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	Each bank of interconnected sets of batteries located in one place (often referred to as Battery Room).
2	Containment (PWR)	Reactor Coolant Pump
3	Containment (PWR)	Transients and Hotwork	General transient combustibles and hotwork activities located in 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 FAQ 12-0064 FAQ 14-0007	4.21E-04	EPRI 3002002936 (NUREG-2169)
4	Control Room	Main Control Board	A control room typically consists of one or two (depending on the number of units) main control boards as the central element of the room.	Each main control board, typically consisting of the main horseshoe and nothing else, is counted separately. This bin may also include "benchboard" panels that are detached from, but directly in front of, the main horseshoe (at some plants such panels are referred to as "consoles"). FAQ-14-008 also clarified that the rear side of the MCB may be treated as part of the MCB if both the rear and front sides are connected together as a single enclosure (including a continuous overhead, or by an overhead with penetrations or vents along it longitudinally, cabinet ceiling, or cables connecting the front and back sides of the MCB).	EPRI 1011989 / NUREG/CR-6850 FAQ 06-0018, Section 5 of Supplement 1 FPRA-FAQ 14-0008	4.91E-03	EPRI 3002002936 (NUREG-2169)
5	Control/Aux/Reactor 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 (Control Building, Auxiliary Building, or Reactor 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 FAQ 12-0064 FPRA-FAQ 16-0010	7.83E-04	EPRI 3002002936 (NUREG-2169)
6	Control/Aux/Reactor Building	Transient fires caused by welding and cutting	Transient fires due to hotwork activities located in the Control Building, Auxiliary Building, or Reactor 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 FAQ 12-0064 FAQ 14-0007	4.44E-03	EPRI 3002002936 (NUREG-2169)
7	Control/Aux/Reactor Building	Transients	General transient combustibles or activities located in the Control Building, Auxiliary Building, or Reactor 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 FAQ 12-0064 FAQ 14-0007	3.33E-03	EPRI 3002002936 (NUREG-2169)
8	Diesel Generator Room	Diesel Generators	Diesel generators are generally well-defined items that include a set of auxiliary subsystems associated with each engine. All diesel generators that are included in the electric power recovery model should be counted here. In addition to the normal safety related diesel generators, this may include the Technical Support Center diesel generators, Security diesel generators, etc. It is recommended that each diesel generator and its subsystems be counted as one unit. The subsystems may include diesel generator air start compressors, air receiver, batteries and fuel storage, and delivery system.	Each diesel generator shall be counted separately. It is recommended that the electrical cabinets for engine and generator control that stand separate from the diesel generator be included as part of “Plant-Wide Components - Electrical Cabinets.” Control panels that are attached to engine may be counted as part of the engine.	EPRI 1011989 / NUREG/CR-6850	7.81E-03	EPRI 3002002936 (NUREG-2169)
9	Plant-Wide Components	Air Compressors	This bin covers the large air compressors that provide plant instrument air included in the Internal Events PRA Model. These compressors are generally well-defined devices. They may include an air receiver, air dryer, and control panel attached to the compressor. These items should be considered part of the air compressor. If portable compressors are part of the model, those compressors should also be included in the equipment count for this bin.	Air compressors are generally well-defined devices (and includes portable units credited in the PRA model). The air compressor skid, which could include an air receiver, air dryer, and control panel attached to the compressor, should be counted as one, as they are considered to be part of the air compressor. NOTE: Compressors associated with the ventilation systems and small air compressors used for specialized functions are NOT part of this bin.	EPRI 1011989 / NUREG/CR-6850	4.69E-03	EPRI 3002002936 (NUREG-2169)
10	Plant-Wide Components	Battery Chargers	These are generally well defined items associated with DC buses.	Each battery charger should be counted separately.	EPRI 1011989 / NUREG/CR-6850	1.12E-03	EPRI 3002002936 (NUREG-2169)
11	Plant-Wide Components	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 (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 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 FAQ 12-0064 FPRA-FAQ 16-0010	2.77E-04	EPRI 3002002936 (NUREG-2169)
12	Plant-Wide Components	Cable Run (self-ignited cable fires)	Self-ignited cables fires postulated in fire compartments with unqualified cables only or a mix of qualified cables and unqualified cables.	The cable loading of each compartment should be established using the same approach as that for Bin 5, except that, in this case, all plant fire compartments should be taken into account. The cable quantity (either total weight or total combustible load) is typically reported in the Fire Hazards Analysis (FHA). For rooms where detailed fire modeling is necessary FAQ 13-0005 provides guidance on how to calculate a scenario level ignition frequency (by dividing the quantity of cables in the tray on fire by the total quantity of cable in the room).	EPRI 1011989 / NUREG/CR-6850 FPRA-FAQ 13-0005 FPRA-FAQ 16-0010	7.02E-04	EPRI 3002002936 (NUREG-2169)
13	Plant-Wide Components	Dryers	Clothes dryers are generally well-defined units.	Each clothes dryer is counted separately.	EPRI 1011989 / NUREG/CR-6850	3.66E-03	EPRI 3002002936 (NUREG-2169)
