 
| In the screening phase of the project, the analyst may conservatively assign the same frequency to all of the items in this group. If the scenario would not screen out, the frequency may then be divided among the various items in this group. A relative ranking scheme may be used for this purpose. The ranking may be based on the relative characteristics of the item and the analysts' judgment.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 30
 
| 30
 
| Turbine Building
 
| Turbine Building
 
| Boiler
 
| Boiler
−
| See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.  
+
| See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
 
|-
 
|-
 
| 31
 
| 31
 
| Turbine Building
 
| Turbine Building
 
| Cable fires caused by welding and cutting
 
| Cable fires caused by welding and cutting
−
| FAQ 13-0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR-6850. However, the current method of evaluating cable fire risk in NUREG/CR-6850 remains an acceptable approach.  
+
| FAQ&nbsp;13&#8209;0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section&nbsp;R.1 of NUREG/CR&#8209;6850. However, the current method of evaluating cable fire risk in NUREG/CR&#8209;6850 remains an acceptable approach.  
−
|[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
|[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
−
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ 13-0005]
+
[https://www.nrc.gov/docs/ML1331/ML13319B181.pdf FAQ&nbsp;13&#8209;0005]
 
|-
 
|-
 
| 32
 
| 32
 
| Turbine Building
 
| Turbine Building
 
| Main Feedwater Pumps
 
| Main Feedwater Pumps
−
| For electrical (motor) fires: NUREG-2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG-6850 Table G-1) by horsepower, as well as growth and decay timing.
+
| Main feedwater pumps are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR&#8209;6850 (0.11 electrical / 0.89 oil).
  
−
For oil fires: FAQ 08-0044 (Section 9 of NUREG/CR-6850 Supplement 1) clarifies the severity factors for small fires (0.966 for a leak that impacts the pump), large fires (0.0306 for 10% inventory spill), and very large fires (0.0034 for 100% inventory spill). See Section G.4 of NUREG/CR-6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. 
+
'''Electrical (motor) fires: ''' HRR distributions and fire durations are provided in Chapter&nbsp;5 of NUREG&#8209;2178, Volume&nbsp;2 / EPRI&nbsp;3002016052. The pump HRR in NUREG/CR&#8209;6850 is bounding compared with the updated values, and is therefore still valid.
−
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
 
  
−
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
'''Oil fire split fractions:''' FAQ&nbsp;08&#8209;0044 (Section&nbsp;9 of NUREG/CR&#8209;6850 Supplement&nbsp;1) clarifies the severity factors for small fires (0.966 for a leak that impacts the pump), large fires (0.0306 for 10% inventory spill), and very large fires (0.0034 for 100% inventory spill).
  
−
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 08-0044, Section 9 of Supplement 1]
+
'''Oil fire HRR:'''  See Section&nbsp;G.4 of NUREG/CR&#8209;6850 for HRR for flammable liquid fires. EPRI&nbsp;3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052]  
  
−
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI 3002005303]
+
[https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 +
 
 +
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ&nbsp;08&#8209;0044, Section&nbsp;9 of Supplement&nbsp;1]
 +
 
 +
[https://www.epri.com/#/pages/product/000000003002005303/?lang=en-US EPRI&nbsp;3002005303]
  
 
|-
 
|-
Line 442: Line 494:
 
| Turbine Building
 
| Turbine Building
 
| Turbine Generator Excitor
 
| Turbine Generator Excitor
−
| Appendix O (Section O.2.1 & Table O-2) recommends assuming the excitor fire is limited to the excitor itself.  
+
| Appendix&nbsp;O (Section&nbsp;O.2.1 & Table O-2) recommends assuming the excitor fire is limited to the excitor itself.  
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 34
 
| 34
 
| Turbine Building
 
| Turbine Building
 
| Turbine Generator Hydrogen
 
| Turbine Generator Hydrogen
−
| Appendix O (Section O.2.2 & Table O-2) provides guidance for both limited and severe T/G Hydrogen fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection.   
+
| Appendix&nbsp;O (Section&nbsp;O.2.2 & Table O-2) provides guidance for both limited and severe T/G Hydrogen fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection.   
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 35
 
| 35
 
| Turbine Building
 
| Turbine Building
 
| Turbine Generator Oil
 
| Turbine Generator Oil
−
| Appendix O (Section O.2.3 & Table O-2) provides guidance for both limited and severe T/G oil fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection.   
+
| Appendix&nbsp;O (Section&nbsp;O.2.3 & Table O-2) provides guidance for both limited and severe T/G oil fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection.   
−
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+
| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850]
 
|-
 
|-
 
| 36
 
| 36
 
| Turbine Building
 
| Turbine Building
 
| Transient fires caused by welding and cutting
 
| Transient fires caused by welding and cutting
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|-
 
|-
 
| 37
 
| 37
 
| Turbine Building
 
| Turbine Building
 
| Transients
 
| Transients
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]] for treatment of transient fires.
−
| See Bin 3
+
| See [[#FMBin3|Bin&nbsp;3]]
 
|}
 
|}
  
 
==Recommended HRR Values ==
 
==Recommended HRR Values ==
−
The following sections and table provide HRR distributions from the most updated research. Other HRR distributions from prior research (such as NUREG/CR-6850) may still be valid for use in some circumstances.
+
The following tables summarize the latest research on HRR probability distributions.  These distributions were developed to increase realism in modeling electrical cabinet fires and transient fires. As such, HRR probability distributions available in earlier publications (such as Appendix G of NUREG/CR-6850) are bounding. In the case of electric motors and transformers, the latest HRR probability distributions are based on equipment sizes so that the fires can also be realistically characterized.
−
===Electrical Cabinets (NUREG-2178 Vol. 1, RACHELLE-FIRE)===
+
===Electrical Cabinets (NUREG&#8209;2178 Volume&nbsp;1)===
−
[https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG-2178 Vol 1 / EPRI 3002005578] provides HRR distributions for electrical enclosures.
+
[https://www.epri.com/#/pages/product/000000003002005578/?lang=en-US NUREG&#8209;2178 Volume&nbsp;1 / EPRI&nbsp;3002005578] provides HRR distributions for electrical enclosures.
  
−
<table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" width="852" style="width:639.0pt;margin-left:3.75pt;border-collapse:collapse;mso-yfti-tbllook:
+
:{| style="font-size: 95%; border: 1px solid #a2a9b1; border-collapse: collapse;"
−
1184;mso-padding-alt:0in 5.4pt 0in 5.4pt">
+
|+ '''Electrical Enclosures'''
−
+
! rowspan="3" style="border-bottom: 1px solid #a2a9b1; background-color:#eaecf0;" | Enclosure Class / Function Group
−
  <tr style="mso-yfti-irow:0;mso-yfti-firstrow:yes;height:14.85pt">
+
! rowspan="3" style="border-bottom: 1px solid #a2a9b1; background-color:#eaecf0;" | Enclosure Ventilation<br>(Open or Closed Doors)
−
  <td width="90" nowrap="" rowspan="3" style="width:67.5pt;border:solid windowtext 1.5pt;
+
! rowspan="3" style="border-bottom: 1px solid #a2a9b1; background-color:#eaecf0;" | <div id="FuelTypeLoc"></div>Fuel Type[[#FuelTypeLegend|<sup>&dagger;</sup>]]<br>(TS/QTP/SIS or TP Cables)
−
  border-right:solid windowtext 1.0pt;mso-border-alt:solid windowtext 1.5pt;
+
! colspan="12" style="background-color:#eaecf0;" | Gamma Distribution
−
  mso-border-right-alt:solid windowtext .5pt;background:#D9D9D9;mso-background-themecolor:
+
|-
−
  background1;mso-background-themeshade:217;padding:0in 2.9pt 0in 2.9pt;
+
! colspan
−
  height:14.85pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><b style="mso-bidi-font-weight:normal"><span style="font-size:8.0pt;color:black">Enclosure
 
−
  Class/Function Group  </span></b></p>
 
−
  </td>
 
−
  <td width="66" nowrap="" rowspan="3" style="width:49.5pt;border-top:solid windowtext 1.5pt;
 
−
  border-left:none;border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
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−
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−
  background1;mso-background-themeshade:217;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:14.85pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size:8.0pt;color:black">Enclosure Ventilation (Open or Closed Doors)  </span></b></p>
 
−
  </td>
 
−
  <td width="72" nowrap="" rowspan="3" style="width:.75in;border-top:solid windowtext 1.5pt;
 
−
  border-left:none;border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  mso-border-right-alt:solid windowtext .5pt;background:#D9D9D9;mso-background-themecolor:
 
−
  background1;mso-background-themeshade:217;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:14.85pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><b><span style="font-size:8.0pt;color:black">Fuel Type* (TS/QTP/SIS or TP Cables) </span></b></p>
 
−
  </td>
 
−
  <td width="624" nowrap="" colspan="12" style="width:6.5in;border-top:solid windowtext 1.5pt;
 
−
  border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.5pt;
 
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−
  background1;mso-background-themeshade:217;padding:0in 2.9pt 0in
 
  
−
  </td>
+
===Motors and Dry Transformers (NUREG&#8209;2178 Volume&nbsp;2)===
−
  <td width="66" nowrap="" style="width:49.5pt;border-top:none;border-left:none;
+
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052] provides HRR distributions for motors and dry transformers.
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">Closed  </span></p>
 
−
  </td>
 
−
  <td width="72" nowrap="" style="width:.75in;border-top:none;border-left:none;
 
−
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−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">TS/QTP/SIS  </span></p>
 
−
  </td>
 
−
  <td width="48" nowrap="" style="width:.5in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.23  </span></p>
 
−
  </td>
 
−
  <td width="42" nowrap="" style="width:31.5pt;border-top:none;border-left:none;
 
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  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">111  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
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−
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−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">25  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
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−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:.5pt;
 
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  mso-border-right-alt:1.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">200  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
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  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext 1.5pt;mso-border-left-alt:solid windowtext 1.5pt;mso-border-top-alt:
 
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  1.5pt;mso-border-left-alt:1.5pt;mso-border-bottom-alt:.5pt;mso-border-right-alt:
 
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.27  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-top-alt:solid windowtext 1.5pt;background:
 
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">51  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
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−
  solid windowtext .5pt;mso-border-top-alt:solid windowtext 1.5pt;background:
 
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
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  solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-top-alt:
 
−
  1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:.5pt;mso-border-right-alt:
 
−
  1.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:solid;background:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">100  </span></p>
 
−
  </td>
 
−
  <td width="48" style="width:.5in;border-top:none;border-left:none;border-bottom:
 
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  1.5pt;mso-border-left-alt:1.5pt;mso-border-bottom-alt:.5pt;mso-border-right-alt:
 
−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.88  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
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−
  solid windowtext .5pt;mso-border-top-alt:solid windowtext 1.5pt;background:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">12  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
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−
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  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
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  solid windowtext 1.0pt;border-right:solid windowtext 1.5pt;mso-border-top-alt:
 
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  1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:.5pt;mso-border-right-alt:
 
−
  1.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:solid;background:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">45  </span></p>
 
−
  </td>
 
−
</tr>
 
−
<tr style="mso-yfti-irow:14;height:19.55pt">
 
−
  <td width="66" nowrap="" style="width:49.5pt;border-top:none;border-left:none;
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">Closed  </span></p>
 
−
  </td>
 
−
  <td width="72" nowrap="" style="width:.75in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">TP  </span></p>
 
−
  </td>
 
−
  <td width="48" nowrap="" style="width:.5in;border-top:none;border-left:none;
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.52  </span></p>
 
−
  </td>
 
−
  <td width="42" nowrap="" style="width:31.5pt;border-top:none;border-left:none;
 
−
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  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">73  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
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  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">50  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">200  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
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−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;background:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.52  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">36  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">25  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">100  </span></p>
 
