Joint Assessment of Cable 

Damage and Quantification of 

Effects from Fire 

(JACQUE-FIRE)

Volume 1:

Phenomena Identification and Ranking 

Table (PIRT) Exercise for Nuclear 

Power Plant Fire-Induced Electrical 

Circuit Failure

U.S. Nuclear Regulatory Commission Electric Power Research Institute

Office of Nuclear Regulatory Research 3412 Hillview Avenue

Washington, D.C. 20555-0001 Palo Alto, CA 94303

NUREG/CR-7150, Vol. 1 EPRI 1026424

BNL-NUREG-98204-2012 Final Report
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Joint Assessment of Cable Damage 

and Quantification of Effects from 

Fire (JACQUE-FIRE)

Volume 1: Phenomena Identification and Ranking Table (PIRT) Exercise 

for Nuclear Power Plant Fire-Induced Electrical Circuit Failure

NUREG/CR-7150, Vol. 1 EPRI 1026424

BNL-NUREG-98204-2012

Final Report

October 2012 

U.S. Nuclear Regulatory Commission Electric Power Research Institute (EPRI)

Office of Nuclear Regulatory Research (RES) 3420 Hillview Avenue

Washington, D.C, 20555-0001 Palo Alto, CA 94304-1338

U.S. NRC-RES Project Manager EPRI Project Manager

M.H. Salley R. Wachowiak
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are registered service marks of the Electric Power Research Institute, Inc. 
iii 

ABSTRACT 

Volume 1 of this report documents the results of a Phenomena Identification and Ranking Table 

(PIRT) exercise that was undertaken on fire-induced electrical circuit failures that may occur in 

nuclear power plants when cables are damaged by fires. Volume 2 documents the PRA expert 

elicitation results and will include the best estimate conditional probabilities of hot short-induced 

spurious operations of control circuits, given fire damage to associated cables. This program 

was sponsored by the U.S. Nuclear Regulatory Commission’s (NRC’s) Office of Nuclear 

Regulatory Research (RES) and the Electric Power Research Institute (EPRI) under the NRCRES/EPRI Memorandum of Understanding (MOU) collaborative research agreement. The 

electrical expert PIRT panel (herein referred to as the PIRT panel) was comprised of a group of 

experts sponsored equally by NRC and EPRI. Staff from Brookhaven National Laboratory 

(BNL) facilitated the efforts of the PIRT panel. 

The objective of this PIRT was to identify phenomena that can affect the fire-induced failure 

modes of electrical circuits after cables are damaged by fire. The PIRT panel used the results 

from recent fire tests performed by the Nuclear Energy Institute (NEI), EPRI and NRC, 

identifying and ranking the parameters that can influence the hot short induced failure modes of 

electrical control circuits. Using these influencing parameters, the results of cable-fire tests, 

expert judgment, and operating experience, the PIRT panel developed circuit configurations 

vulnerable to hot short induced circuit failure modes that can cause the spurious operation of 

certain end devices. In addition to completing the PIRT exercise on control circuits, the PIRT 

panel reached technical consensus on the majority of issues in analyzing fire protection circuits 

such as power-cabling consequential hot shorts, open circuits on the secondary of current 

transformers, and multiple high-impedance faults. The PIRT panel noted the lack of data on 

instrument circuits, including process monitoring indication, needed to support a structured 

evaluation of the influencing phenomena. The panel identified key areas for future research to 

advance the current knowledge base. 

 

v 

CONTENTS 

ABSTRACT ................................................................................................................................. iii

CONTENTS .................................................................................................................................. v

FIGURES ..................................................................................................................................... ix

TABLES ........................................................................................................................................ x

REPORT SUMMARY .................................................................................................................. xi

EPRI PERSPECTIVE ................................................................................................................. xv

PREFACE ................................................................................................................................. xvii 

CITATIONS ................................................................................................................................ xix 

ACKNOWLEDGEMENTS ........................................................................................................ xixi

LIST OF ACRONYMS ............................................................................................................. xxiii

1 INTRODUCTION .................................................................................................................... 1-1

1.1 Background ..................................................................................................................... 1-1

1.2 Objective ......................................................................................................................... 1-2

1.3 The Approach .................................................................................................................. 1-3

1.4 The PIRT Panel ............................................................................................................... 1-5

1.5 Report Organization ........................................................................................................ 1-6

2 OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES .................................... 2-1

2.1 Terminology Used by PIRT Panel ................................................................................... 2-5

2.1.1 Hot Short-Induced Spurious Operation ................................................................... 2-5

2.1.2 Definitions ................................................................................................................ 2-7

2.1.3 Technical Positions by the PIRT Panel ................................................................... 2-8

2.1.4 NRC Regulatory Issue Summary (RIS) 2004-03 – “Risk-Informed Approach 

for Post-Fire Safe-Shutdown Circuit Inspections” ................................................... 2-9

2.1.5 Associated Circuits .................................................................................................. 2-9

2.2 Evaluation of Cable Fire Test Results ........................................................................... 2-10

2.2.1 Categories of Information Available for Cable Fire Tests ...................................... 2-10

2.2.2 Cable Fire Test Data Analysis ............................................................................... 2-11

2.3 Evaluation of Electrical Circuit Configurations ............................................................... 2-12

2.3.1 Influencing Parameters .......................................................................................... 2-13

2.3.2 Electrical Circuits Considered by the PIRT Panel ................................................. 2-14

2.3.2.1 Control Circuits ............................................................................................ 2-14

2.3.2.2 Power Circuits ............................................................................................. 2-16

2.3.2.3 Instrument Circuits ....................................................................................... 2-17

2.3.2.4 Ancillary Electrical Circuit Issues ................................................................. 2-17

2.4 PIRT Panel Evaluation Process for Control Circuits ..................................................... 2-18

2.5 Technical Challenges .................................................................................................... 2-20

3 PIRT PANEL EVALUATION OF CONTROL CIRCUITS........................................................ 3-1

3.1 Impact Assessment of Influencing Parameters ............................................................... 3-1

3.2 Summary of Influencing Parameters Importance .......................................................... 3-20

3.3 Control Circuits Vulnerable to Hot Short-Induced Spurious Operations ...................... 3-22

3.3.1 Evaluation of Fire Test Results .............................................................................. 3-22

3.3.2 Considerations for Defining Control Circuit Configurations ................................... 3-24
vi 

3.3.3 Control Circuit Configuration Scenarios ................................................................ 3-34

3.4 Examples of Control Circuits Vulnerable to Hot Short-Induced Spurious 

Operations .................................................................................................................... 3-35

3.4.1 Control Circuit Configuration Example Sets.......................................................... 3-36

3.4.1.1 Control Circuit Example Set One ....................................................................... 3-37

3.4.1.2 Control Circuit Example Set Two ....................................................................... 3-42

3.4.1.3 Control Circuit Example Set Three .................................................................... 3-47

3.4.2 Control Circuit Configurations for Single and Double Break Designs ................... 3-51

4 PIRT PANEL TECHNICAL POSITIONS ON POWER CIRCUITS ......................................... 4-1

4.1 Background ...................................................................................................................... 4-1

4.2 Three Phase AC Power Circuit ........................................................................................ 4-1

4.3 DC Compound-Wound Motor Power Circuit .................................................................... 4-3

5 PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS ........... 5-1

5.1 Background ..................................................................................................................... 5-1

5.2 Instrumentation and Control Circuit Evaluation ............................................................... 5-1

5.3 Specific Concerns involving Instrument Current Loops ................................................... 5-6

5.3.1 Instrumentation Cabling ........................................................................................... 5-6

5.3.2 Instrumentation Circuit Electronic Devices .............................................................. 5-8

5.4 Summary of Research Recommendations ...................................................................... 5-8

6 PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

ISSUES ................................................................................................................................... 6-1

6.1 Multiple High-Impedance Faults ...................................................................................... 6-1

6.1.1 Background ............................................................................................................. 6-1

6.1.2 PIRT Panel Recommendations on MHIF ................................................................ 6-2

6.1.3 Summary of Technical Analysis on MHIF ................................................................ 6-3

6.1.4 Applicability .............................................................................................................. 6-4

6.2 Open Circuit Secondary of Current Transformers ........................................................... 6-4

6.2.1 Background ............................................................................................................. 6-4

6.2.2 Current Transformer Characteristics with an Open Circuit Secondary .................... 6-5

6.2.3 Plausibility of CT Induced Secondary Fires ............................................................. 6-7

6.2.4 PIRT Panel Recommendations ............................................................................... 6-9

6.3 DC Control Power Common Enclosure/Common Power Supply .................................. 6-10

6.4 Control Power Transformers ......................................................................................... 6-11

6.5 Kapton®-insulated Cables ............................................................................................. 6-14

6.5.1 Background ........................................................................................................... 6-14

6.5.2 Arc-Tracking Degradation Mode ............................................................................ 6-15

6.5.3 Application and Operating Experience at Nuclear Power Plants ........................... 6-16

6.5.4 Temperature Damage Thresholds ......................................................................... 6-17

6.5.5 Conclusions ........................................................................................................... 6-18

6.6 Panel Wiring .................................................................................................................. 6-18

6.6.1 Background ........................................................................................................... 6-18

6.6.2 Discussion ............................................................................................................. 6-19

6.6.3 Recommendation .................................................................................................. 6-20

6.7 High Conductor Count Trunk Cables ............................................................................ 6-21

6.7.1 Background ........................................................................................................... 6-21

6.7.2 Discussion ............................................................................................................. 6-21

6.7.3 Conclusions ........................................................................................................... 6-22
vii 

7 PIRT PANEL RESEARCH RECOMMENDATIONS ............................................................... 7-1

7.1 Control Circuit Research ................................................................................................. 7-1

7.2 Instrumentation Circuit Research .................................................................................... 7-2

7.3 Surrogate Ground Path Research ................................................................................... 7-3

7.4 Current Transformer Research ....................................................................................... 7-3

7.5 Conclusions and Prioritization of Future Research ......................................................... 7-3

8 SUMMARY AND CONCLUSIONS ......................................................................................... 8-1

9 REFERENCES ....................................................................................................................... 9-1

APPENDIX A PANELIST AND FACILITATOR RESUMES ..................................................... A-1

APPENDIX B MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS ............................... B-1

APPENDIX C CONTROL CIRCUIT CONFIGURATIONs FOR SINGLE AND 

DOUBLE BREAK DESIGNS ............................................................................ C-1

APPENDIX D SELECTED PRESENTATION VIEWGRAPHS ................................................. D-1

 

ix 

FIGURES 

Figure 2-1. Flowchart for Electrical PIRT Expert Panel Activities ........................................... 2-3

Figure 3-1. Simplified circuit schematics of single and double break circuits: 

Ungrounded; Grounded; Distribution Bus; Powered from CPT. ........................ 3-25

Figure 3-2. Intra-Cable Hot Short ......................................................................................... 3-30

Figure 3-3. Inter-Cable Hot Short ......................................................................................... 3-30

Figure 3-4. Inter-Cable Ground Fault Equivalent Hot Short ................................................. 3-31

Figure 3-5. Grounded AC circuit schematics and probability table ...................................... 3-39

Figure 3-6. Ungrounded AC circuit schematics and probability table ................................... 3-40

Figure 3-7. Ungrounded DC circuit schematics and probability table (also applies to 

ungrounded AC distribution bus) ....................................................................... 3-41

Figure 3-8. Double break ungrounded AC schematics ........................................................ 3-44

Figure 3-9. Double break ungrounded DC schematics ........................................................ 3-46

Figure 4-1. Typical simplified AC 3-phase motor (power circuit) ............................................ 4-2

Figure 4-2. Typical Simplified DC Compound-Wound Motor (Power Circuit) ......................... 4-4