14	Plant-Wide Components	Electric Motors	The electrical motors with power rating greater than 5hp associated with various devices, not including those counted in other bins, are included in this bin. This may include elevator motors, valve motors, etc.	Motors (not included those counted in other bins) with a rating greater than 5 HP are counted. Totally enclosed motors should be excluded from the count because the motor housing would prevent the extension of flames outside the motor casing. See FAQ 07-0031 for the additional guidance.	EPRI 1011989 / NUREG/CR-6850 FAQ 07-0031, Section 6 of Supplement 1	5.43E-03	EPRI 3002002936 (NUREG-2169)
15	Plant-Wide Components	Electrical Cabinets	Electrical cabinets represent such items as switchgears, motor control centers, DC distribution panels, relay cabinets, control and switch panels (excluding panels that are part of machinery), fire protection panels, etc.	Electrical cabinets in a nuclear power plant vary significantly in size, configuration, and voltage. Size variation range from small-wall mounted units to large walk-through vertical control cabinets, which can be 20’ to 30’ long. The configuration can vary based on number of components that contribute to ignition, such as relays and circuit cards, and combustible loading, which also affects the fire frequency. Voltages in electrical cabinets vary from low voltage (120 V) panels to 6.9 kV switchgears. Even though it is expected that these features affect the likelihood of fire ignition, from a simple analysis of the event data involving the electrical cabinets, it was determined that the variation by cabinet type did not warrant separate frequency evaluation. Therefore, one fire frequency was estimated for the electrical cabinets. The following rules should be used for counting electrical cabinets: – Simple wall-mounted panels housing less than four switches may be excluded from the counting process, – Well-sealed electrical cabinets that have robustly secured doors (and/or access panels) and that house only circuits below 440V should be excluded from the counting process, (In this context, the term “well-sealed” means there are no open or unsealed penetrations, there are no ventilation openings, and potential warping of the sides/walls of the panel would not open gaps that might allow an internal fire to escape. “Robustly secured” means that any doors and/or access panels are all fully and mechanically secured and will not create openings or gaps due to warping during an internal fire. For example, a panel constructed of sheet metal sides “tack welded” to a metal frame would not be considered well-sealed because internal heating would warp the side panels allowing fire to escape through the resulting gaps between weld points. A panel with a simple twist-handle latch mechanism would not be considered robustly secured because the twist handle would not prevent warping of the door under fire conditions. In contrast, a water-tight panel whose door/access panel is bolted in place or secured by mechanical bolt-on clamps around its perimeter would be considered both well-sealed and robustly secured. Also note that panels that house circuit voltages of 440V or greater are counted because an arcing fault could compromise panel integrity (an arcing fault could burn through the panel sides, but this should not be confused with the high energy arcing fault type fires)). – Free-standing electrical cabinets should be counted by their vertical segments. NUREG/CR-6850 (EPRI 1011989) provided guidance to count cabinets in a “typical” or visible vertical section configuration, however additional guidance was necessary for panels with “atypical” configuration where the guidance for vertical segments could be interpreted in different ways. FAQ 06-0016 was proposed to clarify guidance on electrical panel/cabinet counting for fire frequency.	EPRI 1011989 / NUREG/CR-6850 FAQ 06-0016, Section 3 of Supplement 1	3.00E-02	EPRI 3002002936 (NUREG-2169)
16.a	Plant-Wide Components	High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V)	High-energy arcing faults are associated with switchgear and load centers operating between 480 and 1000 Volts. For this bin, similar to electrical cabinets, the vertical segments of the switchgear and load centers should be counted.	Each vertical segment of the switchgear and load center for low voltage (480-1000 V) electrical cabinets is counted separately. MCCs are not included, unless the MCC is associated with switchgear that is used directly to operate equipment such as load centers.	EPRI 1011989 / NUREG/CR-6850 FAQ 06-0017, Section 4 of Supplement 1	1.52E-04	EPRI 3002002936 (NUREG-2169)
16.b	Plant-Wide Components	High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V)	High-energy arcing faults are associated with switchgear and load centers. Switchyard transformers and isolation phase buses are not part of this bin. For this bin, similar to electrical cabinets, the vertical segments of the switchgear and load centers should be counted. Additionally, to cover potential explosive failure of oil filled transformers (those transformers that are associated with 4.16 or 6.9kV switchgear and load centers) may be included in vertical segment counts of the switchgear.	Each vertical segment of the switchgear and load center for medium voltage (above 1000 V) electrical cabinets is counted separately.	EPRI 1011989 / NUREG/CR-6850 FAQ 06-0017, Section 4 of Supplement 1	2.13E-03	EPRI 3002002936 (NUREG-2169)
