Methodology for Low 

Power/Shutdown Fire PRA 

Draft Report for Comment

Office of Nuclear Regulatory Research

NUREG/CR-7114

SAND2011-0027P
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Methodology for Low 

Power/Shutdown Fire PRA 

Draft Report for Comment

Manuscript Completed: December 2011

Date Published: December 2011

Prepared by

Steven P. Nowlen, Tara Olivier

Sandia National Laboratories

Risk and Reliability Analysis Department

P.O. Box 5800

Albuquerque, NM 87185

Hugh Woods, NRC Project Manager

NRC Job Code N6592

Office of Nuclear Regulatory Research

NUREG/CR-7114

SAND2011-0027P
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Draft For Public Comment 

iii 

Abstract

This document presents a probabilistic risk assessment (PRA) method for quantitatively 

analyzing fire risk in commercial nuclear power plants during low power and shutdown (LPSD) 

conditions, including the determination of core damage frequency (CDF) and large early release 

frequency (LERF). Future updates will be made to this document as experience is gained with 

LPSD quantitative risk analyses of both internal events and fires. 

This LPSD fire PRA method is intended to be used in combination with an at-power fire PRA 

performed using the method documented in Nuclear Regulatory Commission (NRC) Office of 

Nuclear Regulatory Research (RES) publication NUREG/CR-6850 and Electric Power Research 

Institute (EPRI) publication TR-1011989, “EPRI/NRC-RES Fire PRA Methodology for Nuclear 

Power Facilities.” This LPSD fire PRA method directly parallels that at-power fire PRA method 

with respect to the structure and objectives of its technical analysis tasks, addressing those 

aspects of the at-power fire PRA that require unique treatment in the context of low-power or 

shutdown conditions. This LPSD fire method also requires an LPSD internal events PRA; that 

is, both the at-power fire PRA and the LPSD internal events PRA are needed as starting points 

for conducting an LPSD fire PRA using the method described in this document. 

The NRC developed this LPSD fire quantitative risk method so analysts would be able to use a 

quantitative approach for estimating fire risk during LPSD conditions. While current LPSD 

safety analyses for fires under National Fire Protection Association Standard 805 (NFPA 805) 

focus on qualitative, defense-in-depth methods, it is envisioned that applications in the future 

may evolve to be more quantitative. At present, this method can provide an alternative for the 

analysis of LPSD fire risk in situations where qualitative methods are not appropriate, or where 

activities such as planning for an outage could benefit from risk reduction insights that could be 

gained from a quantitative analysis. It could also prove essential for the analysis of situations 

involving unusual, complex plant operating states (POSs). 

Draft For Public Comment 

v 

Table of Contents

Abstract ......................................................................................................................................... iii

List of Figures ................................................................................................................................ vi

List of Tables ................................................................................................................................. vi

Executive Summary ...................................................................................................................... vii

Acknowledgements ........................................................................................................................ ix

Abbreviations and Acronyms ........................................................................................................ xi

1 Introduction ...................................................................................................................... 1

1.1 Introduction and Purpose ........................................................................................ 1

1.2 Scope ....................................................................................................................... 1

1.3 Document Organization .......................................................................................... 2

2 Overview of LPSD Fire PRA Methodology .................................................................... 3

2.1 Structural Overview ................................................................................................ 3

2.2 Key Assumptions and Potential Limitations ........................................................... 4

3 LPSD PRA CDF and LERF ........................................................................................... 10

4 Detailed Methodology ................................................................................................... 12

4.1 Task 1: Plant Boundary Definition and Partitioning ............................................. 12

4.2 Task 2: Fire PRA Component Selection ............................................................... 14

4.3 Task 3: Fire PRA Cable Selection ........................................................................ 21

4.4 Task 4: Qualitative Screening ............................................................................... 21

4.5 Task 5: Fire-Induced Risk Model ......................................................................... 22

4.6 Task 6: Fire Ignition Frequencies ......................................................................... 24

4.7 Task 7: Quantitative Screening ............................................................................. 33

4.8 Task 8: Scoping Fire Modeling ............................................................................. 36

4.9 Task 9: Detailed Circuit Failure Analysis ............................................................. 39

4.10 Task 10: Circuit Failure Mode Likelihood Analysis............................................. 43

4.11 Task 11: Detailed Fire Modeling .......................................................................... 43

4.12 Task 12: Post-Fire Human Reliability Analysis ................................................... 52

4.13 Task 13: Seismic-Fire Interactions Assessment .................................................... 54

4.14 Task 14: Fire Risk Quantification ......................................................................... 56

4.15 Task 15: Uncertainty and Sensitivity Analyses .................................................... 57

4.16 Task 16: Fire PRA Documentation ....................................................................... 58

4.17 Task 17: Plant Walkdowns (Support Task A) ...................................................... 58

4.18 Task 18: Fire PRA Database System (Support Task B) ....................................... 59

5 References ...................................................................................................................... 60

A: Appendix for Determination of LPSD Generic Fire Frequencies ............................... A-1

 
Draft For Public Comment 

vi 

List of Figures

Figure 1: Fire PRA Process and Module Structure 8 

Figure 2: General Analysis Flow Chart for Task 11 – Detailed Fire Modeling 45 

List of Tables

Table 1: Fire Ignition Frequency Bins Specific to LPSD Conditions 25 

Table 2: Fire Frequency Bins and Generic Frequencies 28 

Table 3: Quantitative Screening Criteria for Single PAU Analysis 34 

Table 4: Quantitative Screening Criteria for All Screened PAUs 35 

Table 5: Zone of Influence and Severity Factor Recommendations 40 

Table 6: Recommended Severity Factors and Suppression Curves for Ignition 

 Sources in the Frequency Model 47 

Table A-1: Bins Considered for LPSD Data Analysis A-2 

Table A-2: Event Counts by Bin, Challenging Category and Operating Mode A-6 

Table A-3: Generic Fire Ignition Frequency Model for U.S. Nuclear 

 Power Plants A-8 

Table A-4: Fire Type Split Fractions A-9 

Table A-5: Fire Event Classification A-10 
Draft For Public Comment 

vii 

Executive Summary

Methods for the application of Probabilistic Risk Assessment (PRA) to internal fire events 

during full-power operation of Nuclear Power Plants (NPPs) have evolved based on an extensive 

development process that began in the 1970s. Recently, existing fire PRA methods and 

evolutionary advances were consolidated through a collaborative effort between the U.S. Nuclear 

Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) and the Electric 

Power Research Institute (EPRI). This work led to publication, in 2005, of the EPRI/NRC-RES 

Fire PRA Methodology for Nuclear Power Facilities [1]. Even these most recent fire PRA 

methods continue to evolve based on their application by industry and on the communication of 

lessons learned to both industry and the NRC. 

In contrast, fire PRAs for Low Power and Shutdown (LPSD) conditions have been conducted in 

only a few cases and all of the known analyses were based on methods and data that pre-date the 

RES/EPRI full-power fire PRA method. Methods for conducting such studies have not 

previously seen the same level of development as have the full-power methods and no 

comprehensive source for analysis guidance compatible with the current state-of-the art fire risk 

methods (e.g., [1]) is known to exist prior to this document. The LPSD fire PRA methodology 

presented here is presented as an extension of, or supplement to, the RES/EPRI full-power fire 

PRA method. That is, the LPSD method relies extensively on the extension of full-power 

analysis methods to LPSD conditions. As a result, documentation of the methodology as 

presented here focuses on those elements where the full-power methods should be adapted or 

extended to address LPSD conditions. 

LPSD plant operating states (POSs) potentially include a broad range of conditions for power, 

temperature and pressure levels. This methodology assumes that LPSD PRA might include plant 

operations at roughly the 30% power level and lower; hence, the LPSD conditions encompass a 

very broad spectrum of potential operating conditions. 

Draft For Public Comment 

ix 

Acknowledgements

The authors acknowledge the contributions of Dr. Mardy Kazarians of Kazarians and Associates 

to the development of this document. Mardy was a key contributor to the development of the 

initial drafts of this document. We also wish to thank Jeff Mitman of the NRC New Reactors 

Office for his support in developing this document. Jeff provided us with many background 

references relative to low power and shutdown risk analysis, the developing LPSD PRA 

standard, and plant operations. He supported us through the early development stages during a 

series of conversations on these subjects. We also acknowledge the contributions of Dr. Ron 

Boring of Idaho National Laboratory and thank him for his contributions to early drafts of the 

report in the area of human reliability analysis. Finally, we gratefully acknowledge the support 

and patience of our NRC technical monitor, Hugh ‘Roy’ Woods of the NRC Office of Nuclear 

Regulatory Research. 

Draft For Public Comment 

xi 

Abbreviations and Acronyms

ADAMS Agency-wide Documents Access and Management System 

ANS American Nuclear Society 

ANSI American National Standards Institute 

ASME American Society of Mechanical Engineers 

BWR Boiling Water Reactor 

CCDP Conditional Core Damage Probability 

CDF Core Damage Frequency 

CFR Code of Federal Regulations 

CLERP Conditional Large Early Release Probability 

dc Direct current 

EOP Emergency Operating Procedure 

EPRI Electric Power Research Institute 

FAQ Frequently Asked Question 

FEDB Fire Events Database 

FEP Fire Emergency Procedure 

HEAF High Energy Arcing Fault 

HEP Human Error Probability 

HFE Human Failure Event 

HRA Human Reliability Analysis 

HRR Heat Release Rate 

ICDP Incremental Core Damage Probability 

ID Identifier 

ILERP Incremental Large Early Release Probability 

IS Ignition Source 

LCO Limiting Condition of Operation 

LERF Large Early Release Frequency 

LOCA Loss of Coolant Accident 

LPSD Low Power and Shutdown 

MCB Main Control Board 

MCR Main Control Room 

MG Motor-Generator 

NFPA National Fire Protection Association 

NPP Nuclear Power Plant 

NRC Nuclear Regulatory Commission 

PAU Physical Analysis Unit 

POS Plant Operating State 

PRA Probabilistic Risk Assessment 

PWR Pressurized Water Reactor 

RCP Reactor Coolant Pump 

RES The Office of Nuclear Regulatory Research (at NRC) 

RG Regulatory Guide 

RISC Risk Informed Standards Committee 

RPS Reactor Protection System 

SRV Safety Relief Valve 

T/G Turbine/Generator 

ZOI Zone of Influence

Draft For Public Comment 

1 

1 Introduction

1.1 Introduction and Purpose

Methods for the application of Probabilistic Risk Assessment (PRA) to internal fire events 

during full-power operation of Nuclear Power Plants (NPPs) have evolved based on an extensive 

development process that began in the 1970s. Recently, existing fire PRA methods and 

evolutionary advances were consolidated through a collaborative effort between the U.S. Nuclear 

Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) and the Electric 

Power Research Institute (EPRI). This work led to publication, in 2005, of the EPRI/NRC-RES 

Fire PRA Methodology for Nuclear Power Facilities [1] (referred to in this document more 

simply as either “the RES/EPRI full-power fire PRA method” or “reference [1]”). Even these 

most recent fire PRA methods continue to evolve based on their application by industry and on 

the communication of lessons learned to both industry and the NRC. Many of the currently 

operating U.S. NPPs are actively engaged in the conduct of fire PRAs driven, in part, by licensee 

decisions to transition to the alternative risk-informed, performance-based fire protection rules as 

embodied in National Fire Protection Association (NFPA) Standard 805 [2] and the Code of 

Federal Regulations (CFR) Section 10CFR50.48(c) [3]. 

In contrast, fire PRAs for Low Power and Shutdown (LPSD) conditions have been conducted in 

only a few cases and all of the known analyses were based on methods and data that pre-date the 

RES/EPRI full-power fire PRA method. Methods for conducting such studies have not 

previously seen the same level of development as have the full-power methods and no 

comprehensive source for analysis guidance compatible with the current state-of-the art fire risk 

methods (e.g., [1]) is known to exist prior to this document. The methodology presented here is 

presented as an extension of, or supplement to, the RES/EPRI full-power fire PRA method [1]. 

That is, the LPSD method relies extensively on the extension of full-power analysis methods to 

LPSD conditions. As a result, documentation of the methodology as presented here focuses on 

those elements where the full-power methods should be adapted or extended to address LPSD 

conditions. 

1.2 Scope

LPSD plant operating states (POSs) potentially include a broad range of conditions for power, 

temperature and pressure levels. For reference, the American National Standard Low Power and 

Shutdown PRA Methodology1

 [4] defines key terms relevant to LPSD PRAs as follows: 

1) “Low Power - Power levels at which major secondary components are out of service as a 

plant shuts down or starts up. This is typically a transition mode to/from hot/cold 

 

1

 The cited quotes are based on the joint American National Standards Institute (ANSI) and American Nuclear 

Society (ANS) standard ANSI/ANS-58.22-200x, DRAFT #8C, for the Risk Informed Standards Committee (RISC) 

Reballot & Public Review, June 2008. At the time the current document was prepared, this was the most recent 

version of the LPSD PRA standard available. The reader should be aware that the standard is a document in 

transition and should review updated versions, as available, for wording changes. 
Draft For Public Comment 

2 

shutdown. Designated as Startup in a boiling water reactor (BWR) when transitioning 

from cold shutdown to power operations.” 

2) “Low power: a POS (or set of POSs) during which the reactor is at reduced power, below 

full-power conditions. In this POS, the power level may be changed as the reactor is 

shutting down or starting up. The power level that distinguishes full power and low 

power is the power level below which major plant evolutions are required to reduce or 

increase power (e.g., taking manual control of feedwater level).” 

3) “LPSD evolution: a series of connected or related activities, such as a reduction in power 

to a low level, or plant shutdown, followed by the return to full-power plant conditions. 

LPSD evolutions are modeled as a series of POSs. Outage types are a general type of a 

shutdown evolution, and a refueling outage is a specific example. Reducing power to 

30% in order to conduct maintenance or an operational activity is another example of a 

low-power evolution. LPSD evolutions are characterized by a transition down to the POS 

where the activity is conducted, followed by a transition back to full power.” 

Note that even though these definitions all come from the same document, they are not entirely 

consistent. It is anticipated that the final revisions of the draft LPSD PRA standard will resolve 

the differences and settle on final definitions for these terms. Generally, the differences in 

phrasing are relatively minor and this methodology adopts these definitions with the intent of 

maintaining consistency with this quality standard. Consistent with these excerpts and for 

general purposes, this methodology assumes that LPSD PRA might include plant operations at 

roughly the 30% power level and lower. 

One implication of this assumption is that LPSD conditions encompass a very broad spectrum of 

potential operating conditions. At one end of the POS spectrum, the reactor may be producing 

power with the control rods partly out, pressure and temperature of the main cooling loop very 

close to full-power conditions, and decay heat cooling systems not yet functioning (due to 

system pressures). At the other end of the POS spectrum, LPSD includes refueling outage 

conditions where all the rods are inserted, the main reactor vessel is open and flooded with 

refueling pool borated water, and the reactor is at near-ambient temperature. During refueling, 

depending on the maintenance needs, only one decay heat removal loop may be available for a 

limited time and plant modification activities could be underway. 

1.3 Document Organization

An overview of the LPSD fire PRA method is provided in Section 2 below. The overview 

defines the tasks of the methodology. The selection of POSs and the equations for estimating 

overall plant core damage frequency (CDF) and large early release frequency (LERF) are 

discussed in Section 3. Section 4 provides a detailed discussion of each technical element of the 

analysis methodology. Note that the subsections within Section 4 follow the same ordering as 

the chapters and technical tasks as defined in Volume 2 of the RES/EPRI full-power fire PRA 

methodology [1]. 
Draft For Public Comment 

3 

2 Overview of LPSD Fire PRA Methodology

2.1 Structural Overview

An internal fire event during LPSD operations can occur from either an equipment item 

malfunction (e.g., a short in a switchgear may lead to arcing inside the device, rapid release of 

energy, and ignition of switchgear internals) or a transient combustible or activity (e.g., welding 

done for repair or plant upgrade). These are the same two types of fire events considered in fullpower fire PRA. It is possible that the characteristics of an LPSD fire event (e.g., intensity or 

amount of fuel available) may be different from a similar class of events during full-power 

operation. However, the underlying fire behaviors of interest remain the same (e.g., ignition of 

combustible materials leading to plume formation, radiant heating, and other potentially 

damaging effects). Therefore, in principle, the methodology developed for full-power fire PRA 

[1] should be applicable to LPSD conditions. Clearly some of the parameters and conditions 

should be adjusted to reflect the special conditions of LPSD POSs. 

The methodology presented in this document is structured to coincide with the RES/EPRI fullpower fire PRA method. Therefore, the discussions provided in this document assume that the 

reader is familiar with that method and the related data as presented in reference [1]. The task 

elements of the RES/EPRI full-power fire PRA method are each discussed. These discussions 

focus on the differences introduced by virtue of the LPSD perspective. Note that for some task 

elements the differences are quite minor or even nonexistent. 

The RES/EPRI full-power fire PRA methodology defines 16 technical task elements and 

provides a detailed discussion, supporting data, and other information for each task. Figure 1 

(presented at the end of Section 2) is the flow chart used in the RES/EPRI full-power fire PRA 

method to illustrate the interrelationship among the different tasks of the methodology. The 

same set of tasks and flow chart apply to LPSD fire PRA. Each task is discussed separately 

below in Section 3. 

The RES/EPRI full-power fire PRA method for at-power conditions assumes that certain 

information will be available based on prior completion of a corresponding plant internal events 

PRA. If an internal events analysis is not available, then the fire PRA analyst is responsible for 

developing and validating the required information. Similarly, the LPSD fire PRA method 

assumes that certain information will be available based on prior completion of a LPSD internal 

events PRA. The information that is assumed to be available includes: 

 Definition of LPSD POSs that will be addressed in terms of core power level, core 

cooling system pressure and temperature, equipment status (functional or under 

maintenance), special activities (e.g., maintenance and plant upgrade), status of barriers 

(e.g., doors propped open to allow certain activity, etc.); 

 A list of initiating events for each POS as defined in the LPSD internal events PRA 

(e.g., loss of service water, loss of direct current (dc) power, etc.); 

 A plant response model for each LPSD initiating event and for each relevant POS of 

interest; 
Draft For Public Comment 

4 

 A list of equipment and their failure modes of interest to the LPSD internal events 

PRA; and 

 Human error scenarios integrated in the LPSD internal events plant response model. 

It is also assumed that an at-power fire PRA has been completed and is available. Information 

assumed to be available based on the at-power fire PRA includes: 

 Plant partitioning results which divide the plant into fire compartments or, 

equivalently, into physical analysis units (PAUs);2

 The listing of equipment included in the at-power fire PRA plant response model (i.e., 

selected equipment per Task 2 of the RES/EPRI full-power fire PRA method); 

 The listing of cables associated with selected equipment; 

 Any additional initiating events that are specific to the fire analysis; 

 Equipment and ignition source counting results; 

 Control circuit failure modes and effects analysis reports; and 

 Component and cable mapping/routing results for the circuits in the circuit analysis 

report. 

If any of this information is not available, the analyst should generate the needed information. 

2.2 Key Assumptions and Potential Limitations

This methodology is based on a number of key assumptions, and these key assumptions which 

have implications for both the scope of the methodology and for potential limitations to 

application of the methodology. These key assumptions and the associated implications are 

summarized as follows. 

 Assumption 1: The LPSD method assumes that a full-power fire PRA has been 

completed consistent with the general approach defined by the RES/EPRI full-power fire 

PRA methodology. 

 Impact of this assumption on the methodology: The LPSD method takes as given that 

certain analysis tasks have already been completed and will, at most, require review and 

updating to address the LPSD conditions. For example, it is assumed that the task of 

identifying and counting fixed fire ignition sources within the plant has been completed. 

Hence, the LPSD analysis should only consider changes that might be associated with 

LPSD conditions (e.g., changes in the operational status of equipment, changes in the 

nature and likelihood of transient fuel sources that might be introduced during an outage, 

etc.). 

 

2

 NUREG/CR-6850, EPRI 1011989 [1] uses the phrase “fire compartments” and the American Society of 

Mechanical Engineers (ASME) PRA quality standard [10] uses the phrase “physical analysis units.” The 

differences are largely semantic in nature and this method document has adopted the language of the PRA standard 

in this regard. 
Draft For Public Comment 

5 

 Implications: This assumption is thought to carry few practical implications. An 

early conclusion reached by the authors was that it is wholly impractical to perform an 

analysis of LPSD fire risk without first completing an assessment of the full-power fire 

risk. An analyst attempting to conduct an LPSD fire analysis without first completing a 

full-power fire analysis would, in effect, be forced to do nearly all of the work associated 

with a full-power fire risk study simply to establish the required input for beginning the 

LPSD risk study. 

 Assumption 2: The LPSD fire PRA method assumes that an LPSD PRA has already 

been completed for internal event accident initiators. 

 Impact of this assumption on the methodology: This parallels an equivalent 

assumption made in the RES/EPRI full-power fire PRA methodology; namely, that a fullpower internal events PRA has been completed prior to conducting the full-power fire 

PRA. In general, the impact on the LPSD fire PRA methodology is also the same; 

namely, the LPSD fire PRA method calls for the analyst to build a fire plant response 

model beginning from the corresponding model developed for the LPSD internal events 

PRA. The fire method thereby focuses on incorporating required changes and additions 

to address those aspects of plant response that are unique to fire (e.g., fire-induced 

spurious actuation of plant equipment, potential new initiators or sequences, and fire 

response procedures). 

 Implications: The most significant implication of this assumption is that the LPSD 

fire PRA method assumes that the relevant POSs to be evaluated will have been defined 

in the LPSD internal events PRA. This method assumes that, at least nominally, the same 

set of POSs is then carried forward to the fire PRA. Based on this assumption, this 

document does not explicitly address the process or criteria by which the POSs will 

actually be defined. Defining LPSD POSs is an analytical challenge with far-reaching 

implications and is the focus of substantial debate in the more general PRA community. 

The resolution of this challenge lies beyond the scope of this document. It is also 

acknowledged that the fire analysis will present unique challenges with respect to POS 

definition. This method, for example, recommends that the LPSD fire PRA characterize 

and quantify the fire-specific plant configuration changes that occur with respect to each 

POS analyzed (e.g., breaching of fire barriers, staffing by plant personnel and contractors, 

introduction of new transient combustibles, increased hot work, fire protection system 

unavailability, maintenance activities, etc.). The implied work scope could become 

burdensome if a high level of detail for all possible POSs is sought. Methods for the 

management of the work scope challenge will likely develop through practical 

application, but cannot be defined a-priori. One general approach that might be 

especially helpful would be screening methods that would define the subset of POSs to be 

included in, or conversely excluded from, the quantitative fire analysis; but again, the 

more general state of POS definition guidance is not yet mature enough to support 

development of such screening approaches. 