−
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−
  <td width="48" style="width:.5in;border-top:none;border-left:none;border-bottom:
 
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−
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.88  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
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  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">12  </span></p>
 
−
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−
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
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−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">45  </span></p>
 
−
  </td>
 
−
</tr>
 
−
<tr style="mso-yfti-irow:15;height:19.55pt">
 
−
  <td width="66" nowrap="" style="width:49.5pt;border-top:none;border-left:none;
 
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−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">Open  </span></p>
 
−
  </td>
 
−
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−
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  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">TS/QTP/SIS  </span></p>
 
−
  </td>
 
−
  <td width="48" nowrap="" style="width:.5in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.23  </span></p>
 
−
  </td>
 
−
  <td width="42" nowrap="" style="width:31.5pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">182  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">40  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.5pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-right-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">325  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.19  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">92  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-right-alt:solid windowtext 1.5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">150  </span></p>
 
−
  </td>
 
−
  <td width="48" style="width:.5in;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.88  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">12  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;background:white;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.0pt;border-right:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-right-alt:solid windowtext 1.5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">45  </span></p>
 
−
  </td>
 
−
</tr>
 
−
<tr style="mso-yfti-irow:16;height:19.55pt">
 
−
  <td width="66" nowrap="" style="width:49.5pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">Open  </span></p>
 
−
  </td>
 
−
  <td width="72" nowrap="" style="width:.75in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">TP  </span></p>
 
−
  </td>
 
−
  <td width="48" nowrap="" style="width:.5in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.51  </span></p>
 
−
  </td>
 
−
  <td width="42" nowrap="" style="width:31.5pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">119  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-alt:solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt">80<span style="color:black">  </span></span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.5pt;
 
−
  mso-border-top-alt:solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">325  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  .5pt;mso-border-left-alt:1.5pt;mso-border-bottom-alt:1.5pt;mso-border-right-alt:
 
−
  .5pt;mso-border-color-alt:windowtext;mso-border-style-alt:solid;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.30  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">72  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">25  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">150  </span></p>
 
−
  </td>
 
−
  <td width="48" style="width:.5in;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  .5pt;mso-border-left-alt:1.5pt;mso-border-bottom-alt:1.5pt;mso-border-right-alt:
 
−
  .5pt;mso-border-color-alt:windowtext;mso-border-style-alt:solid;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.88  </span></p>
 
−
  </td>
 
−
  <td width="42" style="width:31.5pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">12  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;mso-border-alt:
 
−
  solid windowtext .5pt;mso-border-bottom-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" style="width:45.0pt;border-top:none;border-left:none;border-bottom:
 
−
  solid windowtext 1.5pt;border-right:solid windowtext 1.5pt;mso-border-top-alt:
 
−
  solid windowtext .5pt;mso-border-left-alt:solid windowtext .5pt;background:
 
−
  white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">45  </span></p>
 
−
  </td>
 
−
</tr>
 
−
<tr style="mso-yfti-irow:17;height:19.55pt">
 
−
  <td width="90" style="width:67.5pt;border-top:none;border-left:solid windowtext 1.5pt;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-alt:solid windowtext 1.5pt;
 
−
  mso-border-right-alt:solid windowtext .5pt;background:#D9D9D9;mso-background-themecolor:
 
−
  background1;mso-background-themeshade:217;padding:0in 2.9pt 0in 2.9pt;
 
−
  height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><b style="mso-bidi-font-weight:normal"><span style="font-size:8.0pt">4c - Small
 
−
  Enclosures  </span></b><br>
 
−
  <b style="mso-bidi-font-weight:normal"><span style="font-size:8.0pt">[<span style="color:black">≤</span> 0.34 m<sup>3</sup>  </span></b>
 
−
  <b style="mso-bidi-font-weight:normal"><span style="font-size:8.0pt">(12 ft<sup>3</sup>)]  </span></b></p>
 
−
  </td>
 
−
  <td width="66" nowrap="" style="width:49.5pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:1.5pt;
 
−
  mso-border-right-alt:.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
  solid;background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">Not Applicable  </span></p>
 
−
  </td>
 
−
  <td width="72" nowrap="" style="width:.75in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:1.5pt;
 
−
  mso-border-right-alt:.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
  solid;background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">All  </span></p>
 
−
  </td>
 
−
  <td width="48" nowrap="" style="width:.5in;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:1.5pt;
 
−
  mso-border-right-alt:.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
  solid;background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">0.88  </span></p>
 
−
  </td>
 
−
  <td width="42" nowrap="" style="width:31.5pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:1.5pt;
 
−
  mso-border-right-alt:.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
  solid;background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">12  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.0pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  mso-border-top-alt:1.5pt;mso-border-left-alt:.5pt;mso-border-bottom-alt:1.5pt;
 
−
  mso-border-right-alt:.5pt;mso-border-color-alt:windowtext;mso-border-style-alt:
 
−
  solid;background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">15  </span></p>
 
−
  </td>
 
−
  <td width="60" nowrap="" style="width:45.0pt;border-top:none;border-left:none;
 
−
  border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.5pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext .5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">45  </span></p>
 
−
  </td>
 
−
  <td width="414" colspan="8" style="width:310.5pt;border-top:none;border-left:
 
−
  none;border-bottom:solid windowtext 1.5pt;border-right:solid windowtext 1.5pt;
 
−
  mso-border-top-alt:solid windowtext 1.5pt;mso-border-left-alt:solid windowtext 1.5pt;
 
−
  background:white;padding:0in 2.9pt 0in 2.9pt;height:19.55pt">
 
−
  <p class="MsoNormal" align="center" style="text-align:center"><span style="font-size:8.0pt;color:black">NOT APPLICABLE  </span></p>
 
−
  </td>
 
−
</tr>
 
−
</table>
 
  
−
<div style="font-size:80%">
+
:{| class="wikitable"
−
::'''* Legend for Fuel Type'''
 
−
::::; TS: Thermoset
 
−
::::; TP: Thermoplastic
 
−
::::; QTP: Qualified Thermoplastic
 
−
::::; SIS: Synthetic Insulated Switchboard Wire or XLPE-Insulated Conductor
 
−
</div>
 
−
 
 
−
===Motors and Dry Transformers (NUREG-2178 Vol. 2)===
 
−
[https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Volume 2 / EPRI 3002016052] provides HRR distributions for motors and dry transformers.
 
−
 
 
−
{| class="wikitable"
 
 
|+ '''Motors'''
 
|+ '''Motors'''
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Motor Classification Group
+
! rowspan="2" | Motor<br>Classification Group
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Motor Size (horsepower)
+
! rowspan="2" | Motor Size<br>(horsepower)
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | α
+
! colspan="4" | <p style="font-size:90%;">Gamma Distribution</p>
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | β
 
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 75th Percentile (kW)
 
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 98th Percentile (kW)
 
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | A
+
! α
 +
! β
 +
! ''P<sub>75</sub>'' (kW)
 +
! ''P<sub>98</sub>'' (kW)
 +
|-
 +
| style="text-align: center;" | '''A'''
 
| style="text-align: center;" | >5-30
 
| style="text-align: center;" | >5-30
 
| style="text-align: center;" | 1.34
 
| style="text-align: center;" | 1.34
Line 1,876: Line 758:
 
| style="text-align: center;" | 15
 
| style="text-align: center;" | 15
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | B
+
| style="text-align: center;" | '''B'''
 
| style="text-align: center;" | >30-100
 
| style="text-align: center;" | >30-100
 
| style="text-align: center;" | 1.17
 
| style="text-align: center;" | 1.17
Line 1,883: Line 765:
 
| style="text-align: center;" | 37
 
| style="text-align: center;" | 37
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | C
+
| style="text-align: center;" | '''C'''
 
| style="text-align: center;" | >100
 
| style="text-align: center;" | >100
 
| style="text-align: center;" | 1.10
 
| style="text-align: center;" | 1.10
Line 1,891: Line 773:
 
|}
 
|}
  
−
{| class="wikitable"
+
:{| class="wikitable"
 
|+ '''Dry Transformers'''
 
|+ '''Dry Transformers'''
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Transformer Classification Group
+
! rowspan="2" | Transformer<br>Classification Group
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Transformer Power (kVA)
+
! rowspan="2" | Transformer Power<br>(kVA)
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | α
+
! colspan="4" | <p style="font-size:90%;">Gamma Distribution</p>
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | β
+
|-
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 75th Percentile (kW)
+
! α
−
! style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 98th Percentile (kW)
+
! β
 +
! ''P<sub>75</sub>'' (kW)
 +
! ''P<sub>98</sub>'' (kW)
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | A
+
| style="text-align: center;" | '''A'''
 
| style="text-align: center;" | >45-75
 
| style="text-align: center;" | >45-75
 
| style="text-align: center;" | 0.38
 
| style="text-align: center;" | 0.38
Line 1,907: Line 791:
 
| style="text-align: center;" | 30
 
| style="text-align: center;" | 30
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | B
+
| style="text-align: center;" | '''B'''
 
| style="text-align: center;" | >75-750
 
| style="text-align: center;" | >75-750
 
| style="text-align: center;" | 0.41
 
| style="text-align: center;" | 0.41
Line 1,914: Line 798:
 
| style="text-align: center;" | 70
 
| style="text-align: center;" | 70
 
|-
 
|-
−
| style="text-align: center; background-color:#d9d9d9;" | C
+
| style="text-align: center;" | '''C'''
 
| style="text-align: center;" | >750
 
| style="text-align: center;" | >750
 
| style="text-align: center;" | 0.46
 
| style="text-align: center;" | 0.46
Line 1,922: Line 806:
 
|}
 
|}
  
−
===Transients (NUREG-2233)===
+
===Transients (NUREG&#8209;2233)===
−
[https://www.epri.com/#/pages/product/3002016054/ NUREG-2233 / EPRI 3002018231] provides HRR distributions for both generic and "transient combustible control location" (TCCL) type transient fires. The report also provides values for total energy release (TER) and zones of influence (ZOIs), but only HRRs are included here.
+
[https://www.epri.com/#/pages/product/3002018231/ NUREG&#8209;2233 / EPRI&nbsp;3002018231] provides HRR distributions for both generic and "transient combustible control location" (TCCL) type transient fires. The report also provides values for total energy release (TER) and zones of influence (ZOIs), but only HRRs are included here.
−
{| class="wikitable"
+
:{| class="wikitable"
−
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Type
+
|+ '''Transients'''
−
! colspan="2" style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | HRR (kW)
+
! rowspan="2" | Type
−
! colspan="2" style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Gamma Distribution Parameters
+
! colspan="4" | <p style="font-size:90%;">Gamma Distribution</p>
 
|-
 
|-
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 75th
+
! α
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | 98th
+
! β
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | α
+
! ''P<sub>75</sub>'' (kW)
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | β
+
! ''P<sub>98</sub>'' (kW)
 
|-
 
|-
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | Generic
+
| style="text-align: center;" | '''Generic'''
 +
| style="text-align: center;" | 0.271
 +
| style="text-align: center;" | 141
 
| style="text-align: center;" | 41.6
 
| style="text-align: center;" | 41.6
 
| style="text-align: center;" | 278
 
| style="text-align: center;" | 278
−
| style="text-align: center;" | 0.271
 
−
| style="text-align: center;" | 141
 
 
|-
 
|-
−
| style="text-align: center; font-weight:bold; background-color:#d9d9d9;" | TCCL
+
| style="text-align: center;" | '''TCCL'''
 +
| style="text-align: center;" | 0.314
 +
| style="text-align: center;" | 67.3
 
| style="text-align: center;" | 24.6
 
| style="text-align: center;" | 24.6
 
| style="text-align: center;" | 143
 
| style="text-align: center;" | 143
−
| style="text-align: center;" | 0.314
 
−
| style="text-align: center;" | 67.3
 
 
|}
 
|}
  
 
==Additional Fire Modeling Considerations==
 
==Additional Fire Modeling Considerations==
−
===High Energy Arcing Fault (HEAF) Research===
 
−
EPRI is currently performing additional research on the risk impact of HEAF events, for example the impact of aluminum conductors. A 2019 report [https://www.epri.com/#/pages/product/000000003002015992/ EPRI 3002015992] provides an overview of nuclear power station electrical distribution systems and covers fault protection system concepts, fault isolation times, the potential impact of HEAFs on Class 1E electrical distribution systems, and typical industry practices and programs that help ensure proper operation. This report also provides some preliminary risk insights based on a review of existing data.
 