Figure 5-1. Typical 2-Wire Input Control Loop ....................................................................... 5-7

Figure 6-1. MHIF Example ..................................................................................................... 6-2

Figure 6-2. Voltage Waveform with Open Secondary ............................................................ 6-6

Figure 6-3. CPT size - global approach, AC tests ................................................................ 6-13

Figure 6-4. Typical Panel Wiring Configurations .................................................................. 6-19

Figure 6-5. Photo and Illustration of 37/C Trunk Cable ........................................................ 6-21
x 

TABLES 

Table 2-1. Parameter Applicability Ranking ......................................................................... 2-19

Table 2-2. Research Ease Ranking ...................................................................................... 2-19

Table 2-3. Parameter Importance Ranking .......................................................................... 2-19

Table 2-4. State of Knowledge Ranking ............................................................................... 2-20

Table 3-1. Panel Consensus Ranking of Influencing Parameters for AC Control 

Circuits .................................................................................................................. 3-3

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control 

Circuits .................................................................................................................. 3-8

Table 3-3. Inter-Cable Failure Mode Categorization ............................................................ 3-34

Table 3-4. Control Circuit Example Set One with Single Break Design ............................... 3-37

Table 3-5. Control Circuit Example Set Two with Double Break Design .............................. 3-42

Table 3-6. Double break ungrounded AC probability table ................................................... 3-43

Table 3-7. Double break ungrounded DC probability table .................................................. 3-45

Table 3-8. Control Circuit Example Set Three for Spurious Operation DURATION ............. 3-47

Table 3-9. Spurious Operation Duration - Grounded AC Power Source .............................. 3-48

Table 3-10. Spurious Operation Duration - Ungrounded AC Power Source .......................... 3-49

Table 3-11. Hot Short Duration - Ungrounded DC power source ........................................... 3-49

Table 3-12. Spurious Operation Duration - Ungrounded DC Power Source .......................... 3-50

Table 3-13. Hot Short - Duration - Ungrounded DC Power Source ........................................ 3-50

Table 5-1. Different Types of Instrumentation Circuits ........................................................... 5-2

Table 6-1. CPT size - Global Approach ................................................................................ 6-13

Table 7-1. Potential Research Candidates Due to Low State of Knowledge ......................... 7-2
xi 

REPORT SUMMARY 

Volume 1 of this report documents the results of a Phenomena Identification and Ranking Table 

(PIRT) exercise that was performed on fire-induced electrical circuit failures that may occur in 

nuclear power plants (NPPs) as a result of fire damage to cables. Volume 2 documents the 

findings from the elicitations of a risk assessment expert panel, and will include the best 

estimated conditional probabilities of hot short-induced spurious operations of control circuits, 

given that a fire has damaged the associated cables. This program was sponsored by the U.S. 

Nuclear Regulatory Commission’s (NRC’s) Office of Nuclear Regulatory Research (RES) and 

by the Electric Power Research Institute (EPRI) under the NRC-RES/EPRI Memorandum of 

Understanding (MOU) collaborative research agreement. The electrical expert PIRT panel 

(herein referred to as the PIRT panel) was comprised of a group of electrical and fire protection 

experts half sponsored by the NRC and half by the EPRI. Staff from Brookhaven National 

Laboratory (BNL) facilitated the work of the PIRT panel. 

The PIRT process affords a systematic method of obtaining information from experts in a 

technical area by generating lists of phenomena ranked systematically in tables. Under the 

PIRT process, “phenomena” can refer to a particular reactor condition, a physical- or 

engineering-approximation, a safety-related component or parameter, the importance of 

parameters on the likelihood of spurious operation of equipment, or anything else that might 

influence the chosen criteria. Usually, these phenomena are ranked using scoring criteria, 

consensus, or a combination of both to help determine the importance of an individual 

phenomenon. The ranking process supports identifying and prioritizing future research needs 

for a safety issue, or substantiates the regulatory decision-making process. Thus, the PIRT 

methodology, including the PIRT panel, brings into focus those phenomena that dominate an 

issue, while identifying all plausible effects so to demonstrate its completeness. 

The objective of this PIRT exercise was to identify the phenomena (electrical circuit 

configurations) that can affect the circuit failure modes from fire-induced cable damage. Using 

the results from recent fire tests performed by the Nuclear Energy Institute (NEI)/EPRI in 2002 

and the NRC/Sandia National Laboratories (SNL) (CAROLFIRE in 2008 and DESIREE-Fire in 

2010), the electrical expert PIRT panel identified and ranked the parameters that could influence 

the hot short-induced spurious operations in electrical circuits. Utilizing these parameters, the 

findings from cable fire tests, expert judgment, and operating experience, the PIRT panel 

indentified and developed circuit configurations that would be vulnerable to hot short circuit 

failure modes of concern that can cause certain end devices to operate spuriously. 

This PIRT investigated such fire-induced spurious operations of plant components, evaluating 

both alternating current (ac) and direct current (dc) types of circuits. The PIRT panel’s focus 

encompassed three specific types of electrical circuits, i.e., power, control, and instrument 

circuits. Their primary emphasis was upon the control circuits (e.g., 120 VAC and 125 Vdc) 

because fire-induced damage of these types is considered to pose a higher risk to plant safety 

than does the other types of circuit. Accordingly, the majority of test data from industry, along 

with the NRC’s tests, were related to low-voltage control circuits. Due to the limited test data 

available for instrument circuits, the PIRT could not undertake a complete parametric treatment 

of this type. Available failure modes for power circuits are well understood, except for a few 

unique cases. For certain types of power circuits (for example, three-phase power cables), 
xii 

there were no available findings from specific testing by industry; therefore, the PIRT panel’s 

technical recommendations rested upon their expert judgment involving engineering principles 

and physical configurations for power cables and power-cable installations. In other instances, 

such as the PIRT panel’s considerations of open circuits in the secondary of current 

transformers (CTs), their recommendations were based upon available open-circuit test data, 

manufacturers’ input, operating experience (nuclear and non-nuclear), and expert judgment. 

A key, fundamental assumption made by the PIRT panel during their consideration of all of the 

phenomena was that the assessments of electrical circuit failure-modes assumed that fire had 

damaged the cable(s) of concern. In other words, the panel did not focus on parameters that 

influence the likelihood of cable damage from fire effects, such as ignition, fire growth, and fire 

intensity, nor on the likelihood of a fire occurring, but rather on the effects of circuit failure once 

cable damage from fire had occurred. The panel assumed the cables of interest are damaged 

to the point of insulation failure. 

The PIRT panel ranked the following parameters “as having a” HIGH impact on the likelihood of 

hot short-induced spurious operations, and the duration of a spurious operation: 

• Spurious Operation

o Wiring Configuration (number of sources, target, ground/neutral and their 

locations) 

o Conductor Insulation Material Type [for inter-cable hot shorts (thermoset (TS) 

versus thermoplastic (TP))] 

o Grounding Configurations 

 Cable grounding configuration (e.g., ground or drain wire, shield wrap) 

 Armor Grounded versus Ungrounded Circuit (for grounded AC circuits) 

and Armored versus Unarmored (for ungrounded DC circuits) 

 Grounded versus Ungrounded Circuits (for inter-cable hot shorts) 

o Cable Routing/Raceway – Panel Wiring (ranked as important due to a lack of 

available test data and the belief that testing of this parameter is important) 

o Cable Raceway Fill – Bundles (The PIRT panel considered this important even 

though the panel ranked this medium). 

• Duration

o Fire Exposure Conditions 

o Time-Current Characteristics – fuses/breaker size 

o Wiring Configuration (number of sources, targets, ground/neutrals and their 

locations) 

o Cable Routing/Raceway – Panel Wiring 

o Cable Raceway Fill – Bundles (The PIRT panel considered important even 

though the PIRT panel ranked this medium) 

o Latching Circuit Design (e.g., motor operated valves) - This parameter is related 

to the specific circuit design, and not to any particular aspect of fire-induced 

circuit failure. 

Taking all the above factors into consideration and using their expert judgment and experience, 

the PIRT panel identified thirteen different cases that represent control circuit cable 

configurations vulnerable to hot short-induced spurious operations. Based on this assessment, 

the PIRT panel presented several examples of cases that are currently used in NPPs and are 
xiii 

considered in the post-fire safe-shutdown1

 and fire probabilistic risk assessment (Fire PRA) 

circuit analyses. As examples, this report offers an assessment of the types of failure modes 

possible for the 120 VAC and 125 VDC control circuit including both grounded and ungrounded 

circuit configurations, and the likelihood of such failures, given the various parameters 

considered to be of importance. 

In addition to reviewing and evaluating the spurious operation of the control circuits and its 

duration, the PIRT panel provided their technical recommendations2

 on other aspects of fireinduced circuit failures associated with control and power circuits in the post-fire safe-shutdown 

circuit analyses. Specifically, the PIRT panel concluded the following: 

• The spurious operation of a three-phase AC motor due to proper polarity hot shorts on 

three-phase power cabling is incredible.3

• The spurious operation of DC compound-wound motor due to proper polarity hot shorts 

in the motive/power cabling is incredible. 

• The ignition of a secondary fire from an open circuited CT secondary circuit with a turnsratio of 1200:5 or less is incredible. 

• The guidance given in Nuclear Energy Institute, NEI 00-01, Rev. 2 (Ref. 13), Appendix 

B.1, can be applied safely to fire safe-shutdown methodologies throughout the plant in 

resolving concerns associated with Multiple High-Impedance Faults (MHIFs). (Note: 

Appendix B.1 of NEI 00-01, Rev. 2 offers a basis for concluding that MHIFs need not be 

considered provided there exists breaker coordination for any circuits damaged by the 

fire that should previously have been assessed for the effects of MHIFs and appropriate 

testing and maintenance is performed). 

• The spurious operation likelihood reduction factor of “two” provided in the Fire 

Probabilistic Risk Assessment (Fire PRA) methods when a control power transformer 

(CPT) is the derived energy source for a circuit, does not accurately reflect the entirety of 

the test data; no credit should be taken in the Fire PRA for their use in a CPT-powered 

control AC circuit. (Note: The revised probability in Volume 2 of this NUREG/CR will be 

based on a composite of all testing undertaken, and, hence, the probability offered for 

using with both CPT and non-CPT circuits may be increased by a factor less than 2). 

• Kapton® cable, a polyamide stable from -271 to +400 o

C, should be treated as a 

thermoplastic (TP) material for assessment of circuit failures, including risk-informed 

applications, unless (1) the cable has been fully qualified against the requirements of the 

IEEE Std. 383 severe accident equipment qualification standard, in which case it may be 

treated as a thermoset (TS) cable, or (2) an alternate product/case specific basis can be 

established for the cable’s thermal damage limits (e.g., manufacturer or utility testing). 

 

1

 The term “safe-shutdown” is synonymous with “nuclear-safety capability assessment” for NFPA 805 

plants. 

2

 The PIRT panel recommendations do not represent NRC-accepted guidance or methods, unless 

specifically endorsed by the NRC via generic communication, regulatory guide(s) or some other means. 3

 Incredible as defined in Section 2.1.3 is, “The term “incredible” used in conjunction with the 

phenomenon of a fire-induced circuit failure, signifies the PIRT panel’s conclusion that the event cannot 

occur. In these cases, the PIRT panel could find no evidence of the phenomenon ever occurring, and 

there were no credible engineering principles or technical argument to support its happening during a fire. 