 Assumption 3: Development of detailed human reliability analysis (HRA) 

quantification methods for application to the LPSD fire PRA lie beyond the scope of this 

document. 
Draft For Public Comment 

6 

 Impact of this assumption on the methodology: This parallels an equivalent 

assumption made in the RES/EPRI full-power fire PRA methodology; namely, that postfire HRA methods will rely upon general practice for HRA in other contexts and that 

specific guidance for application to fire conditions will be developed by the HRA 

community. This document does not explicitly address HRA quantification methods. 

 Implications: HRA is a unique area of methodology development whose implications 

extend well beyond the boundaries of a fire PRA. HRA quantification in the context of 

general LPSD plant operations is an active area of debate and development in the HRA 

technical community. A joint effort is already well underway between RES and EPRI to 

develop fire HRA quantification guidance for full-power fire PRA applications (see 

further discussion in Section 4.12). The LPSD fire PRA method assumes that the HRA 

community will ultimately develop LPSD analysis guidance and will extend that 

guidance to include the treatment of fire conditions. Section 4.12 discusses prior LPSD 

HRA analyses and applications, the updated EPRI-RES fire HRA guidance and 

considerations relevant to the application of that guidance to LPSD applications. 

However, the resolution of the LPSD HRA challenge lies beyond the scope of this 

document. 

 Assumption 4: LPSD Fire frequencies are estimated based on past plant experience in 

the same manner that fire frequencies were estimated for the RES/EPRI full-power fire 

PRA methodology and using the same root database (i.e., the EPRI fire event database 

(FEDB)). 

 Impact of this assumption on the methodology: The development of a new FEDB or 

the gathering of substantially new information for incorporation into the existing FEDB 

lie beyond the scope of this project. Hence, this method followed the approach used in 

the RES/EPRI full-power fire PRA methodology. If the RES/EPRI full-power fire PRA 

methodology concluded that the frequency of fires for a given fire source was not 

dependent on the POS, this method has made the same assumption (i.e., the fire 

frequency for many ignition source bins reflects fires occurring during all modes of plant 

operation). New fire frequencies are calculated only for those ignition source bins where 

the RES/EPRI full-power fire PRA methodology concluded that the shutdown fire 

frequency might vary substantially from the at-power fire frequency (e.g., transients and 

hot work fires). 

 Implications: The existing FEDB has limitations that make it difficult to parse fire 

events to the extent that might be considered desirable. While this was also true for the 

RES/EPRI full-power fire PRA methodology, there are some unique implications in the 

context of LPSD conditions. In particular, while there are some exceptions, the fire event 

database does not generally identify the specific POS that a plant was in when a 

particular fire occurred. Rather, the vast majority of records only classify the POS as 

either at-power or shutdown (or they fail to specify a plant state at all). As a result, it is 

not currently possible to provide estimates of fire frequency that are POS-specific. An 

RES/EPRI collaborative effort is underway to expand and improve the EPRI FEDB. The 

planned improvements should afford some opportunity to improve the ability to parse fire 

events. 
Draft For Public Comment 

7 

 Assumption 5: Consistent with the LPSD PRA standard [4]3, the LPSD fire PRA end 

states considered here are limited to CDF and LERF. 

 Impact of this assumption on the Methodology: While the methodology presented 

here could be extended to include other end states, it should be emphasized that this 

document makes no attempt to address any end states other than CDF and LERF. 

 Implications: During certain LPSD POSs, depending on the specific conditions, 

radionuclide release may occur from events other than core damage (the focus of fullpower PRA). For example, during a refueling outage coolant boiling in the core, 

uncovering the core, or fuel bundle mishandling could be considered as possible endstates for a risk analysis. Consistent with the standard [4], these alternative end states lie 

outside the scope of this methodology. Also consistent with the standard [4], this 

document excludes consideration of potential release scenarios associated with either the 

spent fuel pool or on-site dry cask storage of spent fuel. 

 

3

 At the time the current document was prepared, reference [4] was the most recent version of the LPSD PRA 

standard available. The reader should be aware that the standard is a document in transition and should review 

updated versions, as available, for wording or scope changes. 
Draft For Public Comment 

8 

Figure 1: Fire PRA Process and Module Structure (part 1 of 2). 

TASK 1: Plant Boundary & Partitioning

TASK 2: Fire PRA Component Selection

TASK 3: Fire PRA Cable Selection 

TASK 4: Qualitative Screening

TASK 6: Fire Ignition Frequencies

TASK 5: Fire-Induced Risk Model 

TASK 7A: Quantitative Screening -ITASK 8: Scoping Fire Modeling

SUPPORT TASK A: Plant Walk Downs 

SUPPORT TASK B: Fire PRA Database 

TASK 7B: Quantitative Screening - II

TASK 12A: Post-Fire HRA: Screening 

B 
Draft For Public Comment 

9 

Figure 1: Fire PRA Process and Module Structure (part 2 of 2). 

Detailed Fire Scenario Analysis 

B 

TASK 11: Detailed Fire Modeling A. Single Compartment B. Multi-Compartment C. Main Control Room 

TASK 9: Detailed Circuit Failure Analysis

TASK 10: Circuit Failure Mode & Likelihood Analysis 

TASK 14: Fire Risk Quantification TASK 15: Uncertainty & Sensitivity Analyses TASK 16: Fire PRA Documentation 

TASK 12B: Post fire HRA: Detailed & recovery 

TASK 13: Seismic-Fire Interactions 
Draft For Public Comment 

10 

3 LPSD PRA CDF and LERF		

A key challenge of LPSD PRA, both for internal events and fire, is the definition of the POSs to 

be analyzed. There are many possible solutions to this challenge. This document takes no 

position as to the ‘correct’ solution. Whatever approach is ultimately taken, this method assumes 

that a POS set will be defined as a part of the plant’s internal events LPSD PRA and that the 

defined POS set will be equally valid and inclusive so as to serve the needs of the LPSD fire 

PRA. It is therefore assumed that the analyst will have a set of POSs defined prior to attempting 

LPSD fire PRA effort. Two general approaches to defining the POSs are anticipated. The POS 

set could be “complete” so as to cover all possible POSs in substantive detail. The set could also 

be a limited, well defined grouping of POSs intended to represent a typical outage or for use in a 

focused-scope analysis. This method is neutral to this aspect of the analysis. The approach 

taken to defining POSs for analysis will clearly impact the scope of the analysis, but will not 

alter the fundamental nature of the fire PRA methodology. Instead, the choice of approach will 

be driven by the objectives and intended applications of the analysis. 

An evaluation based on a more complete set of POSs will facilitate modeling of actual plant 

configurations and equipment status changes that could increase, or reduce, fire risk. For each 

POS that exists there may be special plant configurations that are unique to a specific outage 

(e.g., steam generator replacement, flooding of the spent fuel pool). These special plant 

configurations will require particular consideration since initiators and mitigating equipment may 

vary from the original POS. PRA models for each POS should also reflect each special 

configuration. 

If the objective of the analysis is to estimate the total risk over the course of an outage sequence 

(e.g., from the beginning of plant shutdown from power to the point of restart), the CDF and 

LERF calculations should be repeated for each POS and combined according to the following 

equation: 

 CDFΣPOS = Σi CDFPOS(i) x ftPOS(i) 

Where: 

CDFΣPOS : The total CDF of all POSs combined in number of events per reactor year 

CDFPOS(i): The instantaneous CDF of specific POS(i) 

ftPOS(i) : The fraction of time that each POS exists 

If a specific one-time POS under a specific set of conditions is analyzed, the CDF and LERF 

should be estimated using the same equation, except that only one POS is considered. Therefore, 

we can write: 

 CDFPOS(i) = CDFPOS(i) x ftPOS(i) 
Draft For Public Comment 

11 

Where: 

CDFPOS(i) : The CDF of POS(i) in number of events per reactor year 

CDFPOS(i): The instantaneous CDF of specific POS(i) 

ftPOS(i) : The fraction of time that POS i exists 

The same set of equations applies to LERF calculations where CDF is simply replaced with 

LERF. 
Draft For Public Comment 

12 

4 Detailed Methodology

4.1 Task 1: Plant Boundary Definition and Partitioning		

The purpose and scope for this task remains the same as presented in reference [1]. This section 

provides supplemental guidance for conducting the plant boundary definition and partitioning 

tasks in support of the LPSD fire PRA. As in the full-power fire PRA, the plant is divided into a 

number of PAUs. The analysis then considers the impact of fires in a given PAU, and fires that 

might impact multiple PAUs. This practice supports both the organization of the PRA 

information and analysis, and provides a framework for reporting risk results. 

Task 1 establishes the process for defining the overall plant boundary and partitioning of the 

plant into PAUs. The product of this task will be a list of PAUs that encompasses the nuclear 

power plant under analysis. 

Analysts have two choices: (1) use the same set of PAUs as per the definitions established in the 

full-power fire PRA or (2) redefine the PAUs based on the barrier configurations and conditions 

specific to the POS. Both approaches have merits but this report advocates for maintaining the 

PAU definitions as per the full-power fire PRA with few exceptions. This approach ensures that 

plant locations are identified consistently among the analyses and will allow the results for the 

same plant location under different operating conditions to be quickly and easily identified. If 

the PAU boundaries are redefined, then tracking results becomes far more difficult and 

burdensome. The two significant exceptions to this recommendation are as follows: 

(1) The analysis should verify that the full-power fire PRA plant boundary encompasses all 

plant areas of potential interest to the LPSD fire PRA. If it does not, then the global 

analysis boundary is expanded and new PAUs are defined. 

(2) The analysis should consider the treatment afforded the containment structure in the 

full-power fire PRA and determine if an alternative treatment is appropriate. 

Containment fires are relatively rare while the plant is at full-power operation. For 

those BWRs with inerted containment, fires during full-power operation are not 

analyzed (no fire frequency is assigned to these containments per the guidance in 

reference [1]). During LPSD operations, these conditions can change and the changes 

could impact containment partitioning decisions. 

The primary challenge to the LPSD fire PRA with respect to Task 1 is that the partitioning 

elements that defined the compartments in the full-power fire PRA (e.g., walls, ceilings/floors, 

spatial separation, etc) are subject to modification during LPSD plant operations. For example, 

equipment hatches in ceilings/floors may be removed, normally closed doors may be propped 

opened, fire barrier penetrations may be breached (e.g., to support equipment or cable work), the 

containment structure may be open, and for BWRs, containment will no longer be inerted. The 

LPSD fire PRA will need to define and address such changes, but this need not force changes to 

previous (i.e., at power) partitioning decisions. Rather, changes in the status or integrity of a 

credited partitioning feature or element can be addressed during Task 11, and in particular Task 

11c - the multi-compartment fire analysis (see Section 3.11 for additional discussion). 

If the decision is made to alter the partitioning of any plant locations, the analysis should (1) 

define the partitioning changes and (2) provide a concise mapping between PAUs as defined in 
Draft For Public Comment 

13 

the full-power fire PRA and in the LPSD fire PRA. As in the full-power fire PRA, the LPSD 

PAUs should collectively encompass all locations within the global analysis boundary with no 

exclusions and no overlap between compartments (the set of PAUs is both complete and 

exclusive). 

In Section 1.3.1 of reference [1]; the guidance cautions the analyst to avoid “excessive 

partitioning” and an over-reliance on multi-compartment fire scenarios as significant contributors 

to plant fire risk. If the recommendations discussed above are followed (i.e., the same PAU 

definitions are retained from the full-power analysis), then it is likely that there will be more 

contributing multi-compartment scenarios for LPSD than the full-power fire PRA. This is 

because normally closed fire barriers and other partitioning features may be opened during LPSD 

operations. This is inevitable, and is not considered to detract from the quality or validity of the 

LPSD fire PRA provided appropriate treatment is afforded to the relevant multi-compartment 

fire scenarios (i.e., in Task 11c). 

The same procedure as that described in reference [1] for full-power fire PRA applies here as 

well with the following clarifications. 

 Step 1: Selection of Global Plant Analysis Boundary: 

This task begins with an assessment of the global plant analysis boundary definition 

established in the full-power fire PRA. The guidance provided in reference [1] seeks a 

liberal definition of the global plant analysis boundary. Hence, for most analyses it is 

considered unlikely that the boundary will need to be expanded to suit the LPSD fire PRA; 

however, the LPSD analysis should determine whether the global plant analysis boundary 

should be expanded to encompass new areas of the plant. The definition of the global plant 

analysis boundary may need to be expanded if any locations excluded from the full-power 

analysis are identified as potentially relevant to the LPSD analysis. For example, the unit 

under analysis may establish electrical ties via temporary cabling to a sister unit during 

shutdown that would not be present while at power (e.g., to make up for de-energized 

power supply busses undergoing maintenance during the shutdown). If these ties meet the 

criteria for equipment/cable selection and the corresponding areas of the sister unit were 

outside the global analysis boundary for the unit’s at-power fire PRA, then the LPSD fire 

PRA global analysis boundary should expand accordingly. 

As with the full-power fire PRA, the LPSD fire PRA global plant analysis boundary should 

encompass all areas of the plant associated with both normal and emergency reactor 

operating and support systems, and power production (e.g., the turbine building). The 

unique aspect of this assessment for the LPSD analysis is that the terms “normal and 

emergency reactor operating and support systems” should encompass all defined POSs to 

be considered in the analysis rather than just full-power conditions. This holds the 

potential to introduce plant locations that were deemed outside the scope of the full-power 

fire PRA. 

Selection of the LPSD fire PRA global plant analysis boundary should begin with the fullpower fire PRA global plant analysis boundary. A review should be performed to ensure 

that locations not included within the full-power boundary could not contribute to fire risk 

under any of the defined LPSD POSs. In particular, the LPSD fire PRA plant analysis 

boundary should encompass all locations, including qualifying locations associated with a 
Draft For Public Comment 

14 

sister unit at a multi-unit site, that house any of the LPSD fire PRA components and cables 

identified in Tasks 2 and 3 (see next two sections). 

 Step 2: Plant Partitioning: 

The discussions provided in Section 1.5.2 of reference [1] apply in full to the LPSD fire 

PRA. As a general practice, this method recommends that the PAUs (i.e., the plant 

partitioning results) as developed for the full-power fire PRA be applied without 

modification to the LPSD fire PRA with two specific exceptions: 

(1) For any new locations added to the global analysis boundary in Step 1, partition those 

locations into PAUs consistent with the guidance in Section 1.5.2 of reference [1]. 

(2) It is recommended that a review of the containment structure be performed to assess 

whether or not additional partitioning is appropriate. 

With respect to item (2) above, in a typical full-power fire PRA the containment structure 

is either not analyzed in detail (i.e., in the case of those plants whose containments are 

inerted during plant operations) or analyzed in limited detail (e.g., due to the relatively low 

frequency of fires inside containment during power operations that can affect core cooling). 

These conditions (inerting and low fire frequency) may not apply to LPSD operations and 

the analyst should anticipate that a more thorough examination of containment fires will be 

required. Hence, the purpose of item (2) above is to ensure that due consideration is given 

to the potential analytical needs of the containment fire analysis during the plant 

partitioning task. As always, partitioning decisions are ultimately up to the analyst but 

additional partitioning of the containment structure should be considered. 

 Step 3: Compartment Information Gathering and Characterization: 

The discussions provided in Section 1.5.3 of reference [1] apply in full to the LPSD fire 

PRA. 

 Step 4: Documentation: 

The discussions provided in Section 1.5.4 of reference [1] apply in full to the LPSD fire 

PRA. In addition, the analyst should take particular care to document any changes in plant 

partitioning made to support the LPSD fire PRA as compared to the full-power fire PRA. 

If any partitioning changes are made, task documentation should define those changes and 

provide a mapping of LPSD PAUs to full-power fire compartments. 

4.2 Task 2: Fire PRA Component Selection

4.2.1 Background

The objective of Task 2 is to create the LPSD fire PRA component list4

. This list identifies the 

plant components that will be modeled in the LPSD fire PRA. The component list also identifies 

 

4

 As in the full-power procedure, the terms “equipment” and “component” as used here are considered synonymous 

and are meant to include plant components such as valves, fans, pumps, etc.; structures; barriers; indicators; alarms; 

and other devices as appropriate. The terms generally exclude electrical cables as these are dealt with explicitly (see 

Task 3). 
Draft For Public Comment 

15 

plant equipment for which the corresponding cables (power, control and instrumentation – see 

Task 3) need to be identified and located. 

This task builds upon foundations of equipment selection established by the full-power fire PRA. 

It also builds upon foundations established in a corresponding internal event LPSD PRA. Hence, 

as noted in Section 2, these two analyses are considered critical inputs to this task. If either 

analysis is not available, the analyst faces a substantial additional burden to generate the 

information that would normally be imported from these analyses and that effort lies outside the 

scope of this document. 

Given the wide range of possible POS conditions, essentially all of the components selected for 

inclusion in the full-power fire PRA will also be relevant to the LPSD fire PRA and should be 

retained in the LPSD fire PRA component list. However, component selection will need to be 

augmented with additional components unique to the conditions posed by the specific POSs 

associated with shutdown and with equipment outages during LPSD conditions (e.g., loss of the 

redundant train of a system to a fire while the other train is out of service for maintenance). 

The process for generating the LPSD fire PRA component list is fundamentally the same as the 

full-power analysis. The analyst, however, should consider each POS separately to ensure that 

potential accident initiators and mitigating equipment relevant to each POS are properly 

accounted for. 

Overall and for each POS, the component list needs to span: 

(1) equipment that, if affected by a fire, will cause an initiating event such that the 

appropriate fire-induced initiators can be defined; 

(2) all equipment necessary to support those mitigating functions and operator actions that 

are credited in the analysis in response to any initiator; and 

(3) equipment that can be a source of undesirable responses adverse to safety during a fireinduced accident sequence, (e.g., fire-induced spurious operations). 

The considerations cited for the selection of equipment in Section 2.2 of reference [1] are fully 

applicable to the LPSD fire PRA. In addition, it is recommended that the LPSD fire component 

list include the following: 

(1) all components included in the full-power fire PRA, and 

(2) all components credited in the Internal Events LPSD PRA, and in particular, equipment 

associated with electrically diverse systems. 

The input to Task 2 is much the same as those identified in Section 2.4.1 of reference [1] with 

the following additions: 

(1) Task 2 includes the mapping of identified components to plant locations (e.g., fire areas 

and/or PAUs). It is strongly recommended that the LPSD fire PRA use the same plant 

boundary and compartment definitions and location identification nomenclature as 

established in the corresponding full-power fire PRA. If the global analysis boundary is 

expanded to accommodate the needs of the LPSD fire PRA, then the additions should be 

clearly documented (e.g., identify locations that were deemed outside the scope of the 

full-power fire PRA but are included in the LPSD fire PRA). This approach will greatly 

simplify the process of component tracing and location documentation. 
Draft For Public Comment 

16 

(2) The internal events LPSD PRA model for the specific POSs under consideration and the 

corresponding equipment lists are a required input. 

(3) Plant procedures applicable to the POSs being considered (e.g., emergency operating 

procedures, fire procedures, annunciator response procedures) are required in addition to 

at-power operating procedures. 

(4) The analysis will need to review plant Technical Specifications to determine possible 

limiting conditions of operation (LCOs) applicable to each defined POS conditions (see 

Task 2 Step 3). 

4.2.2 Procedure

The steps that follow provide a method to create the LPSD fire PRA component list. The step 

structure is identical to that provided in Section 2.5 of reference [1]. As with the full-power fire 

PRA, as a practical matter, the LPSD fire PRA component selection task is an iterative process. 

Hence, as other tasks are performed, there may be reason to revisit and redo portions of Task 2 

during the development, screening, and eventual quantification of the LPSD fire PRA. 

 Step 1: Identify Internal Events LPSD PRA Sequences to be included (and those to be 

excluded) in the LPSD fire PRA Model. 

This step for the fire LPSD task is identical to the corresponding step as described in 

Section 2.5.1 of reference [1] with one modification. For the purposes of the LPSD fire 

PRA, Step 1 reviews accident sequences from the full-power fire PRA and the internal 

events LPSD PRA (rather than only the internal events full-power PRA.) 

Possible Elimination of Sequences and Equipment - The identification of sequences that 

could generally be eliminated from the LPSD fire PRA is similar to the corresponding 

analysis element in reference [1] with the following additions: 

(1) In determining which sequences and equipment to include, or potentially exclude, from 

the LPSD fire PRA, consider all sequences included in the full-power fire PRA and 

those included in the internal events LPSD PRA. 

(2) It is recommended that all components included in the full-power fire PRA be retained 

for (i.e., not eliminated from) the LPSD fire PRA with few exceptions. In essence, the 

full-power fire PRA will already have established component locations and will have 

identified and traced related cables. Hence, there is likely little benefit to be gained by 

excluding such components from the fire LPSD analysis especially given that the LPSD 

fire PRA will include low-power (e.g., startup) POSs that will be quite similar in nature 

to the full-power plant configuration. If any components that were included in the fullpower fire PRA are excluded from the LPSD fire PRA, the exclusion should be noted 

and explained, including a discussion of the potential impact of these exclusions on the 

risk results. 

(3) As in the full-power fire PRA, justification for the exclusion of any sequences or 

equipment and the resulting impact on the “reduced” PRA model should be noted. In 

particular, the analyst should take care not to eliminate sequences or equipment that 

could adversely affect equipment credited in the LPSD fire PRA. For example, 

elements of an electric power distribution system may be considered for elimination 

(e.g., dc power distribution system elements). However, the analyst should be careful 
Draft For Public Comment 

17 

not to eliminate those parts of the system that may be needed for proper functioning of 

credited equipment items (e.g., instrumentation loops). 

Possible Additions of Sequences and Equipment - Considerations relative to the addition of 

sequences and equipment are essentially the same as for the corresponding analysis 

element in the full-power fire PRA with the following clarifications: 

(1) As was the case for the full-power fire PRA as compared to the full-power internal 

events PRA, some sequences that were screened out of the internal events LPSD PRA 

based on low frequency of occurrence may need to be retained in the LPSD fire PRA. 

The bases for such additions would be similar to those leading to additions to the fullpower fire PRA. Specifically, a search should be conducted, in concert with carrying 

out all the steps of this procedure, for new functional challenges in the plant not 

otherwise accounted for especially because of fire-induced spurious actuation 

considerations. 

 For example, spurious actuation of a high pressure pump while the reactor 

vessel is closed but in cold shutdown may lead to pressurizer safety relief valve 

(SRV) lift. Spurious actuation of the pump may have been deemed of sufficiently 

low probability in the internal events LPSD PRA that the sequence may have 

been screened out. However, fire-induced spurious actuation of the same pump 

(e.g., due to control cable failures) might be likely enough to warrant retention of 

the sequence. 

A review should be conducted for such scenarios originally eliminated from the internal 

events LPSD PRA to determine if new components should be added to the LPSD fire 

PRA component list implying that those components, their failure modes, and the 

associated sequences would be included in the LPSD fire PRA plant risk model (see 

Task 5). Particularly when considering the possible effects of spurious operations, new 

accident sequences and associated components of interest beyond those considered in 

the Internal Events LPSD PRA may be identified that should be addressed in the LPSD 

fire PRA. Each POS should be considered individually to determine applicability. 