 
===Time-to-Damage Models for Cables===
 
===Time-to-Damage Models for Cables===
 
Three approaches are documented for assessing the time-to-damage for cables.
 
Three approaches are documented for assessing the time-to-damage for cables.
 +
<div style="margin:1em">
 +
'''''Exposure threshold'''''
 +
The method described in [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI&nbsp;1011989 / NUREG/CR&#8209;6850] Appendix&nbsp;H consists of using the threshold exposure gas temperature or heat flux for determining cable failure. See [[#Fire Damage Criteria|below]] for damage criteria. This is the simplest of the approaches, but it can be fairly conservative because it does not account for the time it takes for cable heating to actually result in damage.
  
−
NUREG/CR-6850 Appendix H (Section H.1.5.2) provides an empirical approach for calculating the time to electrical failure of cables.  
+
'''''Heat soak'''''
 +
The method described in Appendix&nbsp;A of [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052] considers exposure integrated over time based upon the time to failure data provided in Appendix&nbsp;H of NUREG/CR&#8209;6850. This method is less conservative than the above "exposure threshold" method but still conservative when compared with THIEF.
 +
Time to failure data for Kerite-FR materials are provided in [https://www.epri.com/#/pages/product/3002015997/ NUREG&#8209;2232 / EPRI&nbsp;3002015997].
  
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6931/ NUREG/CR-6931 Volume 3] documents the THIEF model, which is a one-dimensional heat conduction model into a cylinder for predicting the internal temperature of cables subjected to fire generated conditions.  The document also provides verification and validation material for the model.  The validation information is based on the CAROLFIRE experiments for investigating electrical shorts in cables, which also collected cable surface and internal temperature information.  Using the THIEF model, temperature predictions can be obtain considering cables in conduits and having different jacket and insulation material.
+
'''''Heat conduction (Thermally-Induced Electrical Failure, "THIEF")'''''
 +
The THIEF approach presented in [https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6931/ NUREG/CR&#8209;6931 Volume&nbsp;3] and [https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1805/s1/ NUREG&#8209;1805 Supplement&nbsp;1] performs a one-dimensional (1-D), cylindrical heat transfer calculation for a cable exposed to a time-varying exposure to determine when the cable jacket will fail based on the jacket’s inner temperature. Validation of the model shows that it does well at computing the temperature rise of the cable jacket; however, because it requires cable-specific data (dimensions and mass), it cannot be applied in a generic manner such as the exposure threshold or heat soak methods.
 +
</div>
  
 
===Location Factor===
 
===Location Factor===
−
When the fire is located near a wall or in a corner, less air can be entrained into the fire plume. Less air entrainment into the fire plume produces higher plume temperatures. The flames from fires in contact with wall and corner surfaces tend to be longer, also resulting in higher plume temperatures. For such fires, a location factor, traditionally 2 for fires near a wall or 4 for fires near a corner, has been applied as a correction to the plume temperature calculation. [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Volume 2 / EPRI 3002016052] Section 6 demonstrates that the traditional approach is overly conservative, and presents new factors of 1 for all wall configurations and either 4, 2, or 1 for corner configurations depending on the distance (4 for a distance of 0-1 ft., 2 for 1-2 ft., and 1 for all distances greater than 2 ft.). [https://www.epri.com/#/pages/product/000000003002005303/ EPRI 3002005303] provides the technical basis for the work in NUREG-2178 Volume 2.
+
When the fire is located near a wall or in a corner, less air can be entrained into the fire plume. Less air entrainment into the fire plume produces higher plume temperatures. The flames from fires in contact with wall and corner surfaces tend to be longer, also resulting in higher plume temperatures. For such fires, a location factor, traditionally 2 for fires near a wall or 4 for fires near a corner, has been applied as a correction to the plume temperature calculation. [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052] Section&nbsp;6 demonstrates that the traditional approach is overly conservative, and presents new factors based on the distance from the source to a corner or wall:
 +
 
 +
:{| class="wikitable"
 +
|-
 +
! rowspan="2" | Configuration
 +
! colspan="3" | Location Factor
 +
|-
 +
! 0–0.3 m [0–1 ft]
 +
! 0.3–0.6 m [1–2 ft]
 +
! >0.6 m [2 ft]
 +
|-
 +
! style="text-align:center;" | Corner
 +
| style="text-align:center;" | 4
 +
| style="text-align:center;" | 2
 +
| style="text-align:center;" | 1
 +
|-
 +
! style="text-align:center;" | Wall
 +
| style="text-align:center;" | 1
 +
| style="text-align:center;" | 1
 +
| style="text-align:center;" | 1
 +
|}
 +
 
 +
[https://www.epri.com/#/pages/product/000000003002005303/ EPRI&nbsp;3002005303] provides the technical basis for the work in NUREG&#8209;2178 Volume&nbsp;2.
  
 
===Radiation effects modeling===
 
===Radiation effects modeling===
−
Chapter 2 of [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Volume 2 / EPRI 3002016052] evaluates radiation emission models used to assess horizontal zone of influence. The two commonly-implemented empirical models – the '''point source''' method and the '''solid flame''' method – are compared against a computational model (Fire Dynamics Simulator). The results of this chapter recommended that the adjusted solid flame model should generally be considered a preferred method over the point source method because the adjusted flame model shows somewhat better characteristics in terms of a) NOT under-predicting and b) improved statistical error and bias. This applies to all fire types, where the flame is ''UNobstructed''. The modeling of ''obstructed'' radiation circumstances as present in electrical cabinets is discussed in the context of Bin 15 electrical cabinet fire modeling, in the table above.
+
Chapter&nbsp;2 of [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2 / EPRI&nbsp;3002016052] evaluates radiation emission models used to assess horizontal zone of influence. The two commonly-implemented empirical models – the '''point source''' method and the '''solid flame''' method – are compared against a computational model (Fire Dynamics Simulator). The results of this chapter recommended that the adjusted solid flame model should generally be considered a preferred method over the point source method because the adjusted flame model shows somewhat better characteristics in terms of a) NOT under-predicting and b) improved statistical error and bias. This applies to all fire types, where the flame is ''un''obstructed. The modeling of obstructed radiation circumstances as present in electrical cabinets is discussed in the context of [[#FmBin15|Bin 15 electrical cabinet fire modeling]].
 +
 
 +
===High Energy Arcing Fault (HEAF) Research===
 +
EPRI and the NRC are currently developing further methods and data on the risk impact of HEAF events; for example frequencies, fault duration, and zone of influence (e.g., copper versus aluminum). EPRI has issued the following white paper reports:
 +
*[https://www.epri.com/#/pages/product/000000003002015992/ EPRI&nbsp;3002015992] provides an overview of nuclear power station electrical distribution systems and covers fault protection system concepts, fault isolation times, the potential impact of HEAFs on Class&nbsp;1E electrical distribution systems, and typical industry practices and programs that help ensure proper operation. This report also provides some preliminary risk insights based on a review of existing data.
 +
*[https://www.epri.com/#/pages/product/000000003002011922/ EPRI 3002011922] reviews the operating experience to gain insights about equipment type, event characteristics, and the range of damage for HEAF events occurring at nuclear power plants within the United States and internationally. This paper also explores recent U.S. and international HEAF test programs for low- and medium-voltage electrical equipment and summarizes the insights gained from these test programs, including the potential role of aluminum oxidation in HEAF severity.
 +
*[https://www.epri.com/#/pages/product/000000003002015459/ EPRI 3002015459] demonstrates that an effective preventive maintenance program is important in minimizing the likelihood and/or severity of a HEAF event. Sixty&#8209;four percent (64%) of HEAF events were determined to be preventable, and the most prevalent cause of failure was inadequate maintenance. These data demonstrate that proper maintenance can prevent most HEAF events. Effective maintenance practices and strategies are summarized in this report by equipment type, including circuit breakers, bus ducts, protective relays, and cables.
  
 
==Fire Propagation and Suppression Guidance==
 
==Fire Propagation and Suppression Guidance==
 
===Detection-Suppression Event Tree===
 
===Detection-Suppression Event Tree===
−
For electrical cabinet fires, Section 5 of [https://www.epri.com/#/pages/product/000000003002016051/ NUREG-2230 / EPRI 3002016051] presents a revised detection-suppression event tree model for characterizing fire detection and suppression activities in response to a fire event (revised compared with the original model described in Appendix P of NUREG/CR-6850 and Chapter 14 of NUREG/CR-6850 Supplement 1). This modification is intended to capture the potential for plant personnel suppression during the early stages of a fire. For other fire types, the original model described in Appendix P of NUREG/CR-6850 and Chapter 14 of NUREG/CR-6850 Supplement 1 should be used.
+
For electrical cabinet fires, Section&nbsp;5 of [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230 / EPRI&nbsp;3002016051] presents a revised detection-suppression event tree model for characterizing fire detection and suppression activities in response to a fire event (revised compared with the original model described in Appendix&nbsp;P of NUREG/CR&#8209;6850 and Chapter&nbsp;14 of NUREG/CR&#8209;6850 Supplement&nbsp;1). This modification is intended to capture the potential for plant personnel suppression during the early stages of an electrical cabinet fire. For other fire types, the original model described in Appendix&nbsp;P of NUREG/CR&#8209;6850 and Chapter&nbsp;14 of NUREG/CR&#8209;6850 Supplement&nbsp;1 should be used.
  
 
===Fire Damage Criteria===
 
===Fire Damage Criteria===
 +
<div style="margin:1em">
 +
'''''Cable Damage Criteria'''''
  
−
''Cable Damage Criteria''
+
[https://www.nrc.gov/docs/ML1807/ML18074A023.html FAQ&nbsp;16&#8209;0011] provides radiant heating and temperature criteria for bulk cable tray ignition (which was not previously provided in NUREG/CR&#8209;6850). The bounding cable damage and ignition criteria remain the same. A summary of the results are shown below. The analyst should refer to both NUREG/CR&#8209;6850 Appendix&nbsp;H and FAQ&nbsp;16&#8209;0011 for full guidance.
−
 
 
−
[https://www.nrc.gov/docs/ML1807/ML18074A023.html FAQ 16-0011] provides radiant heating and temperature criteria for bulk cable tray ignition (which was not previously provided in NUREG/CR-6850. The bounding cable damage and ignition criteria remain the same. A summary of the results are shown below. The analyst should refer to both NUREG/CR-6850 Appendix H and FAQ 16-0011 for full guidance.
 
  
 
{| class="wikitable"
 
{| class="wikitable"
Line 1,985: Line 902:
 
! Temperature
 
! Temperature
 
|-
 
|-
−
| Thermoplastic
+
! Thermoplastic
−
| 6 kW/m<sup>2</sup>
+
| style="text-align: center | 6 kW/m<sup>2</sup>
−
| 205°C
+
| style="text-align: center | 205°C
−
| rowspan="2"| 25 kW/m<sup>2</sup>
+
| rowspan="2" style="text-align: center;" | 25 kW/m<sup>2</sup>
−
| rowspan="2"| 500°C
+
| rowspan="2" style="text-align: center;" | 500°C
 
|-
 
|-
−
| Thermoset
+
! Thermoset
−
| 11 kW/m<sup>2</sup>
+
| style="text-align: center | 11 kW/m<sup>2</sup>
−
| 330°C
+
| style="text-align: center | 330°C
 
|}
 
|}
  
−
For Kerite cables, refer to [https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7102/ NUREG/CR-7102] for damage criteria. Originally FAQ 08-0053 was initiated to clarify failure thresholds for Kerite cables and the resolution can be found in the [https://www.nrc.gov/docs/ML1214/ML121440155.pdf closure memo dated June 6, 2012] following the publication of NUREG/CR-7102.   
+
For Kerite cables, refer to [https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7102/ NUREG/CR&#8209;7102] for damage criteria. Originally FAQ&nbsp;08&#8209;0053 was initiated to clarify failure thresholds for Kerite cables and the resolution can be found in the [https://www.nrc.gov/docs/ML1214/ML121440155.pdf closure memo dated June 6, 2012] following the publication of NUREG/CR&#8209;7102.   
  
