Detailed Fire Modeling (Task 11)

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	Electrical Fire: Oil Fire:	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 EPRI 1011989 / NUREG/CR-6850
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	Placeholder	Placeholder
9	Plant-Wide Components	Air Compressors	Placeholder	Placeholder
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	Pumps (electrical fires) HRR Distribution (Case 6 of Table G-1)	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 EPRI 3002005303
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 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.	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