Any likelihood value assigned to these types of phenomena would have little meaning.” 
xiv 

• Spurious operation caused by shorting conductors through a surrogate ground path in 

ungrounded circuits as a result of fire induced damage, is a failure mode which occurred 

during the DESIREE-Fire testing and is referred to as “Ground Fault Equivalent Hot 

Short.” The probability of this failure mechanism with respect to cable-to-cable hot 

shorts is such that it warrants consideration for including in future testing programs and, 

subsequently, in analyzing post-fire safe-shutdown conditions. 

Additionally, the PIRT panel recommended future research in several areas. The 

recommendations were based upon a lack of knowledge (and available test data) therein, and 

the importance of the configurations to plant operations during a fire and the potential 

consequences of faulty operation of or fire damage to certain electrical devices. The PIRT 

panel recommended considering the following areas in future research: 

1. Instrumentation and Control Circuits (Discussed in Section 5) [highest priority] 

2. Panel Wiring (Discussed in Section 6.6) 

3. Surrogate Ground Path Hot Short (Discussed in Section 7.3) 

4. Control Circuit Cable Testing (Influencing Parameters given in Section 7.1) 

5. Current Transformers (Discussed in Section 6.2 & 7.4) 

6. High Conductor Count Trunk Cables (Discussed in Section 6.7) [lowest priority] 

Finally, based upon the findings of the PIRT panel, BNL will conduct a follow-on expert 

elicitation via a PRA panel to determine the best-estimate conditional probability (or likelihood) 

of failure, given fire-induced cable damage. Their findings are documented in Volume 2 of this 

NUREG/CR report. These probability estimates represent an advancement of the state-of-art 

for the likelihood of circuit failure and could be used for revising, directly replacing, or creating 

new probabilities for Table 10-1 through Table 10-5, entitled “Failure Mode Probability Estimates 

Given Cable Damage,” of NUREG/CR-6850 for conducting Fire PRAs. 

Keywords

Circuit Analysis 

Fire Protection 

Phenomena Identification and Ranking 

Table (PIRT) 

Nuclear Power Plant (NPP) 

Risk-Informed Regulation 

Fire Hazard Analysis (FHA) 

Fire Safety or Fire Safe-shutdown 

Hot Short 

Performance Based 

Probabilistic Risk Assessment (PRA) 

Spurious Operation (or Actuation) 
xv 

EPRI PERSPECTIVE 

Under a joint Memorandum of Understanding (MOU), NRC-RES and EPRI initiated a 

collaborative, results-oriented research program with the primary objective to develop improved 

methods for conducting Fire PRA at nuclear power plants. This report was developed using that 

process and represents a comprehensive assessment of fire-induced circuit failures. The 

Electrical Phenomena Identification and Ranking Table (PIRT) Panel was made up of electrical 

experts sponsored equally by EPRI and the NRC. All panel members have backgrounds in 

nuclear fire protection and circuit failures and also represent a broad range of functional 

disciplines, including research, regulation, program implementation, and technical application. 

This unique mix of individuals was independent and objective and reached conclusions based 

on technically substantiated observations. While the conclusions are objective, the Panel 

members did not agree on all points, which is not surprising given the technical challenges and 

sometimes limited data sets. Nonetheless, the expertise and qualifications of the Panel in 

combination with effective implementation of the PIRT process provides confidence that this 

report represents the most current state of knowledge for fire-induced circuit failures at the time 

of publication. 

The PIRT Panel charter was to investigate and rank the phenomena applicable to fire-induced 

circuit failures based on available test data and other relevant information. The experimental 

data reviewed by the PIRT Panel represented the latest and most comprehensive set of cable 

fire damage data available. Additionally, as part of the process the Panel agreed to address 

several ancillary circuit failure modes not specifically covered by fire test data, the rationale 

being that the test data provided sufficient insights into the other failure modes to afford better 

characterization and application. As noted, the PIRT process was effectively applied by the 

Panel and included significant deliberations, which, due to the diverse background of team 

members, resulted in a critical vetting of consensus positions documented in this report. In 

general, deliberations performed by the PIRT Panel were data-driven. When data were sparse 

or not available, the Panel acknowledged the limitations and provided the appropriate caveats to 

their conclusions. 

Results and conclusions of the Electrical PIRT Panel, as documented in this report, are 

intended as the primary input to a follow-on PRA Expert Panel, which is tasked with establishing 

appropriate application guidelines within a Fire PRA based on the PIRT Panel findings, 

including updated circuit failure likelihood estimates for hot-short induced spurious operations. 

xvii 

PREFACE 

This report supplements previous work related to the effects of fire on cable failure modes and 

circuit response. 

In December 2002, EPRI published EPRI 1003326, Characterization of Fire-Induced Circuit 

Faults. This report documented the results of a comprehensive research and test effort 

undertaken jointly by EPRI and NEI to investigate, characterize, and quantify fire-induced circuit 

failures. This testing series also included monitoring cable electrical performance with a 

patented system developed and fielded by Sandia National Laboratories. The results of which 

are presented in NUREG/CR-6776, Cable Insulation Resistance Measurements Made During 

Cable Fire Tests, June 2002. 

In September 2003, NRC published NUREG/CR-6834, Circuit Analysis – Failure Mode and 

Likelihood Analysis, to address weaknesses in existing fire PRA circuit analysis methods. This 

report reviewed the existing data available on fire-induced cable failure and characterized that 

state of knowledge by conducting a formal failure modes and effects analysis (FMEA). 

In 2008, the NRC published NUREG/CR-6931, Volumes 1-3, Cable Response to Live Fire

(CAROLFIRE), documenting the results of fire-induced failure cable test results to support 

resolution of Regulatory Issue Summary 2004-03, Risk-Informed Approach for Post-Fire SafeShutdown Circuit Inspections, and to provide improvements to fire modeling in the area of cable 

response to fires. 

In 2012, the NRC published NUREG/CR-7100, Direct Current Electrical Shorting in Response to 

Exposure fire (DESIREE-Fire): Test results, documenting the results of fire-induced circuit 

damage to control cables and circuits powered from a direct current power source. 

In 2012, the NRC also published Draft NUREG-2128, Electrical Cable Test Results and 

Analysis during Fire Exposure (ELECTRA-FIRE). This report systematically evaluated the test 

data from the three major fire-induced circuit damage testing programs and provided graphical 

interpretations of various parametric effects on the likelihood of circuit failure modes and the 

associated hot short durations. 

This document does not constitute regulatory requirements. NRC-RES participation in 

this study does not constitute or imply regulatory approval of applications based upon 

this methodology.

 

xix 

CITATIONS 

This report was prepared by the following: 

Brookhaven National Laboratory 

P.O. Box 5000 

Upton, NY 11973 

Principal Investigators: 

M. Subudhi 

J. Higgins 

U.S. Nuclear Regulatory Commission, 

Office of Nuclear Regulatory Research (RES) 

Washington, D.C. 20555-0001 

Principal Investigators: 

H. Barrett 

R. Daley 

M. Salley 

G. Taylor 

Sandia National Laboratories 

P.O. Box 5800 

Albuquerque, NM 87185 

Principal Investigator: 

S. Nowlen 

Electric Power Research Institute (EPRI) 

3412 Hillview Avenue 

Palo Alto, CA 94303 

Principal Investigator: 

R. Wachowiak 

Ratchford Diversified Services, LLC (RDS) 

346 Rheem Blvd., Suite 207D 

Moraga, CA 94556 

Principal Investigator: 

A. Ratchford 

Kleinsorg Group Risk Services 

Division of Hughes Associates, Inc. 

900 Washington St., Suite 830 

Vancouver, WA 98660 

Principal Investigator: 

D. Funk 

Pyrolico Corporation 

1400 W. Amanda Lane 

Tempe, AZ 85284 

Principal Investigator: 

D. Crane 

PPL Susquehanna, LLC 

2 North 9th Street 

Allentown, PA 18101 

Principal Investigator: 

T. Gorman 

This report describes research sponsored jointly by the U.S. Nuclear Regulatory Commission’s 

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

(EPRI). 

The report is a corporate document that should be cited in the literature in the following manner: 

Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE), 

Volume 1: Phenomena Identification and Ranking Table (PIRT) Exercise for Nuclear Power 

Plant Fire-Induced Electrical Circuit Failure, U.S. Nuclear Regulatory Commission, Office of 

Nuclear Regulatory Research (RES), Rockville, MD, 2012, and Electric Power Research 

Institute (EPRI), Palo Alto, CA, NUREG/CR-7150, BNL-NUREG-98204-2012, and EPRI 

1026424. 

xxi 

ACKNOWLEDGEMENTS 

This project was completed using an expert panel, and staff at Brookhaven National Laboratory 

(BNL), Sandia National Laboratories (SNL), the U.S. Nuclear Regulatory Commission (NRC), 

and the Electric Power Research Institute (EPRI). The concept of the project was developed for 

the NRC by Mr. Mark Henry Salley, along with Mr. Ken Canavan and Mr. Richard Wachowiak of 

EPRI, who afforded management guidance and technical direction throughout the course of the 

project. Mr. Nick Melly and Ms. Tammie Pennywell of NRC, and Ms. Tara J. Olivier of SNL 

offered technical support in analyzing data from cable fire tests so that the panel could make 

sound judgments in ranking the influencing parameters. At BNL, Mr. Gerardo Martinez-Guridi 

verified the statistical significance of these parameters based on the panel’s ranking scores by 

the panel; Mr. Ken Sullivan provided insights on various aspects of this project based upon his 

experience in fire protection inspections and technical expertise; Mr. Bill Gunther reviewed and 

commented on the draft report, and Ms. Maryann Julian helped us prepare this manuscript. 

The authors thank the members of the expert panel, Harold Barrett, David Crane, Robert Daley, 

Daniel Funk, Thomas Gorman, Steven Nowlen, Andy Ratchford, and Gabriel Taylor for their 

dedication to this PIRT process. We are grateful for the support of panel members’ 

organizations who cooperatively shared some or all of the cost and time for their participation in 

this study. We thank the panel members for devoting much time to developing the technical 

discussions reported in this document. 

Additionally, we gratefully acknowledge the technical contributions of Steve Nowlen of SNL, a 

panel member, to various sections of this report. Last but not the least; we sincerely thank 

Robert Daley of NRC, also a panel member, for his support in transcribing the consensus 

opinions reached by the PIRT panel during the meetings into this report. Without his ability and 

electrical knowledge, the excellent quality of this report would not have been achieved. 

The authors acknowledge and thank members of the entire PIRT panel for providing review 

comments on the first draft of this report. Finally, our special thank to Ms. Avril Woodhead at 

BNL for technical editing the entire report. 