−
''Treatment of Sensitive Electronics''
+
'''''Treatment of Sensitive Electronics'''''
  
−
[https://www.nrc.gov/docs/ML1332/ML13322A085.pdf FAQ 13-0004] provides supplemental guidance for the application of the lower damage thresholds provided in NUREG/CR-6850 Section 8.5.1.2 and H.2 for solid-state components. Fire Dynamics Simulator (FDS) modeling results support the recommendation that a generic screening heat flux damage threshold for thermoset cables, as observed on the outer surface of the cabinet, can be used as a conservative surrogate for assessing the potential for thermal damage to solid-state and sensitive electronics within an electrical panel (cabinet).  Since the conclusions of the FDS analysis are based on heat flux exposure to the cabinet, the 65°C temperature damage criterion must still be assessed for other types of fire exposures to the enclosed sensitive electronics.
+
[https://www.nrc.gov/docs/ML1332/ML13322A085.pdf FAQ&nbsp;13&#8209;0004] provides supplemental guidance for the application of the lower damage thresholds provided in NUREG/CR&#8209;6850 Section&nbsp;8.5.1.2 and H.2 for solid-state components. Fire Dynamics Simulator (FDS) modeling results support the recommendation that a generic screening heat flux damage threshold for thermoset cables, as observed on the outer surface of the cabinet, can be used as a conservative surrogate for assessing the potential for thermal damage to solid-state and sensitive electronics within an electrical panel (cabinet).  Since the conclusions of the FDS analysis are based on heat flux exposure to the cabinet, the 65°C temperature damage criterion must still be assessed for other types of fire exposures to the enclosed sensitive electronics.
 +
</div>
  
 
===Cable Tray Fire Propagation===
 
===Cable Tray Fire Propagation===
−
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 08-0049, Section 11 of Supplement 1] clarifies the limits of the empirical cable tray fire propagation model in EPRI 1011989, NUREG/CR-6850.  The model can lead to conservative estimates of cable fire growth rates and unrealistically short room burnout times when used outside the Zone of Influence (ZOI)—i.e., outside the fire plume that extends above the ignition source.
+
[[File:TrayFireTesting.png|frameless||right||upright=1.7||alt=Multiple horizontal cable tray test, image from Chanter 8 of NUREG/CR&#8209;7010 Volume&nbsp;1|||Multiple horizontal cable tray test, image from Chanter 8 of NUREG/CR&#8209;7010 Volume&nbsp;1]]
 +
[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ&nbsp;08&#8209;0049, Section&nbsp;11 of Supplement&nbsp;1] clarifies the limits of the empirical cable tray fire propagation model in EPRI&nbsp;1011989, NUREG/CR&#8209;6850.  The model can lead to conservative estimates of cable fire growth rates and unrealistically short room burnout times when used outside the ZOI (i.e., outside the fire plume that extends above the ignition source).
  
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7010/ NUREG/CR-7010] documents the results of experiments to better understand and quantify the burning characteristics of grouped electrical cables commonly found in nuclear power plants. Volume 1 studies horizontal cable trays and Volume 2 studies vertical shafts and corridors. The experiments in Volume 1 address horizontal, ladder-back trays filled with unshielded cables in open configurations. The results of the full-scale experiments have been used to validate a simple model called FLASH-CAT (Flame Spread over Horizontal Cable Trays). The document also provides verification and validation material for the FLASH-CAT model. Volume 2 performed experiments on vertical cable tray configurations and enclosure effects. Volume 2 also extends the FLASH-CAT model to address cable trays within enclosures and vertical tray configurations.
+
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr7010/ NUREG/CR&#8209;7010] documents the results of experiments to better understand and quantify the burning characteristics of grouped electrical cables commonly found in nuclear power plants. Volume&nbsp;1 studies horizontal cable trays and Volume&nbsp;2 studies vertical shafts and corridors. The experiments in Volume&nbsp;1 address horizontal, ladder-back trays filled with unshielded cables in open configurations. The results of the full-scale experiments have been used to validate a simple model called FLASH&#8209;CAT (Flame Spread over Horizontal Cable Trays). The document also provides verification and validation material for the FLASH&#8209;CAT model. Volume&nbsp;2 performed experiments on vertical cable tray configurations and enclosure effects. Volume&nbsp;2 also extends the FLASH&#8209;CAT model to address cable trays within enclosures and vertical tray configurations.
−
 
+
<br style="clear: both;" />
−
[[File:TrayFireTesting.png|700px||center|Multiple horizontal cable tray test, image from Chanter 8 of NUREG/CR-7010 Volume 1]]
 
  
 
===Manual Non-Suppression Probability Estimates===
 
===Manual Non-Suppression Probability Estimates===
−
*[https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG-2169 EPRI 3002002936] provides updated manual non-suppression probability data through the year 2010. The manual NSPs documented in FAQ 08-0050 (NUREG/CR-6850 Supplement 1 Chapter 14) do not contain the latest NSP estimates.
+
Various reports have documented updates to the manual non-suppression probability data. The latest updates for each event type are summarized below.
−
 
 
−
*[https://www.nrc.gov/docs/ML1807/ML18075A086.html FAQ 17-0013] provides an update to the HEAF suppression curve (beyond that provided in NUREG-2169)
 
−
 
 
 
{| class="wikitable"
 
{| class="wikitable"
−
|+ style="text-align: left;" | Table 7-3 of [https://www.epri.com/#/pages/product/000000003002016051/ EPRI 3002016051 / NUREG-2230], Probability Distribution for Rate of Fires Suppressed Per Unit Time, λ
+
|+ style="text-align: center;" | Probability Distribution for Rate of Fires Suppressed Per Unit Time, λ
−
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Calculation Source Document
 
 
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Suppression Curve
 
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Suppression Curve
−
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Number of Events in Curve
+
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Number of Events<br>in Curve
−
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Total Duration (minutes)
+
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Total Duration<br>(minutes)
 
! colspan="4" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Rate of Fire Suppressed (λ)
 
! colspan="4" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Rate of Fire Suppressed (λ)
 +
! rowspan="2" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Calculation Source Document
 
|-
 
|-
 
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Mean
 
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Mean
−
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 5th Percent
+
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | ''P<sub>5</sub>''
−
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 50th Percent
+
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | ''P<sub>50</sub>''
−
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 95th Percent
+
| style="text-align: center; font-weight:bold; background-color:#dee2e6;" | ''P<sub>95</sub>''
 
|-
 
|-
−
| NUREG-2169
 
 
| Turbine-generator fires
 
| Turbine-generator fires
 
| style="text-align: center;" | 30
 
| style="text-align: center;" | 30
 
| style="text-align: center;" | 1167
 
| style="text-align: center;" | 1167
−
| style="text-align: center;" | 0.026
+
| style="text-align: center; padding: 0 1em 0 1em;" | 0.026
−
| style="text-align: center;" | 0.019
+
| style="text-align: center; padding: 0 1em 0 1em;" | 0.019
−
| style="text-align: center;" | 0.025
+
| style="text-align: center; padding: 0 1em 0 1em;" | 0.025
−
| style="text-align: center;" | 0.034
+
| style="text-align: center; padding: 0 1em 0 1em;" | 0.034
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2178, Vol. II
 
 
| Control room
 
| Control room
 
| style="text-align: center;" | 10
 
| style="text-align: center;" | 10
Line 2,044: Line 958:
 
| style="text-align: center;" | 0.372
 
| style="text-align: center;" | 0.372
 
| style="text-align: center;" | 0.604
 
| style="text-align: center;" | 0.604
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2]
 
|-
 
|-
−
| NUREG-2169
 
 
| Pressurized water reactor containment (at power)
 
| Pressurized water reactor containment (at power)
 
| style="text-align: center;" | 3
 
| style="text-align: center;" | 3
Line 2,053: Line 967:
 
| style="text-align: center;" | 0.067
 
| style="text-align: center;" | 0.067
 
| style="text-align: center;" | 0.157
 
| style="text-align: center;" | 0.157
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Containment (low power-shutdown)
 
| Containment (low power-shutdown)
 
| style="text-align: center;" | 31
 
| style="text-align: center;" | 31
Line 2,061: Line 975:
 
| style="text-align: center;" | 0.075
 
| style="text-align: center;" | 0.075
 
| style="text-align: center;" | 0.103
 
| style="text-align: center;" | 0.103
−
| style="text-align: center;" | 0.0136
+
| style="text-align: center;" | 0.136
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Outdoor transformers
 
| Outdoor transformers
 
| style="text-align: center;" | 24
 
| style="text-align: center;" | 24
Line 2,071: Line 985:
 
| style="text-align: center;" | 0.026
 
| style="text-align: center;" | 0.026
 
| style="text-align: center;" | 0.035
 
| style="text-align: center;" | 0.035
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Flammable gas
 
| Flammable gas
 
| style="text-align: center;" | 8
 
| style="text-align: center;" | 8
Line 2,080: Line 994:
 
| style="text-align: center;" | 0.033
 
| style="text-align: center;" | 0.033
 
| style="text-align: center;" | 0.056
 
| style="text-align: center;" | 0.056
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Oil fires
 
| Oil fires
 
| style="text-align: center;" | 50
 
| style="text-align: center;" | 50
Line 2,089: Line 1,003:
 
| style="text-align: center;" | 0.088
 
| style="text-align: center;" | 0.088
 
| style="text-align: center;" | 0.111
 
| style="text-align: center;" | 0.111
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Cable fires
 
| Cable fires
 
| style="text-align: center;" | 4
 
| style="text-align: center;" | 4
Line 2,098: Line 1,012:
 
| style="text-align: center;" | 0.127
 
| style="text-align: center;" | 0.127
 
| style="text-align: center;" | 0.267
 
| style="text-align: center;" | 0.267
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2230
+
| <div id="ECabLoc"></div>Electrical fires [[#ECabNote|<sup>&Dagger;</sup>]]
−
| Electrical fires*
 
 
| style="text-align: center;" | 74
 
| style="text-align: center;" | 74
 
| style="text-align: center;" | 653
 
| style="text-align: center;" | 653
Line 2,107: Line 1,021:
 
| style="text-align: center;" | 0.113
 
| style="text-align: center;" | 0.113
 
| style="text-align: center;" | 0.136
 
| style="text-align: center;" | 0.136
 +
| [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230]
 
|-
 
|-
−
| NUREG-2230
 
 
| Interruptible fires (Bin 15)
 
| Interruptible fires (Bin 15)
 
| style="text-align: center;" | 43
 
| style="text-align: center;" | 43
Line 2,116: Line 1,030:
 
| style="text-align: center;" | 0.148
 
| style="text-align: center;" | 0.148
 
| style="text-align: center;" | 0.189
 
| style="text-align: center;" | 0.189
 +
| [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230]
 
|-
 
|-
−
| NUREG-2230
 
 
| Growing fires (Bin 15)
 
| Growing fires (Bin 15)
 
| style="text-align: center;" | 18
 
| style="text-align: center;" | 18
Line 2,125: Line 1,039:
 
