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 | Placeholder | Placeholder | |||
2 | Containment (PWR) | Reactor Coolant Pump | Placeholder | Placeholder | |||
3 | Containment (PWR) | Transients and Hotwork | Placeholder | Placeholder | |||
4 | Control Room | Main Control Board | Placeholder | Placeholder | |||
5 | Control/Aux/Reactor Building | Cable fires caused by welding and cutting | Placeholder | Placeholder | |||
6 | Control/Aux/Reactor Building | Transient fires caused by welding and cutting | Placeholder | Placeholder | |||
7 | Control/Aux/Reactor Building | Transients | Placeholder | Placeholder | |||
8 | Diesel Generator Room | Diesel Generators | Placeholder | Placeholder | |||
9 | Plant-Wide Components | Air Compressors | Placeholder | Placeholder | |||
10 | Plant-Wide Components | Battery Chargers | Placeholder | Placeholder | |||
11 | Plant-Wide Components | Cable fires caused by welding and cutting | Placeholder | Placeholder | |||
12 | Plant-Wide Components | Cable Run (self-ignited cable fires) | Placeholder | Placeholder | |||
13 | Plant-Wide Components | Dryers | Placeholder | Placeholder | |||
14 | Plant-Wide Components | Electric Motors | Placeholder | Placeholder | |||
15 | Plant-Wide Components | Electrical Cabinets | Placeholder | Placeholder | |||
16.a | Plant-Wide Components | High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V) | Placeholder | Placeholder | |||
16.b | Plant-Wide Components | High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V) | Placeholder | Placeholder | |||
16.1 | Plant-Wide Components | HEAF for segmented bus ducts | Placeholder | FAQ 07-0035, Section 7 of Supplement 1 | |||
16.2 | Plant-Wide Components | HEAF for iso-phase bus ducts | Placeholder | FAQ 07-0035, Section 7 of Supplement 1 | |||
17 | Plant-Wide Components | Hydrogen Tanks | Placeholder | Placeholder | |||
18 | Plant-Wide Components | Junction Boxes | Generally, a junction box is defined as a fully enclosed metal box containing terminals for joining or splicing cables. The box must be fully enclosed with metal panels or welded together but not necessarily well sealed. Cables entering or exiting the junction box should be in metal conduits and have mechanical connections to the metal box. The junction box should include only terminals for joining and splicing cables. For a full definition, refer to FAQ 13-0006. | The number of junction boxes may be difficult to determine. The frequency can be apportioned based on ratio of cables in the area to the total cable in the plant. Therefore, the ignition source-weighting factor of the cables may be used for this bin as well.
As an alternative (described in FAQ 13-0006), the frequency of junction box fires in each fire compartment can be apportioned based on the number of junction boxes in the fire compartment divided by the total number of junction boxes in the plant as determined by the cable and raceway database system or (when the cable and raceway database cannot provide this information), the number of junction boxes may be estimated in each PAU. See FAQ 13-0006 for full guidance. |
EPRI 1011989 / NUREG/CR-6850 | 3.61E-03 | EPRI 3002002936 (NUREG-2169) |
19 | Plant-Wide Components | Miscellaneous Hydrogen Fires | This bin includes hydrogen fires in miscellaneous systems other than hydrogen cylinder storage, generator cooling, and battery rooms. It is not necessary to count the ignition sources related to this bin. | Each system found in miscellaneous hydrogen systems shall be counted separately. This does not include hydrogen cylinder storage, generator cooling, and battery rooms. An alternative is to not count the ignition sources related to this bin and to establish an ignition frequency associated with the components of this bin for a specific compartment or a pipe segment.