Typically, new sequences might arise as a result of spurious events that: 

 cause a loss of coolant accident (LOCA), e.g., drain down events; 

 adversely affect plant pressure control, e.g., letdown or safety relief valve 

events; 

 cause loss of cooling to core; or 

 introduce other “new” scenarios that may not be addressed in the internal 

events LPSD PRA. 

(2) As with the full-power fire PRA, a review of the fire emergency procedures (FEPs) or 

similar fire-related instructions as such instructions apply to various LPSD POSs should 

be conducted (see also Task 12). In particular, fire-specific manual actions designed to 

preclude or overcome spurious operations will likely not have been addressed in the 

Internal Events LPSD PRA. For example: 

 An FEP may require shutdown of a pump from the switchgear to avoid 

spurious actuation of the pump and pump damage due to cavitation. This may 
Draft For Public Comment 

18 

cause demands on the pressurizer SRV and lead to sequences not modeled in the 

Internal Events LPSD PRA. 

 Fire specific manual actions may cause an unintentional failure of a safety 

function or a subset of that functional response. For example, a proceduralized 

action may be to trip a power supply thereby disabling (“failing”) certain 

equipment in the plant. 

 As with full-power considerations, the likely timing of the operator action as 

compared to when the affected component is needed should also be considered. 

 Step 2: Review the Internal Events LPSD PRA Model Against the Fire Safe Shutdown 

Analysis: 

The impact of Step 2 on the LPSD fire PRA is likely to be more limited than the impact of 

this step on the full-power fire PRA. However, this step does retain some relevance to the 

LPSD fire PRA and should not be neglected. 

The fire safe shutdown analysis addresses regulatory requirements to demonstrate that, in 

the event of a plant fire, the plant will retain the ability to achieve hot-shutdown (or hotstandby) and ultimately to achieve and maintain cold shutdown. Hence, the safe shutdown 

procedures will overlap some of the POSs that will likely be defined in the LPSD fire PRA. 

To the extent that this overlap exists, Step 2 should be completed. 

The underlying steps (i.e., steps 2.1 through 2.5) are executed largely consistent with the 

treatment afforded in the full-power fire PRA. The most significant difference is that the 

review compares the fire safe shutdown analysis to the plant risk model developed for the 

internal events LPSD PRA rather than the treatment provided in the internal events fullpower PRA. The reconciliation effort in steps 2.1 through 2.4 compares the fire safe 

shutdown analysis to the internal events LPSD PRA rather than to the internal events fullpower PRA. When reconciling system or equipment differences due to end-state 

and mission considerations, the fire safe shutdown analysis will likely not deal at all with 

various POSs associated with the LPSD fire PRA. In particular, the fire safe shutdown 

analysis will typically not address any aspects of plant operations during refueling stages of 

a plant shutdown. When considering specific review of manual actions, the reconciliation 

effort should compare the fire safe shutdown analysis to the internal events LPSD PRA 

rather than to the internal events full-power PRA. Also, with respect to manual actions to 

be credited in the LPSD fire PRA, considerations should include both the need to achieve 

and maintain safe shutdown (e.g., given an automatic or manual trip from a low-power 

POS) and the need to maintain safe and stable conditions during other non-power POSs 

(e.g., refueling evolutions). 

 Step 3: Identify Fire-Induced Initiating Events Based on Equipment Affected: 

The role of this step in the analysis is essentially identical for the LPSD fire PRA as for the 

full-power fire PRA. That is, to the extent the above steps have not already done so, this 

step addresses that equipment which, if affected by a fire, could cause an initiating event 

(e.g., forced shutdown of the plant from a low power state or a drain down event for other 

shutdown evolutions). As in the full-power analysis, the goal of Step 3 is to identify what 

initiator(s) will likely occur if a fire in any given compartment affects equipment identified 

on the LPSD fire PRA component list. For guidance, see Section 2.5.3 of reference [1] 
Draft For Public Comment 

19 

with the following clarification: In addition to the considerations applicable to the fullpower fire PRA, for the LPSD fire PRA, consideration also extends to equipment whose 

failure would compromise the ability to maintain a safe and stable condition for each POS 

being considered. It is anticipated that new initiating events may need to be identified 

stemming from the specific conditions imposed by the POS. It must be noted here again 

that this guidance is focused on CDF and LERF. Other radionuclide release possibilities 

are not considered as part of the scope of this document. 

 Step 4: Identify Equipment with Potential Spurious Actuations that may Challenge the 

Ability to Safely Maintain the Plant During Each POS: 

The role of this step in the analysis is essentially identical for the LPSD fire PRA as for the 

full-power fire PRA. This step is aimed at further expanding the LPSD fire PRA 

component list, and thus potentially the LPSD fire PRA plant risk model (Task 5), to 

include adequate consideration of the potential for harmful fire-induced spurious 

actuations. For guidance, see Section 2.5.4 of reference [1] with the following 

clarifications: 

(1) In addition to the considerations applicable in the full-power fire PRA, for the LPSD 

fire PRA it also extends to equipment whose spurious actuation would compromise the 

ability to maintain a safe and stable condition for each POS being considered. 

(2) The systematic review of potential spurious actuation concerns is conducted on the basis 

of accident sequence types and related mitigation system functions included in the 

internal events LPSD PRA plant risk model rather than the internal events full-power 

PRA plant risk model. 

(3) Table 2-2 of reference [1] presents (illustrative only) examples of how single and 

multiple spurious actuation failures might be important for some accident sequences. In 

addition to those examples provided for full-power conditions, the LPSD PRA should 

include consideration of spurious actuations impacting secondary-side cooling functions 

because these either may not have been considered, or may have been considered and 

screened out, during the full-power fire PRA. 

 Step 5: Identify Additional Mitigating, Instrumentation, and Diagnostic Equipment 

Important to Human Response: 

The goal of this step in the LPSD fire PRA is identical to that of the corresponding step in 

the full-power fire PRA [1]. Namely, the goal is to expand the LPSD fire PRA component 

list, and thus potentially the LPSD fire PRA plant risk model (Task 5) to include other 

mitigating equipment, instrumentation, and diagnostic equipment necessary for human 

actions if not already addressed in previous steps for each POS. The structure and role of 

the underlying steps (5.1 and 5.2) remains unchanged. 

 Step 5.1: Identify Human Actions of Interest: See Section 2.5.5.1 of reference [1] for 

guidance with the following clarifications: 

(1) The identification of human actions gives consideration to those human actions 

credited in the internal events LPSD PRA rather than those actions credited in the 

internal events full-power PRA. 
Draft For Public Comment 

20 

(2) The review of human actions should consider all relevant plant procedures for all 

POSs being considered. This should include both general plant operations and any 

fire-specific procedures as available. 

 Step 5.2: Identify Instrumentation and Diagnostic Equipment Associated with both 

Credited and Potentially Harmful Human Actions: See Section 2.5.5.2 of reference [1] 

for guidance. The following is an alternative example to those offered in reference [1] 

that should be included during the performance of Step 5.2: 

(1) The LPSD fire PRA will need to consider the potential role of the plant’s alternate 

shutdown panel in LPSD operations. If, for example, a main control room (MCR) 

fire were to occur during a shutdown evolution, the analysis will need to assess what 

benefit could be gained through use of the alternate shutdown panel(s) to control 

some of the plant systems. 

 Step 6: Include “Potentially High Consequence” Related Equipment: 

As the final analysis step in performing Task 2, consideration is given to equipment 

associated with potentially high consequence events. The goal is to ensure that such events 

are not be prematurely screened, but are analyzed in more detail to determine their risk 

significance. 

High consequence events for full-power conditions are potentially relevant to low-power 

operations as well. These are defined per Section 2.5.6 of reference [1] (list items (a) and 

(b) in that section). To the extent that such events are relevant to low-power operations 

they should be considered consistent with the full-power fire PRA guidance. In addition to 

(a) and (b) in reference [1], for the purposes of the LPSD fire PRA, consideration of 

potentially high consequence events should be extended to include events where: 

(c) one or more related component failures, including spurious operations, where at least 

one failure/spurious operation is induced by a fire that by themselves results in fuel 

bundle damage either (1) when the reactor vessel and secondary containment structure 

are open (i.e., no primary or secondary containment) or (2) in a location outside 

containment to the extent that plant operations associated with the removal of fuel 

bundles from containment are included in the defined POS(s). 

 Step 7: Assemble LPSD fire PRA component list: 

As in the full-power fire PRA, the final step is to assemble the LPSD fire PRA component 

list. This list is generally maintained in a supporting database. The most important 

elements of the database will be the component identifiers and the location of the 

component. This effectively defines the PRA damage targets within each PAU in terms of 

components. Section 2.5.7 of reference [1] provides recommendations relative to the type 

of information that should be recorded for each item on the component list. Similar 

information will be needed to support the LPSD fire PRA, but this information will also 

need to extend to all POSs being considered. Some component characteristics (e.g., 

equipment identifier (ID), description, locations, system designation, and type) will remain 

the same regardless of the plant operating state. However, others (e.g., the normal 

position/status, desired position/status, failed electrical position, and failed air position) will 

change depending on the POS. It is recommended that the database structure be expanded 
Draft For Public Comment 

21 

to capture, as relevant, variable aspects of each component identified and the relevant 

entries as applicable to each identified POS. Additionally, there could be temporarilystaged equipment (e.g., auxiliary diesel), which may be a part of the safe plant operation 

during a POS. These new equipment items would need to be added to the list. 

4.3 Task 3: Fire PRA Cable Selection

The approach and process for identifying cables of potential interest to the LPSD fire PRA is 

essentially identical to that applied to the full-power fire PRA as documented in Section 3 of 

reference [1]. However, the following clarifications should be noted: 

 Any and all cables selected for inclusion in the full power fire PRA will likely be 

included in the LPSD fire PRA. Any exceptions to this general practice should be 

identified and justified. 

 The cable identification process considers the equipment and components identified in 

Task 2 of the LPSD fire PRA rather than the set of equipment identified in the 

corresponding full-power fire PRA. The LPSD fire PRA equipment list may contain new 

components not included in the full-power fire PRA and the cable selection process should 

be repeated for these new components. If, as part of maintenance activities during a POS, 

for equipment on the component list, temporary cables are installed or existing cables are 

re-routed, those cables should be added to the list. 

 The full-power cable selection results should also be reviewed to ensure that 

component failure modes that may not have been of interest to the full-power fire PRA but 

that have unique implications to the LPSD POSs are identified and addressed. This might, 

for example, include the re-introduction of cables leading to spurious equipment actuations 

that were considered benign in the full-power analysis but which might not be benign in the 

context of one or more LPSD POSs. For example, the spurious operation of valves 

associated only with shutdown cooling systems might have little or no impact on at-power 

operations, but might compromise core cooling during one or more LPSD POS. Hence, it 

is possible that components, and their associated cables, that were properly screened out 

from the at-power fire PRA would need to be added to the LPSD fire PRA equipment and 

cable lists. 

 Cable selection considers the potential impact of cable failures in the context of each 

POS being considered in the LPSD fire PRA. 

The final outcome of this task is a set of entries in the fire PRA Database identifying the cables 

of interest in terms of associated component serviced by the cable, cable function, and cable 

locations (see Section 3.5.6.1 of reference [1] for further detail). This information establishes the 

PRA damage targets in each PAU in terms of cables. 

4.4 Task 4: Qualitative Screening

The purpose of this task is to qualitatively screen PAUs before the quantitative analysis is 

initiated. Since CDF and LERF are the focus of the LPSD fire PRA, the method and criterion 

provided in Chapter 4 of reference [1] are applicable to the LPSD fire PRA. The criterion 

provided in reference [1] is repeated here: 
Draft For Public Comment 

22 

 Screen a PAU if the compartment does not contain any of the equipment (including 

circuits and cables) identified in Tasks 2 and 3, and 

 In concert with Section 2.5.3 of the Task 2 procedure, the compartment is such that 

fires in the compartment will not impact plant status. For example, there would not be a 

reactor trip if the reactor is critical or loss of decay heat cooling if the reactor is in cold 

shutdown. 

As in the case of full-power fire PRA, these criteria are specifically intended to allow the 

qualitative screening of PAUs that do not contain any of the equipment or cables identified in 

Tasks 2 and 3, but where a prolonged fire might lead operators to implement alternative or 

preemptive measures to maintain the POS or to place the plant in a more stable condition. That 

is, the full-power methodology assumes that a PAU where a fire cannot directly threaten any of 

the fire PRA equipment or cables will not represent a substantive contributor to fire risk even if 

operators might take preemptive actions to, for example, trip the plant. For this case the fire 

represents just one more potential source of a plant trip with no loss of mitigating equipment, 

scenarios already captured in the internal events PRA. Analogous situations are likely for LPSD 

conditions. For example, if a fire were to occur during plant startup, operators might choose to 

initiate a preemptive trip even though no important plant systems or equipment have been lost or 

are threatened. The criteria above would allow for the screening of such PAUs so long as there 

is no direct threat to the LPSD fire PRA equipment or cables identified as important to the 

POS(s) associated with plant startup. 

It should be noted that compartments qualitatively screened in this task will be reexamined in 

Task 11 for the potential for affecting adjacent compartments in the multi-compartment fire 

analysis. 

Compartments that would be qualitatively screened out in this task and later in Task 11 as part of 

the multi-compartment analysis are concluded to be of little risk significance to be tracked for 

risk contribution. 

4.5 Task 5: Fire‐Induced Risk Model

In this task the plant model is put together using event trees and fault trees for calculating the 

CDF and LERF of LPSD fire PRA. The same procedure as for full-power fire PRA applies here. 

The same modeling approaches (i.e., either fault tree linking or event trees with boundaries [1]) 

can be used for LPSD conditions. A separate model may need to be developed for each POS. In 

other words, this task may need to be repeated for each POS separately. If the complete set of 

LPSD POSs (i.e., the average or typical outages as discussed in Section 3.0 above) is of interest, 

a separate model should be developed for each POS of the set. Similarly, if a one-of-a-kind 

outage is under consideration, the model should reflect the specific conditions of that POS. 

For full-power PRA model, in addition to emergency operating procedures (EOPs), the analysts 

may use FEPs to establish the chain of events in response to an initiating event. In the case of 

LPSD, practices will vary from plant to plant. Some plants may develop specialized EOPs and 

FEPs to address specific conditions of the POS or a one-of-a-kind outage. Those EOPs and 

FEPs should be consulted when developing the plant model for LPSD fire PRA (see Section 

4.2.2 for further detail). If MCR evacuation is part of a fire scenario, the specific conditions of 

the LPSD POS should be considered when using the FEP for such events. Plant management 
Draft For Public Comment 

23 

may need to be consulted to ensure that POS specific procedures and guidelines are incorporated 

in the development of the LPSD fire PRA model. 

Similar to full-power fire PRA, an internal events model serves as the starting point for this 

purpose. That is, this method assumes that an internal events LPSD PRA model for the specific 

POS of the study does exist. The same approach can be used as in the full-power case defined in 

reference [1] to arrive at the LPSD fire PRA plant model. A set of initiating events applicable to 

the fire analysis should be identified first and then the internal events analysis event trees and 

fault trees are modified as necessary to establish the set of fire-induced failures and operator 

errors that could lead to core damage or large early release. Similar to the full-power case, the 

process may include temporary changes to the Internal Events LPSD PRA that are later modified 

as PAUs and fire scenarios are screened from further analysis. In the temporary models, 

conservative measures are incorporated to expedite the analysis, which are later refined and 

applied to risk significant scenarios. 

As noted above, the same procedure described in reference [1] applies here. The assumptions, 

input from other tasks and output to other tasks remain the same. When analyzing a specific 

POS, especially in the case of one-of-a-kind outage, it is possible that only a small part of the 

plant could be affected. For those cases, the analyst may elect to limit the analysis only to those 

parts of the plant. The same procedure should apply regardless of the scope of the analysis with 

the following clarifications: 

 Step 1–Develop the Fire PRA CDF/CCDP Model: 

In this case the model is focused on specific LPSD POS conditions. The conditional core 

damage probability (CCDP) and CDF models are the same. To obtain the CCDP, the 

model is quantified using 1.0 for the initiating event frequency. Step 1 is divided into three 

sub-steps as follows: 

 Step 1.1: Select Appropriate Fire-Induced Initiating Events and Sequences and Verify 

Against the Component List and Failure Modes: The initiating events identified in Step 3 

of Task 2 are reviewed and verified in this step. It should be noted that new initiating 

events (i.e., other than those adopted from the full-power fire PRA and internal events 

LPSD analyses) may be identified here based on the special conditions created by a 

specific POS. 

 Step 1.2: Incorporate Fire-Induced Equipment Failures: Equipment failure due to fire 

impact is carefully studied in the full-power fire PRA. The same information should 

apply to LPSD conditions. Clearly, special conditions should be taken into account. For 

example, if the doors of a normally closed active electrical cabinet are opened for the 

duration of a task or POS, the analyst should consider reviewing the assumptions made in 

the fire model for that cabinet and adjust the fire characteristics accordingly. 

 Step1.3: Incorporate Fire-Induced Human Failures: The manual actions credited in 

the full-power fire PRA model should be reviewed and modified to reflect the special 

conditions that may exist during the postulated POS. If POS specific FEPs are 

developed, the manual actions credited in those procedures should also be reviewed 

carefully and incorporated in the model. 
Draft For Public Comment 

24 

 Step 2–Develop the Fire PRA LERF/CLERP Model: 

The same discussions apply to the LERF and conditional large early release probability 

(CLERP) model as in Step 1 above. Under certain POS conditions, the containment may 

be open to the atmosphere. In that case, the LERF model could be very simple. If the 

containment is closed, the analyst should develop a LERF model based on the internal 

events LPSD model and review and verify the applicability of equipment failures and 

operator actions as in the case of the CDF model. 

4.6 Task 6: Fire Ignition Frequencies		

4.6.1 Background Information

Similar to Task 6 of reference [1], the LPSD fire PRA should estimate fire-ignition frequencies 

and their respective uncertainties for ignition sources and compartments. The ignition frequency 

task represents the first step in quantifying fire scenarios as they are defined and analyzed in later 

tasks. A generic set of fire-ignition frequencies for various generic equipment types (ignition 

sources) typically found in certain plant locations was developed as a starting point for the fullpower analysis. The same analysis approach described in Task 6 of reference [1] applies to 

LPSD conditions with a few exceptions as discussed below. 

The frequencies provided in reference [1] were based on events that either occurred during all 

operating modes or just during power operation. That is, as a part of the full-power methodology 

development, each of the identified fire ignition source bins was reviewed. Judgment was 

applied to assess whether or not the frequency of fire events would be substantially dependent on 

the plant operating mode. Two fire frequency cases resulted as follows: 

 Case 1: If the fire ignition frequency of an ignition source bin was judged to be 

independent of the operating mode, then the fire frequency analysis considered all fire 

events occurring over all plant operating states and the corresponding years of reactor 

experience. For these fire frequency bins, no changes are needed and the full-power fire 

frequency values apply to the LPSD fire PRA unchanged. 

 Case 2: If the fire ignition frequency for a fire ignition source bin was judged to be 

dependent on the plant operating mode, then only those fire events occurring during plant 

power operations were considered along with the corresponding at-power reactor 

experience (i.e., the fraction of the time that the plants were not in power mode) in 

developing the full-power fire frequency estimates. For these cases, re-analysis of the fire 

frequency is required to support the LPSD fire PRA. 

Table 1 provides the list of bins that fell into the second case. For these bins, a reanalysis of the 

fire frequency has been performed and LPSD-specific fire frequency values determined. Note 

the following: 

 One event involving a gas-turbine was observed during LPSD operation that was not 

considered in the full-power analysis. Since the number of gas-turbines and corresponding 

experience base (i.e., total number of operating years) is not readily available, an ignition 

frequency for this bin is not estimated. 

 Fires are not considered plausible inside inerted BWR containments in the full-power 

fire PRA. In contrast, several transient and hot work events have taken place inside BWR 

containments during shutdown, events not considered in the full-power analysis. Since 
Draft For Public Comment 

25 

BWR and pressurized water reactor (PWR) containments are quite different, a new bin is 

defined specifically for transient and hot-work fires in BWR containments (bin 3B) and the 

PWR containment transient and hot-work fire bin has been renamed (bin 3P rather than 

simply bin 3 as in the full-power set). 

Table 1: Fire Ignition Frequency Bins Specific to LPSD Conditions. 

Bin # Location Ignition Source 

(Equipment Type)

2 Containment (PWR) Reactor Coolant Pump (RCP) 

3P Containment (PWR) Transients and Hotwork 

3B Containment (BWR) Transients and Hotwork 

5 Control/Aux/Reactor Building Cable fires caused by welding and cutting 

6 Control/Aux/Reactor Building Transient fires caused by welding and cutting 

7 Control/Aux/Reactor Building Transients 

11 Plant-Wide Components Cable fires caused by welding and cutting 

20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) 

22 Plant-Wide Components Reactor protection system (RPS) motor-generator 

(MG) Sets 

24 Plant-Wide Components Transient fires caused by welding and cutting 

25 Plant-Wide Components Transients 

27 Transformer Yard Transformer – Catastrophic 

28 Transformer Yard Transformer - Non Catastrophic 

29 Transformer Yard Yard transformers (Others) 

31 Turbine Building Cable fires caused by welding and cutting 

32 Turbine Building Main Feedwater Pumps 

33* Turbine Building Turbine Generator (T/G) Exciter* 

34 Turbine Building T/G Hydrogen 

35 Turbine Building T/G Oil 

36 Turbine Building Transient fires caused by welding and cutting 

37 Turbine Building Transients 

* Bin #33 frequency was not quantified assuming that under all POS conditions, the main generator 

would not be generating power. 
Draft For Public Comment 

26 

As in reference [1], the combination of locations and equipment types (ignition source) are 

referred to here as ignition frequency bins. Table 2 provides the list of these bins and their 

respective generic mean frequencies (i.e., the mean value of the uncertainty distribution) in terms 

of the number of events per year assuming that the plant is in the specific operating mode the 

entire year. Table 2 is the LPSD version of the original study (i.e., Table 6-1 of reference [1]). 

Only those ignition frequency bins identified in Table 1 have been changed (i.e., recalculated). 

All of the other ignition source bins (i.e., those not in Table 1) have simply been reproduced here 

directly from Table 6-1 of reference [1] with no change in value. 

Appendix A describes the frequency analysis approach, assumptions and derivation method. The 

general approach is the same as that applied to the full-power fire frequency analysis. It should 

be noted that proposed modifications to various ignition source bins for full-power conditions 

have been put forth via the NFPA-805 Frequently Asked Questions (FAQ) process (see 

FAQ08-0048 in the NRC Agency-wide Documents Access and Management System (ADAMS) 

accession number ML092190457). The FAQ proposes that a change (reduction) in fire 

frequencies was observed after 1990 and recalculates fire frequencies on that basis. The analysis 

presented in this document (i.e., in Appendix A) uses the complete set of fire event data 

consistent with the original treatment in NUREG/CR-6850. That is, the analysis performed here 

does assume that general fire frequencies dropped beginning in 1990. This approach preserves a 

larger event set for the LPSD-specific fire frequency bins. 