| style="text-align: center;" | 0.098
 
| style="text-align: center;" | 0.098
 
| style="text-align: center;" | 0.142
 
| style="text-align: center;" | 0.142
 +
| [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230]
 
|-
 
|-
−
| NUREG-2169
 
 
| Welding fires
 
| Welding fires
 
| style="text-align: center;" | 52
 
| style="text-align: center;" | 52
Line 2,134: Line 1,048:
 
| style="text-align: center;" | 0.107
 
| style="text-align: center;" | 0.107
 
| style="text-align: center;" | 0.133
 
| style="text-align: center;" | 0.133
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| NUREG-2169
 
 
| Transient fires
 
| Transient fires
 
| style="text-align: center;" | 43
 
| style="text-align: center;" | 43
Line 2,143: Line 1,057:
 
| style="text-align: center;" | 0.111
 
| style="text-align: center;" | 0.111
 
| style="text-align: center;" | 0.141
 
| style="text-align: center;" | 0.141
 +
| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en-US NUREG&#8209;2169]
 
|-
 
|-
−
| FAQ 17-0013
 
 
| HEAFs
 
| HEAFs
−
| style="text-align: center;" | 11
+
| style="text-align: center;" | 15
−
| style="text-align: center;" | 385
+
| style="text-align: center;" | 576
−
| style="text-align: center;" | 0.029
+
| style="text-align: center;" | 0.026
 
| style="text-align: center;" | 0.016
 
| style="text-align: center;" | 0.016
−
| style="text-align: center;" | 0.029
+
| style="text-align: center;" | 0.025
−
| style="text-align: center;" | 0.044
+
| style="text-align: center;" | 0.038
 +
| [https://www.epri.com/research/products/000000003002025942 NUREG-2262]
 
|-
 
|-
−
| NUREG-2169, NUREG-2230
 
 
| All fires
 
| All fires
−
| style="text-align: center;" | 398
+
| style="text-align: center;" | 401
−
| style="text-align: center;" | 5878
+
| style="text-align: center;" | 5661
−
| style="text-align: center;" | 0.068
+
| style="text-align: center;" | 0.071
−
| style="text-align: center;" | 0.062
+
| style="text-align: center;" | 0.065
−
| style="text-align: center;" | 0.068
+
| style="text-align: center;" | 0.071
−
| style="text-align: center;" | 0.073
+
| style="text-align: center;" | 0.077
 +
| [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230]
 
|-
 
|-
−
| colspan="8" style="background-color:#ffffff;" | * Electrical fire include non-cabinet electrical sources, such as electrical motors, indoor transformers, and junction boxes, among other electrical equipment.
+
| colspan="8" style="background-color:#ffffff; border-bottom: 0.5px solid white; border-left: 0.5px solid white; border-right: 0.5px solid white;" | <div id="ECabNote" style="font-size:88%; margin-right: 2em; margin-left: 2em; text-indent: -1em;">[[#ECabLoc|&Dagger;]] ''Electrical fires include non-cabinet electrical sources, such as electrical motors, indoor transformers, and junction boxes, among other electrical equipment.''</div>
 
|}
 
|}
  
 
===Incipient Detection===
 
===Incipient Detection===
−
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr2180/ NUREG-2180] NRC guidance on crediting incipient detection systems in fire PRA is discussed in NUREG-2180. The issuance of NUREG-2180 retires FAQ 08-0046 (Chapter 13 of NUREG/CR-6850 Supplement 1) as documented in the [https://www.nrc.gov/docs/ML1616/ML16167A444.pdf July 1, 2016 letter to NEI].
+
[https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr2180/ NUREG&#8209;2180] NRC guidance on crediting incipient detection systems in fire PRA is discussed in NUREG&#8209;2180. The issuance of NUREG&#8209;2180 retires FAQ&nbsp;08&#8209;0046 (Chapter&nbsp;13 of NUREG/CR&#8209;6850 Supplement&nbsp;1) as documented in the [https://www.nrc.gov/docs/ML1616/ML16167A444.pdf July 1, 2016 letter to NEI].
 +
 
 +
In 2024, EPRI and the NRC updated the alpha and pi parameters of the NUREG-2180 event tree in [https://www.epri.com/research/products/000000003002028821 NUREG-2180 Supplement 1]. Additionally, NUREG-2180 Supplement 1 Section 5 provides guidance on how to use NUREG-2180 with the framework in NUREG-2230. In summary, the concepts in [https://www.epri.com/#/pages/product/000000003002016051/ NUREG&#8209;2230] (interruptible fires) and NUREG-2180 (pre-flaming conditions) are considered independent.
 +
 
 +
Table 4-2, reproduced below provide the most recent alpha factors from NUREG-2180.
 +
{| class=wikitable
 +
|+ style="text-align: left;" | Fraction of fires in NUREG-2180 Supp. 1 that do not have an incipient phase
 +
|-
 +
! scope="col" style="width: 250px;" | Category
 +
! scope="col" style="width: 250px;" | Mean Alpha Fraction (5<sup>th</sup>/95<sup>th</sup>)
 +
|-
 +
|-
 +
| style="text-align: center;" | Power cabinets
 +
| style="text-align: center;" | 0.41 (0.30/0.53)
 +
|-
 +
| style="text-align: center;" | Low-voltage control cabinets
 +
| style="text-align: center;" | 0.10 (0.01/0.25)
 +
|}
 +
 
 +
For enhanced suppression, Table 4-3 and Table 4-5 in NUREG-2180 Supplement 1 provide the enhanced suppression rates which are summarized in the table below:
 +
 
 +
{| class="wikitable"
 +
|+ style="text-align: left;" | Enhanced Suppression Rates for Incipient Detection, λ
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Suppression Curve
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | Mean
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 5<sup>th</sup> percent
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 50<sup>th</sup> percent
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | 95<sup>th</sup> percent
 +
! rowspan="1" style="text-align: center; font-weight:bold; background-color:#dee2e6;" | NSP Reference
 +
|-
 +
| &pi;<sub>1</sub> In-cabinet enhanced suppression (using the Control room suppression curve)
 +
| style="text-align: center;" | 0.385
 +
| style="text-align: center;" | 0.209
 +
| style="text-align: center;" | 0.372
 +
| style="text-align: center;" | 0.604
 +
| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG&#8209;2178 Volume&nbsp;2]
 +
|-
 +
| &pi;<sub>2</sub> Area-wide, enhanced suppression
 +
| style="text-align: center;" | 0.226
 +
| style="text-align: center;" | 0.131
 +
| style="text-align: center;" | 0.220
 +
| style="text-align: center;" | 0.344
 +
| [https://www.epri.com/research/products/000000003002028821 NUREG-2180 Supplement 1]
 +
|}

Latest revision as of 21:15, 10 December 2024

EnclosureDynamics.png

Task Overview

Background

This task describes the method to examine the consequences of a fire. This includes consideration of scenarios involving single compartments, multiple fire compartments, and the main control room. Factors considered include initial fire characteristics, fire growth in a fire compartment or across fire compartments, detection and suppression, electrical raceway fire barrier systems, and damage from heat and smoke. Special consideration is given to turbine generator (T/G) fires, hydrogen fires, high-energy arcing faults, cable fires, and main control board (MCB) fires. There are considerable improvements in the method for this task over the EPRI FIVE and EPRI's Fire PRA Implementation Guide (TR‑105928, no longer available on epri.com) in nearly all technical areas.

Purpose

In the preceding tasks, the analyses were organized around compartments, assuming that a fire would have widespread impact within the compartment. In Task 11, for those compartments found to be potentially risk-significant (i.e., unscreened compartments), a detailed analysis approach is provided. As part of the detailed analysis, fire growth and propagation is modeled and possibility of fire suppression before damage to a specific target set is analyzed.

The detailed fire modeling process generally follows a common step structure, but the details of the analyses often vary depending on the specifics of the postulated fire scenario. This task provides separate procedures for three general categories of fire scenarios: fires affecting target sets located inside one compartment (discussed in Section 11.5.1); fires affecting the main control room (MCR; Section 11.5.2); and fires affecting target sets located in more than one fire compartment (multicompartment fire analysis; Section 11.5.3).

Task 11 provides final estimates for the frequency of occurrence of fire scenarios involving a specific fire ignition source failing a predefined target set before fire protection succeeds in protecting the target set. This result is combined in the final quantification steps that follow this task, with the CCDP/CLERP given failure of the target set to estimate the CDF/LERF contribution for each fire scenario. The CCDP/CLERP may include modified human error probabilities based on fire scenario specifics.

Scope

Detailed fire modeling encompasses an analysis of the physical fire behavior (i.e., fire growth and propagation analysis), equipment damage, fire detection, and fire suppression. The fire scenarios to analyze as part of this detailed analysis task are divided into three categories:

  • General single compartment fire scenarios. This general category covers fire scenarios damaging target sets located within the same compartment, exclusive of those scenarios within or impacting the MCR. In general, in this category, the fire ignition source is in the same compartment as the target set. The majority of fire scenarios analyzed generally falls into this category. The procedures applicable to the analysis of these fire scenarios are presented in Section 11.5.1.
  • MCR fire scenarios. This general category covers all fires that occur within the MCR. This category also covers scenarios involving fires in compartments other than the MCR that may force MCR abandonment. The MCR analysis procedures are presented in Section 11.5.2.
  • Multicompartment fire scenarios: This general category covers all fire scenarios where it is postulated that a fire may spread from one compartment to another and damage target elements in multiple compartments. In this category of scenarios, damaging effects of a fire (e.g., heat) are assumed to spread beyond the compartment of fire origin. The multicompartment fire analysis procedures are presented in Section 11.5.3.

A detailed fire modeling analysis is performed for each fire scenario in each unscreened fire compartment. For many compartments, it may be appropriate to develop several fire scenarios to appropriately represent the range of unscreened fire ignition sources (i.e., scenarios that would not screen out in Task 8) that might contribute to the fire risk. Detailed fire modeling may utilize a range of tools to assess fire growth and damage behavior, and the fire detection and suppression response, for specific fire scenarios.

ScreeningDetailed.png

The ultimate output of Task 11 is a set of fire scenarios, frequency of occurrence of those scenarios, and a list of target sets (in terms of fire PRA components) associated with the scenarios. For scenarios involving the MCR, the possibility of forced abandonment is also noted. Note that a fire scenario represents a specific chain of events starting with ignition of a fire ignition source, propagation of the fire effects to other items, and possibility of damaging a set of items identified as a target set before successful fire suppression.

Related Element of ASME/ANS PRA Standard

Fire Scenario Selection (FSS)

Related EPRI 1011989 NUREG/CR‑6850 Appendices

Appendix E, Appendix for Chapters 8 and 11, Severity Factors

Appendix F, Appendix for Chapter 8, Walkdown Forms

Appendix G, Appendix for Chapters 8 and 11, Heat Release Rates

Appendix H, Appendix for Chapters 8 and 11, Damage Criteria

Appendix L, Appendix for Chapter 11, Main Control Board Fires

Appendix M, Appendix for Chapter 11, High Energy Arcing Faults

Appendix N, Appendix for Chapter 11, Hydrogen Fires

Appendix O, Appendix for Chapter 11, Turbine Generator Fires

Appendix P, Appendix for Chapter 11, Detection and Suppression Analysis

Appendix Q, Appendix for Chapter 11, Passive Fire Protection Features

Appendix R, Appendix for Chapter 11, Cable Fires

Appendix S, Appendix for Chapter 11, Fire Propagation to Adjacent Cabinets

Appendix T, Appendix for Chapter 11, Smoke Damage

Fire Modeling Tools

Fire modeling tools include a range of complexity, from Excel-based tools which rely on physics-based algebraic relationships such as EPRI FIVE and the NRC FDTs, to moderately complex tools such as CFAST's two-zone computational model, up to the most complex (and computationally-demanding) finite element analysis tools such as FDS.