NOTE: It is important to have a clear definition of system boundaries to ensure that, between this bin and Bin 34, all hydrogen-carrying items of the plant are properly accounted for. |
EPRI 1011989 / NUREG/CR-6850 | 4.82E-03 | EPRI 3002002936 (NUREG-2169) |
20 | Plant-Wide Components | Off-gas/H2 Recombiner (BWR) | Generally there are at least two recombiner systems per BWR. | Each recombiner system should be counted as one unit. | EPRI 1011989 / NUREG/CR-6850 | 5.81E-03 | EPRI 3002002936 (NUREG-2169) |
21 | Plant-Wide Components | Pumps and large hydraulic valves | This bin includes pumps and large hydraulic valves. Due to a lack of sufficient statistical data, a separate bin was not defined for large valves that include hydraulic fluid powered mechanisms. It is recommended such valves (e.g. Main Steam Isolation Valves, and Turbine Stop Valves) be counted and included in the pump bin. | Each pump with a rating greater than 5 hp should be counted separately (do not count pumps with a horsepower rating of 5 hp or below). | EPRI 1011989 / NUREG/CR-6850 | 2.72E-02 | EPRI 3002002936 (NUREG-2169) |
22 | Plant-Wide Components | RPS MG Sets | In PWRs, the RPS MG sets are well-defined devices. | Each RPS MG set is counted separately. Electrical cabinets associated with the RPS MG set should not be counted, as they are considered to be part of the RPS MG set. | EPRI 1011989 / NUREG/CR-6850 | 2.31E-03 | EPRI 3002002936 (NUREG-2169) |
23a | Plant-Wide Components | Transformers (oil filled) | All indoor transformers that are not an integral part of larger components. Control power transformers and other small transformers, which are subcomponents in electrical equipment, should be ignored. Examples include 4160V/480V transformers attached to AC load centers, low-voltage regulators, and essential service lighting transformers. The large yard transformers are not part of this count. | Each indoor oil filled transformers should be counted separately. | EPRI 1011989 / NUREG/CR-6850 | 9.56E-03 | EPRI 3002002936 (NUREG-2169) |
23b | Plant-Wide Components | Transformers (dry) | All indoor transformers that are not an integral part of larger components. Control power transformers and other small transformers, which are subcomponents in electrical equipment, should be ignored. Examples include 4160V/480V transformers attached to AC load centers, low-voltage regulators, and essential service lighting transformers. Transformers with a 45kVa rating or higher are counted. The large yard transformers are not part of this count. | Each dry transformer with a rating greater than 45 kVa should be counted separately. | EPRI 1011989 / NUREG/CR-6850 | 9.56E-03 | EPRI 3002002936 (NUREG-2169) |
24 | Plant-Wide Components | Transient fires caused by welding and cutting | Transient fires due to hotwork activities located in the Power Block, but not in the Control Building, Auxiliary Building, Reactor Building, Turbine Building, or Containment (PWR). | The ignition source weighting factor of transient fires caused by welding and cutting is estimated using a ranking scheme that takes into account the hot work factor. The hot work ranking factors are described in Table 6-2 (as updated in FAQ 12-0064). Guidance for this bin is updated in FAQ 12-0064 Section 6.5.7.2 and Fire PRA FAQ 14-0007 (distributing transient influence factors for smaller spaces than fire compartments). | EPRI 1011989 / NUREG/CR-6850 | 4.79E-03 | EPRI 3002002936 (NUREG-2169) |
25 | Plant-Wide Components | Transients | General transient combustibles or activities located in the Power Block, but not in the Control Building, Auxiliary Building, Reactor Building, Turbine Building, or Containment (PWR). | The ignition source weighting factor of transient fires is estimated using a ranking scheme that takes into account maintenance activities, occupancy level, and storage of flammable materials. These steps are outlined in FAQ 12-0064 Section 6.5.7.2. The introduction of developing transient influence factors for smaller spaces than fire compartments is discussed in FAQ 14-0007. | EPRI 1011989 / NUREG/CR-6850 | 8.54E-03 | EPRI 3002002936 (NUREG-2169) |
26 | Plant-Wide Components | Ventilation Subsystems | This category includes components such as air conditioning units, chillers, fan motors, air filters, dampers, etc. A fan motor and compressor housed in the same component are counted as one component. Do not count ventilation fans if the drive motor is 5 hp or less. | Each component with a rating greater than 5 HP should be counted separately. | EPRI 1011989 / NUREG/CR-6850 | 1.64E-02 | EPRI 3002002936 (NUREG-2169) |
27 | Transformer Yard | Transformer - Catastrophic | The high-voltage power transformers typically installed in the yard belong to this bin. They include plant output power transformers, auxiliary-shutdown transformers, and startup transformers, etc. Isolation phase bus ducts are also included in this bin to simplify fire frequency analysis. | Each high-voltage power transformer installed in the yard is counted separately. | EPRI 1011989 / NUREG/CR-6850 | 6.61E-03 | EPRI 3002002936 (NUREG-2169) |
28 | Transformer Yard | Transformer - Non Catastrophic | "Similar to Bin 27 this bin includes the high-voltage power transformers typically installed in the yard. However, isolation phase bus ducts are not included in this bin.