There is an ongoing effort between NRC/RES and EPRI to develop an enhanced fire event 

database that should resolve this frequency trend issue. The analyst should be aware that a new 

set of fire frequencies for both full-power and LPSD conditions will likely be developed in the 

near future. 

As with the full-power analysis, a two-stage Bayesian update method [5] was used to account for 

plant-to-plant variability. The 5th, 50th and 95th percentiles of the uncertainty distributions are 

also provided in Appendix A. As in full-power fire PRA, single stage Bayesian update methods 

can be used to modify the generic frequencies to reflect the influence of plant specific fire event 

experience. 

As in reference [1], different fire types can be postulated for some of the ignition sources. For 

example, the bin “plant-wide components/pumps” can refer to both electric and oil fires. In 

those cases, Table 2 provides a split fraction for each fire type. The split fraction was determined 

according to fire events in the FEDB. Continuing with the plant-wide-components/pumps 

example, the pump fire events in the database were reviewed and classified as oil or electrical 

fires. This classification serves as the basis for the split fraction. 

If the quantification process needs the fire frequency associated with a compartment, the 

following equation remains valid for the LPSD operating modes: 

λJ,L = Σ λIS WL WIS,J,L

where the right-hand side is summed over all ignition sources (IS) in compartment J of location 

L and where: 

λJ,L = Compartment (J) level fire frequency 

λIS = Plant-level fire frequency associated with ignition source IS 

WL = Location weighting factor associated with the ignition source 
Draft For Public Comment 

27 

WIS,J,L = Ignition source weighting factor reflecting the quantity of the ignition source 

type present in compartment J of location L. 

Note that the frequencies presented in Table 2 are instantaneous values that are assumed to 

remain constant over the POS. As presented in Section 3.0 above, the CDF calculated based on 

these frequencies should be adjusted for the fraction of the time that the plant is in the specific 

operating mode. 

Plant-level fire frequencies (i.e., λIS) are either taken directly from Table 2 or can be updated 

using plant-specific fire experience. The location weighting factor, WL, adjusts the frequencies 

for those situations where a common location (e.g. turbine building) or set of equipment types 

are shared between multiple units. The ignition source weighting factor, in general terms, is the 

fraction of an ignition source type found in a specific compartment. The discussions provided in 

reference [1] for these parameters apply to LPSD conditions as well. 

4.6.2 Assumptions

The same set of assumptions as in reference [1] applies to LPSD fire ignition frequencies. 

Because of their importance, they are repeated below: 

 Fire ignition frequencies remain constant over time; 

 Among the plants, total ignition frequency is the same for the same equipment type, 

regardless of differences in the quantity and characteristics of the equipment type that may 

exist among the plants; 

 Within each plant, the likelihood of fire ignition is the same across an equipment type. 

For example, pumps are assumed to have the same fire ignition frequency regardless of 

size, usage level, working environment, etc. 

 The ignition frequency is the same among all POSs 

 Clearly there are marked differences among the POSs that might influence the ignition 

frequencies. The level of detail provided in FEDB could not support a meaningful 

resolution among POSs. Therefore, one set of frequencies were estimated for all the POSs. 

4.6.3 Procedure

The same procedure as in reference [1] applies to LPSD conditions. The following general 

conditions apply as in the full-power case: 

 This task needs the list of unscreened PAUs generated in Task 4, Qualitative Screening, 

to establish fire frequencies by compartment. 

 Fire event records available at the plant applicable to the bins defined in Table 1 may 

be used to update ignition frequencies of those bins using plant-specific data. (Note that it 

is assumed that the frequencies of the bins not included in Table 1 are already examined for 

plant specific fire experience and other conditions as part of the Full-power fire PRA.) 
Draft For Public Comment 

28 

Table 2: Fire Frequency Bins and Generic Frequencies. 

Bin 

# Location Ignition Source (Equipment Type) Mode 

Generic Freq 

(per rx yr) 

Split Fraction for Fire Type 

Electrical 

Oil 

Transient 

Hotwork 

Hydrogen 

High energy 

arc fault 

(HEAF) 

1 Battery Room Batteries All 7.5E-04 1.0 0 0 0 0 0 2 Containment (PWR) Reactor Coolant Pump LPSD or Undetermined 6.6E-03 0.25 0.75 0 0 0 0 

3P Containment (PWR) Transients and Hotwork LPSD or Undetermined 3.1E-02 0.00 0.00 0.39 0.61 0.00 0.00 

3B Containment (BWR) Transients and Hotwork LPSD or Undetermined 3.5E-02 0.05 0.00 0.24 0.71 0.00 0.00 

4 MCR Main Control Board (MCB) All 2.5E-03 1.0 0 0 0 0 0 5 Control/Auxiliary/Rea ctor Building Cable fires caused by welding and cutting LPSD or Undetermined 1.2E-03 0 0 0 1.0 0 0 6 Control/Auxiliary/Rea ctor Building Transient fires caused by welding and cutting LPSD or Undetermined 9.3E-03 0 0 0.09 0.91 0 0 7 Control/Auxiliary/Rea ctor Building Transients LPSD or Undetermined 4.7E-03 0 0 1.0 0 0 0 8 Diesel Generator Room Diesel Generators All 2.1E-02 0.16 0.84 0 0 0 0 9 Plant-Wide Components Air Compressor All 2.4E-03 0.83 0.17 0 0 0 0 

10 Plant-Wide Components Battery Chargers All 1.8E-03 1.0 0 0 0 0 0 11 Plant-Wide Components Cable fires caused by welding and cutting LPSD or Undetermined 8.8E-04 0 0 0 1.0 0 0 12 Plant-Wide Components Cable Run (Self-ignited cable fires) All 4.4E-03 1.0 0 0 0 0 0 13 Plant-Wide Components Dryers All 2.6E-03 0 0 1.0 0 0 0 14 Plant-Wide Components Electric Motors All 4.6E-03 1.0 0 0 0 0 0 15 Plant-Wide Components Electrical Cabinets All 4.5E-02 1.0 0 0 0 0 0 
Draft For Public Comment 

29 

Table 2: Fire Frequency Bins and Generic Frequencies. 

Bin 

# Location Ignition Source (Equipment Type) Mode 

Generic Freq 

(per rx yr) 

Split Fraction for Fire Type 

Electrical 

Oil 

Transient 

Hotwork 

Hydrogen 

High energy 

arc fault 

(HEAF) 

16 Plant-Wide Components High Energy Arcing Faults1 All 1.5E-03 0 0 0 0 0 1.0 17 Plant-Wide Components Hydrogen Tanks All 1.7E-03 0 0 0 0 1.0 0 18 Plant-Wide Components Junction Boxes All 1.9E-03 1.0 0 0 0 0 0 19 Plant-Wide Components Misc. Hydrogen Fires All 2.5E-03 0 0 0 0 1.0 0 20 Plant-Wide Components Off-gas/Hydrogen recombiner (BWR) LPSD or Undetermined 2.0E-02 0.33 0 0.33 0 0.33 0 21 Plant-Wide Components Pumps All 2.1E-02 0.54 0.46 0 0 0 0 22 Plant-Wide Components RPS MG sets LPSD or Undetermined 3.2E-03 1.0 0 0 0 0 0 

23a Plant-Wide Components Transformers (Oil filled) All 9.9E-03 0 1.0 0 0 0 0 

23b Plant-Wide Components Transformers (Dry) 1.0 0 0 0 0 0 

24 Plant-Wide Components Transient fires caused by welding and cutting LPSD or Undetermined 1.1E-02 0 0 0 1.0 0 0 25 Plant-Wide Components Transients LPSD or Undetermined 5.8E-03 0.1 0 0.90 0 0 0 26 Plant-Wide Components Ventilation Subsystems All 7.4E-03 0.95 0.05 0 0 0 0 27 Transformer Yard Transformer - catastrophic LPSD or Undetermined 7.2E-03 0.70 0.30 0.00 0.00 0.00 0.00 28 Transformer Yard Transformer - noncatastrophic LPSD or Undetermined 3.8E-03 0.80 0.00 0.00 0.20 0.00 0.00 29 Transformer Yard Yard Transformers (others) LPSD or Undetermined 2.0E-03 1.0 0 0 0 0 0 30 Turbine Building Boiler All 1.1E-03 0 1.0 0 0 0 0 
Draft For Public Comment 

30 

Table 2: Fire Frequency Bins and Generic Frequencies. 

Bin 

# Location Ignition Source (Equipment Type) Mode 

Generic Freq 

(per rx yr) 

Split Fraction for Fire Type 

Electrical 

Oil 

Transient 

Hotwork 

Hydrogen 

High energy 

arc fault 

(HEAF) 

31 Turbine Building Cable fires caused by welding and cutting LPSD or Undetermined 1.3E-03 0 0 0 1.00 0 0 32 Turbine Building Main feedwater pumps LPSD or Undetermined 1.9E-03 0 1.0 0 0 0 0 33 Turbine Building T/G exciter At-power only 6.2E-04 1.0 0 0 0 0 0 34 Turbine Building T/G hydrogen LPSD or Undetermined 3.0E-03 0.25 0 0 0 0.75 0 35 Turbine Building T/G oil LPSD or Undetermined 2.5E-03 0 1.0 0 0 0 0 36 Turbine Building Transient fires caused by welding and cutting LPSD or Undetermined 2.2E-02 0.00 0.07 0.29 0.64 0.00 0.00 37 Turbine Building Transients LPSD or Undetermined 1.0E-02 0.00 0.04 0.96 0.00 0.00 0.00 
Draft For Public Comment 

 31 

 At least one plant or unit walkdown is recommended to identify ignition sources. In the 

case of LPSD, it is expected that transient and hot work related fire frequencies would be 

different from full-power conditions. Those parts of the plant where maintenance activities 

are planned may need to be examined carefully. Plant personnel involved in planning the 

outage may need to be consulted to establish the type and range of transient activities to 

establish the types of ignition sources that may be introduced in certain compartments. 

As in reference [1], this task is organized around the following eight steps: 

Step 1 Mapping plant ignition sources to generic sources, 

Step 2 Plant fire event data collection and review, 

Step 3 Plant specific updates of generic ignition frequencies, 

Step 4 Mapping plant-specific locations to generic locations, 

Step 5 Location weighting factors, 

Step 6 Fixed fire ignition source counts, 

Step 7 Ignition source weighting factors, and 

Step 8 Ignition source and compartment fire frequency evaluation. 

These steps are further discussed below: 

 Step 1: Mapping Plant Ignition Sources to Generic Sources 

This step should already be completed as part of the full-power fire PRA. That is, the 

characteristics of fixed ignition sources in the plant should not change based on POS in the 

context of this step. If any new plant locations have been added to the LPSD study, then 

some additional mapping may be required. It is recommended that any temporary ignition 

sources introduced during LPSD be treated as transient fire sources rather than as fixed fire 

sources. 

 Step 2: Plant Fire Event Data Collection and Review 

For fire event data collection and review, the same approach as that presented in reference 

[1] can be followed for LPSD operating modes. In this case the fire events that had 

occurred during LPSD operating modes are collected and analyzed. The same two 

questions, as in full-power case apply here: 

(1) Are there any unusual fire occurrence patterns in the plant? 

(2) Is plant-specific fire frequency evaluation warranted? 

Guidance provided in reference [1] on determining the response to these two questions 

applies to LPSD operating modes as well. 

 Step 3: Plant Specific Updates of Generic Ignition Frequencies 

As in reference [1], this step should be followed for those frequencies that will be based on 

plant-specific fire event data. The approach described in reference [1] applies here with the 

exception of one minor difference. The generic bin frequencies can be updated using a 

Bayesian approach [5] that includes Poisson distribution for the likelihood function of plant 

specific fire events. The Poisson distribution requires number of reactor years (T). In the 
Draft For Public Comment 

 32 

case of LPSD operating modes, this should be the total time that the affected unit has been 

in LPSD operating modes since commercial operation (i.e., "reactor-in-LPSD-years" rather 

than "reactor-at-full-power-years."). 

 Step 4: Mapping Plant-Specific Locations to Generic Locations 

The location mapping of the full-power fire PRA should be validated for LPSD specific 

conditions. For example, in the case of the BWRs, the containment may need to be added 

to the list because maintenance work may be scheduled inside the containment. 

 Step 5: Location Weighting Factor 

Plant configuration may be reviewed to verify that changes planned for LPSD conditions 

do not affect WL. For example, if Unit 1 is shutdown with several systems under 

maintenance and part of Unit 2 systems are used to provide the necessary functions, the fire 

PRA analyst may need to include parts of Unit 2 in the Unit 1 analysis. In such a case, the 

analyst should define the method for counting ignition sources carefully so that relevant 

compartments and ignition sources from Unit 2 can be correctly included in the Unit 1 

LPSD fire PRA. To further expand this example, consider 10 pumps in Units 1 and 2 each 

and two of the Unit 2 pumps are being used for Unit 1 service during a specific LPSD 

operating mode. Also, consider that those two pumps are located in the same compartment, 

J, with 3 other Unit 2 pumps (total of 5 pumps). The fire ignition frequency in that 

compartment associated with pump operation would then be calculated by the following 

equation: 

J, pump = bin 21 x WIS, J, L x WL

where: 

bin 21 = 2.1E-02 per reactor year, frequency of a fire from any one of the 

pumps in one of the two units. 

WIS, J, L = 5/20 Fraction of the pumps present in this room with respect to 

all the pumps in the two units 

WL = 2 The correction factor for counting both units in the total pump 

count 

 Step 6: Fixed Fire Ignition Source Counts: 

To estimate the frequency of fire occurrence per ignition source or per compartment, it is 

necessary to obtain the total number of items within a unit that belong to each bin. The 

counting approaches recommended in reference [1] augmented by responses to the FAQs 

generated after the publication of reference [1] should apply to LPSD operating modes. 

Generally, the number of countable items (e.g. pumps and electrical cabinets) should 

remain the same between full-power and LPSD conditions. However, for those bins for 

which LPSD specific ignition frequencies are established, the analyst should review the 

equipment configurations during LPSD conditions to verify that full-power counts remain 

valid. Transients and hot work related ignition source weighting factors could be different 

during LPSD operating modes, which is discussed as part of Step 7 below. 

 Step 7: Ignition Source Weighting Factors: 
Draft For Public Comment 

 33 

The Ignition source weighting factor, WIS,J,L, is the fraction of ignition source (IS) that is 

present in compartment J. The WIS,J,L are evaluated for all the ignition sources identified in 

Step 1 of this task and all the compartments identified in Task 1. The bins listed in the 

preceding section can be classified in three categories: countable items, transients, and 

large systems. The procedure presented in reference [1] for all three types of items should 

apply to LPSD operating modes. 

It is anticipated that the relative likelihood of transient and hot-work related fires in various 

plant locations will shift during LPSD operations as compared to full-power operation and 

the analysis should account for these differences. Transient combustible controls programs 

may be relaxed or may allow for routine exemptions to the normal controls. Transient 

materials not expected to be found during full-power operations (e.g., larger quantities of 

grease or oil and various equipment packing materials) may be introduced into the plant 

given that a range of longer-term maintenance activities will be undertaken. Hot work 

(e.g., welding and cutting) may be allowed in locations where that type of work would 

normally be disallowed during power operations. Plant traffic and occupancy factors 

would also be different. 

As a result, for the ignition source bins related to “general transients” (i.e., bins 3A, 3B, 7, 

25 and 37), “transient fires caused by welding and cutting” (i.e., bins 6, 24, and 36) and 

“cable fires caused by welding and cutting” (i.e., bins 5, 11 and 31) the influencing factors 

assigned to each compartment should be adjusted to reflect the specific LPSD conditions. 

This will require updating of the location-specific frequencies accordingly. For example, 

for those compartments where maintenance work is planned, “very high” may be assigned 

to the maintenance factor. For the passageways that lead to that compartment, the 

occupancy factor could be “high” as well. 

 Step 8: Ignition Source and Compartment Fire Frequency 

Fire frequencies (generic or plant-specific) for a single fire ignition source, λIS-J, and fire 

frequencies for an entire PAU (i.e., considering the combined frequency for all ignition 

sources in the PAU) are calculated using the same process as was described in reference 

[1]. 

4.7 Task 7: Quantitative Screening

The objective of this task is to apply quantitative screening criteria to reduce the list of PAUs and 

fire scenarios carried forward for detailed analysis. This is an important task used commonly in 

fire PRA to limit the level of effort and yet maintain the integrity of the analysis. Screening does 

not imply removing a PAU or fire scenario from the analysis. Rather screening simply implies 

that no further analysis effort (e.g., to increase the level of analysis detail) will be expended on 

that scenario or PAU. The CDF and LERF of the screened PAU or scenario would be based on 

the existing level of detail (a screening result) and the risk contribution would be ranked among 

all other PAUs and fire scenarios on that basis. 

For full-power PRA, screening criteria are defined in reference [1] for CDF, LERF, incremental 

core damage probability (ICDP) and incremental large early release probability (ILERP). The 

same criteria may be used for LPSD fire PRA. For ease of reference, the criteria presented in 

reference [1] are repeated here in Tables 3 and 4. Note that the quantitative measures (e.g., 
Draft For Public Comment 

 34 

CDF) are expressed in reactor years, which means that they include the fraction of time that the 

plant is in the postulated POS. 

The criteria presented in Tables 3 and 4 may be met by reducing the duration of a POS. One 

then may argue that defense in depth can be reduced significantly while meeting the screening 

criteria. Defense in depth related and all other regulatory requirements remain in effect during a 

POS. The PRA provides a measure to establish the overall risk and relative ranking of various 

contributors that can be used to determine if added risk reduction measures are necessary and 

where those measures can be most effective. 

It should be noted that these are suggested screening criteria. Also note that the cumulative 

screening criteria presented in Table 4 compare the LPSD fire PRA to the corresponding internal 

events LPSD analysis results on a POS by POS basis. This approach is intended, in part, to 

maintain consistency with this document’s neutrality relative to how the POSs to be analyzed are 

defined, and in particular, with how complete the POS set is. This screening approach works 

equally well whether the analysis quantifies a complete set of very specific POSs, quantifies a 

generally defined set of average outage conditions, or quantifies just one POS. Moreover, if a 

large number of compartments or fire scenarios meet the criteria in Table 3, it may not be 

possible to meet the criteria presented in Table 4. The analyst may encounter this situation after 

a few screening phases. To meet Table 4 criteria, the analyst may need to adjust Table 3 criteria 

downward (make the criteria more stringent). 

Table 3: Quantitative Screening Criteria for Single PAU Analysis. 

Quantification Type CDF and LERF Compartment 

Screening Criteria 

ICDP and ILERP Compartment 

Screening Criteria (Optional) 

PAU CDF 

CDF < 1.0E-07/year* 

Note: This criterion should be 

reduced, as necessary, to ensure that 

the CDF criterion in Table 4 is met. 

PAU CDF with Intact 

Trains/Systems 

Unavailable 

ICDP < 1.0E-7 

Note: This criterion should be reduced, 

as necessary, to ensure that the ICDP 

criterion in Table 4 is met

PAU LERF 

LERF < 1.0E-08/year* 

Note: This criterion should be 

reduced, as necessary, to ensure that 

the LERF criterion in Table 4 is met

PAU LERF with Intact 

Trains/Systems 

Unavailable 

ILERP < 1.0E-8 

Note: This criterion should be 

reduced, as necessary, to ensure that 

the ILERP criterion in Table 4 is met 

* All quantitative measures include the fraction of time that the plant is in the postulated POS. 

 
Draft For Public Comment 

 35 

Table 4: Quantitative Screening Criteria for All Screened PAUs. 

Quantification Type Screening Criteria 

Sum of CDFs for all screened out PAUs for each POS 

analyzed 

< 0.1 * [Internal Event CDF for the same 

POS] 

Sum of LERFs for all screened out PAUs for each POS 

analyzed 

< 0.1 * [Internal Event LERF for the 

same POS] 

Sum of ICDPs for all screened out PAUs for each POS 

analyzed < 1.0E-06 

Sum of ILERPs for all screened out PAUs for each POS 

analyzed < 1.0E-07 

As in reference [1], it should be emphasized that the screening criteria are meant to be applied as 

part of the fire PRA Model building and quantifying process. The screening criteria are not the 

same, nor should they be confused with the acceptance criteria for applications of PRA. For 

example, the screening criteria herein are not directly correlated to the delta-CDF and deltaLERF criteria used in Regulatory Guide 1.174 [6] for the acceptability of making permanent 

changes to the plant. The screening criteria are intended to complement the Regulatory Guide 

(RG) 1.174 criteria and to allow for the use of fire PRA results in a RG 1.174 application, but 

they are also intended to serve the broader objectives of a typical fire PRA. 

The overall approach described in reference [1] is applicable to LPSD conditions. The same 

assumptions and input and output discussions apply here as well. Several stages of quantitative 

screening are expected to be necessary to identify plant areas that need detailed analysis and 

establish risk ranking of PAUs and fire scenarios. Four phases of quantitative screening are 

identified in reference [1] (Tasks 7A through 7D) based on implementation of Tasks 8 through 

10 of the methodology. The same phases may be used in LPSD fire PRA. Clearly, conducting a 

screening phase would depend on the analyst’s preferences and the results of each task (i.e., 

Tasks 8 through 10). 

 Step 1–Quantify CDF Model: 

The model developed in Task 5 is quantified in this step. The CCDP is quantified first 

followed by CDF. This step involves 3 sub-steps as follows. 

 Step 1.1: Quantify CCDP Model: The CCDP is calculated by setting the fire scenario 

frequency as 1.0 per reactor year. Event trees and fault trees are quantified using internal 

events failure probabilities and human error probabilities (HEPs) estimated in Task 12. 

In the initial stages of screening, the circuit failure probabilities may be set at 1.0 and 

screening HEPs may be used (see Task 12). In later stages of screening, more refined 

values may be used. The outcome of this step is a list of PAUs and fire scenarios 

organized by CCDP. This result provides an important insight into fire risk significance 

of a PAU or scenario. 

 Step 1.2: Quantify CDFs: CDF results can be calculated for a single fire scenario, for 

a group of fire scenarios (e.g., a group of electrical cabinets), for a PAU, or for the entire 

plant. Quantitative screening is generally based at the fire scenarios and/or PAU level. 

For quantification, the fire frequency is matched to the screening level applied (e.g., fire 
Draft For Public Comment 

 36 

frequency might reflect a single fire source, a group of fire sources, or an entire PAU). 

The CDF of a specific POS is calculated using the following equation (from Section 3.0 

above): 

CDFPOS(i) = CDFPOS(i) x ftPOS(i) 

Where: 

CDFPOS(i) = λfire x CCDPPOS(i)

λfire = The fire frequency of the PAU or fire scenario (depending on screening 

level being applied) from Task 6 or Task 11 per reactor year. 

CCDPPOS(i) = The CCDP of POS(i) calculated in Step 1.1 above. 