 

xxiii 

LIST OF ACRONYMS 

A or Amp Ampere 

ac Alternating Current 

AOV Air-Operated Valve 

ARM Armature 

AWG American Wire Gauge 

BNL Brookhaven National Laboratory 

CAROLFIRE Cable Response to Live Fire 

CFR Code of Federal Regulations 

CPE Chlorinated Polyethylene 

CPT Control Power Transformer 

CSPE Chloro-Sulfonated Polyethylene 

CT Current Transformer 

DESIREE-Fire Direct Current (dc) Electrical Shorting in Response to Exposure Fire 

DID Defense-in-depth 

dc Direct Current 

EPR Ethylene-Propylene Rubber 

EPRI Electric Power Research Institute 

EQ Equipment (or Environmental) Qualification 

Fire PRA Fire Probabilistic Risk Assessment 

FMEA Failure Mode and Effects Analysis 

FP Fire Protection 

FPP Fire Protection Program 

FR Fire-Rated 

GDC General Design Criteria 

GL Generic Letter 

HGL Hot Gas Layer 

HIF High Impedance Fault 

HS Hot Short 

I&C Instrumentation and Control 

IEEE Institute of Electrical and Electronics Engineers 

IR Insulation Resistance 

IRMS Insulation Resistance Measurement System 

kV Kilovolt 

LER Licensee Event Report 

LLC Limited Liability Company 

mA milli-Ampere 

MCC Motor Control Center 

MHIF Multiple High Impedance Fault 

MIL STD Military Standard 

MOU Memorandum of Understanding 

MOV Motor Operated Valve 

n/C ‘n’ Number of Conductor 

NC Normally Closed 

NEI Nuclear Energy Institute 

NFPA National Fire Protection Association 

NO Normally Open 
xxiv 

NPP Nuclear Power Plant 

NRC Nuclear Regulatory Commission 

NRR Office of Nuclear Reactor Regulation, NRC 

NSCA Nuclear Safety Capability Assessment 

PE Polyethylene 

PIRT Phenomena Identification and Ranking Table 

PORV Power-Operated Relief Valve 

PPL Pennsylvania Power and Light Corporation 

PRA Probabilistic Risk Assessment 

PT Pressure Transmitter 

PVC Poly-Vinyl Chloride 

R Resistive Impedance 

RDS Ratchford Diversified Services 

RES Office of Nuclear Regulatory Research, NRC 

RG Regulatory Guide 

SA Spurious Actuation 

SCDU Surrogate Circuit Diagnostic Unit 

SME Subject Matter Expert 

SNL Sandia National Laboratories 

SO Spurious Operation 

SOV Solenoid Operated Valve 

SR Silicone-Rubber 

SSCs Structures, Systems and Components 

SSD Safe-shutdown 

STD Standard 

SWGR Switchgear 

TCP Transmission Control Protocol 

TEF Tefzel 

TP Thermoplastic 

TR Technical Report 

TS Thermoset 

US United States 

V Volt 

Vac Voltage in AC 

Vdc Voltage in DC 

VA Voltage-Ampere 

EXCEL MICROSOFT ® EXCEL 

X Reactive Impedance 

XLPE Cross-Linked Polyethylene 

XLPO Cross-Linked Polyolefin
1-1 

1

INTRODUCTION 

1.1 Background 

The primary objectives of fire protection programs (FPPs) at U.S. nuclear power plants (NPPs) 

are to minimize the probability of the occurrence of fire, and its consequences. In meeting 

these objectives, the FPPs for operating NPPs are designed to provide reasonable assurance, 

through defense-in-depth (DID), that a fire will not prevent the operation of the necessary 

reactor safe-shutdown functions, and that should there be a fire, radioactive releases to the 

environment will be minimized. The goals of the DID concept for fire protection are to assure a 

high degree of fire safety in an NPP by preventing fires from starting, timely detecting those that 

do start, and promptly suppressing them. In addition, the DID concept affords protection for the 

structures, systems, and components (SSCs) important to safety, so that if a fire is not promptly 

extinguished, it will not prevent the safe-shutdown of the reactor. 

To achieve DID, each operating reactor has a Nuclear Regulatory Commission (NRC) - 

approved fire protection program that, when properly designed, implemented, and maintained, 

will satisfy Section 50.48, “Fire Protection,” of Title 10 of the Code of Federal Regulations, Part 

50 (10 CFR 50.48) (Ref. 1). This regulation requires that each holder of an operating license 

issued under 10 CFR 50, “Domestic Licensing of Production and Utilization Facilities” (Ref. 2) or 

10 CFR 52, “Licenses, Certifications, and Approval for Nuclear Power Plants” (Ref. 3), has a fire 

protection plan that satisfies General Design Criterion (GDC) 3, “Fire Protection,” of Appendix A 

to 10 CFR 50, (Ref. 4). The GDC 3 requires that SSCs important to safety are designed and 

strategically located to minimize the probability and the effect of fires and explosions. GDC 3 

also establishes the criteria for detecting fires, for firefighting systems, and for using 

noncombustible and heat-resistant materials throughout the plant. 

In recent years, the NRC encouraged utilities operating NPPs to use risk-informed, 

performance-based approaches as an alternative to the existing deterministic fire protection 

requirements (e.g., Appendix R to 10 CFR 50, “Fire Protection Program for Nuclear Power 

Facilities Operating Prior to January 1, 1979” (Ref. 5)). The NRC amended its fire protection 

requirements in 10 CFR 50.48 to permit existing reactor licensees to voluntarily adopt the fireprotection requirements detailed in the National Fire Protection Association’s (NFPA’s) Standard 

805, “Performance-Based Standard for Fire Protection for Light Water Reactor Electric 

Generating Plants, 2001 Edition” (Ref. 6). 

The Browns Ferry Fire of 1975 and confirmatory testing of representative circuits revealed that 

fire-induced failures of electrical circuit, leading to spurious equipment operations, can occur in 

the event of a fire. The type of circuit failure that may result from fire-induced cable damage, 

depends on many factors including the type of circuits (i.e., power, control, or instrument), the 

cable’s failure modes (i.e., open circuit, short to ground, or hot short), the specific circuit design 

and construction, and the location of the cable with respect to the site of the fire (e.g., cable’s 

orientation, raceway routing and fill, circuit grounding). Once a cable is damaged by a fire, 

faults in a circuit can result in the malfunction of a component or system, including hot shortinduced spurious operation of safety components, or false indication of instrumentation and 

control (I&C) circuits. 
INTRODUCTION 

1-2 

To better understand these phenomena, both the NRC’s Office of Nuclear Regulatory Research 

(RES) through Sandia National Laboratories (SNL), and the Electric Power Research Institute 

(EPRI), in collaboration with the Nuclear Energy Institute (NEI), conducted fire testing of various 

cables in controlled environments. These tests helped in determining the likelihood of such 

failures, and in understanding the effects of those parameters affecting the hot short 

phenomenon in electrical circuits during a fire. More specifically, in 2002, EPRI/NEI reported a 

cable-test program addressing the nature and characteristics of such fire-induced failures of 

alternating current (ac) control circuits, particularly the potential of hot shorts to initiate the 

spurious operation of equipment (Ref. 7). Subsequently, NRC sponsored the CAROLFIRE 

(CAble Response tO Live FIRE) test program to (1) offer an experimental basis for resolving the 

issues identified as “Bin 2 Items” in Regulatory Issue Summary 2004-03, “Risk-Informed 

Approach for Post-Fire Safe-Shutdown Circuit Inspections” (Ref. 8); (2) improve fire-modeling 

tools to aid in predicting cable damage under fire conditions; and, (3) complement the EPRI/NEI 

test results for AC control circuits. In 2008, NRC/SNL published the results of this CAROLFIRE 

test program on electrical performance and fire-induced cable failure (Ref. 9). NRC also 

sponsored tests under the DESIREE-Fire (Direct Current Electrical Shorting In REsponse to 

Exposure Fire) effort to assess cable failure modes and effects on the behavior of direct current 

(dc) control circuits. In 2010, a draft form of the findings from this program became available, 

and in 2012, NRC/SNL detailed the outcomes of the electrical performance and fire-induced 

cable-failure tests (Ref. 10). This project was sponsored by the NRC-RES with support from 

EPRI under a collaborative research agreement termed in the NRC-RES/EPRI Memorandum of 

Understanding (MOU). 

In May 2002, EPRI also published a technical report (EPRI Technical Report 1006961, 

“Spurious Operation of Electrical Circuits Due to Cable Fires – Results of an Expert Elicitation”) 

detailing the results of an expert elicitation process on the EPRI/NEI cable-fire test results to 

develop best-estimate conditional probabilities for spurious operation of devices in electrical 

circuits due to fire-induced damage to electrical cables (Ref. 11). These results were 

incorporated into the current state-of-the-art method for conducting Fire Probabilistic Risk 

Assessments (Fire PRAs) documented in NUREG/CR-6850, “EPRI/NRC-RES Fire PRA 

Methodology for Nuclear Power Facilities” (Ref. 12). In addition, findings from the EPRI/NEI 

and CAROLFIRE tests were included in the industry’s deterministic guidance document 

NEI 00-01, Rev. 2, “Guidance for Post Fire Safe-shutdown Circuit Analysis,” (Ref. 13) for 

evaluating fire-induced circuit failures. 

1.2 Objective 

In 2010, under the auspices of the NRC-RES and supported by EPRI through an NRC-RES/ 

EPRI MOU, Brookhaven National Laboratory (BNL) conducted a Phenomena Identification and 

Ranking Table (PIRT) study of fire-induced electrical-circuit failures. This effort used all the 

cable test findings from EPRI/NEI and NRC/SNL, along with eliciting expert judgment as a basis 

for ranking various influencing parameters on hot short-induced spurious operational 

phenomena caused by a fire. Therefore, factors leading to influencing cable damage by a fire 

were outside the scope of this PIRT panel. This PIRT identified the influencing parameters, 

assuming that the fire damaged a cable that can affect the failure modes of induced electrical 

circuit faults. Thereafter, they ranked the current knowledge relative to each identified 

phenomena. Using these PIRT results, BNL will assemble a PRA panel to conduct a separate 

follow-on expert elicitation of these occurrences to assess their conditional probability (or 

likelihood) of failure after fire-induced damage to the cable This second PRA effort will revisit 

and complement the expert elicitation work undertaken by EPRI in 2002 (Ref. 11), but with the 
INTRODUCTION

1-3

addition of the data from the CAROLFIRE and DESIREE-Fire testing. The electrical expert 

PIRT panel and the Expert Elicitation PRA Panel4

 will deliver both qualitative and quantitatively 

important data for use in Fire PRAs in applying NFPA 805 (Ref. 6), and possibly also for 

incorporating into deterministic post-fire safe-shutdown circuit analyses. 

Volume 1 of this NUREG/CR report discusses the PIRT process and the results obtained from 

the PIRT panel in identifying the influencing factors and ranking their importance to the hot short 

phenomenon in the failure of electrical circuits leading to spurious operation of devices after the 

cable is damaged by fire. It also identifies the PIRT panel’s prioritization of the future research 

needed to resolve technical challenges considered important in characterizing the fire-induced 

hot short phenomenon and establishing the risk significance associated with certain equipment, 

conditions or configurations. Volume 2 of this NUREG/CR details the findings from the PRA 

panel; they will give the conditional probabilities for use in Fire PRAs, particularly on the 

spurious operation of devices due to hot short mode of failure of control circuits following fire 

damage to the associated cables. 

1.3 The Approach 

The expert elicitation process conducted in this PIRT study is based on methods employed by 

other PIRT panels that the NRC used in many areas (Refs. 14 & 15), where no tests or 

analyses could address the technical issues with the desired level of certainty. The PIRT 

process systematically obtains information from experts about the concerns that involve 

generating lists (tables) of phenomena, where “phenomena” also can refer to a particular 

reactor condition, a physical- or engineering-approximation, a safety-related component or 

parameter, the importance of parameters on the likelihood of spurious operation of equipment, 

or anything else that might influence the chosen figures-of-merit or criteria. The process often 

entails ranking of these observable events using scoring criteria, consensus, or a combination of 

them to determine what is the most important. That ranking, as well as the information 

explaining and justifying it, allows the NRC to prioritize research needs for a safety issue, or to 

support some decision-making process. Thus, the PIRT methodology, including the expert 

panel, highlights the phenomena that dominate an issue, while identifying all plausible effects to 

demonstrate completeness. 

Each PIRT application is unique in some respect; the electrical expert PIRT is no exception. 