Fire Model Verification and Validation

NUREG‑1824 EPRI 1011999 documents the verification and validation (V&V) of five fire models that are commonly used in NPP applications. The models in the V&V report include:

  • NRC's NUREG‑1805 Revision 1
  • EPRI's Fire-Induced Vulnerability Evaluation Revision 1 (FIVE-REV 1)
  • National Institute of Standards and Technology's (NIST) Consolidated Model of Fire Growth and Smoke Transport (CFAST) Version 5
  • NIST's Fire Dynamics Simulator (FDS) Version 4
  • Electricite de France's (EdF) MAGIC Version 4.1.1

NUREG‑1824 Supplement 1 EPRI 3002002182 updates the original NUREG‑1824 / EPRI 1011999 report with additional experiments and uses the latest versions of the fire modeling software available at the time of publication. The models in the V&V report include:

  • NRC's Fire Dynamics Tools (FDTs Version 1805.1)
  • EPRI's Fire-Induced Vulnerability Evaluation (FIVE Revision 2)
  • NIST's CFAST Version 7.0.0
  • EdF's MAGIC Version 4.1.3
  • NIST's FDS Version 6.2.0

Fire Models Included in V&V Guidance

EPRI FIVE

NRC Fire Dynamics Tools - NUREG‑1805

NIST CFAST

NIST FDS and Smokeview

EdF's MAGIC is available through EPRI for EPRI members

Fire Model User's Guide

NUREG‑1934 EPRI 1023259 provides guidance on the proper application of fire models to nuclear power plant fire scenarios. Eight (8) different example fire scenarios are developed and discussed in this report.

Ignition Source Specific Fire Modeling Guidance

Bin Plant Location Ignition Source Fire Modeling Guidance Fire Modeling Reference
1 Battery Room Batteries Use HRR distribution for Motors (Distribution 7 of Table G-1) EPRI 1011989 / NUREG/CR‑6850
2 Containment (PWR) Reactor Coolant Pumps Reactor coolant pump fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.14 electrical / 0.86 oil).

Electrical (motor) fires: HRR distributions and fire durations are provided in Chapter 5 of NUREG‑2178, Volume 2 / EPRI 3002016052. The pump HRR in NUREG/CR‑6850 is bounding compared with the updated values, and is therefore still valid.

Oil fire split fractions: The oil spill size fractions recommended in NUREG/CR‑6850 Appendix E.3 should be applied.

Oil fire HRR: See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.

NUREG‑2178 Volume 2 / EPRI 3002016052

EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

3 Containment (PWR) Transients and Hotwork
NUREG‑2233 / EPRI 3002018231 provides updated HRR distributions and zones of influence for generic transient fires and also transient combustible control locations (TCCLs). These HRRs are based upon the laboratory testing conducted by EPRI and the NRC on relevant transient ignition sources expected in nuclear power plants (see EPRI 3002015997 / NUREG‑2232). The HRR distribution (Distribution 8 of Table G‑1 in NUREG/CR‑6850) is bounding compared with the updated generic HRR distribution, and is therefore still valid.

NUREG‑2233 / EPRI 3002018231 also recommends fire modeling parameters including fire growth and decay parameters, yields of minor products of combustion, heat of combustion, and the physical size and effective elevation of the fire.

NUREG‑2233 / EPRI 3002018231

NUREG‑2232 / EPRI 3002015997

NUREG/CR‑6850 / EPRI 1011989

4 Control Room Main Control Board Target damage: Appendix L of NUREG/CR‑6850 provides a statistical model for estimating the conditional probability of damage to a set of target items inside the main control board. §

Target damage: NUREG‑2178 Volume 2 / EPRI 3002016052 Section 7 provides an alternative to the method described in Appendix L of NUREG/CR‑6850 for evaluating the risk of fire events originating in the MCB, whereby MCB fire scenarios are modeled as a progression of damage states using an event tree model. § In this formulation, each damage state requires the definition of a target set, which consists of one or more MCB functions that can be damaged by fire. The functions within the scope of this analysis are those that are represented with basic events in the plant response model and supported with cables routed within the MCB. The alternative model described in this guidance explicitly incorporates two characteristics of MCB fires observed in operating experience—relatively small fires in low-voltage panels and the ability for prompt detection and suppression by control room operators. Operating experience suggests that the majority of fires in the MCB are limited to a single subcomponent or group of subcomponents near the point of ignition. In addition, these fires are promptly detected and suppressed by control room operators. Therefore, the event tree model explicitly accounts for the operator’s ability to quickly detect and suppress the fire before growth and/or propagation.

§ The original NUREG/CR‑6850 Appendix L method and NUREG‑2178 Volume 2 event tree method BOTH remain viable as methods for assessing MCB fires.

HRR distributions: NUREG‑2178 Volume 1 / EPRI 3002005578 provides updated HRR distributions for the main control board based on control cabinet size (either Function Group 4a (Large Enclosures) or Group 4b (Medium Enclosures)).

Propagation to adjacent cabinet: NUREG‑2178 Volume 2 / EPRI 3002016052 Section 4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.

EPRI 1011989 / NUREG/CR‑6850

NUREG‑2178 Volume 1 / EPRI 3002005578

NUREG‑2178 Volume 2 / EPRI 3002016052

5 Control/Aux/Reactor Building Cable fires caused by welding and cutting FAQ 13‑0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR‑6850. However, the current method of evaluating cable fire risk in NUREG/CR‑6850 remains an acceptable approach. EPRI 1011989 / NUREG/CR‑6850

FAQ 13‑0005

6 Control/Aux/Reactor Building Transient fires caused by welding and cutting See Bin 3 for treatment of transient fires. See Bin 3
7 Control/Aux/Reactor Building Transients See Bin 3 for treatment of transient fires. See Bin 3
8 Diesel Generator Room Diesel Generators There is limited guidance on modeling diesel generator fires in NUREG/CR-6850:
  • Diesel generator fires have an electrical (motor) component and an oil component. The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.16 electrical / 0.84 oil).
  • Section G.4 of NUREG/CR‑6850 provides guidance on flammable liquid (oil) fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.
 EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

9 Plant-Wide Components Air Compressors Air compressor fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.83 electrical / 0.17 oil).

Electrical (motor) fires: HRR distributions and fire durations are provided in Chapter 5 of NUREG‑2178, Volume 2 / EPRI 3002016052.

Oil fire split fractions: The oil spill size fractions recommended in NUREG/CR‑6850 Appendix E.3 should be applied.

Oil fire HRR: See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.

NUREG‑2178 Volume 2 / EPRI 3002016052

EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

10 Plant-Wide Components Battery Chargers Table 7‑1 of NUREG‑2178 Volume 1 provides HRR distributions for Group 2 electrical enclosures, including battery chargers. NUREG‑2178 Volume 1 / EPRI 3002005578
11 Plant-Wide Components Cable fires caused by welding and cutting FAQ 13‑0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR‑6850. However, the current method of evaluating cable fire risk in NUREG/CR‑6850 remains an acceptable approach. EPRI 1011989 / NUREG/CR‑6850

FAQ 13‑0005

12 Plant-Wide Components Cable Run (self-ignited cable fires) FAQ 13‑0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR‑6850. However, the current method of evaluating cable fire risk in NUREG/CR‑6850 remains an acceptable approach. EPRI 1011989 / NUREG/CR‑6850

FAQ 13‑0005

13 Plant-Wide Components Dryers The transient HRR is recommended for Bin 13 dryer fires (refer to Table 11‑1 of NUREG/CR‑6850). NUREG‑2233 / EPRI 3002018231 provides updated HRR distribution and zones of influence for generic transient fires (see also Bin 3). NUREG‑2233 / EPRI 3002018231

NUREG/CR‑6850 / EPRI 1011989

14 Plant-Wide Components Electric Motors
Chapter 5 of NUREG‑2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for electric motors (compared with the original distribution from NUREG/CR‑6850 Table G-1). To improve realism, the HRRs in NUREG‑2178 Volume 2 are characterized by horsepower, and NUREG‑2178 Volume 2 also provides growth and decay timing. 		NUREG‑2178 Volume 2 / EPRI 3002016052
15 Plant-Wide Components Electrical Cabinets
Propagation from electrical cabinets: FAQ 08‑0042 (Section 8 of Supplement 1) clarifies the treatment of fire spread beyond the ignition source for electrical cabinets considering conditions such as the presence of ventilation, robust door construction, and seal penetration. This clarification was needed due to conflicting language in Chapters 6 and 11 and Appendix G of NUREG/CR‑6850. FAQ 08‑0042 states that the wording in Chapter 11 is correct.

Propagation to adjacent cabinet: NUREG‑2178 Volume 2 / EPRI 3002016052 Section 4 provides a method for refining the postulated spread of fires from one cabinet to an adjacent cabinet. This report provides screening guidance, a conditional probability (split fraction), a limitation of spread to a single adjacent cabinet only, and timing for the spread.

Propagation for Well-Sealed MCCs Greater Than 440V: FAQ 14‑0009 provides clarification for the treatment of fire propagation from well-sealed MCCs operating at greater than 440V.

Heat Release Rates: NUREG‑2178 Volume 1 / EPRI 3002005578 provides updated heat release distributions for electrical enclosures. The analyst should review the equipment function or size to determine an appropriate heat release rate distribution provided in Table 7-1. Heat release rates for electrical cabinets are also found in Table G-1 of EPRI 1011989 / NUREG/CR‑6850.

Fire location: FAQ 08‑0043 clarifies the treatment of fire location in electrical cabinets.

Fire diameter: NUREG‑2178 Volume 1 / EPRI 3002005578 Section 4.2 provides guidance on the selection of an appropriate fire diameter.

Obstructed plume model: NUREG‑2178 Volume 1 / EPRI 3002005578 Section 6 provides a method to account for the impact of the enclosure on the vertical thermal zone of influence above the enclosure during a fire. A summary of the obstructed plume methodology and the results can be found here.

Obstructed radiation model: NUREG‑2178 Volume 2 / EPRI 3002016052 Section 3 provides a method to account for the impact of the enclosure on the horizontal (radial) zone of influence surrounding the enclosure during a fire. This report establishes values for the ZOI measured from the cabinet face as a function of the cabinet type, cable type, fuel loading, and fire size.