The fraction of time that POS(i) is in effect (i.e., ftPOS(i)) is estimated in this step and used 

in CDF calculation. 

In the first quantitative screening stage, the frequency (i.e., λfire ) would be gleaned from 

Task 6 where fire frequencies are estimated at the PAU level. At later stages of analysis, 

the refined fire frequency calculated in Task 11 is used. By applying the screening 

criteria discussed above, PAUs or fire scenarios are set aside from further analysis. 

 Step 1.3: Quantify ICDP Values (Optional): This is an optional task that may not be 

applicable to LPSD conditions since Limiting Conditions of Operation (LCOs) may not 

be applicable. The same approach may be used as in reference [1] to define and calculate 

ICDP values. 

 Step 2–Quantify LERF Model: 

The same formulations and process as for CDF can be used to establish the LERF for each 

PAU or fire scenario. Similar to Step 1, this step is defined in three substeps where CLERP 

is calculated first. Similar to CDF, LERF is calculated as the product of CLERP, fire 

frequency (i.e., λfire ) and fraction of time POS is in effect (i.e., ftPOS(i)). 

 Step 3–Quantitative Screening: 

In this step, the CDF, LERF, ICDP (optional), and ILERP (optional) values are compared 

against the quantitative screening criteria provided in Tables 3 and 4. PAUs and fire 

scenarios that fall below the screening criteria are screened out from further analysis but 

retained for overall risk quantification and risk ranking of significant contributors. As this 

screening task progresses, the analyst may have to reduce the criteria presented in Table 3 

to allow the results to meet Table 4 criteria. 

4.8 Task 8: Scoping Fire Modeling

4.8.1 General Discussion

Scoping fire modeling is the first task where computational fire modeling tools are used to 

identify those fixed ignition sources that may impact the fire risk of the plant. Note that transient 

related ignition sources are not examined in this task. Screening some of the fixed ignition 

sources, along with the application of severity factors to the unscreened ones, may reduce the 

compartment fire frequency previously calculated in Task 6. 
Draft For Public Comment 

 37 

The process for completing the LPSD fire PRA Scoping Fire Modeling Task is fundamentally 

the same as the full power analysis described in reference [1]. The analysis considers the 

potential for each fire ignition source to induce either fire spread to secondary combustibles or 

damage to PRA targets (equipment and cables) without fire spread. 

For this task, the analyst may, in fact, be able to draw upon results obtained in the full-power fire 

PRA to a large extent. The nature of the fires associated with fixed fire sources may be 

independent of the plant operating mode. The nature and proximity of fixed secondary 

combustibles are also unlikely to change. The primary challenge may lie in two areas; namely, 

changes to the nature or location of PRA targets and potential changes to the configuration or 

characteristics of certain types of fixed fire ignition sources. 

In the case of PRA targets, several factors could change the relationship between ignition source 

and target. LPSD fire PRA targets may exist in locations that do not contain full-power fire PRA 

targets. The damage targets of concern may also change depending on the POS being analyzed, 

so the analysis needs to either bound all POSs or consider each POS separately. Damage targets 

may also be of a different type than were considered in the full-power analysis (e.g., a different 

type of cable or presence of electronic equipment rather than cables as the most easily damaged 

target). 

The second factor that should be considered is the possibility of altered conditions of a fixed 

ignition source. Altered conditions may lead to a fire more severe than the most severe 

conditions postulated in full-power analysis for a given ignition source. For example, an 

electrical cabinet that is normally fully enclosed during full-power operations may be operated 

with the doors open during a specific POS (e.g., to allow for maintenance or monitoring 

activities). Opening the cabinet door increases the potential fire intensity and the potential for 

fire spread outside the cabinet. This could, in turn, affect other aspects of the fire scenario 

including time to detection and time to fire damage. 

4.8.2 Crediting Equipment Operational Status

Altered equipment conditions might also effectively preclude specific types of fires with certain 

types of ignition sources. For example, a bus duct that has been de-energized during a particular 

POS cannot act as a source of a high energy arc fault (HEAF) and fire. Other types of equipment 

that are fully shut down during specific POSs might also preclude, or sharply limit, certain types 

of fires. For example, an electrical motor fire would not be considered plausible for a motor that 

is never energized during a particular POS because it is the electric potential that creates the fire 

hazard. 

Whether or not special treatment is warranted for de-energized or non-operating equipment 

should be determined on a case-specific basis. That is, the analyst should make the argument for 

elimination or modification of a specific fire ignition source (or a specific type of fire for a given 

fire ignition source; e.g., electrical fires for a pump) based on the plant configuration and 

equipment status. The results could then be factored into the scoping fire modeling analysis by 

incorporating the modified fire characteristics or by screening out the fire source. 

There is a substantive difference between full-power and LPSD conditions that impacts the 

viability of this approach. For the full-power fire PRA, de-energizing plant equipment is not 

considered as a mitigating factor in the potential for fires to occur [1] largely because the 

analysis should span all potential operating configurations which could include swapping of 

active and standby equipment trains. Demonstrating that a specific set of equipment would 
Draft For Public Comment 

 38 

never be operated or energized during power operations is quite difficult for most of the 

equipment of interest. The approach is more viable for LPSD plant operations because a broader 

range of plant equipment will be deenergized and non-operational during certain POSs. For 

example, unless the plant is actively generating electric power, the turbine generator exciter will 

not be active, the turbine lube oil system will not be pressurized, and the iso-phase bus duct will 

be deenergized. For various LPSD POSs, a broad range of reactor systems will be shut down 

and non-operational (e.g., high pressure flow and inventory control systems during refueling). 

As a result, LPSD conditions present a greater opportunity to credit equipment status as a factor 

in fire likelihood because it will be easier to demonstrate that certain equipment will, in fact, be 

non-operational and/or deenergized. This is especially true and potentially advantageous for 

analyses built on a foundation of specific POSs able to deal with specific equipment line-ups. 

For a detailed outage-specific approach, the analysis could include consideration of the fire 

potential of equipment based on whether or not that equipment is energized and/or operating 

(e.g., whether or not electrical potentials are present or whether or not oil systems are 

pressurized). If the analysis is based on an average POS approach, it will be more difficult to 

argue that certain types of equipment will never be energized. In particular, the analysis would 

likely not be able to take advantage of train outages for LPSD equipment, but might still take 

advantage of the shutdown of other equipment exclusively associated with power operations 

(e.g., BOP equipment). 

Specific potential considerations in this regard are as follows: 

 Portions of a circuit that are isolated from electric power during a particular POS would 

not be subject to electrical fires. Note that consideration should be given to both power 

circuits and control circuits. As an example, even if a switchgear breaker is “racked out,” if 

control power remains available, a potential for electrical fires also remains.5

 However, a 

switchgear breaker that is “racked out” would deenergize the power circuits and cables fed 

by that breaker eliminating the potential for electrical fires in the downstream power 

circuits. 

 Some lubrication systems may be depressurized during various LPSD POSs. No 

specific analysis of oil fires in pressurized versus non-pressurized systems has been 

conducted so it is not possible to speculate on the impact of system pressurization on fire 

frequencies. Note that for some specific cases LPSD specific fire frequencies have been 

calculated (i.e., main feedwater pump oil fires and turbine generator lube oil fires) while 

other cases assume the same fire frequency for all modes of plant operation. In general, 

two types of oil fires are possible; namely, oil spills burning as a pool fire and pressuredriven oil spray fires. For a normally pressurized oil system that is de-pressurized during 

LPSD conditions, the potential for an oil spray fire becomes localized to system elements 

subject to a static pressure head (e.g., leaks at a low-elevation outlet valve on a storage 

tank). For locations not subject to a static pressure head, a spill consistent with leakage 

from a non-pressurized system should be assumed. It is common practice to locate oil 

 

5

 Note that non-operational equipment might still be vulnerable to fire-induced spurious actuation, but this would be 

a potential consequence of a fire involving some other fire ignition source and not a factor that would contribute to 

the potential for fire ignition. 
Draft For Public Comment 

 39 

reservoirs at a relatively low point in the system so much of the system piping for a 

normally pressurized system will likely be at or near atmospheric conditions when the 

system is de-pressurized. Some system elements may also be drained of oil. For locations 

that retain oil, a reduced pressure would also impact potential leak rates. A review of any 

oil fire scenarios postulated in the full-power fire PRA is recommended to ensure that the 

assumed fire conditions and characteristics are consistent with the actual status of the 

lubricating system. 

In general, most aspects of the ignition frequency analysis need not be revisited. In particular, 

de-energized equipment would not need to be removed from the equipment type counts in Task 6 

in order to take advantage of these approaches. This recommendation is based on the notion that 

the Task 6 approach to estimating ignition frequencies inherently reflects the fact that any given 

piece of equipment will cycle through periods of both in and out of service times. The method 

does not attempt to estimate, for example, pump operating years but rather uses reactor years as 

the frequency basis. In the specific case of the LPSD analysis, specific equipment line-ups are 

likely based on the POS definition, and it would be appropriate to reflect a known line-up to the 

extent feasible in the risk evaluation. 

Beyond these possible modifications, the general task objectives and approach for Task 8 remain 

the same for LPSD fire PRA. The only differences are applied in Table 5 (modified version of 

Table 8-1 of reference [1]) where one new bin is introduced: 3A, Containment PWR. Table 5 

emphasizes the ignition sources that can and cannot be screened out in this task. Note again that 

this task focuses only on fixed ignition sources. 

4.9 Task 9: Detailed Circuit Failure Analysis

This is the second phase of circuit analysis where circuit operation and functionality are 

examined to determine equipment responses to specific cable failure modes. These relationships 

are then used to further refine the original cable selection by screening out cables that cannot 

prevent a component from completing its credited function. The approach presented in reference 

[1] should also apply to LPSD conditions. Since control circuits are not generally altered during 

any LPSD POS, it is anticipated that the analysis done and information generated as part of fullpower fire PRA would also be applicable to LPSD conditions. However, it is recommended that 

as in Task 3, the information obtained from full-power fire PRA be reviewed carefully to verify 

that it is applicable to the specific conditions imposed by the postulated LPSD POS(s). 

In an LPSD fire PRA additional circuits may be identified needing a detailed analysis. The same 

methodology as that described in Chapter 9 of reference [1] can be applied here to conduct that 

analysis. This includes adding the new information to the circuit failure data base created as part 

of full-power fire PRA. 

As in full-power fire PRA, the output of this task supports the quantitative screening process 

under Task 7. 
Draft For Public Comment 

40 

Table 5: Zone of Influence (ZOI) and Severity Factor Recommendations. 

ID Location Ignition Source Ignition Source Screening Approach Recommended Method(1)

1 Battery Room Batteries Calculate ZOI using Figure F-2 in 

[1] 

Electric motors 

2 Containment (PWR) Reactor coolant pump Do not screen in Task 8 Assume 1.0 

3P Containment (PWR) Transients and hotwork Do not screen in Task 8 Assume 1.0 3B Containment (BWR) Transients and hotwork Do not screen in Task 8 Assume 1.0 

4 MCR Electrical cabinets Calculate ZOI using Figure F-2 in 

[1] 

Applicable electrical cabinet 

5 Control/Auxiliary/Reactor 

Building 

Cable fires caused by welding and cutting 

Do not screen in Task 8 Assume 1.0 

6 Control/Auxiliary/Reactor 

Building 

Transient fires caused by welding and cutting 

Do not screen in Task 8 Assume 1.0 

7 Control/Auxiliary/Reactor 

Building 

Transients Do not screen in Task 8 Assume 1.0 

8 Diesel Generator Room Diesel generators Do not screen in Task 8 Assume 1.0 9 Plant-Wide Components Air compressors Do not screen in Task 8 Assume 1.0 

10 Plant-Wide Components Battery chargers Calculate ZOI using Figure F-2 in 

[1] 

Electrical cabinets 

11 Plant-Wide Components Cable fires caused by welding and 

cutting 

Do not screen in Task 8 Assume 1.0 

12 Plant-Wide Components Cable run (self-ignited cable fires) Do not screen in Task 8 Assume 1.0 13 Plant-Wide Components Dryers Calculate ZOI using Figure F-2 in 

[1] 

Transients 
Draft For Public Comment 

41 

Table 5: Zone of Influence (ZOI) and Severity Factor Recommendations. 

ID Location Ignition Source Ignition Source Screening 

A h

Recommended Method(1)

14 Plant-Wide Components Electric motors Calculate ZOI using Figure F-2 in 

[1] 

Electric motors 

15 Plant-Wide Components Electrical cabinets Calculate ZOI using Figure F-2 in 

[1] 

Electrical cabinets 

16 Plant-Wide Components High-energy arcing faults Do not screen in Task 8 Assume 1.0 17 Plant-Wide Components Hydrogen tanks Do not screen in Task 8 Assume 1.0 18 Plant-Wide Components Junction box Calculate ZOI using Figure F-2 in 

[1] 

Electric motors 

19 Plant-Wide Components Miscellaneous hydrogen fires Do not screen in Task 8 Assume 1.0 20 Plant-Wide Components Off-gas/Hydrogen recombiner (BWR) Do not screen in Task 8 Assume 1.0 21 Plant-Wide Components Pumps Do not screen in Task 8 Assume 1.0 22 Plant-Wide Components RPS MG sets Calculate ZOI using Figure F-2 in 

[1] 

Electric motors 

23a Plant-Wide Components Transformers (oil filled) Do not screen in Task 8 Assume 1.0 23b Plant-Wide Components Transformers (dry) Calculate ZOI using Figure F-2 in 

[1] 

Electric motors 

24 Plant-Wide Components Transient fires caused by welding and 

cutting 

Do not screen in Task 8 Assume 1.0 

25 Plant-Wide Components Transients Do not screen in Task 8 Assume 1.0 26 Plant-Wide Components Ventilation subsystems Calculate ZOI using Figure F-2 in 

[1] 

Assume 1.0 

27 Transformer Yard Transformer - catastrophic Do not screen in Task 8 Assume 1.0 28 Transformer Yard Transformer - noncatastrophic Do not screen in Task 8 Assume 1.0 
Draft For Public Comment 

42 

Table 5: Zone of Influence (ZOI) and Severity Factor Recommendations. 

ID Location Ignition Source Ignition Source Screening 

A h

Recommended Method(1)

29 Transformer Yard Yard transformers (Others) Do not screen in Task 8 Assume 1.0 30 Turbine Building Boiler Do not screen in Task 8 Assume 1.0 31 Turbine Building Cable fires caused by welding and 

cutting 

Do not screen in Task 8 Assume 1.0 

32 Turbine Building Main feedwater pumps Do not screen in Task 8 Assume 1.0 33 Turbine Building T/G exciter Not considered for non-power 

POSs 

34 Turbine Building T/G hydrogen Do not screen in Task 8 Assume 1.0 35 Turbine Building T/G oil Do not screen in Task 8 Assume 1.0 36 Turbine Building Transient fires caused by welding and 

cutting 

Do not screen in Task 8 Assume 1.0 

37 Turbine Building Transients Do not screen in Task 8 

Table Notes: 

(1) This column provides a recommended approach for establishing the probability distribution for severity factor. See Appendix E of 

reference [1] and related responses to the FAQs that appeared after publication of reference [1]. 
Draft For Public Comment 

 43 

4.10 Task 10: Circuit Failure Mode Likelihood Analysis

The purpose of this task is to estimate the failure mode probabilities of circuits that are identified 

in the previous tasks for further analysis. As noted in reference [1], the methods and data for 

deriving circuit failure probabilities are based on limited information and the field continues to 

evolve. The analyst is encouraged to use the latest information, if this task is included in an 

LPSD fire PRA. 

There is no reason to conclude that the methods and underlying test data used for estimating 

circuit failure probabilities should be different between full-power and LPSD POS conditions. 

Therefore, the discussions provided in Chapter 10 of reference [1] should apply to LPSD 

conditions as well. The assumptions provided in Section 10.3.2 of reference [1] are also 

applicable to LPSD conditions, except that some of the circuits may be de-energized during a 

specific POS. 

It is anticipated that the majority of circuits that would be identified in Task 9 of LPSD fire PRA 

for further analysis would have already been addressed in the full-power fire PRA. It is 

recommended that the existing analyses be reviewed to ensure that all underlying assumptions 

remain valid under the specific conditions of the LPSD POS. For example, if the analyst 

adjusted a probability value because of special conditions affecting a cable, the LPSD analysis 

should confirm that those special conditions remain valid during the postulated POS. 

4.11 Task 11: Detailed Fire Modeling

4.11.1 Purpose and Scope

Detailed fire modeling provides the 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 this 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. 

The detailed fire modeling process generally follows a common structure, but the details of the 

analyses often vary depending on the specifics of the postulated fire scenario. This chapter 

addresses three general categories of fire scenarios: fires affecting target sets located inside one 

compartment; fires affecting the main control room (MCR); and fires affecting target sets located 

in more than one PAU (multi-compartment fire analysis). 

For LPSD fire PRA, the detailed fire modeling process is generally the same as the RES/EPRI 

full-power fire PRA methodology in reference [1]. The same input and output information 

applies. Focused walkdowns are an important part of this task. The supporting information 

provided in the Appendices of reference [1] is also applicable6

. Clearly, the analyst should use 

the latest information applicable to each scenario analysis. Though the general fire modeling 

 

6

 Note that some aspects of various fire modeling approaches have been modified or amended based on feedback 

from the NFPA-805 pilot plant applications. Modifications documented via the NFPA implementation FAQ process 

are considered equally applicable to the LPSD fire PRA. 
Draft For Public Comment 

 44 

approach and process is essentially unchanged between LPSD and full-power, the plant 

configuration will impact the choice of fire scenario damage targets, and may alter the 

relationship between fire source and damage targets (e.g., relative locations, damage thresholds, 

and intervening combustibles). These changes could in turn alter the objectives and results of 

the detailed fire modeling task. Therefore, to the extent that fire source and target relationships 

change, fire modeling analyses may need to be repeated for different POSs to ensure that all POS 

specific factors are incorporated and evaluated. 

A detailed fire modeling analysis may be performed for each fire scenario in each unscreened 

PAU, with the focus placed on those fire scenarios with the highest contribution to the 

CDF/LERF. For many compartments, it may be appropriate to develop several fire scenarios in 

order to appropriately represent the range of unscreened fire ignition sources (i.e., ignition 

sources that were not screened in Task 8). 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. These tools include computational fire models, statistical models, and 

empirical models. 

The ultimate output of Task 11 is a set of fire scenarios, each including: 

 a defined fire ignition source; 

 a defined target set consisting of those LPSD fire PRA components and cables that are 

subject to fire-induced damage given ignition of the fire ignition source; 

 an estimate of the frequency of fires involving the defined fire ignition source leading 

to loss of the defined target set (including the fire ignition frequency, applicable severity 

factors, and corresponding non-suppression probability values); and 

 an examination of forced abandonment scenarios involving fire in the MCR or in other 

plant areas that could lead to MCR abandonment (i.e., due to loss of MCR functions). 

4.11.2 General Approach. 

The general approach to fire scenario modeling remains the same for the LPSD fire PRA as in 

the full-power fire PRA [1]. Figure 2 provides a block diagram of the overall process. Note that 

the step definitions are the same as those cited in reference [1]. Clearly, the special conditions of 

each POS should be taken into account when conducting each step, but the nature and objectives 

of each step remain unchanged. 

The factors that may require special consideration for the LPSD fire PRA include the following: 

 For certain POSs, the status of compartment boundaries could be significantly different 

from full-power conditions. For example, during a maintenance outage certain doors that 

are normally closed may be propped open by temporary piping and cables passing through 

the doorway, penetrations may be un-sealed to allow for cable or piping work, equipment 

hatches may be removed, and/or the containment structure may be open. 

 As noted with regard to scoping fire modeling (Task 8), the characteristics of an 

ignition source may be altered. For example, cabinet doors may be opened whereas they 

are normally closed. 
Draft For Public Comment 

 45 

 

Figure 2: General Analysis Flow Chart for Task 11 – Detailed Fire Modeling. 

 The status of fire detection and suppression systems could be altered. For example, fire 

protection systems may be unavailable due to maintenance or may be intentionally disabled 

due to other maintenance activities under way in the protected space (e.g., to prevent 

spurious actuation). 

 Fire brigade access paths may be altered because of maintenance or plant upgrade 

activities. 

Step 1 

Characterize Relevant 

Features of PAU 

Step 2 

Identify and Characterize 

Fire Detection and 

S iF i

Step 3 

Identify and Characterize 

Fire Ignition Sources 

Step 4 

Identify and Characterize 

Secondary Combustibles 

Step 5 

Identify and Characterize 

Target Sets 

Step 6 

Define Fire Scenarios to 

be Analyzed 

Step 7 

Conduct Fire Growth and 

Propagation Analysis 

Step 8 

Conduct Fire Detection 

and Suppression Analysis 

Step 9 

Calculate NonSuppression Probability 

d S iF

Step 10 

Calculate Scenario 

Frequency 

Step 11 

Document Analysis 

Results 
Draft For Public Comment 

 46 

 New transient combustibles may be present in a compartment. For example, packing 

materials for new or replacement equipment may be introduced, combustible controls 

restrictions for specific areas may be relaxed, pump oils may be changed out so that a 

larger quantity of oil than might normally be present is introduced into an area (e.g., both 

the old oil and new replacement oil loads may be present and exposed), and/or combustible 

cutting oil may be brought into a compartment for certain repair or modification work. 

 Welding and cutting operations may be undertaken in areas where such activities would 

be either prohibited or very unlikely during at-power operations (e.g., the MCR, cable 

spreading room, cable vault and tunnel areas, emergency switchgear rooms, etc.). 

 Staffing changes could alter fire watches and other general personnel traffic and 

occupancy patterns. For example, compensatory measure fire watches may be suspended 

or a space that is not routinely manned during power operations may be manned during a 

specific POS. 

 The containment structure may be open with substantive work activities underway. In 

particular, for BWRs with inerted containment, de-inerting of the containment introduces a 

potential for fires in areas never considered in the full-power fire PRA. 

The approach for addressing these issues is exactly the same as that described in reference [1]. 

The analyst should simply gather and apply the appropriate data to support the analysis for the 

POS of interest. Table 6 provides a list of the ignition sources and recommended severity factor 

and suppression curves. There are relatively few differences between the information provided 

in Table 6 and that provided in reference [1]. It should be noted that, as discussed below, the 

manual suppression curves may need to be adjusted to reflect the specific conditions of a POS. 

The available LPSD suppression data were not sufficient to support a statistical analysis of the 

LPSD versus full-power suppression timing. Hence, it is recommended that a judgment-based 

adjustment be applied to address the specific plant conditions and changes as compared to full 

power conditions. That is, it may not be possible to fully characterize those aspects of the fire 

scenarios that would impact manual fire fighting and suppression reliability. The characteristics 

of interest (e.g., fire watches, location accessibility, fire fighting system outages, staffing levels, 

etc.) might vary over the course of a given POS, from POS to POS, or from outage to outage. 