This PIRT investigates the fire-induced spurious operation of plant components, encompassing 

AC and DC circuit types. The PIRT focus falls into three specific electrical circuit types, namely, 

power, control, and instrument, with the primary focus on control circuits (e.g., 120 VAC and 125 

Vdc), because fire-induced mal-operation of these types of circuits is considered to pose a 

higher risk to plant safety in comparison to the other circuit types. Accordingly, the majority of 

available industry and NRC test data was related to low-voltage control circuits. Due to the 

limited amount of test data available for instrument circuits, a complete parametric treatment of 

this circuit type was not possible. Available failure modes for power circuits are well 

understood, with the exception of a few unique cases. For certain types of power circuits (for 

example, three-phase power cables), specific industry testing was not available; therefore, the 

PIRT panel developed technical recommendations based on their expert judgment involving 

engineering principles and physical configurations for power cables and power-cable 

 

4

 In this report, hereafter the “PIRT panel” refers to the “Electrical Expert PIRT Panel” and the “PRA 

panel” refers to the “Expert Elicitation PRA Panel.” 
INTRODUCTION 

1-4 

installations. In other instances, such as open circuits in current transformer (CT) secondary 

circuits, the PIRT panel developed recommendations based upon available open circuit test 

data, manufacturers’ input, operating experience (nuclear and non-nuclear), and expert 

judgment. 

The evaluation of circuit impacts for each electrical circuit type assumed that the cable(s) of 

concern was damaged by fire and fire damage has resulted in loss of cable functionality. In 

other words, the panel did not focus on parameters that influence the likelihood of cable 

damage from fire effects, such as ignition, fire growth, fire intensity, nor the likelihood of a fire 

occurring. The fire-induced hot short mode of failure entailing the spurious operation of 

equipment of interest is influenced by the following three elements: 

1. Fire-induced hot shorts: Individual conductors of the same or different cables that come in 

contact with each other and that may result in an impressed voltage or current on the circuit 

being analyzed (definition per Regulatory Guide 1.189, “Fire Protection for Nuclear Power 

Plants” (Ref. 16)). 

2. Hot short-induced spurious operations: A circuit-fault mode wherein an operational mode of 

the circuit is initiated (in full or in part) due to failure(s) in one or more components (including 

the cables) of the circuit5

; examples are a pump spuriously starting, or the spurious 

repositioning of a valve. 

3. Duration of the spurious operation: Length of time that a hot short-induced spurious 

operation condition exists. 

The following are the two figures-of-merit associated with these elements: 

1. FIGURE-OF-MERIT 1: Spurious Operation6

: After fire-induced cable damage has 

occurred to an appropriate conductor in an electrical circuit resulting in a hot short(s), a 

spurious operation(s) of the component occurs driven by the same electrical circuit. Note 

that an appropriate conductor in an electrical circuit is one with the potential to cause an 

inadvertent change of state of the component or device. 

2. FIGURE-OF-MERIT 2: Duration of Spurious Operation: Duration is the amount of time 

during which the fire-induced hot short transfers voltage or current to an appropriate 

conductor of a specific component or device that then can cause the component to move or 

travel in the undesired direction. 

The duration evaluated in this report is the length of time that the impressed voltage or 

current on the circuit can cause a spurious operation. It can be affected by the grounding of 

the conductor or the opening of a fuse. In practice, the length of the spurious operation 

would take into account the specific circuit-design of the component and whether this design 

resulted in a “sealed-in” or “latched” condition once the circuit was energized to move in the 

undesired direction. For both conditions, clearing or removing the hot short (i.e., de-

 

5

 The PIRT panel defined this based on the definition of spurious actuation in RG 1.189 (Ref. 16), “The 

undesired operation of equipment, considering all possible functional states, resulting from a fire that 

could affect the capability to achieve and maintain safe-shutdown.” 

6

 The PIRT panel used the term “spurious actuation” during their early deliberations and later changed to 

the term “spurious operation”. Both terms were used interchangeably. 
INTRODUCTION

1-5

energizing the circuit) does not reverse the position of the component to the pre-hot short 

condition. 

In addition to reviewing and evaluating spurious operations and their duration for control circuits, 

the PIRT panel considered other fire-induced circuit failures that are included in this report, 

some of which are listed below. 

• Power cabling consequential hot shorts (AC and DC) 

• Open circuit secondary of current transformers (CTs) 

• Multiple high impedance faults – MHIFs (AC and DC) 

• Common enclosure and common power supply concerns 

Although not all these topics are directly associated with spurious operations of a device or 

component they are postulated failure modes with which both industry and regulators have 

historically struggled, and that the PIRT panel believed could be resolved during the PIRT 

process. Sources of information for the PIRT panel primarily included, but were not limited to, 

the findings from the EPRI/NEI and the NRC/SNL tests of both AC- and DC-circuits. In addition, 

the overall conclusions of this PIRT befitted from expert knowledge about the plant-specific 

cable and circuit configurations, publically accessible utility test information on armored cables 

(e.g., Refs. 17 & 18), the findings from fire protection inspections and Fire PRAs. 

1.4 The PIRT Panel 

The staff at NRC/RES and the EPRI identified members of the electrical expert PIRT panel. 

Those selected possess extensive expertise in electrical circuits, post-fire safe-shutdown circuit 

analysis, and overall knowledge of post-fire safe-shutdown SSCs. The panel representation 

was balanced evenly among the regulator (i.e., four members from the NRC) and the nuclear 

power industry (i.e., four members from EPRI). 

Brief resumes of the panel members listed below, along with their affiliations, are given in 

Appendix A. 

Harold Barrett, U.S. Nuclear Regulatory Commission (NRC) 

 David Crane, Pyrolico Corporation 

Robert Daley, U.S. Nuclear Regulatory Commission (NRC) 

 Daniel Funk, Kleinsorg Group Risk Services (KGRS) 

 Thomas Gorman, PPL Susquehanna, LLC 

Steven Nowlen, Sandia National Laboratories (SNL) 

Andy Ratchford, Ratchford Diversified Services (RDS), LLC 

 Gabriel Taylor, U.S. Nuclear Regulatory Commission (NRC) 

 

BNL staff provided technical support to the PIRT panel. Mark Henry Salley of NRC and Rick 

Wachowiak of EPRI also attended and offered general assistance at the panel meetings and 

oversight. Finally, Mano Subudhi or Jim Higgins of BNL served as the moderator of panel 

meetings held at the NRC/RES Church Street Office in Rockville, Maryland. 
INTRODUCTION 

1-6 

1.5 Report Organization 

Section 2 gives an overview of the deliberations of the electrical expert PIRT panel on electrical 

circuits. This section also presents the definitions and process used by the panel in developing 

the scenarios and the influencing parameters for the control circuits. The panel’s scoring 

process and technical challenges also are discussed. Section 3 provides the findings of the 

PIRT panel’s evaluation findings for control circuits and discusses their conclusions. Section 4 

summarizes the panel’s technical positions about several issues in analyzing circuits associated 

with control and power circuits. Section 5 describes their recommendations for future testing to 

better understand the hot short-induced spurious operations in instrumentation and control (I&C) 

circuits. Section 6 details the panel’s technical positions on various problems related to safeshutdown circuit analysis. The research priorities identified via the findings from this PIRT 

process are summarized in Section 7. Finally, Section 8 gives the summary discussions and 

conclusions by the PIRT panel. 

Appendix A includes the resumes of PIRT panel members and the moderators. Appendix B 

presents the MICROSOFT ® EXCEL scoring sheets on ranking the influencing parameters on 

the hot short-induced spurious operation of control circuit devices. Appendix C describes the 

electrical control circuit scenarios selected by the PIRT panel for their deliberations and for the 

PRA panel’s consideration in calculating the best-estimate conditional failure probabilities. 

Finally, Appendix D includes a number of viewgraphs that were shown to the panel at the first 

PIRT meeting. 
2-1 

2

OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL 

ACTIVITIES 

The electrical expert PIRT panel convened six separate times, in 21⁄2-day meetings at the NRC’s 

RES Office in Rockville, Maryland. These meetings were held from November 2010 through 

December 2011. 

In the first meeting, the results of the EPRI/NEI (Ref. 7) and NRC/SNL (Refs. 9 &10) cable-fire 

test programs were presented to the panel members (Appendix D), along with the findings from 

other publically available results from industry tests (Refs. 17 and 18). They identified that hot 

short-induced spurious operations of control circuit device(s) or associated components could 

be induced by fires damaging the cables in nuclear power plants. One of the primary objectives 

of these test programs was to better understand these phenomena of induced spurious 

operation so that this knowledge could be used to improve both deterministic fire-safety 

protection and fire probabilistic safety assessments (Fire PRAs). Using these test results, the 

following were the specific objectives of this overall project: 

• to identify the parameters of the phenomena that lead to fire-induced hot shorts causing the 

spurious operation of equipment important to safety; 

• to rank the influencing parameters affecting fire-induced hot shorts, and subsequently, to 

determine the duration of such induced operations, and to assess the current level of 

knowledge for each of the identified phenomena; and, 

• to develop best-estimates for the conditional probability (or likelihood) of these phenomena 

representing the current NPP design and cable configurations, and for the durations of those 

phenomena where the length of its persistence could affect the circuit function of the 

component or device being considered. 

To achieve these objectives, two independent panels of experts were formed: an “Electrical 

Expert PIRT Panel” and an “Expert Elicitation PRA Panel.” Using the PIRT process, the former 

identified and ranked various influencing parameters that could affect the hot short-induced 

circuit failures. Their findings will be used by the latter, the “Expert Elicitation PRA Panel” to 

develop the best-estimate conditional probabilities for using in Fire PRA applications; their 

findings are not documented in this report, but are the subject of Volume 2 of this NUREG/CR 

report. 

The first question posed to the electrical expert PIRT panel was “Under what circuit and cable 

configurations could a fire resulting in cable damage cause hot short-induced spurious 

operations of electrical or electronic circuits?” The second question, posed to the Expert 

Elicitation PRA Panel, was “What is the probability of such spurious operations, given that fireinduced cable damage has occurred?” Volume 1 of this NUREG/CR report addresses the 

electrical expert PIRT panel’s conclusions on the first question covering the first two objectives 

above. The second question that deals with the third objective above will be addressed by the 

Expert Elicitation PRA Panel who will take into account these results and conclusions of the 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-2 

electrical expert PIRT panel to accomplish the third objective. The PRA panel will calculate the 

best-estimate conditional probabilities of the likelihood of hot short-induced spurious operation 

given cable damage due to a fire, and their results are documented in Volume 2 of this 

NUREG/CR report. These probability estimates could be used to revise, directly replace, or 

create new probabilities for Table 10-1 through Table 10-5, entitled “Failure Mode Probability 

Estimates Given Cable Damage,” of NUREG/CR-6850 (Ref. 12). 

The electrical PIRT process can be described in terms of the nine steps as depicted in 

Figure 2-1. The general meaning and application of these steps are detailed below7

.

Step 1: Selecting The Electrical Expert PIRT Panel: As discussed in Section 1.4 of this report, 

eight members comprised the electrical expert PIRT panel. They represented a range of areas 

of expertise and background, i.e., researchers, consultants, regulators, and plant inspectors, 

along with fire protection and electrical engineers currently working in practical field applications. 

Factors considered in selecting the panel members included their expertise, availability and 

willingness to serve, absence of financial conflicts of interest, impartiality, and prior experience 

working as subject matter experts (SMEs) in related committees, subcommittees, and advisory 

panels. 

Step 2: Defining the Impact and Terminology of Cable Failure: The PIRT panel initially 

established three primary terms and associated definitions for evaluating fire-induced circuit 

failures, i.e., fire-induced hot shorts, spurious operations, and duration of the hot short and 

spurious operation. However, later in the process, the PIRT panel determined that it would be 

difficult to characterize the first two separately from the kind of fire-test results available to them. 