Growth and suppression: NUREG‑2230 / EPRI 3002016051 includes the following updates:

1) Updated fire ignition frequency (Task 6)
2) Classification of electrical cabinet fires into one of two profiles:
Interruptible fires 0.723
Growing fires 0.277
3) HRR timing for interruptible and growing fires:

Interruptible fires – Option 1:

Pre-growth (negligible HRR) 9 minutes
Growth 7 minutes
Steady state 5 minutes
Decay 13 minutes

Interruptible fires – Option 2:
(NUREG/CR‑6850 timing profile supplemented with pre-growth period)

Pre-growth (negligible HRR) 4 minutes
Growth 12 minutes
Steady state 8 minutes
Decay 19 minutes

Growing fires:
 (unchanged from NUREG/CR‑6850)

Growth 12 minutes
Steady state 8 minutes
Decay 19 minutes
4) Changes to the detection-suppression event tree to better represent the operating experience.
The detection-suppression event tree was revised to better represent the manual suppression outcomes observed in operating experience (including the development of two new manual suppression curves). See EPRI 3002016051 / NUREG‑2230 for full details.
 EPRI 1011989 / NUREG/CR‑6850

FAQ 08‑0042, Section 8 of Supplement 1

FAQ 14‑0009

NUREG‑2178 Volume 1 / EPRI 3002005578

FAQ 08‑0043, Section 12 of Supplement 1

NUREG‑2230 / EPRI 3002016051

NUREG‑2178 Volume 2 / EPRI 3002016052

16.a Plant-Wide Components High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V) Appendix M (M.4.2) provides an empirical model for determination of the ZOI from High Energy Arcing Faults (HEAFs). EPRI 1011989 / NUREG/CR‑6850
16.b Plant-Wide Components High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V) Appendix M (M.4.2) provides an empirical model for determination of the ZOI from HEAFs. EPRI 1011989 / NUREG/CR‑6850
16.1 Plant-Wide Components HEAF for segmented bus ducts Section 7.2.1.5 of Supplement 1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for segmented bus duct fires. FAQ 07-0035, Section 7 of Supplement 1
16.2 Plant-Wide Components HEAF for iso-phase bus ducts Section 7.2.1.5 of Supplement 1 (FAQ 07-0035) provides an empirical model for estimating the ZOI for iso-phase duct fires. FAQ 07-0035, Section 7 of Supplement 1
17 Plant-Wide Components Hydrogen Tanks See Appendix N of NUREG/CR‑6850. EPRI 1011989 / NUREG/CR‑6850
18 Plant-Wide Components Junction Boxes FAQ 13‑0006 provides a definition for junction boxes that allows the characterization and quantification of these scenarios in fire compartments that require detailed fire modeling analysis. FAQ 13‑0006
19 Plant-Wide Components Miscellaneous Hydrogen Fires See Appendix N of NUREG/CR‑6850. EPRI 1011989 / NUREG/CR‑6850
20 Plant-Wide Components Off-gas/H2 Recombiner (BWR) See Appendix N of NUREG/CR‑6850. EPRI 1011989 / NUREG/CR‑6850
21 Plant-Wide Components Pumps and large hydraulic valves Pump fires are classified as either electrical (motor) or oil. The split fraction between pump electrical and oil fires is updated in EPRI 3002002936 / NUREG‑2169 (0.69 electrical / 0.31 oil).

Electrical (motor) fires: In NUREG/CR‑6850, Bin 21 pump electrical fires were distinguished from non-pump motor fires. Research documented in NUREG‑2178 Volume 2 / EPRI 3002016052 suggests that there is little or no difference between pump motor fires and non-pump motor fires, and so electric motors and motor-driven pumps have been consolidated into a single ignition source. To improve realism, the HRRs in NUREG‑2178 Volume 2 are characterized by horsepower, and NUREG‑2178 Volume 2 also provides growth and decay timing. The pump HRR in NUREG/CR‑6850 is bounding compared with the updated values, and is therefore still valid.

Oil fire split fractions: The methods panel decision letter (ML12171A583) updates the likelihood and oil spill sizes for general pump oil fires other than large hydraulic valves. Specifically:

  • 88% of oil fires from pumps limit damage to the pump itself,
  • 7% of oil fires from pumps produce oil pools of 10% capacity, and
  • 5% of oil fires from pumps produce oil pools of 100% capacity.

For large hydraulic valves (which are included in Bin 21), the oil spill size fractions recommended in NUREG/CR‑6850 Appendix E.3 should still be applied.

Oil fire HRR: See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.

EPRI 3002002936 / NUREG‑2169

NUREG‑2178 Volume 2 / EPRI 3002016052

Methods Panel Decision, ML12171A583

EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

22 Plant-Wide Components RPS MG Sets The motor HRR is recommended for Bin 22 RPS MG Sets (refer to Table 11‑1 of NUREG/CR‑6850). See Bin 14. EPRI 1011989 / NUREG/CR‑6850

See Bin 14

23a Plant-Wide Components Transformers (oil filled) See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

23b Plant-Wide Components Transformers (dry) Chapter 5 of NUREG‑2178 Volume 2 / EPRI 3002016052 provides updated HRR distributions for dry transformers (compared with the original distribution from NUREG‑6850) based on power rating, as well as growth and decay timing. NUREG‑2178 Volume 2 / EPRI 3002016052
24 Plant-Wide Components Transient fires caused by welding and cutting See Bin 3 for treatment of transient fires. See Bin 3
25 Plant-Wide Components Transients See Bin 3 for treatment of transient fires. See Bin 3
26 Plant-Wide Components Ventilation Subsystems Ventilation subsystem fires are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.95 electrical / 0.05 oil).

Electrical (motor) fires: HRR distributions and fire durations are provided in Chapter 5 of NUREG‑2178, Volume 2 / EPRI 3002016052.

Oil fire split fractions: The oil spill size fractions recommended in NUREG/CR‑6850 Appendix E.3 should be applied.

Oil fire HRR: See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.

NUREG‑2178 Volume 2 / EPRI 3002016052

EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

27 Transformer Yard Transformer - Catastrophic The catastrophic failure of a large transformer is defined as an energetic failure of the transformer that includes a rupture of the transformer tank, oil spill, and burning oil splattered a distance from the transformer. The analyst should use the frequency and 1.) determine availability of offsite power based on the function of the transformer(s) and 2.) consider propagation to adjacent (not nearby) buildings or components. A propagation path may be considered at the location of open or sealed penetrations, e.g., where a bus-duct enters from the Yard into the Turbine Building. Structural damage need only be considered only where appropriate shields are not present to protected structures and components against blast or debris. EPRI 1011989 / NUREG/CR‑6850
28 Transformer Yard Transformer - Non Catastrophic In this failure, oil does not spill outside the transformer tank and the fire does not necessarily propagate beyond the fire source transformer. Analyst can use all the frequency and assume total loss of the "Transformer/ Switch Yard" or may split this frequency equally among the large transformers of the area and assume loss of each transformer separately. Loss of offsite power should be determined based on the function of the affected transformer(s). EPRI 1011989 / NUREG/CR‑6850
29 Transformer Yard Yard Transformers (Others) In the screening phase of the project, the analyst may conservatively assign the same frequency to all of the items in this group. If the scenario would not screen out, the frequency may then be divided among the various items in this group. A relative ranking scheme may be used for this purpose. The ranking may be based on the relative characteristics of the item and the analysts' judgment. EPRI 1011989 / NUREG/CR‑6850
30 Turbine Building Boiler See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires. EPRI 1011989 / NUREG/CR‑6850

EPRI 3002005303

31 Turbine Building Cable fires caused by welding and cutting FAQ 13‑0005 provides additional guidance for detailed fire modeling on both self-ignited cable fires and cable fires caused by welding and cutting. This FAQ outlines a more realistic approach for addressing these types of fires in cable trays and suggests replacement text for Section R.1 of NUREG/CR‑6850. However, the current method of evaluating cable fire risk in NUREG/CR‑6850 remains an acceptable approach. EPRI 1011989 / NUREG/CR‑6850

FAQ 13‑0005

32 Turbine Building Main Feedwater Pumps Main feedwater pumps are classified as either electrical (motor) or oil. The split fraction between electrical and oil fires is provided in NUREG/CR‑6850 (0.11 electrical / 0.89 oil).

Electrical (motor) fires: HRR distributions and fire durations are provided in Chapter 5 of NUREG‑2178, Volume 2 / EPRI 3002016052. The pump HRR in NUREG/CR‑6850 is bounding compared with the updated values, and is therefore still valid.

Oil fire split fractions: FAQ 08‑0044 (Section 9 of NUREG/CR‑6850 Supplement 1) clarifies the severity factors for small fires (0.966 for a leak that impacts the pump), large fires (0.0306 for 10% inventory spill), and very large fires (0.0034 for 100% inventory spill).

Oil fire HRR: See Section G.4 of NUREG/CR‑6850 for HRR for flammable liquid fires. EPRI 3002005303, although not formally reviewed by the NRC, provides a method to more realistically characterize the HRR profile and duration for liquid spill fires.

NUREG‑2178 Volume 2 / EPRI 3002016052

EPRI 1011989 / NUREG/CR‑6850

FAQ 08‑0044, Section 9 of Supplement 1

EPRI 3002005303

33 Turbine Building Turbine Generator Excitor Appendix O (Section O.2.1 & Table O-2) recommends assuming the excitor fire is limited to the excitor itself. EPRI 1011989 / NUREG/CR‑6850
34 Turbine Building Turbine Generator Hydrogen Appendix O (Section O.2.2 & Table O-2) provides guidance for both limited and severe T/G Hydrogen fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection. EPRI 1011989 / NUREG/CR‑6850
35 Turbine Building Turbine Generator Oil Appendix O (Section O.2.3 & Table O-2) provides guidance for both limited and severe T/G oil fires. Table O-2 also provides a conditional probability for a catastrophic T/G fire involving the hydrogen, oil and blade ejection. EPRI 1011989 / NUREG/CR‑6850
36 Turbine Building Transient fires caused by welding and cutting See Bin 3 for treatment of transient fires. See Bin 3
37 Turbine Building Transients See Bin 3 for treatment of transient fires. See Bin 3

Recommended HRR Values

The following tables summarize the latest research on HRR probability distributions. These distributions were developed to increase realism in modeling electrical cabinet fires and transient fires. As such, HRR probability distributions available in earlier publications (such as Appendix G of NUREG/CR-6850) are bounding. In the case of electric motors and transformers, the latest HRR probability distributions are based on equipment sizes so that the fires can also be realistically characterized.

Electrical Cabinets (NUREG‑2178 Volume 1)

NUREG‑2178 Volume 1 / EPRI 3002005578 provides HRR distributions for electrical enclosures.

Electrical Enclosures
Enclosure Class / Function Group Enclosure Ventilation
(Open or Closed Doors)
Fuel Type†
(TS/QTP/SIS or TP Cables) 		Gamma Distribution
(a) Default (b) Low Fuel Loading (c) Very Low Fuel Loading
    α         β     P75 (kW) P98 (kW)     α         β     P75 (kW) P98 (kW)     α         β     P75 (kW) P98 (kW)
1 - Switchgear and Load Centers Closed TS/QTP/SIS 0.32 79 30 170 Not Applicable Not Applicable
Closed TP 0.99 44 60 170
2 - MCCs and Battery Chargers Closed TS/QTP/SIS 0.36 57 25 130 Not Applicable Not Applicable
Closed TP 1.21 30 50 130
3 - Power Inverters Closed TS/QTP/SIS 0.23 111 25 200 Not Applicable Not Applicable
Closed TP 0.52 73 50 200
4a - Large Enclosures
    >1.42 m3 (>50 ft3) 		Closed TS/QTP/SIS 0.23 223 50 400 0.23 111 25 200 0.38 32 15 75
Closed TP 0.52 145 100 400 0.52 73 50 200 0.88 21 25 75
Open TS/QTP/SIS 0.26 365 100 700 0.26 182 50 350 0.38 32 15 75
Open TP 0.38 428 200 1000 0.38 214 100 500 0.88 21 25 75
4b - Medium Enclosures
    ≤1.42 m3 (50 ft3) and
    > 0.34 m3 (12 ft3) 		Closed TS/QTP/SIS 0.23 111 25 200 0.27 51 15 100 0.88 12 15 45
Closed TP 0.52 73 50 200 0.52 36 25 100 0.88 12 15 45
Open TS/QTP/SIS 0.23 182 40 325 0.19 92 15 150 0.88 12 15 45
Open TP 0.51 119 80 325 0.3 72 25 150 0.88 12 15 45
4c - Small Enclosures
    ≤ 0.34 m3 (12 ft3) 		Not Applicable All 0.88 12 15 45 Not Applicable Not Applicable
† Legend for Fuel Type: TS = Thermoset, TP = Thermoplastic, QTP = Qualified Thermoplastic, SIS = Synthetic Insulated Switchboard Wire or XLPE-Insulated Conductor

Motors and Dry Transformers (NUREG‑2178 Volume 2)

NUREG‑2178 Volume 2 / EPRI 3002016052 provides HRR distributions for motors and dry transformers.