Hence, the recommended approach is to apply judgment based adjustments to, for example, 

reflect the possibility that an area might be manned at the time of the fire increasing the 

likelihood of rapid detection and suppression or, conversely, that ongoing work may interfere 

with fire fighters reaching the scene and thereby delay the response. 

4.11.3 Assumptions 

The same assumptions apply to LPSD fire scenario analyses as in the full-power fire PRA [1]. 

The key assumptions are repeated below: 

 The analysis is limited to considering a single fire occurring at any given time. 

 If a fixed, water-based fire suppression system is available, actuation of that system is 

assumed to disrupt the process of fire growth and spread sufficient to achieve and maintain 

effective control of the fire so that additional damage to potential fire PRA targets will not 

occur. 
Draft For Public Comment 

 47 

Table 6: Recommended Severity Factors and Suppression Curves for Ignition Sources in 

the Frequency Model. 

ID Location Ignition Source 

Heat Release Rate (HRR) 

Probability Distribution for 

Calculation of Severity Factor 

Suppression Curve 

1 Battery Room Batteries Electric motors Electrical 

2 Containment 

(PWR) 

Reactor coolant Pump Pumps (Electrical)/Oil spills Containment 

3P Containment 

(PWR) 

Transients and hotwork Transients Containment 

3B Containment 

(BWR) 

Transients and hotwork Transients Containment 

4a MCR Electrical cabinets Applicable electrical cabinet MCR 

4b MCR MCB See Appendix L of [1] See Appendix L of 

[1] 

5 Control/Auxiliary/R

eactor Building 

Cable fires caused by 

welding and cutting 

See Appendix R of [1] Welding 

6 Control/Auxiliary/R

eactor Building 

Transient fires caused by 

welding and cutting 

Transients Welding 

7 Control/Auxiliary/R

eactor Building 

Transients Transients Transients 

8 Diesel Generator 

Room 

Diesel generators Oil spills Electrical/Oil 

9 Plant-Wide 

Components 

Air compressors Electrical/Oil spills Electrical/Oil 

10 Plant-Wide 

Components 

Battery chargers Electrical cabinets Electrical 

11 Plant-Wide 

Components 

Cable fires caused by 

welding and cutting 

See Appendix R of [1] Welding 

12 Plant-Wide 

Components 

Cable run (Self-ignited 

cable fires) 

See Appendix R of [1] Electrical 
Draft For Public Comment 

 48 

Table 6: Recommended Severity Factors and Suppression Curves for Ignition Sources in 

the Frequency Model. 

ID Location Ignition Source 

Heat Release Rate (HRR) 

Probability Distribution for 

Calculation of Severity Factor 

Suppression Curve 

13 Plant-Wide 

Components 

Dryers Transients Transients 

14 Plant-Wide 

Components 

Electric motors Electric motors Electrical 

15 Plant-Wide 

Components 

Electrical cabinets Electrical cabinets Electrical 

16 Plant-Wide 

Components 

High energy arcing faults See Appendix M of [1] See Appendix M of 

[1] 

17 Plant-Wide 

Components 

Hydrogen Tanks See Appendix N of [1] Flammable gas 

18 Plant-Wide 

Components 

Junction box Electric motors Electrical 

19 Plant-Wide 

Components 

Miscellaneous hydrogen 

fires 

See Appendix N of [1] Flammable gas 

20 Plant-Wide 

Components 

Off-gas/Hydrogen 

recombiner (BWR) 

See Appendix N of [1] Flammable gas 

21 Plant-Wide 

Components 

Pumps Pump (Electrical)/Oil spills Electrical/Oil 

22 Plant-Wide 

Components 

RPS MG sets Electric motors Electrical 

23a Plant-Wide 

Components 

Transformers (Oil filled) Oil spills Oil 

23b Plant-Wide 

Components 

Transformers (Dry) Electric motors Electrical 

24 Plant-Wide 

Components 

Transient fires caused by 

welding and cutting 

Transients Welding 

25 Plant-Wide 

Components 

Transients Transients Transients 

26 Plant-Wide 

Components 

Ventilation subsystems Electric motors/Oil spills Electrical/Oil/ 

Transients 

27 Transformer Yard Transformer – 

catastrophic 

See Section 6.5.6 of [1] Outdoor transformers 

28 Transformer Yard Transformer - 

noncatastrophic 

See section 6.5.6 of [1] Outdoor transformers 
Draft For Public Comment 

 49 

Table 6: Recommended Severity Factors and Suppression Curves for Ignition Sources in 

the Frequency Model. 

ID Location Ignition Source 

Heat Release Rate (HRR) 

Probability Distribution for 

Calculation of Severity Factor 

Suppression Curve 

29 Transformer Yard Yard transformers 

(others) 

See section 6.5.6 of [1] Outdoor transformers 

30 Turbine Building Boiler Oil spills Oil 

31 Turbine Building Cable fires caused by 

welding and cutting 

See Appendix R of [1] Welding 

32 Turbine Building Main feedwater pumps Pump (Electrical)/Oil spills Electrical/Oil 

33 Turbine Building T/G exciter Not considered for non-power 

POSs 

34 Turbine Building T/G hydrogen See Appendix O of [1] Turbine generator 

35 Turbine Building T/G oil See Appendix O of [1] Turbine generator 

36 Turbine Building Transient fires caused by 

welding and cutting 

Transients Welding 

37 Turbine Building Transients Transients Transients 

 If a fixed, gaseous fire suppression system is available, actuation of that system is 

assumed to disrupt the process of fire growth and spread sufficient to achieve effective 

control of the fire. However, the duration of control is assumed to be the time period over 

which it has been demonstrated, by test or analysis, that a sufficient suppressant 

concentration, per applicable standards, can be maintained. 

 Core damage would occur if the MCR operators are unable to use the main control 

board (MCB) and no actions are taken from outside the MCR. 

4.11.4 Single Compartment Fire Scenarios 

The overall process for analyzing single compartment fire scenarios for LPSD fire PRA, 

regardless of the POS, remains the same as what is presented in reference [1] for full-power fire 

PRA. For LPSD fire PRA, the analyst should ensure that the following issues are addressed: 

 The heat release rate (HRR) of the ignition sources and other combustibles reflect the 

conditions of the POS. For example, if the doors of an electrical cabinet are opened during 

a specific POS, the heat release rate of that cabinet should be modified to reflect the POSspecific condition. 

 Status of protective barriers should be verified. For example, heat shields may be 

removed temporarily for maintenance work while the ignition sources remain operational. 

 Status of detection and suppression systems should be verified. For example, parts of 

an automatic suppression system may be valved off for repair or modification work. 
Draft For Public Comment 

 50 

 If the fire brigade is credited, the path between fire brigade equipment and the PAU 

should be reviewed and the response time adjusted. Longer response times should be used 

if there is a possibility of maintenance or other activities in the PAUs along the fire 

brigade’s path. 

 Transient ignition sources should be characterized carefully to reflect the additional 

items that may be brought into the PAU. Under certain POS that include maintenance 

activity or plant modification, the quantity and type of transient materials may be different. 

 Secondary combustibles should be specifically characterized in case of POS that 

include maintenance activities and plant upgrade. Quantity, type and position of potential 

combustible materials should be identified. Where in doubt, conservative assumptions 

should be used and carefully recorded. 

 If there is a potential for erecting scaffolding or other structures to be used as a 

temporary platform for staging maintenance work, the analyst should postulate secondary 

combustibles accordingly using conservative assumptions where the specifics of the 

activity may not be completely defined. 

4.11.5 Analysis of Fire Scenarios in the MCR 

The MCR analysis methodology remains the same as in reference [1]. The conditions within the 

MCR, and especially the alternate shutdown system, may be markedly different under certain 

POS. However, the same key concerns apply to LPSD conditions. The MCB should be 

examined for specific areas where fire damage can lead to a significant CCDP. All other control 

boards and electrical cabinets should be examined for potential risk impact. Finally, the 

possibility and likelihood of MCR abandonment should be examined. 

For LPSD fire PRA, the analyst should ensure that the following issues are addressed: 

 Activities within the MCR should be characterized and changes that can impact the fire 

risk profile identified. For example, the number of personnel within the MCR may 

increase. Multiple parallel activities may be taking place. Electricians could be working 

inside the MCB. 

 When analyzing the MCB, the analyst should understand which controls will be tagged 

and the position of the control device while tagged. 

 The MCB fire propagation and suppression curve presented in Appendix S of reference 

[1] can be used for all POS cases except those that include a maintenance activity behind 

the main face of the board. If such an activity is planned, the specifics of those tasks 

should be identified and evaluated. A set of fire scenarios may need to be identified to 

address those specific activities. Those scenarios should cover new ignition sources 

introduced inside the MCB and fire growth starting with that source and propagating to 

secondary combustibles (i.e., vertical and horizontal wire bundles and electrical and 

electronic devices). The target sets should be identified carefully in terms of the circuits 

present in the affected wire bundles and controls on the control board. The detection and 

suppression curves for MCR fires may still be used for these cases. 
Draft For Public Comment 

 51 

 Operating procedures for LPSD conditions will need to be reviewed and assessed. 

Substantial changes to fire-related operator manual actions may occur when the plant 

transitions to LPSD operations. 

 Both remote and alternate shutdown capabilities should be re-examined using the 

specific condition imposed by the POS to assess their role in, and relevance to, LPSD 

operations. Access to the remote/alternate shutdown location(s) could be different during 

LPSD. The alternate shutdown circuits could also be altered. These issues should be 

identified and taken into account when analyzing operator error using the alternate 

shutdown capability. 

 MCR abandonment calculations may need to be reviewed and verified for applicability 

to the specific POS conditions. If the transient combustibles profile or electrical cabinet 

characteristics are altered, the calculations for MCR abandonment should be verified. 

4.11.6 Analysis of Fire Scenarios Initiated Outside the MCR that May Impact MCR 

Functions or Habitability 

The possibility of adversely impacting the MCR function by a fire outside the room, as in fullpower fire PRA, should also be examined. As discussed in reference [1], there could be other 

compartments where a fire may damage sufficient control circuits rendering a part of the MCR 

function inoperable or affect the information displayed for the operators. Also, there could be 

locations where a fire may adversely impact the MCR environment forcing abandonment. It is 

very possible that these compartments are the same as those identified in the full-power fire 

PRA. However, it is recommended that the analyst revisit this task and re-examine the 

underlying assumptions and information. Conditions associated with a specific POS may lead to 

areas within the plant or fire scenarios other than those identified in the full power analysis that 

can adversely affect the MCR. Two specific areas of consideration should be included as 

follows: 

 The locations that might lead to functional degradation of the MCR control and 

indication systems could change based on the POS and plant status. This is because the 

systems and indications which are most important to maintaining core integrity will change 

depending on the POS, which means the location of equipment and cables of potential 

concern could also change. 

 The status of fire barrier elements (e.g., opened doors or breached barriers) could create 

smoke, heat, and fire spread paths that were not considered plausible in the full-power fire 

PRA. 

4.11.7 Analysis of Fire Scenarios Impacting Multiple Compartments 

Multi-compartment fire propagation and damage analysis as presented in reference [1] uses four 

screening steps to arrive at fire scenarios that could be risk significant and that thereby may 

warrant a more detailed analysis. The detailed analysis uses the same general approach as does 

the single-compartment fire analysis. The same screening steps can be used for LPSD conditions 

as those described in reference [1]; however, the conditions relevant to screening could be 

markedly different under certain POSs. 
Draft For Public Comment 

 52 

For LPSD fire PRA, the analyst should ensure that the following issues are addressed: 

 The exposing and exposed compartment matrix should be reviewed and updated to 

reflect the POS-specific status of PAU partitioning elements (e.g., breached barriers or 

open hatches and doorways). 

 Multi-compartment fire damage target sets will need to be re-defined to reflect the 

equipment and cables important to maintaining core integrity for each identified POS. 

 Once the compartment relationships have been re-defined, the same screening 

assumptions and criteria can be used to identify compartment combinations that warrant 

more detailed analysis. However, the screening analysis should consider that fire 

protection features and systems that were credited in the full-power fire PRA may be 

unavailable or degraded under LPSD conditions. Screening should be performed 

accordingly. 

 For barriers whose status and integrity are not changed, the failure probabilities and 

guidance provided in reference [1] can be used. 

 If a particular barrier element will be breached during a specific POS (e.g., hatch 

removal or a specific outage plan that involves breaching of fire barrier elements) it is 

recommended that the analysis should treat the breached barrier as a non-confining 

partitioning element relative to the spread of fire or fire products (e.g., smoke, heat and 

toxic gas). The importance of breaching such barriers can be assessed in a sensitivity study 

if necessary. 

4.12 Task 12: Post‐Fire Human Reliability Analysis		

4.12.1 Background

While considerable effort has been directed toward the development of human reliability analysis 

(HRA) methods and approaches, historically, most of these efforts have resulted in methods and 

approaches that are intended to apply to full-power internal events PRA applications. 

One exception is the recent joint development of fire HRA guidance by EPRI and NRC-RES7

 

which supersedes that given in NUREG/CR-6850, EPRI TR-1011989. Consequently, it is 

recommended that for the purposes of LPSD fire PRA, the updated joint RES-EPRI fire HRA 

guidance be used, in combination with the special considerations for LPSD conditions given 

below. As with other elements of the LPSD fire PRA methodology, Task 12 also assumes the 

existence of a LPSD, internal events PRA that includes corresponding HRA elements. 

It is also recommended that only the detailed HRA analysis approaches as described in the joint 

RES-EPRI fire HRA guidance be used. No specific development effort for LPSD Fire HRA 

guidance has been undertaken so it is not known how relevant the screening and scoping HRA 

 

7

 Publication of the final RES/EPRI fire HRA guidance remains pending. The guidance document has been released 

as a draft for public comment (see reference: NUREG-1921, EPRI TR-1019196) and is available at the following 

web address: http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1921/. 
Draft For Public Comment 

 53 

approaches from the joint guidance document would be to LPSD conditions. Finally, consistent 

with overall fire PRA guidance and standards, the fire HRA guidance does not address preinitiator human failure events (HFEs) (or latent human failures). Pre-initiator HFEs will need to 

be addressed using typical full-power, PRA approaches, supplemented by any special 

considerations for LPSD conditions. 

At present, no specific HRA guidance has been developed for LPSD PRA, paralleling that for atpower fire HRA/PRA. However, a variety of applications of HRA for LPSD internal events 

PRA have been performed, including two PRAs sponsored by the NRC [7,8]. Also, preliminary 

development work to support a LPSD HRA method was performed in the early 1990s [9,10]. 

Consequently, there is some basis for performing LPDS HRA/PRA even in absence of a 

comprehensive LPSD-specific approach. 

4.12.2 Special Considerations Related to LPSD

Since, as discussed above, no comprehensive LPSD-specific HRA method has been developed, 

the recommended approach, at present, is to combine some known, LPSD-specific 

considerations with the joint RES-EPRI guidance developed for at-power fire HRA. 

The following are examples of such considerations (but should not be considered a complete 

list): 

 Plant conditions or configurations typically are different for LPSD than for full-power 

(potentially resulting in function, system, equipment, instrumentation and control, as well 

as indication and alarm, unavailability). HRA analysts should be aware that some of these 

condition or configuration differences may matter only to the operators (i.e., there may be 

no impact on plant equipment as in the case, for example, of control room indication 

unavailability). For fires during LPSD, indications needed to identify the fire location may 

be effected. Also, the HRA analyst should collect information on how control room 

operators maintain an awareness of plant conditions and configurations (e.g., log books, 

shift turnover briefings, schematics, risk monitors). 

 Success criteria for plant functions are likely to be different during LPSD conditions, 

changing operator actions (e.g., number of pumps that need to be started, manual action 

required for initial response rather than backup/recovery of automatic actuation) and 

changing the required timing for response. 

 Different and additional human failure events should be addressed in LPSD HRA, 

largely because of the two preceding items. In particular: 

 The HRA may be needed to explicitly address human-induced initiating events. As 

noted in NRC's Good Practices Guidance [11], if there are important dependencies 

between operator actions that cause an initiating event and the actions required for 

accident response, then the human-induced initiator should be addressed explicitly. 

 Because of the increased number of maintenance, testing, and other outage activities 

during shutdown, the number of potential pre-initiator HFEs or latent failures also 

increases. The HRA analyst should review relevant information to identify such 

opportunities and realistically provide credit for recovery of such failures (i.e., do not 

credit multiple, independent verifications). 
Draft For Public Comment 

 54 

 Which procedures are used for accident mitigation, how they are used, and how they 

are entered can be different for LPSD than for full-power. The HRA analyst should review 

all of these aspects with respect to procedure usage. 

 Operator training for response to LPDS accidents is likely to be different, in frequency 

and depth, from that for full-power. Similarly, training for LPDS fire events may be even 

less than that for general LPSD plant operations. 

 Staffing of the control room during LPSD is likely to be different than that for fullpower and should be reviewed by the HRA analyst. In addition, as in the at-power fire 

HRA guidance, the HRA analyst should determine if some control room staff will be 

required to serve roles on the fire brigade, making them unavailable for control room 

actions. 

 There can be concerns related to staffing, procedures, and training in combination for 

fire HRA/PRA for both full-power and LPSD. In particular, the HRA analyst should 

identify situations in which the following occurs: 

 Fewer operators are in the control room for a fire event than for an internal events 

accident, and/or 

 multiple procedures (e.g., emergency operating procedures and fire response 

procedures) are being used with individual operators assigned to independently 

implement one of the two or more procedures (i.e., the control room operators are no 

longer operating as a normal crew), and 

 use of multiple procedures (especially, use of fire response procedures) is not normal 

operating practice and there is infrequent training on the use of multiple procedures that 

require coordination. 

There are other considerations that can be important in performing LPSD HRA such as: 

 ex-control room or local actions (with, for example, different human-machine interface 

issues than the control room), 

 accessibility of equipment, 

 environmental factors (such as habitability), 

 special fitness needs, and 

 needs for special equipment or tools. 

These issues (and others) are explicitly addressed in the joint RES-EPRI fire HRA guidance and, 

therefore, are not discussed here. The same approaches for dealing with such factors as are 

outlined for at-power conditions are expected to apply to LPSD conditions. 

4.13 Task 13: Seismic‐Fire Interactions Assessment

A qualitative approach is used in reference [1] to address potential seismic-fire interaction cases 

using the approach recommended in the Fire Risk Scoping Study [12]. That approach identified 

the following four seismic-fire interaction issues: 

 Seismically induced fires, 
Draft For Public Comment 

 55 

 Degradation of fire suppression systems and features, 

 Spurious actuation of suppression and/or detection systems, and 

 Degradation of manual firefighting effectiveness. 

All four issues are applicable to plant conditions during LPSD POS(s). The main assumption 

about low risk of seismically induced fire events can be extrapolated to LPSD conditions. 

However, during LPSD conditions, many activities will occur in the plant that would not be 

observed, or will be undertaken in areas where they would be disallowed, during full power 

operation. For example, welding and cutting operations could introduce portable compressed gas 

cylinders in unexpected locations, transient combustible control restrictions may be relaxed, 

maintenance activities may introduce a range of temporary storage items in various plant 

locations, and operations involving temporary hoisting or rigging equipment may be undertaken. 

These factors would tend to indicate that the probability of a seismic-fire interaction event given 

an earthquake (i.e., an event that can be attributed to one of the four issues listed above) is 

expected to be higher during an LPSD condition than full-power. Nonetheless, the overall risk is 

deemed to remain low largely because of the short duration of LPSD conditions. 

The following assumptions are made relative to the seismic-fire analysis: 

 A full-power Seismic-Fire Interaction Assessment exists. 

 A post-earthquake plant response analysis exists for the specific POS being considered. 

 A separate, stand-alone assessment should be conducted for each postulated POS. 

 The assessment should be walkdown-based and may be qualitative. 

The same seven step approach applied to the full-power fire PRA can be used for LPSD. The 

following notes summarize the key issues of seismic-fire interaction assessment related to LPSD: 

 Step 1: Identify key seismic-fire interaction analysis PAU: The PAUs that contain postearthquake response components and circuits are identified in this step. Component and 

circuit conditions may be altered during LPSD conditions. Those PAUs where altered 

components and circuits are located should specifically be identified in this task. Similarly, 

those PAUs where a manual action is credited should be included in the analysis. 

 Step 2: Assess potential impact of seismically induced fires: The special conditions 

during a POS should be taken into account to assess the potential impact of seismically 

induced fires. As in the full-power case, the assessment should be focused on the PAUs 

that were identified in Step 1. A plant walkdown and a review of potential special 

conditions during a POS are essential in this step. 

 Step 3: Assess seismic degradation of fire suppression systems and features: The 

analysis conducted for full-power conditions can be reviewed and modified if any part of 

the fire suppression systems and features will be modified during the postulated POS. 

 Step 4: Assess the potential impact of spurious fire detection signals: Spurious fire 

detection signal as a result of dust or steam (caused by equipment shaking or pipe break) 

could be more likely because of maintenance activities. The full-power analysis can be 

reviewed and modified to reflect the special conditions of postulated maintenance 

activities. 
Draft For Public Comment 

 56 

 Step 5: Assess the potential impact of spurious fire suppression system actuations: The 

full-power analysis can be used to establish the cases where spurious fire suppression 

actuations are possible. The impact of such events should be reviewed against the 

conditions postulated for each POS and modified accordingly. 

 Step 6: Assess the potential impact of a seismic event on manual firefighting: For each 

compartment identified in Step 1, the manual fire fighting possibility should be reviewed in 

the same way as for full-power analysis by taking into account the LPSD conditions. 

 Step 7: Complete documentation: Apply the same guidelines as provided for the fullpower analysis. 

4.14 Task 14: Fire Risk Quantification

The objectives and overall approach for risk quantification is the same as in full-power fire PRA 

as described in reference [1]. However, the basis of quantification may vary depending on the 

intended objectives and applications. In this task, the final LPSD fire PRA model is quantified to 

obtain the final fire risk results in terms of CDF and LERF for each fire scenario defined in Task 

11. The scope of this task will depend on the scope of the LPSD analysis. If an overall or 

average outage analysis is the main objective, the CDF and LERF calculations should be 

repeated for each POS and combined according to the equations in Section 3 above. If a specific 

POS (or subset of POSs) is analyzed, the CDF and LERF should be estimated using the same 

equation, except that only one POS (or a specific group of POSs) is considered. 

Similar to full-power PRA, it is expected that the nature (e.g., type of sequences) of the screened 

out compartments/scenarios is at least identified. As a check of the cumulative screening criteria 

discussed in Task 7, it is recommended that the screened CDFs and LERFs also be summed 

separately to provide a perspective on the total residual risk from the screened 

compartments/scenarios. It should be emphasized that these screened portions of the results 

represent various levels of analysis (for instance, some may only involve fire scoping modeling; 

others may involve both detailed fire modeling and some detailed circuit analysis, etc.). 