In a non-catastrophic transformer failure oil does not spill outside 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)." |
Each high-voltage power transformer installed in the yard is counted separately. | EPRI 1011989 / NUREG/CR-6850 | 6.53E-03 | EPRI 3002002936 (NUREG-2169) |
29 | Transformer Yard | Yard Transformers (Others) | Items associated with yard transformers but not the transformers themselves (e.g., oil power output cables) are part of this bin. In the screening phase of the project, the analyst may conservatively assign the same frequency to all 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 items and analysts’ judgment. | Items associated with yard transformers but not the transformers themselves (e.g., oil power output cables) are counted separately. | EPRI 1011989 / NUREG/CR-6850 | 3.69E-03 | EPRI 3002002936 (NUREG-2169) |
30 | Turbine Building | Boiler | Boilers are generally well-defined items. | Each boiler should be counted separately. All ancillary items associated with each boiler may be included as part of the boiler. Control panels that are installed separate from a boiler may be included in the “Electrical Cabinets (Plant-Wide Components)” bin. | EPRI 1011989 / NUREG/CR-6850 | 1.09E-03 | EPRI 3002002936 (NUREG-2169) |
31 | Turbine Building | Cable fires caused by welding and cutting | For this bin, it is assumed that all exposed cables (i.e., cables that are not in conduits or wrapped by noncombustible materials) have an equal likelihood of experiencing a fire caused by welding and cutting across the entire location (Turbine Building). | The ignition source weighting factor of cable fires caused by welding and cutting is estimated using the hot work factor and cable quantity in the fire compartment. The hot work ranking factors are described in Table 6-2 (as updated in FAQ 12-0064). Guidance for this bin is updated in FAQ 12-0064 Section 6.5.7.2 and Fire PRA FAQ 16-0010. The hot work factor is then weighed in combination with a relative numerical estimate of the quantity of cables in the location to the total quantity of cables in the entire location set to generate the final location weighting factor. The cable quantity (either total weight or total combustible load) is typically reported in the Fire Hazards Analysis (FHA). | EPRI 1011989 / NUREG/CR-6850 | 3.47E-04 | EPRI 3002002936 (NUREG-2169) |
32 | Turbine Building | Main Feedwater Pumps | Main feedwater pumps are generally well-defined entities. | Main feedwater pumps are generally well-defined entities. Ancillary components associated with each pump are considered a part of the pump and should not be counted separately. | EPRI 1011989 / NUREG/CR-6850 | 4.38E-03 | EPRI 3002002936 (NUREG-2169) |
33 | Turbine Building | Turbine Generator Excitor | The turbine generator excitor is a well-defined item. Generally, there is only one excitor per unit. | Each turbine generator excitor shall be counted separately. | EPRI 1011989 / NUREG/CR-6850 | 8.36-04 | EPRI 3002002936 (NUREG-2169) |
34 | Turbine Building | Turbine Generator Hydrogen | A complex of piping, valves, heat exchangers, oil separators, and often skid-mounted devices are associated with turbine generator hydrogen. | A complex of piping, valves, heat exchangers, oil separators, and often skid-mounted devices are associated with turbine generator hydrogen. Consider the entire complex as one system and assign the ignition frequency of this bin to that system. It is important to have a clear definition of system boundaries to ensure that, between this bin and Bin 19, all hydrogen-carrying items of the plant are properly accounted for. Similar to Bin 29, in the screening phase of the project, the analyst may conservatively assign the same frequency to all the items in this bin. If the scenario would not screen out, the frequency may then be divided among the various items using a relative ranking scheme. The ranking may be based on the relative characteristics of the items and the analysts’ judgment.
NOTE: It is important to have a clear definition of system boundaries to ensure that, between this bin and Bin 19, all hydrogen-carrying items of the plant are properly accounted for. |
EPRI 1011989 / NUREG/CR-6850 | 4.12E-03 | EPRI 3002002936 (NUREG-2169) |
35 | Turbine Building | Turbine Generator Oil | Similar to hydrogen, a complex of oil storage tanks, pumps, heat exchangers, valves, and control devices belong to this bin. | A complex of piping, valves, heat exchangers, oil separators, and often skid-mounted devices are associated with turbine generator hydrogen. It is recommended to treat the entire complex as one system and assign the ignition frequency of this bin to that system. Similar to the preceding bin and Bin 29, in the screening phase of the project, the analyst may conservatively assign the same frequency to all the items in this bin. If the scenario would not screen out, the frequency may then be divided among the various items using a relative ranking scheme. The ranking may be based on the relative characteristics of the items and analysts’ judgment. | EPRI 1011989 / NUREG/CR-6850 | 5.49E-03 | EPRI 3002002936 (NUREG-2169) |
36 | Turbine Building | Transient fires caused by welding and cutting | Transient fires due to hotwork activities located in the Turbine Building. | The ignition source weighting factor of transient fires caused by welding and cutting is estimated using a ranking scheme that takes into account the hot work factor. The hot work ranking factors are described in Table 6-2 (as updated in FAQ 12-0064). Guidance for this bin is updated in FAQ 12-0064 Section 6.5.7.2 and Fire PRA FAQ 14-0007 (distributing transient influence factors for smaller spaces than fire compartments). | EPRI 1011989 / NUREG/CR-6850 | 4.67E-03 | EPRI 3002002936 (NUREG-2169) |
37 | Turbine Building | Transients | General transient combustibles or activities located in the Turbine Building. | The ignition source weighting factor of transient fires is estimated using a ranking scheme that takes into account maintenance activities, occupancy level, and storage of flammable materials. These steps are outlined in FAQ 12-0064 Section 6.5.7.2. The introduction of developing transient influence factors for smaller spaces than fire compartments is discussed in FAQ 14-0007. | EPRI 1011989 / NUREG/CR-6850 | 6.71E-03 | EPRI 3002002936 (NUREG-2169) |