Detailed Fire Modeling (Task 11)

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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

EPRI 3002005303

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 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

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

EPRI 3002005303

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 Transient Combustible HRR Distribution (Case 8 of Table G-1) EPRI 1011989 / NUREG/CR-6850
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 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 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 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 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

EPRI 3002005303

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) 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) 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 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

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 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