This task uses the LPSD fire PRA Model to quantify CDF and LERF. The model is initially 

developed in Task 5 (Fire Induced Risk Model), and modified in the quantitative screening 

performed in Task 7. This task also requires input from Task 10 (Circuit Failure Mode 

Likelihood Analysis), Task 11 (Detailed Fire Modeling), and Task 12 (Post-Fire Human 

Reliability Analysis). 

The fire PRA analysts will need basic event occurrence probabilities from the Internal Events 

LPSD PRA Model to be able to quantify accident sequence frequencies where the fire scenario 

does not affect all basic events of the sequence. Also, the analyst should have access to the 

software tools required to quantify the PRA Model. 

As noted above, the procedure in this task is the same as the RES/EPRI full-power fire PRA 

methodology. With the exception of fire-specific elements of the quantification process, this 

procedure relies heavily on the approach provided in the ASME/ANS PRA Standard [13]. The 

LPSD fire PRA Model developed in previous tasks is used to quantify CDFs and LERFs for each 

fire ignition event. 
Draft For Public Comment 

 57 

4.15 Task 15: Uncertainty and Sensitivity Analyses

This procedure provides an overall approach to all the other tasks on suggested ways to address 

the uncertainties associated with each task in the LPSD fire PRA process. In addition to 

uncertainty analysis, the identification of possible sensitivity analysis cases is addressed in this 

procedure. The discussions provided in Chapter 15 of reference [1] on uncertainty and 

sensitivity analyses and the guidance provided in reference [1] apply to LPSD cases as well. 

This task describes the approach for identifying and treating uncertainties and identifying 

sensitivity analysis cases. It also prescribes a review for the identified uncertainties among the 

fire PRA analysts to establish an integrated approach for addressing the effects of these 

uncertainties on the final results. 

Many of the inputs that make up the LPSD CDF and LERF estimates, as in full-power fire PRA, 

are uncertain (e.g., fire frequencies, extent of fire growth, equipment failure probabilities, 

operator action probabilities, etc.). Additionally, there may be uncertainty in the fraction of the 

time that the plant could be in a specific POS. See Section 3 above for a brief discussion on the 

use of these fractions. Uncertainties in the input parameters lead to epistemic uncertainties in the 

LPSD Fire CDF and LERF. The same methods as for full-power fire PRA can be used to 

estimate the uncertainty distributions for the LPSD PRA analysis. 

Similar to full-power fire PRA, it is important that users of the results of the LPSD fire PRA 

understand the fundamental modeling assumptions underlying the analysis and the sources of 

uncertainty associated with the results. Some uncertainties may be specifically included in the 

quantification of the results; others may only be qualitatively addressed or not addressed at all. 

The analysts for Tasks 1 through 13 are expected to follow the overall approach provided in this 

procedure to articulate and quantify, when necessary, the uncertainties in their numerical results. 

For each affected task, the following information will be needed for uncertainty analysis: 

 Sources of uncertainties, and 

 Proposed approach for addressing each of the identified uncertainties. 

It is expected that specific parameters and assumptions for which uncertainty or sensitivity 

analyses can provide valuable insights on the LPSD Fire CDF and LERF will be identified 

during the performance of an LPSD fire PRA. To that extent, the issues addressed here should be 

modified to reflect the key uncertainties identified on a plant-specific basis. 

The same procedure as that described in reference [1] for full-power fire PRA applies here as 

well. 

 Step 1: Identify Uncertainties Associated with Each Task: Where applicable, the 

outcome of each preceding task should include a discussion on the uncertainties in the 

results of the task. That information is collected and reviewed in this step. The 

uncertainties in the fraction of the time that the plant could be in a specific POS should also 

be addressed in this step. A determination should be made about the extent of those 

uncertainties and including them in the uncertainty analysis process. 

 Step 2: Develop Strategies for Addressing the Uncertainties: Analysis strategies 

developed for the full-power fire PRA or LPSD internal events PRA could be applicable to 

LPSD conditions as well. Those strategies may be reviewed and adopted as appropriate. 
Draft For Public Comment 

 58 

 Step 3: Perform Review of Uncertainties to Make Final Decisions as to Which 

Uncertainties Will Be Addressed and How: A review of the parameters to identify those 

that will be included in the uncertainty analysis is conducted in this step. Another 

important result of this step is a set of sensitivity analysis cases. 

 Step 4: Perform the Uncertainty and Sensitivity Analyses: Uncertainties are propagated 

through the model and sensitivity cases are performed. The same methods as in the fullpower fire PRA or LPSD internal events PRA can be used to propagate the uncertainties. 

Sensitivity analyses may require their own unique approach depending on the sensitivity 

case, but should not be different from the methods used for full-power fire or LPSD 

internal events cases. 

 Step 5: Include the Results of the Uncertainty and Sensitivity Analyses in the fire PRA 

Documentation: The same documentation approach can be used as in full-power case. 

4.16 Task 16: Fire PRA Documentation

The objective of this task is to ensure there is adequate documentation of the fire PRA to allow 

review of the PRA development and its results, as well as to provide a written basis for any 

future uses of that PRA. The recommended documentation in reference [1] applies to LPSD fire 

PRA as well. A recommended outline of the report and a list of supporting documents are 

provided in Tables 16-1 and 16-2 of reference [1]. That outline and recommended supporting 

documents apply to LPSD fire PRA as well. Certainly the LPSD fire PRA report should have a 

clear discussion of the POSs analyzed and the assumptions made to define the POSs. As noted 

in reference [1], the documentation should provide an adequate summary of the development of 

the LPSD fire PRA, including the performance and results of all the previous tasks in this 

document and the results of the LPSD fire PRA itself (with uncertainties, sensitivities, 

observations, etc.). 

4.17 Task 17: Plant Walkdowns (Support Task A)

Plant walkdown is defined in reference [1] as an inspection of local areas in an NPP where 

systems and components are physically located to ensure accuracy of procedures and drawings, 

equipment location, operating status of equipment, and environmental or system interaction 

effects on equipment during accident conditions. As noted in reference [1] and for LPSD 

conditions, paper and electronic documents are not sufficient to provide all the information 

needed for a proper fire PRA. Therefore, plant walkdowns are critically important when 

conducting an LPSD fire PRA. 

The guidance provided in reference [1] applies to LPSD conditions as well. The walkdowns 

already conducted in support of full-power fire PRA should provide the baseline information that 

will be modified according to the special conditions imposed by the LPSD POS. It is anticipated 

that a separate set of walkdowns will be necessary in support of each POS. The pattern of the 

walkdowns (i.e., those defined in Table 17-1 of reference [1]) is expected to remain the same. 

However, not all walkdown types may be necessary. In addition to the guidance provided in 

Chapter 17 of reference [1], the following notes are provided for LPSD fire PRA related 

walkdowns: 

 A separate set of walkdowns and especially walkdown notes should be created for each 

POS. 
Draft For Public Comment 

 59 

 As part of the initial walkdown, a separate meeting with plant management should be 

requested. In this meeting the specific conditions of the POS being studied should be 

reviewed and verified. 

 Engineering documents (e.g., plant layout drawings) may need to be taken to the plant 

and marked up to reflect the anticipated changes during a specific POS. 

 An effort should be made to discuss anticipated POS related transient combustibles and 

hot work with plant personnel to establish the changes to the extent possible. 

 Plant areas where changes may take place should be visited and the walkdown notes 

updated or new ones created for the affected compartments. 

 A walkdown may be planned during the plant shutdown to confirm the information that 

was gathered prior to the shutdown. This walkdown may take place after LPSD fire PRA 

is completed. If marked differences are noted, management should be notified to make a 

determination about updating the PRA. 

4.18 Task 18: Fire PRA Database System (Support Task B)

The fire PRA Database System is a relational database of equipment, circuits and plant locations. 

It may also include cable raceway information and equipment failure modes. The main purpose 

of the database is to assist in fire scenario development, establishing the target set of each 

scenario and equipment failure modes given fire damage. The database developed for full-power 

fire PRA can be used in LPSD fire PRA as a starting point. The same assumptions apply to 

LPSD. Tasks 2 and 3 related information should be reviewed to identify components, circuits 

and cables other than those included in the full-power PRA. The database should be updated to 

include the new information. All other features of the database remain the same as those 

discussed in reference [1]. 
Draft For Public Comment 

 60 

5 References

[1] EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, a joint publication 

of the U.S. NRC and EPRI, NUREG/CR-6850, EPRI TR #1011989, Volume 2, September 2005. 

[2] NFPA Standard 805, Performance-Based Standard for Fire Protection for Light Water 

Reactor Electric Generating Plants, 2001 Edition. 

[3] Code of Federal Regulations: Section 10CFR50.48, “Fire Protection,” subsection (c), 

“National Fire Protection Association Standard NFPA 805.” 

[4] “American National Standard, Low Power and Shutdown PRA Methodology”, 

ANSI/ANS-58.22-200x, DRAFT #8C, for RISC Reba lot & Public Review, June 2008. 

[5] NUREG-1921/EPRI 1019196, “EPRI/NRC-RES Fire Human Reliability Analysis 

Guidelines,” Draft Document for Public Comment, U.S. Nuclear Regulatory Commission, 

Washington, DC, July 2009. 

[6] Kaplan, “On a ‘Two-Stage’ Bayesian Procedure for Determining Failure Rates from 

Experiential Data,” IEEE Transactions on Power Apparatus and Systems, Volume 

PAS-102, 1983, pp. 195-202. 

[7] An Approach for Using Probabilistic Risk Assessment In Risk-Informed Decisions on 

Plant-Specific Changes to the Licensing Basis, U.S. NRC, Regulatory Guide 1.174, Revision 1, 

November 2002. 

[8] “Wolf Creek Incident Investigation Team Report,” 94-04, Revision 2, U.S. Nuclear 

Regulatory Commission, April 15, 1995. 

[9] NUREG-1624, “Technical Basis and Implementation Guidelines for A Technique for 

Human Event Analysis (ATHEANA),” Rev. 1, U.S. Nuclear Regulatory Commission, 

Washington, DC, May 2000. 

[10] NUREG-1880, “ATHEANA User’s Guide,” U.S. Nuclear Regulatory Commission, 

Washington, DC, May 2007. 

[11] Fire Risk Scoping Study: Investigation of Nuclear Power Plant Fire Risk, Including 

Previously Unaddressed Issues, USNRC, NUREG/CR-5088, January 1989. 

[12] Standard for Probabilistic Risk Assessment for Nuclear Power Plant Applications, 

ASME/ANS RA-S-2008, and Addenda, ASME/ANS RA-Sa-2009. 
Draft for Public Comment 

A-1 

A:			APPENDIX FOR DETERMINATION OF LPSD GENERIC FIRE

FREQUENCIES

A generic set of fire frequency distributions were developed to support full-power Fire PRA (see 

Table 6-1 of reference A-1). Those frequencies were based on EPRI Fire Events Database 

(FEDB) ending at January 1, 2000. A part of those frequencies that cover all operating states 

(i.e., full-power and shutdown phases) can be directly used in LPSD Fire PRA. These are bins in 

Table 6-1 of reference A-1 that are noted with “All” under the Mode column. The frequencies 

for the bins that are noted with “Power” had to be estimated for LPSD conditions. This 

Appendix is intended to describe the fire event data analysis and methodology used to estimate 

the fire frequencies to be applied in the LPSD Fire PRA. 

A.1 Screening Events for Inclusion in the Calculation of Generic Fire

Frequencies

There are 1,405 event records in FEDB that had been reviewed as part of the full-power 

frequency analysis for reference A-1. Events contained in the FEDB were screened for inclusion 

into (or exclusion from) the fire event frequency calculation based on two general considerations. 

The first consideration is when and where the fire occurred. The second consideration is whether 

or not a given event either did or could have become a potentially challenging fire (see the 

definition below). 

A.1.1 Where and When a Fire Occurred

The FEDB was filtered to include only those events that were not assigned in the original study 

(i.e., the study supporting reference A-1) to “power” mode bins. Table A-1 provides the list of 

bins that were considered for LPSD specific fire frequency evaluation. Of the 1,405 events, 4318

event records were assigned to a bin that needed an LPSD specific frequency analysis. The 

following notes are in order: 

 Bin assignment was reviewed and one additional bin had to be defined to capture 

events in BWR containments. During power operation, BWR containments are inerted 

precluding the possibility of a fire event in that POS. Since BWR and PWR containments 

are quite different, a new bin is defined specifically for transient and hot-work fires in 

BWR containments (bin 3B) and the PWR containment transient and hot-work fire bin has 

been renamed (bin 3P rather than simply bin 3 as in the full-power set in reference A-1). 

 Similar to the full-power case, although there were fire events associated with gas 

turbine-driven emergency generators, they are not included in this analysis because the 

number of emergency generators in nuclear power plants using gas turbines is not known. 

 

8

 One of the 431 events involved a gas-turbine based emergency generator. That event was not included in the 

frequency analyses. 
Draft for Public Comment 

A-2 

A.1.2 Potentially Challenging Events

The second stage of event screening considered whether or not a particular event did, or had the 

potential to become challenging. The intent of this step is to identify reported events involving 

an incipient fire, fire ignition event, or explosion event that had the potential to develop into a 

self-sustaining fire. Events that lack this potential were screened out from the fire frequency 

calculation as “not-challenging”. A detailed discussion of the screening process can be found in 

Appendix C of reference A-1. Although the FEDB events associated with the bins in Table A-1 

were already screened for challenging fire, the entire set was reviewed anew to verify the 

original assignments. Since this screening process is one of the important steps of data analysis, 

the criteria are repeated below. 

Table A-1: Bins Considered for LPSD Data Analysis. 

Bin # Location Ignition Source 

(Equipment Type)

2 Containment (PWR) Reactor Coolant Pump 

3B Containment (BWR) Transients and Hotwork 

3P Containment (PWR) Transients and Hotwork 

5 Control/Aux/Reactor Building Cable fires caused by welding and cutting 

6 Control/Aux/Reactor Building Transient fires caused by welding and cutting 

7 Control/Aux/Reactor Building Transients 

11 Plant-Wide Components Cable fires caused by welding and cutting 

20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) 

22 Plant-Wide Components RPS MG Sets 

24 Plant-Wide Components Transient fires caused by welding and cutting 

25 Plant-Wide Components Transients 

27 Transformer Yard Transformer – Catastrophic 

28 Transformer Yard Transformer - Non Catastrophic 

29 Transformer Yard Yard transformers (Others) 

31 Turbine Building Cable fires caused by welding and cutting 

32 Turbine Building Main Feedwater Pumps 

34 Turbine Building Turbine Generator Hydrogen 

35 Turbine Building Turbine Generator Oil 

36 Turbine Building Transient fires caused by welding and cutting 

37 Turbine Building Transients 
Draft for Public Comment 

A-3 

The criteria for identifying potentially challenging events include objective and subjective 

elements. The objective criteria are based on reportable facts related to the means of fire 

suppression, the extent of fire growth and/or damage, fire duration, and other indicators. The 

objective criteria are applied in a mechanical manner–i.e., yes/no checkboxes. The subjective 

criteria involve the application of judgment. Factual information related to the objective criteria 

is often lacking in the event reports. Hence, the analysts had to use judgment to determine 

whether or not the event was potentially challenging, typically based on a review of the 

descriptive text provided for the event. 

Per the objective classification criteria, a fire event was classified as potentially challenging if 

any one of the following is true. 

 A hose stream, multiple portable fire extinguishers, and/or a fixed fire suppression 

system (either manually or automatically actuated) were used to suppress the fire. 

 One or more components outside the boundaries of the fire ignition source were 

affected where the term “outside the boundaries of the fire ignition source” will depend to 

some degree on the specific ignition source (see further discussions below). 

 Combustible materials outside the boundaries of the fire ignition source were ignited 

(with a similar use of the term “outside the fire ignition source” implied). 

A fire event was also classified as potentially challenging if two or more of the following 

features are cited in an event report: 

 Actuation of an automatic detection system, 

 A plant trip was experienced, 

 A reported loss of greater than $5,000 (not including any lost business damages), or 

 A burning duration or suppression time of 10 minutes or longer. 

After the objective criteria are applied, a fire event may still be classified as potentially 

challenging if there are sufficient indications to determine that the fire was self-sustaining or that 

it might have affected components or ignited materials outside the fire ignition source. This 

subjective method may be based on the general tone of the event report or on the observation of 

specific aspects of a fire event. In general, observations of the following features in an event 

report can be indicative of a potentially challenging fire. 

 It is apparent that active intervention was needed to prevent potential spread. 

 There are indications that the heat that was generated had sufficient intensity and 

duration to affect components outside the fire ignition source, had such been in close 

proximity to the ignition source. 

 There are indications that flames or heat were generated of sufficient intensity and 

duration to cause the ignition of secondary combustibles outside the fire ignition source, 

had such been in close proximity to the ignition source. 

 Substantial smoke was generated (e.g., a room was reported to be smoke-filled when 

first responders arrived on the scene, or the report includes a description such as “heavy” or 

“dense” smoke). 
Draft for Public Comment 

A-4 

The original “potentially challenging” or “not-challenging” assignments were reviewed for each 

event identified as occurring during plant low power or shutdown conditions, and the assignment 

was modified where deemed necessary. The assignments for events occurring during power 

operations were left as per the original NUREG/CR-6850 assessment (they were not revised). 

A.1.3 Plant Operating Mode

Each event was also examined for the plant operating mode. Most event descriptions had a clear 

statement about the operating mode. Since the database was filtered excluding “power” 

operating mode, all the events that were analyzed either clearly stated that the plant (or one of the 

units) was in LPSD mode or no information was provided. In the latter cases, the operating 

mode was assigned as “undetermined”. In one case, the POS assignment of the event was 

modified from “low power/shutdown” to “full-power”. In another case, the event had occurred 

during the de-commissioning phase of the plant. 

A.2 Event Counting Method

To estimate the fire occurrence frequency for each bin, the total number of events associated 

with the bin and years of plant experience are needed. The calculation method described in 

Section C.4 of reference A-1 applies in the case of LPSD frequency calculations. That is, the 

following equation is applicable to LPSD fire frequency computations (see Section C.4.1 of 

reference A-1 for a description): 

Fplant,i = Ki + Ci·q + Bi·p + BCi·p·q + Ai/N + (ACi/N)·q + (ABi/N)·p + (ABCi/N)·p·q 

All the parameters of this equation have the same definition as for the full-power case with the 

exception of “p”. The parameter “p” in the case of LPSD is the fraction of the events of known 

operating mode that had occurred during LPSD. In effect pLPSD = 1 - pfull-power. 

Note that there was no attempt made to further classify the events that occurred during LPSD 

based on the specific LPSD POS of the plant when these events occurred. That is, there is an 

implicit assumption that each LPSD event applied, for ignition frequency purposes, equally 

throughout LPSD (i.e., equally to all potential POSs). 

A.3 Uncertainty Analysis

Uncertainty distributions of bin frequencies were established using the non-homogeneous 

Bayesian analysis method option of the R-DAT computer program (reference A-2). Similar to 

the two-stage Bayesian approach, fire event statistics of each plant are entered into the 

uncertainty estimation process separately to allow plant-to-plant variability influencing the 

uncertainty distributions. The results of this process are shown in Table A-3 in terms of the 

mean, 5th, 50th and 95th percentiles of the each distribution. The mean values can be used as 

point estimates for each ignition frequency bin. 

A.4 Event Counts and Generic Frequencies

As noted above, the 431 events were reviewed and screened for challenging category and 

operating mode assignment. For a large number of cases, the challenging category was modified 

from the original study (i.e., reference A-1). Also, several of these events were concluded to be 

not applicable to LPSD Fire PRA. In a few cases the bin assignment had to be modified. Seven 
Draft for Public Comment 

A-5 

events were removed from analysis. Table A-2 provides the number of events by bins, power 

level (i.e., LPSD or not) and “challenging” assignment. 

The total number of events that should be used for frequency calculation was estimated using the 

equation presented in Section A.2 above using 0.5 for q and p parameters. The results are 

presented in Table A-3. The corresponding total number of plant years is also presented in 

Table A-3 for each bin. The number of reactor years for LPSD operating mode is calculated in 

exactly the same way as that described in reference A-1 for the full-power operating mode. 

The frequencies presented in Table A-3 are simple division of the number of fire events and the 

number of plant years noted. 

A.5 Fire Type Split Fraction

As it is discussed in reference A-1, different fire types can be postulated for most of the ignition 

sources. For example, the bin “Containment (PWR) / Reactor Coolant Pumps” can refer to both 

electric and oil fires. The same six fire types, postulated in reference [1], are used here. Table 

A-4 provides the split fraction for each fire type for the LPSD specific bins. The split fractions 

are based on interpretations of the FEDB events. 

A.6 Fire Event Classification

As it is discussed above, EPRI’s FEDB events, filtered for non full-power operating mode, were 

reviewed to verify the appropriate ignition source bin, the status relative to potentially 

challenging determination, and the operating mode assignments. For a large number of cases, 

the challenging category was modified. Also, a few events were concluded to be not applicable 

to LPSD Fire PRA. In a few cases the bin assignment had to be modified. Table A-5 provides a 

complete list of the events that were reviewed. Corresponding bin assignment, operating mode 

and challenging category are also shown. Notes are provided to indicate changes in event 

assessment (e.g., if “challenging” assignment was altered from the original study). Also, it is 

noted if the event is not included in the frequency estimation. 

A.7 References

A-1 “Fire PRA Methodology for Nuclear Power Facilities; Volume 2: Detailed 

Methodology”, U.S. NRC and EPRI. NUREG/CR-6850 and EPRI 1011989, September 

2005. 

A-2 “R-DAT and R-DAT Plus 1.5 User’s Manual”, Prediction Technologies, College Park, 

MD, 2002. 
Draft for Public Comment 

A-6 

Table A-2: Event Counts by Bin, Challenging Category and Operating Mode. 

Bin # Location Ignition Source Power Level Not Challenging Potentially Challenging Undetermined 

2 Containment (PWR) Reactor Coolant Pump LPSD 1 3 1 Undetermined 1 0 0 

3P Containment (PWR) Transient fires caused by welding and cutting LPSD 32 10 11 Undetermined 7 2 0 

3B Containment (BWR) Transient fires caused by welding and cutting LPSD 45 10 11 Undetermined 1 0 0 

5 Control/Aux/Reactor Building Cable fires caused by welding and cutting LPSD 0 0 0 Undetermined 0 0 1 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting LPSD 32 4 5 Undetermined 17 0 2 7 Control/Aux/Reactor Building Transients LPSD 8 1 2 Undetermined 4 2 2 

11 Plant-Wide Components Cable fires caused by welding and cutting LPSD 0 0 0 Undetermined 0 0 1 20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) LPSD 0 3 0 Undetermined 0 0 0 22 Plant-Wide Components RPS MG sets LPSD 5 1 4 Undetermined 0 0 1 24 Plant-Wide Components Transient fires caused by welding and cutting LPSD 9 6 3 Undetermined 12 1 0 25 Plant-Wide Components Transients LPSD 11 1 1 Undetermined 12 1 7 27 Transformer Yard Transformer – Catastrophic LPSD 0 5 0 Undetermined 0 0 0 28 Transformer Yard Transformer - Non Catastrophic LPSD 1 1 4 Undetermined 1 0 0 29 Transformer Yard Cable fires caused by welding and cutting LPSD 1 1 0 Undetermined 0 0 0 32 Turbine Building Main feedwater pumps LPSD 0 1 0 Undetermined 0 0 1 34 Turbine Building T/G Hydrogen LPSD 0 2 0 Undetermined 0 0 0 
Draft for Public Comment 

A-7 

Table A-2: Event Counts by Bin, Challenging Category and Operating Mode. 