Additionally, the PIRT panel concluded that identifying hot shorts independently from spurious 

operation was unnecessary; since hot short-induced spurious operations better define the 

failure event that must be evaluated. Also, combining the terms would better translate into Fire 

PRA applications that utilize the estimates, “...probability of spurious actuation given cable 

damage” in Tables 10-1 through 10-5 of NUREG/CR-6850. Therefore, the PIRT panel 

ultimately combined the first two terms (fire-induced hot short and spurious operation) to one 

(hot short-induced spurious operation). Thereafter, the panel established two figures-of-merit: 

1) Spurious Operation; and, 2) Duration of Spurious Operation, defined in Section 1.3 of this 

report. 

We note that the PIRT panel ultimately limited the term “spurious operation” to the operation of 

a component as presented in Section 1.3 of this report. Therefore, a spurious operation was 

defined by a change in the operating state or the repositioning of a piece of equipment due to a 

hot short; this definition thereby excluded control circuit activations, such as false light 

indications of equipment status. 

 

 

7

 The parameter identification and ranking process used by the PIRT panel was performed for grounded 

AC and ungrounded DC control circuits, since these control circuit types were believed to be the most 

common types used in US Nuclear Power Plants. Later on in the process, however, ungrounded AC 

control circuits powered from a control power transformer (CPT) and ungrounded AC control circuits from 

an AC distribution system were included in this report addressing control circuit configurations. The 

inclusion of these latter two types of control circuits was done for completeness, since some Nuclear 

Power Plants may use these types of control circuits. Although these latter two types of control circuit 

configurations were included in this report, the ranking tables (in Section 3 and Appendix B) were never 

updated to include these control circuit types. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-3

Figure 2-1. Flowchart for Electrical PIRT Expert Panel Activities 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-4 

This omission of indicating lights was based on two primary functional differences between an 

indicating light and an electro-mechanical device. The first is that, even when fully energized, 

indicating lights will draw a lower total energy (e.g., watts) than most electro-mechanical 

components. Indicating lights generally are designed to draw current of about 0.1 Ampere (A) 

or less; electro-mechanical devices may draw a wide range of amperages, usually greater than 

0.1A. The second difference is that indicating lamps generally have no true lower pickup 

threshold as do most electro-mechanical devices; that is, before an electro-mechanical device 

will operate, the minimum pickup voltage and current must be exceeded. In contrast, an 

indicating lamp may “glow” even when partially energized, for example, by a relatively low 

quality (high impedance) electrical short. By comparison, an electro-mechanical component 

requires a higher quality (lower impedance) short to transmit sufficient power to operate the 

component. 

During Step 2 of the PIRT activities, several additional terms were defined. These frequently 

used terms during the PIRT panel discussions are defined in Section 2.1. 

Step 3: Identifying Influencing Parameters on Hot short-Induced Spurious Operation: The 

PIRT panel identified parameters that could affect the hot short-induced spurious operation of 

safe-shutdown equipment from the following four broad groups: physical properties and 

configuration of cables; routing of cables in raceways; electrical function of the circuit; and, fireexposure conditions (Ref. 19). These items are detailed in Section 2.3.1 of this report. Based 

on these parameters, the PIRT panel developed MICROSOFT ® EXCEL worksheets for scoring 

by individual panel members for all three circuit types, namely, power, control, and instrument. 

However, later the PIRT panel found that there was insufficient test data for power and 

instrument circuits. Accordingly, the PIRT panel limited the PIRT evaluation process to control 

circuits. 

Step 4: Evaluating Test Data: While evaluating the available data from the EPRI/NEI and 

NRC/SNL tests, the PIRT panel found that the form of the test data was not in a form suitable to 

assure their reaching a sound technical judgment about the influence of certain parameters on 

hot short-induced spurious operations of control circuits. Consequently, under the oversight of 

the PIRT panel, all test data was analyzed, parsed, and summarized in a more useful format. 

The results of this work are documented in draft NUREG-2128 (Ref. 20), as discussed in 

Section 2.2 of this report. 

Step 5: Determining Evaluation Methodology for Control, Power, and Instrument Circuits: As 

discussed in Step 3, because of the dearth of test data for instrument circuits, a complete 

parametric treatment of this circuit type was not possible. Available failure modes for power 

circuits are well understood, with the exception of a few unique cases. For certain types of 

power circuits (for example, three-phase power cables), specific industry testing was not 

available; therefore, the PIRT panel developed technical recommendations based on their 

expert judgment involving engineering principles and physical configurations for power cables 

and power cable installations. 

Step 6: Developing Technical Positions on Power and Instrument Circuits: For power circuits, 

the PIRT panel produced a consensus technical position about the credibility of certain fireinduced failure modes. For instrument circuits, the PIRT panel again proffered technical 

positions on credible failure modes and issues of concern. Additionally, since certain modes of 

instrument circuit failure could impact plant safety in a fire event, the PIRT panel recommended 

undertaking testing for certain instrumentation and control circuit-configurations as discussed in 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-5

Section 2.3.2. The resulting technical positions for power circuits are detailed in Section 4, and 

for instrumentation and control (I&C) circuits, in Section 5 of this report. 

Step 7: Ranking Influence Parameter: Steps 7 through 9 specifically pertain to control circuits. 

Based upon the information obtained in Step 4, “Evaluating Test Data,” the PIRT panel used the 

MICROSOFT ® EXCEL worksheets for AC and DC control circuits, and scored the effect of each 

influencing parameter on hot short-induced spurious operations, as defined in the figures-ofmerit. Thus, the PIRT panel scored the hot shorts for intra- and inter-cable shorting, including 

multiple ground-plane interactions for ungrounded DC circuits. The PIRT panel also included in 

the scoring sheets the effect on the duration of hot short. Section 2.4 discusses how the panel 

scored the impact of an influencing parameter on the intra- and inter-cable hot short-induced 

spurious operation and its duration. At first, the PIRT panel ranked these sheets independently 

and discussed their differences in subsequent PIRT meetings or in teleconferences. However, 

toward the end of the process, the panel members had reconciled most differences in individual 

rankings; hence, they decided to finalize the rankings based upon consensus among the panel 

members rather than relying on individual rankings. The final ranking of all influencing 

parameters are based on test data statistics given in draft NUREG-2128 (Ref. 20), the PIRT 

panel’s operating experience, and their cumulative knowledge of phenomenological behavior 

under high thermal conditions, as is discussed in Sections 3.1 and 3.2. 

Step 8: Developing Control Circuit Configuration Scenarios: Based upon the scoring, the PIRT 

panel identified high importance parameters and included them when defining the control 

circuits that should be considered in analyzing the circuits. Parameters whose influences on the 

figures-of-merit ranked low to medium were, for the most part, not considered in defining the 

control circuits requiring circuit analysis for spurious operations. The panel employed those 

parameters with a significant influence ranking to identify and develop various circuit 

configuration scenarios, as described in Section 3.3. 

Step 9: Developing PIRT Scenarios for Each Control Circuit Configuration of Concern and 

Transferring to PRA Expert Panel for Estimating Conditional Probabilities: The PIRT panel 

based the final PIRT ranking tables upon different scenarios of control circuit configurations. 

These tables were provided to the expert elicitation PRA Panel to use in estimating the 

conditional probabilities of cable spurious operations after cable damage. Principally, using 

mostly the high importance influencing parameters, each case includes a base case and 

additional special cases representing the actual plant’s circuit design and configuration. This is 

fully described in Section 3.4. Appendix C gives the electrical control circuits representing these 

special cases for use by the expert elicitation PRA panel. 

2.1 Terminology Used by PIRT Panel 

2.1.1 Hot Short-Induced Spurious Operation 

Based on reviewing the results of the EPRI/NEI’s and NRC/SNL’s cable tests on control cables, 

and applying their technical expertise, the electrical expert PIRT panel considered that taking 

two steps would address the likelihood of the spurious operation of electrical equipment arising 

from a fire-induced hot short failure-mode : 1) Determine the likelihood of a hot short between 

the target and source conductors located in the same or different cable(s); and, 2) Assess the 

likelihood of a spurious operation of a device or equipment after the hot short has occurred. Not 

all hot shorts potentially can cause spurious operations; hence, the PIRT panel originally 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-6 

believed that splitting the hot shorts and the hot short-induced spurious operations into two 

phases would be the best approach to qualitatively assessing the parameters that influence 

either one of the failure modes. However, later they considered that this approach was not 

feasible, and so they reduced the figures-of-merit to the two presented in Section 1.3, i.e., 

spurious operation, and its duration. 

The PIRT panel determined a hot short to be a subset of conductor-to-conductor shorts (i.e., a 

low-impedance electrical contact not involving an external ground) with one conductor being 

initially energized, and at least the other conductor being neither energized nor grounded. 

Thereupon, the PIRT panel categorized the spurious operations resulting from intra-cable hot 

short(s) (within a multiconductor cable) between conductors, and inter-cable hot shorts 

(between two separate cables) due to direct conductor-to-conductor contact. In addition, the 

panel separately evaluated those inter-cable hot short-induced spurious operations caused by 

multiple conductors shorting to a surrogate ground path, such as a raceway (i.e., other than 

direct conductor contacts). Also, the duration and their energy level (quality) of the hot shorts 

may play a major role in the spurious operation of an electrical device or equipment. The 

influencing parameters modulating this phenomenon of spurious operation are associated with 

the failure of a cable due to fire (i.e., a breakdown in the electrical insulation of the conductor in 

a cable, such that it no longer can perform its intended design function of maintaining the 

electrical integrity and continuity of its conductors), the routing configuration, and the 

conductor’s configuration in the circuit of concern. 

Although the findings from both the EPRI/NEI and the NRC/SNL tests are not applicable directly 

to the functional response of the power circuits, certain generic characteristics of the failure of 

cable insulation due to fire effects are independent of the circuit’s application (e.g., a thermoset 

(TS) cable is more resistant to fire damage than is a thermoplastic (TP) cable). For power and 

control circuits, partial degradation of the cable’s insulation (at the level of abnormal leakage 

current) may not cause failure in the circuit. For these circuits to trigger a complete failure, the 

value of the insulation’s resistance must be below a certain threshold (typically at, or below 

1,000 ohms based on the fact that CAROLFIRE test results were analyzed for 1,000 ohms). 

However, this is not valid for instrument circuits, since they rely on low-level electrical signals 

that represent various process- and diagnostic-parameters. A small amount of leakage current 

can impair the instrument circuit’s performance measurably in a manner that has functional 

implications. Therefore, low-level degradation of the insulation should be considered in 

assessing an instrument’s performance (e.g., 30,000 ohms insulation resistance corresponds to 

a 5% signal error in a standard 4-20 mA instrument loop) (Ref. 7). 

The likelihood of conductor-to-conductor shorts varies with the cable’s construction and physical 

configuration. Some parameters that the panel considered important in influencing the 

likelihood of conductor-to-conductor shorts within a cable (intra-cable shorts) include 

• the number of conductors, 

• conductor’s size, 

• insulating materials of the conductor and jacket , 

• armor or ground/shield conductor, 

• cable raceway and routing configuration, and, 

• raceway fill. 

 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-7

Some other parameters affecting the hot short may include the number of source and target 

conductors and their proximity to each other, along with the relative location of the ground 

plane. 