16.1	Plant-Wide Components	HEAF for segmented bus ducts	A bus duct where the bus bars are made up of multiple sections bolted together at regular intervals (transition points). Here, the bus bars are contained within open-ended sections of metal covers that are bolted together to form a continuous grounded enclosure running the full distance between termination points. Segmented bus ducts are able to accommodate tap connections to supply multiple equipment termination points. – Segmented bus ducts tend to be longer in comparison to the nonsegmented bus ducts. Segmented bus ducts are used in cases where the required lengths and/or geometries make the use of nonsegmented bus ducts impractical. – The length of each segment may vary depending on supplier and installation details. – Segmented bus ducts tend to connect end devices that are remote from each other. Example: A segmented bus duct might be used to connect an oil-filled transformer located in an outdoor area to equipment (e.g., switchgear) located inside the plant buildings. Note: This bin does not cover nonsegmented or continuous bus ducts or cable ducts. The arc faults for these two categories are inherently included in the treatment of the end device, and no further treatment is needed.	The analyst will need to choose between one of two recommended practices for counting segmented bus ducts as a fire ignition source. The choice will be dependent on whether or not the transition points can be identified based on an external visual inspection of the bus duct. Counting approach 1: If the transition points along the length of the segmented bus duct can be identified by external visual inspection, or based on plant electrical construction drawings, then count the total number of transition points. Note that transition point counting excludes the bus end termination points, which are considered a part of the end device for fire frequency purposes. Transition points may be identifiable based on visual observation or review of design drawings. Transition points for the bus bars may, or may not, correspond to junctions in the outer ducting that surrounds the bus bars. It is not intended that the protective duct be removed to identify transition points. However, industry feedback indicates that the joints or junctions in the outer ducting surrounding a bus duct cannot be assumed to correspond to junctions in the bus bars themselves without confirmation. A representative sample of plant applications should be inspected to ensure that the internal bus bar transition points and external duct junctions do in fact align with each other. Once the total count of transition points has been obtained, the plant-wide fire frequency is then partitioned to a specific location based on the number of transition points in the location of interest divided by the total number of transition points for the entire plant. Counting approach 2: If the transition points cannot be identified based on external visual inspection, or by plant electrical construction drawings, then the partitioning of fire frequency to a specific fire scenario is based on apportioning of the fire frequency equally along the length of the bus duct. Hence, the analysis must estimate the total length of segmented bus duct present in the plant under analysis. A “per linear foot” fire frequency can then be estimated by dividing the plant-wide fire frequency by the total length of segmented bus duct in the plant. That is, the fire frequency for a given fire scenario would be based on the ratio of the length of duct for which identified targets fall within the bus duct arc fault zone of influence (see discussion below for a definition of the zone of influence) to the total length of bus duct in the plant. A lower limit to the assumed fire frequency for any given fire scenario is also applied. That is, if the length of bus duct for which the identified target(s) fall within the zone of influence is less than 12 linear feet, then a minimum length of 12 feet should be assumed. This lower bound is based on the assumption that, lacking specific information on segment lengths, a nominal segment length of 12 feet should be assumed. Any single scenario is then assigned a fire frequency equivalent to that associated with one bus bar segment 12 feet in length (i.e., equivalent to one nominal transition point).	FAQ 07-0035, Section 7 of Supplement 1	1.10E-03	EPRI 3002002936 (NUREG-2169)
16.2	Plant-Wide Components	HEAF for iso-phase bus ducts	A bus duct where the bus bars for each phase are separately enclosed in their own protective housing. The use of iso-phase buses is generally limited to the bus work connecting the main generator to the main transformer.	There should generally be one iso-phase bus per unit (an iso-phase bus includes all three phases). If there is more than one iso-phase bus, simply count the total number of iso-phases buses per unit. For individual fire scenarios, the plant-wide frequency is applied (i.e. partitioned) equally to each end of each iso-phase bus duct counted.	FAQ 07-0035, Section 7 of Supplement 1	5.91E-04	EPRI 3002002936 (NUREG-2169)
17	Plant-Wide Components	Hydrogen Tanks	Hydrogen storage tanks are generally well-defined items. Multitank hydrogen trailers, because they are interconnected, should be counted as one unit.	Each hydrogen tank shall be counted separately. Multitank hydrogen trailers shall be counted separately.	EPRI 1011989 / NUREG/CR-6850	4.93E-03	EPRI 3002002936 (NUREG-2169)
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 FAQ 13-0006	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 FAQ 07-0031, Section 6 of Supplement 1	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 FAQ 07-0031, Section 6 of Supplement 1	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 FAQ 07-0031, Section 6 of Supplement 1	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 FAQ 12-0064 FAQ 14-0007	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 FAQ 12-0064 FAQ 14-0007	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 FAQ 07-0031, Section 6 of Supplement 1	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 FAQ 12-0064 FPRA-FAQ 16-0010	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 FAQ 12-0064 FAQ 14-0007	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 FAQ 12-0064 FAQ 14-0007	6.71E-03	EPRI 3002002936 (NUREG-2169)