Bin # Location Ignition Source Power Level Not Challenging Potentially Challenging Undetermined 

35 Turbine Building T/G Oil LPSD 2 1 0 Undetermined 0 0 0 36 Turbine Building Transient fires caused by welding and cutting LPSD 38 8 8 Undetermined 17 1 4 37 Turbine Building Transients LPSD 11 3 4 Undetermined 8 2 3 

 Totals 278 70(1) 76 

 (1) One fire event that was deemed as potentially challenging involved a gas-turbine. The event is not shown in this table. 
Draft for Public Comment 

A-8 

Table A-3: Generic Fire Ignition Frequency Model for U.S. Nuclear Power Plants. 

Bin # Location Ignition Source # of Events Total Reactor Years Frequency (R-DAT Results ) Mean 5th 50th 95th

2 Containment (PWR) Reactor Coolant Pump 3.5 519.9(1) 6.6E-03 2.6E-04 3.3E-03 1.8E-02 

3P Containment (PWR) Transients and Hotwork 16.5 519.9 3.1E-02 2.9E-03 2.1E-02 8.2E-02 

3B Containment (BWR) Transients and Hotwork 15.5 298.5(2) 3.5E-02 2.3E-04 7.3E-03 1.2E-01 

5 Control/Auxiliary/Reactor Building Cable fires caused by welding and cutting 0.25 822.5(3) 1.2E-03 2.3E-05 3.8E-04 3.5E-03 6 Control/Auxiliary/Reactor Building Transient fires caused by welding and cutting 7 822.5 9.3E-03 3.6E-04 5.0E-03 2.5E-02 7 Control/Auxiliary/Reactor Building Transients 3.5 822.5 4.7E-03 2.0E-04 2.5E-03 1.3E-02 

11 Plant-Wide Components Cable fires caused by welding and cutting 0.25 822.5 8.8E-04 1.8E-05 2.9E-04 2.8E-03 20 Plant-Wide Components Off-gas/Hydrogen recombiner (BWR) 3 298.5 2.0E-02 8.5E-05 3.1E-03 3.8E-02 22 Plant-Wide Components RPS MG sets 3.25 822.5 3.2E-03 1.5E-04 1.7E-03 9.0E-03 24 Plant-Wide Components Transient fires caused by welding and cutting 8 822.5 1.1E-02 4.0E-04 5.8E-03 3.0E-02 25 Plant-Wide Components Transients 3.75 822.5 5.8E-03 2.1E-04 2.9E-03 1.5E-02 27 Transformer Yard Transformer - catastrophic 5 822.5 7.2E-03 8.9E-05 2.3E-03 2.1E-02 28 Transformer Yard Transformer - noncatastrophic 3 822.5 3.8E-03 1.6E-04 1.9E-03 1.1E-02 29 Transformer Yard Yard Transformers (others) 1 822.5 2.0E-03 2.7E-05 6.1E-04 5.7E-03 31 Turbine Building Cable fires caused by welding and cutting 0 822.5 1.3E-03 2.2E-05 4.0E-04 3.7E-03 32 Turbine Building Main feedwater pumps 1.25 822.5 1.9E-03 7.6E-05 8.9E-04 5.6E-03 34 Turbine Building T/G hydrogen 2 822.5 3.0E-03 4.8E-05 1.1E-03 8.7E-03 35 Turbine Building T/G oil 1 822.5 2.5E-03 3.5E-05 7.5E-04 6.9E-03 36 Turbine Building Transient fires caused by welding and cutting 13.5 822.5 2.2E-02 2.5E-04 5.5E-03 7.1E-02 37 Turbine Building Transients 6.75 822.5 1.0E-02 2.2E-04 4.3E-03 3.0E-02 

(1) Total number of years PWRs were in an LPSD POS up to December 31, 2000. (2) Total number of years BWRs were in an LPSD POS up to December 31, 2000. 

(3) Total number of years all NPPs were in an LPSD POS up to December 31, 2000. 
Draft for Public Comment 

A-9 

Table A-4: Fire Type Split Fractions. 

Bin # Location Ignition Source Electrical Oil Transient Hotwork Hydrogen HEAF 

2 Containment (PWR) Reactor Coolant Pump 0.25 0.75 0.00 0.00 0.00 0.00 

3P Containment (PWR) Transients and Hotwork 0.00 0.00 0.39 0.61 0.00 0.00 

3B Containment (BWR) Transients and Hotwork 0.05 0.00 0.24 0.71 0.00 0.00 

5 Control/Auxiliary/Reactor Building Cable fires caused by welding and cutting 0.00 0.00 0.00 1.00 0.00 0.00 6 Control/Auxiliary/Reactor Building Transient fires caused by welding and cutting 0.00 0.00 0.09 0.91 0.00 0.00 7 Control/Auxiliary/Reactor Building Transients 0.00 0.00 1.00 0.00 0.00 0.00 

11 Plant-Wide Components Cable fires caused by welding and cutting 0.00 0.00 0.0 1.00 0.00 0.00 20 Plant-Wide Components Off-gas/Hydrogen recombiner (BWR) 0.33 0.00 0.33 0.00 0.33 0.00 22 Plant-Wide Components RPS MG sets 1.00 0.00 0.00 0.00 0.00 0.00 24 Plant-Wide Components Transient fires caused by welding and cutting 0.00 0.00 0.0 1.00 0.00 0.00 25 Plant-Wide Components Transients 0.10 0.00 0.90 0.00 0.00 0.00 27 Transformer Yard Transformer - catastrophic 0.70 0.30 0.00 0.00 0.00 0.00 28 Transformer Yard Transformer - noncatastrophic 0.80 0.00 0.00 0.20 0.00 0.00 29 Transformer Yard Yard Transformers (others) 1.00 0.00 0.00 0.00 0.00 0.00 31 Turbine Building Cable fires caused by welding and cutting 0.00(1) 0.00 0.00 1.00 0.00 0.00 32 Turbine Building Main feedwater pumps 0.00 1.00 0.00 0.00 0.00 0.00 34 Turbine Building T/G hydrogen 0.25 0.00 0.00 0.00 0.75 0.00 35 Turbine Building T/G oil 0.00 1.00 0.00 0.00 0.00 0.00 36 Turbine Building Transient fires caused by welding and cutting 0.00 0.07 0.29 0.64 0.00 0.00 37 Turbine Building Transients 0.00 0.04 0.96 0.00 0.00 0.00 

 (1) Since no events were recorded during LPSD, the split fraction of the full-power analysis (i.e., reference [1]) is used. 
Draft for Public Comment 

A-10 

Table A-5: Fire Event Classification. 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy t Arcing Faul

Challenging 

-Challenging toN

d Undetermine Comments 

9 20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) Low Power Operation FALSE TRUE FALSE FALSE 

11 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 

16 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE This event assessment was changed 

18 ? Plant-Wide Components Gas Turbines Low Power Operation FALSE TRUE FALSE FALSE This event assessment was changed 25 27 Transformer Yard Transformer - Catastrophic Low Power Operation FALSE TRUE FALSE FALSE 26 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 30 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

33 20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) Low Power Operation FALSE TRUE FALSE FALSE 56 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 60 32 Turbine Building Main feedwater pumps Low Power Operation FALSE TRUE FALSE FALSE 80 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 88 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 
Draft for Public Comment 

A-11 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy t Arcing Faul

Challenging 

-Challenging toN

d Undetermine Comments 

95 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 96 2 Containment (PWR) Reactor Coolant Pump Low Power Operation FALSE TRUE FALSE FALSE 

107 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

112 2 Containment (PWR) Reactor Coolant Pump Low Power Operation FALSE TRUE FALSE FALSE This event assessment was changed 123 37 Turbine Building Transients Low Power Operation FALSE TRUE FALSE FALSE 148 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 149 34 Turbine Building T/G Hydrogen Low Power Operation FALSE TRUE FALSE FALSE 152 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

153 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE FALSE TRUE 167 2 Containment (PWR) Reactor Coolant Pump Low Power Operation FALSE FALSE FALSE TRUE 179 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE FALSE TRUE 187 25 Plant-Wide Components Transients Undetermined FALSE TRUE FALSE FALSE 196 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE TRUE FALSE 203 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 
Draft for Public Comment 

A-12 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

206 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE FALSE The plant was decommissioned at the time of the event. 210 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

225 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 226 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 227 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 232 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 245 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 247 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 248 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 253 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 265 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 272 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 274 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-13 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

276 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 277 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 278 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 281 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 283 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 284 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 287 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 290 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE 

293 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 294 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 297 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 303 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-14 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

309 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 311 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 313 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 314 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 315 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 316 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 325 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 334 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 335 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

336 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 337 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 339 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-15 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

342 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 343 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 344 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 345 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 348 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 

350 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 355 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 356 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 359 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

360 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 

This event was identified as Containment (PWR), Transient Fires Caused by Cutting and Welding. It was reworded it to Transient and Hotwork. 
Draft for Public Comment 

A-16 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

362 37 Turbine Building Transients Low Power Operation FALSE TRUE FALSE FALSE 371 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 373 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 375 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 377 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 378 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 379 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

380 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 382 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 383 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 386 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 387 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 392 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

393 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-17 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

394 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 408 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 409 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 411 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 412 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 424 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 426 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 429 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 430 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 443 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 447 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 450 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE TRUE FALSE FALSE 464 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 
Draft for Public Comment 

A-18 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

466 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 470 37 Turbine Building Transients Undetermined FALSE TRUE FALSE FALSE 471 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 473 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 496 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

502 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 506 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE FALSE This event was removed from the LPSD analysis because the Mode of Operation is "Power" 517 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE 525 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 528 20 Plant-Wide Components Off-gas/Hydrogen Recombiner (BWR) Low Power Operation FALSE TRUE FALSE FALSE 530 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE TRUE FALSE 532 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE FALSE TRUE 539 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-19 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

540 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 545 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 552 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 556 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 557 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE TRUE FALSE FALSE 568 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 580 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

581 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 582 37 Turbine Building Transients Low Power Operation FALSE FALSE FALSE TRUE 583 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

586 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

588 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE 
Draft for Public Comment 

A-20 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

589 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 

590 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE 

591 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 

592 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

594 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

599 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 600 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE 601 35 Turbine Building T/G Oil Low Power Operation FALSE TRUE FALSE FALSE 604 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

605 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

611 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 
Draft for Public Comment 

A-21 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

613 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

616 35 Turbine Building T/G Oil Low Power Operation FALSE FALSE TRUE FALSE 618 37 Turbine Building Transients Low Power Operation FALSE FALSE FALSE TRUE 619 37 Turbine Building Transients Low Power Operation FALSE TRUE FALSE FALSE 630 35 Turbine Building T/G Oil Low Power Operation FALSE FALSE TRUE FALSE 635 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 638 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 639 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 640 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 641 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 643 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

647 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 648 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 682 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 
Draft for Public Comment 

A-22 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

686 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE TRUE FALSE 687 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 692 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 693 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 694 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 697 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 698 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 703 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 705 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE 712 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 713 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 717 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 718 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 
Draft for Public Comment 

A-23 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

719 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 720 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 722 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 724 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 730 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 738 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE FALSE TRUE 740 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 751 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 

754 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

761 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 772 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 773 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 779 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 
Draft for Public Comment 

A-24 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

782 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE TRUE FALSE 788 28 Transformer yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE FALSE TRUE 800 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE TRUE FALSE 801 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 835 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 838 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 839 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE TRUE FALSE 840 21 Plant-Wide Components Pumps Low Power Operation FALSE FALSE TRUE FALSE 845 27 Transformer Yard Transformer - Catastrophic Low Power Operation FALSE TRUE FALSE FALSE 849 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 858 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 862 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 919 29 Transformer Yard 

Cable fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

941 27 Transformer Yard Transformer - Catastrophic Low Power Operation FALSE TRUE FALSE FALSE 
Draft for Public Comment 

A-25 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

963 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 964 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 965 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 966 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 968 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 969 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

970 3 Containment (BWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE 972 37 Turbine Building Transients Undetermined FALSE FALSE FALSE TRUE 974 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 981 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 983 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 

990 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE TRUE FALSE 992 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE 995 29 Transformer Yard 

Cable fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-26 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

997 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 

1004 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

1007 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 1009 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1010 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 1011 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 1012 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 1025 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 1031 2 Containment (PWR) Reactor Coolant Pump Low Power Operation FALSE FALSE TRUE FALSE 1032 27 Transformer Yard Transformer - Catastrophic Low Power Operation FALSE TRUE FALSE FALSE 1040 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 1044 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 1051 37 Turbine Building Transients Low Power Operation FALSE FALSE FALSE TRUE 1054 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-27 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1060 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 1094 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 1106 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE FALSE FALSE Decommissioned plant. Removed from LPDS analysis. 1109 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 1111 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 1117 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1120 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1121 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1136 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 1138 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 1143 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1144 37 Turbine Building Transients Undetermined FALSE FALSE FALSE TRUE 
Draft for Public Comment 

A-28 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1145 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

1146 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1149 37 Turbine Building Transients Undetermined FALSE TRUE FALSE FALSE 1153 37 Turbine Building Transients Low Power Operation FALSE FALSE FALSE TRUE 1154 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE FALSE TRUE 

1157 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

1158 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 1161 37 Turbine Building Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 1164 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE FALSE TRUE 1165 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 1166 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 1172 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE TRUE FALSE 1177 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 1180 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-29 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1192 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 1198 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE Changed the location to Control/Rx/Aux Bldg 1199 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1202 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE 1203 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1221 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

1222 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1228 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1229 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

1230 25 Plant-Wide Components Transients Low Power Operation FALSE TRUE FALSE FALSE This event assessment was changed 1231 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1233 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-30 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1204 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1206 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1208 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 1209 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1210 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE FALSE TRUE 1214 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1216 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE FALSE TRUE 

1219 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

1234 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE TRUE FALSE FALSE This event assessment was changed 

1235 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1237 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 1242 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-31 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1243 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1247 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE 1249 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE This event assessment was changed 1252 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1272 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1273 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1275 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 

1278 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 1291 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 1299 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE 1300 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1301 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-32 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1302 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1303 3 Containment (PWR) Transient and Hotwork Undetermined FALSE TRUE FALSE FALSE This event assessment was changed 1304 3 Containment (PWR) Transient and Hotwork Undetermined FALSE TRUE FALSE FALSE 1305 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

1306 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

1307 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

1311 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1312 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 1313 7 Control/Aux/Reactor Building Transients Undetermined FALSE TRUE FALSE FALSE This event assessment was changed 1316 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE 1324 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 1325 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE FALSE TRUE 
Draft for Public Comment 

A-33 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1329 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1341 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1345 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 1347 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 1352 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1354 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

1360 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 1361 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 1388 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 1389 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 1398 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 1401 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 1424 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE 
Draft for Public Comment 

A-34 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

1427 25 Plant-Wide Components Transients Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 1505 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE FALSE FALSE FALSE 

This event was moved to Bin 16 (HEAF) and was not considered for LPSD analysis. 

2100 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2102 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 2106 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 2108 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2110 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2111 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2113 5 Control/Aux/Reactor Building Cable fires caused by welding and cutting Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 2115 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2116 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2117 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2118 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-35 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2126 11 Plant-Wide Components Cable fires caused by welding and cutting Undetermined FALSE FALSE FALSE TRUE This event assessment was changed 2129 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2131 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2132 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 2134 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2137 28 Transformer Yard Transformer - Non Catastrophic Undetermined FALSE FALSE TRUE FALSE 2138 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2143 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE FALSE TRUE 2145 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2146 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2147 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 
Draft for Public Comment 

A-36 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2148 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2149 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2150 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2154 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2162 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE TRUE FALSE FALSE 2166 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2169 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2173 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 2177 27 Transformer Yard Transformer - Catastrophic Low Power Operation FALSE TRUE FALSE FALSE This event was reassigned to Bin #27. 2182 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2183 32 Turbine Building Main feedwater pumps Undetermined FALSE FALSE FALSE TRUE 2184 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-37 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2188 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 

2190 22 Plant-Wide Components RPS MG sets Undetermined FALSE FALSE FALSE TRUE 2192 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2193 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2196 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2198 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2199 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2201 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2203 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2215 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2216 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-38 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2220 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2223 2 Containment (PWR) Reactor Coolant Pump Low Power Operation FALSE TRUE FALSE FALSE 2232 22 Plant-Wide Components RPS MG sets Low Power Operation FALSE FALSE FALSE TRUE 2238 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2241 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE TRUE FALSE FALSE 

2244 2 Containment (PWR) Reactor Coolant Pump Undetermined FALSE FALSE TRUE FALSE 2245 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 2247 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 2248 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE FALSE FALSE This event was moved to Bin 12, which is not included in LPSD PRA 2257 7 Control/Aux/Reactor Building Transients Undetermined FALSE TRUE FALSE FALSE 2258 24 Plant-Wide Components Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2259 34 Turbine Building T/G Hydrogen Low Power Operation FALSE TRUE FALSE FALSE 2260 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2270 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-39 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2271 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2279 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE TRUE FALSE FALSE 2286 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 2291 7 Control/Aux/Reactor Building Transients Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 2293 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2296 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2298 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2299 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2300 37 Turbine Building Transients Low Power Operation FALSE FALSE TRUE FALSE 2306 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2307 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2320 28 Transformer Yard Transformer - Non Catastrophic Low Power Operation FALSE TRUE FALSE FALSE 
Draft for Public Comment 

A-40 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2321 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2324 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE FALSE FALSE 

"Outside the engineering office" most likely means that the location of this fire was at a place that normally gets screened out in a Fire PRA. This event was removed from the LPSD analysis. 

2327 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 2330 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 2340 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2347 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 

2363 3 Containment (BWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2376 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2379 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2384 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-41 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2385 25 Plant-Wide Components Transients Low Power Operation FALSE FALSE TRUE FALSE 2398 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2403 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2414 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2415 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2421 21 Plant-Wide Components Pumps Low Power Operation FALSE FALSE TRUE FALSE 2423 36 Turbine Building 

Transient fires caused by welding and cutting 

Low Power Operation FALSE FALSE TRUE FALSE 

2444 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 2446 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 2448 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 2450 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 2455 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE 2458 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 2459 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-42 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy 

t Arcing Faul

Challenging 

-Challenging t o N

d Undetermine Comments 

2460 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2461 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2462 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2463 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2464 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2465 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2466 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2467 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2469 24 Plant-Wide Components Transient fires caused by welding and cutting Undetermined FALSE TRUE FALSE FALSE 2470 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2472 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2473 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2477 37 Turbine Building Transients Undetermined FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-43 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy t Arcing Faul

Challenging 

-Challenging toN

d Undetermine Comments 

2480 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2482 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2483 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2484 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2485 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Undetermined FALSE FALSE TRUE FALSE 2486 36 Turbine Building 

Transient fires caused by welding and cutting 

Undetermined FALSE FALSE TRUE FALSE 

2488 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE 2491 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE This event assessment was changed 2492 25 Plant-Wide Components Transients Undetermined FALSE FALSE TRUE FALSE 2493 3 Containment (PWR) Transient and Hotwork Undetermined FALSE FALSE TRUE FALSE 2495 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 
Draft for Public Comment 

A-44 

Table A-5: Fire Event Classification (continued). 

Incident No. 

Bin # 

Location Ignition Source Power Level 

High Energy t Arcing Faul

Challenging 

-Challenging toN

d Undetermine Comments 

2496 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 2497 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE This event assessment was changed 2504 3 Containment (PWR) Transient and Hotwork Low Power Operation FALSE FALSE TRUE FALSE 2505 7 Control/Aux/Reactor Building Transients Low Power Operation FALSE FALSE FALSE TRUE This event assessment was changed 2511 6 Control/Aux/Reactor Building Transient fires caused by welding and cutting Low Power Operation FALSE FALSE TRUE FALSE 
BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse)

NRC FORM 335

(9-2004)

NRCMD 3.7

U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

(Assigned by NRC, Add Vol., Supp., Rev.,

 and Addendum Numbers, if any.)

3. DATE REPORT PUBLISHED

MONTH YEAR

4. FIN OR GRANT NUMBER

2. TITLE AND SUBTITLE

5. AUTHOR(S) 6. TYPE OF REPORT

7. PERIOD COVERED (Inclusive Dates)

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC, provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor,

9. SPONSORING ORGANIZATION - NAME AND ADDRESS (If NRC, type "Same as above"; if contractor, provide NRC Division, Office or Region, U.S. Nuclear Regulatory Commission, 

provide name and mailing address.)

and mailing address.)

10. SUPPLEMENTARY NOTES

11. ABSTRACT (200 words or less)

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating the report.)

14. SECURITY CLASSIFICATION

13. AVAILABILITY STATEMENT

unlimited

(This Page)

unclassified

(This Report)

unclassified

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (9-2004) PRINTED ON RECYCLED PAPER

NUREG/CR-7114

Methodology for Low Power/Shutdown Fire PRA - Draft for Public Comment

December 2011

USNRC JCN N6592

Steven P. Nowlen and Tara Olivier Technical

8/4/2008 - 11/30/2012

Sandia National Laboratories

Risk and Reliability Analysis Department 6761

P.O. Box 5800

Albuquerque, NM 87185

Division of Risk Analysis

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555

H. Woods, NRC Project Manager

The U.S. Nuclear Regulatory Commission (NRC) approved the risk-informed and performance-based alternative regulation 10

CFR 50.48(c) in July, 2004, which allows licensees the option of using fire protection requirements containted in the National

Fire Protection Association (NFPA) Standard 805, "Performance Based Standard for Fire Protection for Light-Water Reactor

Electric Generating Plants, 2001 Edition," with certain exceptions. To support licensees' use of that option, the NRC and the

Electric Power Research Institute (EPRI) jointly issued NUREG/CR-6850 (EPRI 1011989) "Fire PRA Methodology for Nuclear

Power Facilities," in September 2005. That report documents the state-of-the-art methods, tools, and data for conducting a fire

Probabilistic Risk Assessment (PRA) in a commercial nuclear power plant (NPP) during full power operation. This document

complements NUREG/CR-6850 (EPRI 1011989) by presenting a method for conducting a fire PRA in a commercial NPP during

low power and shutdown conditions.

fire, performance-based, risk-informed regulation, fire hazard analysis (FHA), fire safety, fire

protection, nuclear power plant, probabilistic risk assessment (PRA), fire modeling, circuit analysis,

shutdown, low power, fire risk, fire PRA, fire PSA, post-fire safe shutdown analysis, spurious

actuation, spurious operation