Additionally, factors directly related to the type of electrical control circuit also may impact the 

likelihood of a spurious operation actually adversely affecting safe-shutdown. For example, a 

hot short to a solenoid must be maintained energized to keep its controlled device (e.g., 

solenoid operated valve (SOV)) in an undesired or spurious position. If the hot short 

subsequently changes to a different failure mode, such as a short to ground or open circuit, the 

solenoid will be de-energized, so returning its controlled device to its normal (de-energized) 

state. This scenario is not the case for control circuits that have a seal-in or latching feature, for 

example, pumps and some motor-operated-valve (MOV) circuits that require only a hot short of 

sufficient duration to actuate the latching circuit Components such as pumps and MOVs only 

require a hot short/spurious operation of a limited duration to cause a change of position for the 

component, e.g. pump start or valve open. Even if the hot short changes state, i.e. short-toground or open circuit, after this limited duration, the position of the pump or valve will not be 

altered. Other circuit-design factors that may also influence the likelihood of spurious 

operations that can impact safe-shutdown are the grounding scheme (e.g., ungrounded DC 

versus grounded AC circuits), pick-up and drop-out current and voltage levels, fuse ratings, and 

device connections, such as motor, breaker, switchgear, solenoids, and relays. 

2.1.2 Definitions 

The panel decided to define the following terms that were used throughout the PIRT 

discussions: 

Cable – A conductor with insulation or a stranded conductor with or without insulation or other 

coverings (single-conductor cable) or a combination of conductors insulated from one another 

(multiple-conductor cable). (Ref. 22) 

Cable Armor – A metallic element or envelope inserted in or around a cable sheath to provide 

mechanical protection against rodents, severe installation conditions, etc. (Ref. 22) 

Cable Fire Damage – Cable fire damage (or failure) implies that the cable is no longer able to 

perform its intended function which is to maintain the electrical integrity and electrical continuity 

of the associated circuit sufficient to ensure proper operation of the circuit. For a cable to 

perform its intended function, each individual conductor within the cable must maintain both 

electrical integrity and continuity. Hence, cable failure implies that one or more of the cable 

conductors have lost electrical integrity or electrical continuity. (Ref. 19) 

Cable Functional Damage – Functional damage of the cable is defined to be one of the 

following states: Short to ground (e.g., raceway, ground /drain conductor, metal foil shield wrap, 

or armored sheath), short to another cable co-located in the same raceway (inter-cable short), 

short to another conductor within the same cable (intra-cable short), or an open circuit (e.g., a 

fire-induced break in a conductor resulting in the loss of circuit continuity, fuse blow, or breaker 

trip), or short to another cable via a conductive ground plane (inter-cable, referred to as a 

ground equivalent hot short), such that the cable cannot perform its design function. (PIRT 

panel) 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-8 

Circuit – A conductor or system of conductors through which an electric current is intended to 

flow. (Ref. 22) 

Hot Short – Individual conductors of the same or different cables that come in contact with each 

other and that may result in an impressed voltage or current on the circuit being analyzed 

(definition per Regulatory Guide 1.189, “Fire Protection for Nuclear Power Plants” (Ref. 16)). 

This mode of failure can be considered as a transient phenomenon associated with cable 

damage between an energized conductor (the source) and another conductor (the target) that 

may or may not be energized for the following cable configurations: 

• Intra-cable Hot Short, conductor-to-conductor shorting within the same cable; (see 

Figure 3-2), 

• Inter-cable Hot Short, conductor-to-conductor shorting between co-located cables in the 

same raceway; (see Figure 3-3), or 

• Inter-cable Ground Fault Equivalent Hot Short, the inter-cable phenomenon that 

includes a source cable co-located with the target cable in the same raceway or different 

raceways wherein the interaction takes place via multiple ground fault equivalent hot 

shorts rather than direct conductor-to-conductor shorting; (see Figure 3-4). 

Open Circuit – A fire-induced break in a conductor resulting in a loss of circuit continuity. (Ref. 

13) 

Spurious Operation – A circuit fault mode wherein an operational mode of the circuit is initiated 

(in full or in part) due to failure(s) in one or more of the circuit’s components (including cables). 

For example, such modes include a pump (starting or stopping) or a valve spuriously 

repositioning. 

Source Cable or Source Conductor – A cable or conductor that is energized (e.g., before the 

fire) and therefore, can produce a hot short should it make contact with a target conductor(s). 

Target Cable or Target Conductor – A cable or conductor (initially energized or not) that, if 

energized by contact (directly or indirectly) with an appropriate source cable or conductor, would 

generate a hot short, and possibly, a spurious operation if the target cable or conductor was 

associated with equipment or device(s) that would operate spuriously. 

2.1.3 Technical Positions by the PIRT Panel 

The final disposition of the electrical expert PIRT panel’s evaluation on some specific issues or 

scenarios was characterized as “incredible” or “implausible.” For the purpose of the PIRT 

panel’s disposition of an issue, the following define these terms: 

Incredible – The term “incredible” used in conjunction with the phenomenon of a fire-induced 

circuit failure, signifies the PIRT panel’s conclusion that the event will not occur. In these cases, 

the PIRT panel could find no evidence of the phenomenon ever occurring, and there were no 

credible engineering principles or technical argument to support its happening during a fire. Any 

likelihood value assigned to these types of phenomena would have little meaning. 

 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-9

Implausible – The term “implausible” when used in conjunction with a fire-induced circuit failure 

phenomenon, supports the PIRT panel’s conclusion that the happening, while theoretically 

possible, would require the convergence of a combination of factors that are so unlikely to occur 

that the likelihood of the phenomenon can be considered statistically insignificant. In these 

cases, the PIRT panel could find no evidence of the phenomenon ever occurring neither in 

operating experience nor during a fire test. Any likelihood value assigned to these types of 

phenomena would have little meaning. 

2.1.4 NRC Regulatory Issue Summary (RIS) 2004-03 – “Risk-Informed 

Approach for Post-Fire Safe-Shutdown Circuit Inspections” 

This subsection is included to define the terminology “BIN 2” items that the panel frequently 

used during their deliberation process throughout their meetings. 

Based on the results of the industry’s (EPRI/ NEI’s) cable-fire tests, modes of fire-induced circuit 

failure that could cause equipment to spuriously operate were defined and “binned” during a 

facilitated workshop conducted by the NRC in February 2003. Specifically, the failure modes 

binned are as follows: 

BIN 1 - Items to Be Considered During Inspection (Circuits most likely to fail) includes spurious 

operation failure modes that were to be included in the scope of fire protection (FP) inspections, 

primarily because they are (a) based on the results of industry ‘s cable-fire testing (EPRI/NEI 

tests) that determined they were “likely” (e.g. conductor-to conductor faults within a single multiconductor cable (intra-cable faults);” or (b) had a potentially high consequences (e.g., High Low 

Pressure Interface Valve circuits) 

BIN 2 - Items Deferred Pending Additional Research includes cable and circuit faulting 

configurations for which the experimental evidence then was determined to be inconclusive. 

However, recent NRC/SNL tests on AC circuits (CAROLFIRE) and DC circuits (DESIREE-Fire) 

address most of these issues associated with the Bin 2 items. 

BIN 3 – Configurations That Are Unlikely or Least Likely to Cause Failure and included in the 

first version of the RIS 2004-03 and circuit configurations that are unlikely to cause failure and 

do not need to be considered during future FP inspections. 

2.1.5 Associated Circuits 

Those safety-related and nonsafety-related Class 1E and non-Class 1E cables the physical 

separation of which is less than that specified in Section III.G.2 of Appendix R to 10 CFR Part 

50 and have one of the following (Ref. 23, Enclosure 2): 

• Common Power Source – A power source (e.g., switchgears, motor control centers (MCCs), 

fuse and circuit breaker panels) that is shared with the shutdown equipment (redundant or 

alternative) and is not electrically protected from the circuit of concern by coordinated 

breakers, fuses, or similar devices. 

• Common Enclosure – An enclosure (e.g., raceway, panel, or junction box) that is shared 

with the shutdown cables (redundant or alternative) and (1) is not electrically protected by 

circuit breakers, fuses, or similar devices, or (2) will allow propagation of the fire into the 

common enclosure. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-10 

An associated circuit of concern for post-fire safe-shutdown may include any circuit or cable that 

is not needed to support the operation of the required shutdown equipment (i.e., a nonessential 

circuit), but could adversely affect the plant’s ability to achieve and maintain safe-shutdown 

conditions should it be damaged by fire. 

2.2 Evaluation of Cable Fire Test Results 

2.2.1 Categories of Information Available for Cable Fire Tests 

The PIRT panel broke down into three categories the physical configurations tested during the 

industry- and NRC-sponsored test programs, based on the information available from the tests: 

1. Physical configurations for which the PIRT panel has significant test data. This category 

has sufficient data such that the panel can predict, with high certainty, the probability and 

duration of spurious operations, given thermally-induced cable damage. In this category are 

the following physical configurations: 

a. Control cables, with IEEE STD-383-qualified8

 TS and non-qualified TP insulations, used 

to control various power plant components via AC electric power. This category includes 

single conductor, multiple conductors, cables in trays, conduits and/or air drops in either 

grounded or ungrounded circuits. 

b. Control cables, with IEEE STD-383-qualified TS and non-qualified TP insulations, used 

to control various power plant components using DC electric power. This includes a 

single conductor, multiple conductors, cables in trays, conduits, and/or air drops in 

ungrounded circuits. 

2. Physical configurations for which the PIRT panel has sparse data, but which the electrical 

experts believed reasonably can be represented by the existing test data based on energy 

level, cable type, and circuit design. This category has sparse test data from which the 

PIRT panel can predict, with moderate certainty, the probability and duration of spurious 

operations, given thermally-induced cable damage. In this category are the following 

configurations: 

a. Armored Control cables, with IEEE STD-383-qualified TS and non-qualified TP 

insulations, used to control various power-plant components using AC- or DC-electric 

power. This includes single conductor, multiple conductors, cables in trays, conduits 

and/or air drops in either grounded or ungrounded circuits. 

b. Three phase AC and two phase DC power cables due to the similarity in fire-induced 

failure characteristics to the cables fire tested for AC and DC control circuits. The results 

of the control circuit testing when coupled with the expert knowledge of the PIRT panel 

members was considered to be an acceptable combination of knowledge for the 

determinations made in this report relative to AC and DC power cables. 

3. Physical configurations for which the PIRT panel has little or no data, and hence the 

electrical experts can offer only provisional estimates. Due to the lack of test data, the PIRT 

 

8 Environmentally qualified per IEEE STD-383, “IEEE Standard for Type Test of Class 1E Electric Cables, Field 

Slices, and Connections for Nuclear Power Generating Stations,” 1974.
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-11

panel can predict only with low certainty, the probability of spurious operations, given 

thermally-induced cable damage. In this category are the following configurations: 

a. Wiring inside electrical cabinets/panels 

b. Trunk cables 

c. Fiber optic cables 

d. Electrical conductors used in digital control systems 

e. Instrumentation and control circuit cables 

2.2.2 Cable Fire Test Data Analysis 

The EPRI/NEI test data analyses were analyzed thoroughly, and results are detailed in EPRI 

Technical Report 1006931, dated May 2002 (Ref. 11). However, the PIRT panel initially noted 

that the test data obtained from both CAROLFIRE (AC tests) (Ref. 9) and DESIREE-Fire (DC 

tests) (Ref. 10) performed at SNL under the sponsorship of the NRC had not been analyzed for 

direct use in this PIRT evaluation. Based on the PIRT panel’s suggestions and oversight, all 

test data including both EPRI/NEI and NRC/SNL were analyzed for the following conditions: 

For Intra-Cable Hot short-induced Spurious Operation and Duration

• Conductor Count 

• Thermal Exposure Condition 

• Cable Orientation 

• Raceway Routing 

• Raceway Fill 

• Insulation Type (TS or TP) 

• Insulation Materials 

• Circuit Type (for DC tests only) 

• Insulation-Jacket Material Combinations (TS-TS, TP-TP, TS-TP)9

• Control Power Transformer (CPT) Size (for AC circuits) and Fuse Size (for DC circuits) 

• Circuit Grounding for AC circuits only 

• Wiring Configuration 

• Conductor Size 

• Suppression Effects for AC circuits only 

• Cable Shielding for DC circuits only 

• Circuit Concurrence of Hot Shorts for both AC and DC circuits 

For Inter-Cable Hot short-induced Spurious Operation and Duration

• Ground Fault Equivalent Hot Shorts for DC circuits only 

• Inter-cable (direct cable-to-cable) interaction for both AC and DC circuits 

The panel chose several other influencing parameters for the PIRT, but did not include them in 

their analyses of the test data since the tests’ results would not directly exhibit their impacts on 

• Cable Aging 

 

9

 PIRT panel did not consider the TP-TS because the panel members did not know any US NPPs 

currently utilizing any such insulation-jacket material combination cables. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-12 

• Supply Voltage Level 

• Fire Suppression Effect 

• Latching versus Non-Latching Device Configuration 

For these four parameters, the PIRT panel used their expert knowledge, phenomenological 

models, and operating experience in evaluating their effects on the hot short-induced spurious 

operation in applicable control circuits. 

