Detailed Fire Modeling (Task 11)
Contents
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 Fire PRA Implementation Guide 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 chapter 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.
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.
Related Element(s) of ASME/ANS PRA Standard, ASME-RA-Sb-2013
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
Recommended HRR Values for Electrical Fires
|
Enclosure Class/Function Group |
Enclosure Ventilation (Open or Closed Doors) |
Fuel Type* (TS/QTP/SIS or TP Cables) |
Gamma Distribution Characteristics |
|||||||||||
|
(a) Default |
(b) Low Fuel Loading |
(c) Very Low Fuel Loading |
||||||||||||
|
Alpha |
Beta |
75th Percentile (kW) |
98th Percentile (kW) |
Alpha |
Beta |
75th Percentile (kW) |
98th Percentile (kW) |
Alpha |
Beta |
75th Percentile (kW) |
98th Percentile (kW) |
|||
|
1 - Switchgear and Load Centers |
Closed |
TS/QTP/SIS |
0.32 |
79 |
30 |
170 |
|
|||||||
|
Closed |
TP |
0.99 |
44 |
60 |
170 |
|
||||||||
|
2 - MCCs and Battery Chargers |
Closed |
TS/QTP/SIS |
0.36 |
57 |
25 |
130 |
|
|||||||
|
Closed |
TP |
1.21 |
30 |
50 |
130 |
NOT APPLICABLE |
||||||||
|
3 - Power Inverters |
Closed |
TS/QTP/SIS |
0.23 |
111 |
25 |
200 |
|
|||||||
|
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 |
0.30 |
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 |
|||||||
|
Vertical cabinets, one cable bundle |
Closed |
TS/QTP/SIS |
0.84 |
59.3 |
69 |
211 |
NOT APPLICABLE |
|||||||
|
Closed |
TP |
1.6 |
41.5 |
90 |
211 |
|||||||||
|
Vertical cabinets, more than one cable bundle |
Closed |
TS/QTP/SIS |
0.7 |
216 |
211 |
702 |
NOT APPLICABLE |
|||||||
|
Closed |
TP |
2.6 |
67.8 |
232 |
464 |
|||||||||
|
Open |
TP |
0.46 |
386 |
232 |
1002 |
|||||||||
|
Pumps (electrical fires) |
N/A |
N/A |
0.84 |
59.3 |
69 |
211 |
NOT APPLICABLE |
|||||||
|
Motors |
N/A |
N/A |
2.0 |
11.7 |
32 |
69 |
NOT APPLICABLE |
|||||||
|
Transient Combustibles |
N/A |
N/A |
1.8 |
57.4 |
142 |
317 |
NOT APPLICABLE |
|||||||
Supplemental Guidance
| Bin | Plant Location | Ignition Source | Fire Modeling Guidance | Fire Modeling Reference |
|---|---|---|---|---|
| 1 | Battery Room | Batteries | Use HRR distribution for Electric Motors (Case 7 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 2 | Containment (PWR) | Reactor Coolant Pump | For electrical fires: Pumps (electrical fires) HRR Distribution (Case 6 of Table G-1)
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. |
EPRI 1011989 / NUREG/CR-6850 |
| 3 | Containment (PWR) | Transients and Hotwork | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 4 | Control Room | Main Control Board | NUREG-2178 provides updated HRR Distribution for the main control board based on control cabinet size (either Function Group 4a (Large Enclosures) or Group 4b (Medium Enclosures).
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. |
NUREG-2178 / EPRI 3002005578 |
| 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. | FPRA-FAQ 13-0005 |
| 6 | Control/Aux/Reactor Building | Transient fires caused by welding and cutting | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 7 | Control/Aux/Reactor Building | Transients | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 8 | Diesel Generator Room | Diesel Generators | 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 |
| 9 | Plant-Wide Components | Air Compressors | 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 |
| 10 | Plant-Wide Components | Battery Chargers | HRR Distribution for Enclosure Class 2, MCCs and Battery Chargers | NUREG-2178 / 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. | FPRA-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. | FPRA-FAQ 13-0005 |
| 13 | Plant-Wide Components | Dryers | Placeholder | Placeholder |
| 14 | Plant-Wide Components | Electric Motors | Electric Motor HRR Distribution (Case 7 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 15 | Plant-Wide Components | Electrical Cabinets | NUREG-2178 / 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. | NUREG-2178 / EPRI 3002005578 |
| 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 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 | Placeholder | Placeholder |
| 18 | Plant-Wide Components | 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 13-0006 |
| 19 | Plant-Wide Components | Miscellaneous Hydrogen Fires | Placeholder | Placeholder |
| 20 | Plant-Wide Components | Off-gas/H2 Recombiner (BWR) | Placeholder | Placeholder |
| 21 | Plant-Wide Components | Pumps and large hydraulic valves | For electrical fires: Pumps (electrical fires) HRR Distribution (Case 6 of Table G-1)
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. |
EPRI 1011989 / NUREG/CR-6850 |
| 22 | Plant-Wide Components | RPS MG Sets | Use HRR distribution for Electric Motors (Case 7 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 23a | Plant-Wide Components | Transformers (oil filled) | Placeholder | Placeholder |
| 23b | Plant-Wide Components | Transformers (dry) | Use HRR distribution for Electric Motors (Case 7 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 24 | Plant-Wide Components | Transient fires caused by welding and cutting | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 25 | Plant-Wide Components | Transients | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 26 | Plant-Wide Components | Ventilation Subsystems | For electrical fires: Use HRR distribution for Electric Motors (Case 7 of Table G-1)
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. |
EPRI 1011989 / NUREG/CR-6850 |
| 27 | Transformer Yard | 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. | EPRI 1011989 / NUREG/CR-6850 |
| 28 | Transformer Yard | Transformer - Non Catastrophic | In this failure, oil foes 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 |
| 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. | FPRA-FAQ 13-0005 |
| 32 | Turbine Building | Main Feedwater Pumps | Placeholder | Placeholder |
| 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 | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
| 37 | Turbine Building | Transients | Transient Combustible HRR Distribution (Case 8 of Table G-1) | EPRI 1011989 / NUREG/CR-6850 |