Motors
Motor
Classification Group 		Motor Size
(horsepower)

Gamma Distribution

α β P75 (kW) P98 (kW)
A >5-30 1.34 3.26 6 15
B >30-100 1.17 8.69 14 37
C >100 1.10 24.19 37 100
Dry Transformers
Transformer
Classification Group 		Transformer Power
(kVA)

Gamma Distribution

α β P75 (kW) P98 (kW)
A >45-75 0.38 12.84 6 30
B >75-750 0.41 28.57 15 70
C >750 0.46 50.26 30 130

Transients (NUREG‑2233)

NUREG‑2233 / EPRI 3002018231 provides HRR distributions for both generic and "transient combustible control location" (TCCL) type transient fires. The report also provides values for total energy release (TER) and zones of influence (ZOIs), but only HRRs are included here.

Transients
Type

Gamma Distribution

α β P75 (kW) P98 (kW)
Generic 0.271 141 41.6 278
TCCL 0.314 67.3 24.6 143

Additional Fire Modeling Considerations

Time-to-Damage Models for Cables

Three approaches are documented for assessing the time-to-damage for cables.

Exposure threshold The method described in EPRI 1011989 / NUREG/CR‑6850 Appendix H consists of using the threshold exposure gas temperature or heat flux for determining cable failure. See below for damage criteria. This is the simplest of the approaches, but it can be fairly conservative because it does not account for the time it takes for cable heating to actually result in damage.

Heat soak The method described in Appendix A of NUREG‑2178 Volume 2 / EPRI 3002016052 considers exposure integrated over time based upon the time to failure data provided in Appendix H of NUREG/CR‑6850. This method is less conservative than the above "exposure threshold" method but still conservative when compared with THIEF. Time to failure data for Kerite-FR materials are provided in NUREG‑2232 / EPRI 3002015997.

Heat conduction (Thermally-Induced Electrical Failure, "THIEF") The THIEF approach presented in NUREG/CR‑6931 Volume 3 and NUREG‑1805 Supplement 1 performs a one-dimensional (1-D), cylindrical heat transfer calculation for a cable exposed to a time-varying exposure to determine when the cable jacket will fail based on the jacket’s inner temperature. Validation of the model shows that it does well at computing the temperature rise of the cable jacket; however, because it requires cable-specific data (dimensions and mass), it cannot be applied in a generic manner such as the exposure threshold or heat soak methods.

Location Factor

When the fire is located near a wall or in a corner, less air can be entrained into the fire plume. Less air entrainment into the fire plume produces higher plume temperatures. The flames from fires in contact with wall and corner surfaces tend to be longer, also resulting in higher plume temperatures. For such fires, a location factor, traditionally 2 for fires near a wall or 4 for fires near a corner, has been applied as a correction to the plume temperature calculation. NUREG‑2178 Volume 2 / EPRI 3002016052 Section 6 demonstrates that the traditional approach is overly conservative, and presents new factors based on the distance from the source to a corner or wall:

Configuration Location Factor
0–0.3 m [0–1 ft] 0.3–0.6 m [1–2 ft] >0.6 m [2 ft]
Corner 4 2 1
Wall 1 1 1

EPRI 3002005303 provides the technical basis for the work in NUREG‑2178 Volume 2.

Radiation effects modeling

Chapter 2 of NUREG‑2178 Volume 2 / EPRI 3002016052 evaluates radiation emission models used to assess horizontal zone of influence. The two commonly-implemented empirical models – the point source method and the solid flame method – are compared against a computational model (Fire Dynamics Simulator). The results of this chapter recommended that the adjusted solid flame model should generally be considered a preferred method over the point source method because the adjusted flame model shows somewhat better characteristics in terms of a) NOT under-predicting and b) improved statistical error and bias. This applies to all fire types, where the flame is unobstructed. The modeling of obstructed radiation circumstances as present in electrical cabinets is discussed in the context of Bin 15 electrical cabinet fire modeling.

High Energy Arcing Fault (HEAF) Research

EPRI and the NRC are currently developing further methods and data on the risk impact of HEAF events; for example frequencies, fault duration, and zone of influence (e.g., copper versus aluminum). EPRI has issued the following white paper reports:

  • EPRI 3002015992 provides an overview of nuclear power station electrical distribution systems and covers fault protection system concepts, fault isolation times, the potential impact of HEAFs on Class 1E electrical distribution systems, and typical industry practices and programs that help ensure proper operation. This report also provides some preliminary risk insights based on a review of existing data.
  • EPRI 3002011922 reviews the operating experience to gain insights about equipment type, event characteristics, and the range of damage for HEAF events occurring at nuclear power plants within the United States and internationally. This paper also explores recent U.S. and international HEAF test programs for low- and medium-voltage electrical equipment and summarizes the insights gained from these test programs, including the potential role of aluminum oxidation in HEAF severity.
  • EPRI 3002015459 demonstrates that an effective preventive maintenance program is important in minimizing the likelihood and/or severity of a HEAF event. Sixty‑four percent (64%) of HEAF events were determined to be preventable, and the most prevalent cause of failure was inadequate maintenance. These data demonstrate that proper maintenance can prevent most HEAF events. Effective maintenance practices and strategies are summarized in this report by equipment type, including circuit breakers, bus ducts, protective relays, and cables.

Fire Propagation and Suppression Guidance

Detection-Suppression Event Tree

For electrical cabinet fires, Section 5 of NUREG‑2230 / EPRI 3002016051 presents a revised detection-suppression event tree model for characterizing fire detection and suppression activities in response to a fire event (revised compared with the original model described in Appendix P of NUREG/CR‑6850 and Chapter 14 of NUREG/CR‑6850 Supplement 1). This modification is intended to capture the potential for plant personnel suppression during the early stages of an electrical cabinet fire. For other fire types, the original model described in Appendix P of NUREG/CR‑6850 and Chapter 14 of NUREG/CR‑6850 Supplement 1 should be used.

Fire Damage Criteria

Cable Damage Criteria

FAQ 16‑0011 provides radiant heating and temperature criteria for bulk cable tray ignition (which was not previously provided in NUREG/CR‑6850). The bounding cable damage and ignition criteria remain the same. A summary of the results are shown below. The analyst should refer to both NUREG/CR‑6850 Appendix H and FAQ 16‑0011 for full guidance.

Bounding Cable Damage / Ignition Criteria Bulk Cable / Tray Ignition Criteria
Cable Type Radiant Heating Temperature Radiant Heating Temperature
Thermoplastic 6 kW/m2 205°C 25 kW/m2 500°C
Thermoset 11 kW/m2 330°C

For Kerite cables, refer to NUREG/CR‑7102 for damage criteria. Originally FAQ 08‑0053 was initiated to clarify failure thresholds for Kerite cables and the resolution can be found in the closure memo dated June 6, 2012 following the publication of NUREG/CR‑7102.

Treatment of Sensitive Electronics

FAQ 13‑0004 provides supplemental guidance for the application of the lower damage thresholds provided in NUREG/CR‑6850 Section 8.5.1.2 and H.2 for solid-state components. Fire Dynamics Simulator (FDS) modeling results support the recommendation that a generic screening heat flux damage threshold for thermoset cables, as observed on the outer surface of the cabinet, can be used as a conservative surrogate for assessing the potential for thermal damage to solid-state and sensitive electronics within an electrical panel (cabinet). Since the conclusions of the FDS analysis are based on heat flux exposure to the cabinet, the 65°C temperature damage criterion must still be assessed for other types of fire exposures to the enclosed sensitive electronics.

Cable Tray Fire Propagation

Multiple horizontal cable tray test, image from Chanter 8 of NUREG/CR‑7010 Volume 1

FAQ 08‑0049, Section 11 of Supplement 1 clarifies the limits of the empirical cable tray fire propagation model in EPRI 1011989, NUREG/CR‑6850. The model can lead to conservative estimates of cable fire growth rates and unrealistically short room burnout times when used outside the ZOI (i.e., outside the fire plume that extends above the ignition source).

NUREG/CR‑7010 documents the results of experiments to better understand and quantify the burning characteristics of grouped electrical cables commonly found in nuclear power plants. Volume 1 studies horizontal cable trays and Volume 2 studies vertical shafts and corridors. The experiments in Volume 1 address horizontal, ladder-back trays filled with unshielded cables in open configurations. The results of the full-scale experiments have been used to validate a simple model called FLASH‑CAT (Flame Spread over Horizontal Cable Trays). The document also provides verification and validation material for the FLASH‑CAT model. Volume 2 performed experiments on vertical cable tray configurations and enclosure effects. Volume 2 also extends the FLASH‑CAT model to address cable trays within enclosures and vertical tray configurations.

Manual Non-Suppression Probability Estimates

Various reports have documented updates to the manual non-suppression probability data. The latest updates for each event type are summarized below.

Probability Distribution for Rate of Fires Suppressed Per Unit Time, λ
Suppression Curve Number of Events
in Curve 		Total Duration
(minutes) 		Rate of Fire Suppressed (λ) Calculation Source Document
Mean P5 P50 P95
Turbine-generator fires 30 1167 0.026 0.019 0.025 0.034 NUREG‑2169
Control room 10 26 0.385 0.209 0.372 0.604 NUREG‑2178 Volume 2
Pressurized water reactor containment (at power) 3 40 0.075 0.020 0.067 0.157 NUREG‑2169
Containment (low power-shutdown) 31 299 0.104 0.075 0.103 0.136 NUREG‑2169
Outdoor transformers 24 928 0.026 0.018 0.026 0.035 NUREG‑2169
Flammable gas 8 234 0.034 0.017 0.033 0.056 NUREG‑2169
Oil fires 50 562 0.089 0.069 0.088 0.111 NUREG‑2169
Cable fires 4 29 0.138 0.047 0.127 0.267 NUREG‑2169
Electrical fires ‡ 		74 653 0.113 0.093 0.113 0.136 NUREG‑2230
Interruptible fires (Bin 15) 43 288 0.149 0.114 0.148 0.189 NUREG‑2230
Growing fires (Bin 15) 18 179.5 0.100 0.065 0.098 0.142 NUREG‑2230
Welding fires 52 484 0.107 0.084 0.107 0.133 NUREG‑2169
Transient fires 43 386 0.111 0.085 0.111 0.141 NUREG‑2169
HEAFs 15 576 0.026 0.016 0.025 0.038 NUREG-2262
All fires 401 5661 0.071 0.065 0.071 0.077 NUREG‑2230
‡ Electrical fires include non-cabinet electrical sources, such as electrical motors, indoor transformers, and junction boxes, among other electrical equipment.

Incipient Detection

NUREG‑2180 NRC guidance on crediting incipient detection systems in fire PRA is discussed in NUREG‑2180. The issuance of NUREG‑2180 retires FAQ 08‑0046 (Chapter 13 of NUREG/CR‑6850 Supplement 1) as documented in the July 1, 2016 letter to NEI.

In 2024, EPRI and the NRC updated the alpha and pi parameters of the NUREG-2180 event tree in NUREG-2180 Supplement 1. Additionally, NUREG-2180 Supplement 1 Section 5 provides guidance on how to use NUREG-2180 with the framework in NUREG-2230. In summary, the concepts in NUREG‑2230 (interruptible fires) and NUREG-2180 (pre-flaming conditions) are considered independent.

Table 4-2, reproduced below provide the most recent alpha factors from NUREG-2180.

Fraction of fires in NUREG-2180 Supp. 1 that do not have an incipient phase
Category Mean Alpha Fraction (5th/95th)
Power cabinets 0.41 (0.30/0.53)
Low-voltage control cabinets 0.10 (0.01/0.25)

For enhanced suppression, Table 4-3 and Table 4-5 in NUREG-2180 Supplement 1 provide the enhanced suppression rates which are summarized in the table below:

Enhanced Suppression Rates for Incipient Detection, λ
Suppression Curve Mean 5th percent 50th percent 95th percent NSP Reference
π1 In-cabinet enhanced suppression (using the Control room suppression curve) 0.385 0.209 0.372 0.604 NUREG‑2178 Volume 2
π2 Area-wide, enhanced suppression 0.226 0.131 0.220 0.344 NUREG-2180 Supplement 1
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