The panel also discussed each of the above items thoroughly so that the outcome of the test 

data analyses could be used directly in the PIRT process. The NRC staff analyzed the 

CAROLFIRE data on AC control circuits, including some selected EPRI/NRC data applicable to 

the specific analysis; the SNL staff analyzed the DESIREE-Fire data on DC control circuits. The 

results of both analyses then were presented to the panel members for evaluation. The NRC is 

in the process of publishing the final results of these evaluations in NUREG-2128 (Ref. 20). 

2.3 Evaluation of Electrical Circuit Configurations 

The electrical expert PIRT panel evaluated three types of electrical circuits (i.e., power, control, 

and instrument circuits). The panel initially had formulated a scoring scheme that considered all 

potential influencing parameters for both hot short and spurious operations associated with each 

of these types. However, after considering the impact of various influencing parameters, the 

panel concluded that the insufficient test data precluded a meaningful evaluation of power and 

instrument circuits, deciding that they could only score the control circuit sheets with high 

certainty. 

For the power and instrument circuits, the panel dropped the ranking approach and used the 

expert elicitation approach for specific fire-induced failure modes. Particularly, for power 

circuits, the panel generated consensus technical positions on the credibility of certain failure 

modes. For instrument circuits, they again stated their technical position on credible failure 

modes and issues of concern. Additionally, since certain instrument circuit-failure modes could 

have a significantly impact safety in a fire event, they recommended undertaking testing for 

certain instrumentation and control (I&C) circuit configurations. 

For control circuits, the PIRT panel completed detailed scoring sheets to rank the influencing 

parameters of fire-induced hot shorts that could entail spurious operations, using the following 

strategy to assess each influencing parameter: 

• Review and discuss, as necessary, the cable’s configuration with respect to the circuit of 

concern, the figures-of-merit (stated in Section 1.3 of this report), and test results presented 

in the draft NUREG-2128 (Ref. 20), 

• Rank the applicability of each influencing parameter to current plant circuit designs, 

• Grade the quality of test data available for the cable’s configuration. If the influencing 

parameter is not adequately represented by the test data, then rank the ease of research 

needed for characterizing its impact, and, 

• Denote the parameter’s importance and state of knowledge for hot short-induced spurious 

operations and their durations for both intra-cable and inter-cable conductor shorts. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-13

2.3.1 Influencing Parameters 

The PIRT panel identified a range of factors that may affect the conditional probability of hot 

short-induced spurious operation in a control circuit. Given fire-induced damage to a cable, a 

particular mode of circuit failure might be observed. Various factors also might influence the 

timing of potential faults being observed and of fault-mode transitions (e.g., hot short transition 

to a short to ground or fuse blown). The influencing factors known to the PIRT panel can be 

roughly categorized into one of four broad groups as follows (Ref. 19): 

• Physical properties and configuration of the cable, 

• Routing of the cable on raceways, 

• Electrical function of the circuit, and, 

• Fire exposure conditions. 

Based on detailed discussions of the various aspects of hot short-induced spurious operation, 

the PIRT panel developed the MICROSOFT ® EXCEL scoring sheets (shown in Appendix B) for 

the intra-cable and inter-cable hot short-induced spurious operations, and their duration using 

the following influencing parameters: 

1. Conductor Count (a. 1/C (one conductor); b. 2-6/C; c. 7-9/C; d. 10-15/C; e. >15/C) 

2. Fire Exposure Condition (a. Flame; b. Plume; c. Hot Gas Layer; d. Time/temperature) 

3. Cable Routing / Raceway (a. Cable Tray Vertical; b. Cable Tray Horizontal; c. Conduit 

Horizontal; d. Conduits Vertical; e. Air Drop; f. Tray type (Ladder/Solid)) 

g. Panel Wiring (Note: treated separately due to lack of sufficient test data) 

4. Cable Raceway Fill (a. Maximum Loading; b. Intermediate Loading; c. Minimum Loading (1 

or 2 cables)) 

d. Bundles (Note: treated separately since test data was available for different bundle 

configurations) 

5. Conductor Insulation Material (TS/TP) 

6. Cable Aging 

7. Cable Jacket Insulation Material (a. Material (TS/TP); b. Coatings; each treated separately) 

8. Time-Current Characteristics (Fuse/breaker size) Available fault current 

Note: CPT Size later was dropped due to inadequate support in NRC tests when compared 

with EPRI test findings. 

9. Cable Grounding Configuration (for AC Circuits only) (a. Ground or Drain Wire; b. Shield 

Wrap – each treated separately). 

10. Power Supply Voltage (for AC Circuits only) (a. < 100V; b. 120V; c. > 150V). 

11. Armor Grounded versus Ungrounded (for AC Circuits); Armored versus Unarmored Cable 

(for DC Circuits) 

12. Cable Wiring Configuration (a. Number of Sources; b. Number of Targets; c. Locations of 

Sources & Targets; d. Number of Grounds/Neutrals) 

13. Conductor Size 

14. Fire Suppression (a. Water Spray; b. Hose) 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-14 

15. Latching versus Non-latching Device (a. Latching MOV; b. Non-Latching MOV) 

16. Grounded versus Ungrounded Circuit (for AC circuits only). 

As the base cases, the PIRT panel assumed that typically all AC circuits are grounded, while all 

DC circuits are ungrounded; they did not consider grounded DC circuits. However, since some 

plants have ungrounded AC circuits, they were included as one of the special cases (i.e., item 

16 above) later in the deliberation of the PIRT panel. (See also footnote 7 on page 2-3). 

2.3.2 Electrical Circuits Considered by the PIRT Panel 

The following discussions address the PIRT panel’s evaluation process of the three circuit 

types: control, power, and instrument circuits. In addition, several ancillary circuit-related issues 

or concerns associated with fire-induced safe-shutdown analyses are identified by the PIRT 

panel for discussion. 

2.3.2.1 Control Circuits 

Typical control cables used in NPPs have a voltage rating of 600 V for 120-125V range circuits. 

Primarily, multi-conductor cables with 3, 7, or 11 conductor configurations and 16-10 American 

Wire Gauge (AWG) conductor sizes are typically used in the control circuits. These cables are 

available armored or unarmored. Armored cable has a metallic outer sheath (or armor) made 

from interlocked aluminum or steel; however, unarmored control cables are more common in 

NPPs. 

The PIRT panel used the scoring sheets to rank the influencing parameters on hot shortinduced spurious operations. The PIRT panel also defined the following columns in the 

MICROSOFT ® EXCEL scoring sheets for the likelihood of hot short-induced spurious operation 

for both intra-cable and inter-cable shorts, and its duration effect, given cable damage due to a 

fire: 

• Effect of Parameters on the Likelihood – Intra-Cable Hot Short-Induced Spurious Operation 

• Effect of Parameters on the Likelihood – Inter-Cable Hot Short-Induced Spurious Operation 

• Effect of Parameters on the Likelihood – Inter-Cable Ground Fault Equivalent Hot ShortInduced Spurious Operation 

• Effect of Parameters on the Duration – Hot Short-Induced Spurious Operation 

The hot shorts of concern are those energized source conductors coming into contact with a 

separate target conductor, other than neutral or ground, with the potential to provide voltage 

and/or current to a device such as a relay or coil. This includes an energized source conductor 

coming into contact with a spare conductor. The only hot short of interest is one of sufficient 

quality (with sufficient duration and energy) to actuate the end device. 

The spurious operations of concern are those that cause an inadvertent energization of a device 

wherein an operational mode of the circuit is initiated. In applying their quantification method, 

the PRA scenario defines one or more specific spurious operation devices of interest. In the 

context of interpreting fire-test data, the device of interest only includes the end devices 

subjected to the test, which were 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-15

• solenoids 

• motor starter contactors 

• breaker close and trip coils. 

The PIRT panel’s evaluation did not include the following modes as a spurious operation: 

• energization of spare conductors 

• energization of indicating lights (burden resistors simulating light bulbs). 

For the “Effect of Parameters on the Likelihood – Intra-Cable Hot Short-Induced Spurious 

Operation” and “Effect of Parameters on the Likelihood – Inter-Cable Hot Short-Induced 

Spurious Operation,” the panel made the following assumptions in ranking them: 

• Fire damage has occurred, meaning in this context, that the insulation of the cable 

conductor was damaged to the point of functional failure. 

• The hot short has occurred as per the definition above and may or may not be associated 

with the “device of concern”: 

- solenoids 

- motor starter contactors 

- breaker close and trip coils. 

• The duration of a hot short between two conductors in a circuit is long enough to cause this 

device to operate spuriously. 

• The duration of a spurious operation is long enough to cause change of any sort in the state 

of the device. 

For the “Effect of Parameters on the Likelihood – Inter-Cable Ground Fault Equivalent Hot 

Short-Induced Spurious Operation,” the following assumptions were made for panel’s ranking: 

• Fire damage has occurred, i.e., insulation of the cable conductor was damaged to the point 

of functional failure. 

• The hot short has occurred as defined above and may or may not be associated with the 

“device of concern”: 

- solenoids 

- motor starter contactors 

- breaker close and trip coils. 

• The duration of a hot short through a ground plane in a circuit persists long enough to cause 

a spurious operation of the device of concern. 

• The duration of a spurious operation is long enough to cause any change in the state of the 

device of concern. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-16 

For the Effect of Parameters on the Duration – Hot Short-Induced Spurious Operation,” the 

following assumptions were made for PIRT panel’s ranking: 

• Fire damage has occurred, i.e. the cable conductor’s insulation has been damaged to the 

point of functional failure. 

• The duration of hot short-induced spurious operation lasts long enough to cause any change 

in the state of the device of concern. 

Cable tests indicate that spurious operations have a relatively high likelihood after fire-induced 

damage to a control cable. Several influencing factors were noted that could impact this 

behavior. Existing evidence implies that multiple concurrent spurious operations are possible 

and potentially likely after fire damage to multiple control cables that are susceptible to hot 

shorts. The PIRT panel developed scoring sheets that described the effect of each influencing 

parameter on the hot short-induced spurious operation, and its duration for both intra-cable and 

inter-cable configurations. 

Using the collective expertise of the PIRT panel in analyzing fire-induced circuit failures and 

their level of knowledge, together with the results of industry and NRC cable-fire tests, a 

consensus score for each of the items was developed. This consensus was followed by an 

individual scoring by each of the panel members who gave comments or different views should 

a member’s view differ from that of the majority opinion. Specifically, each panel member 

evaluated and provided on MICROSOFT ® EXCEL scoring sheets with their independent scores 

for each influencing parameter for hot short-induced spurious operations, and their duration. If 

an individual score was very different from the consensus, the PIRT panel members offered 

comments explaining their opinion on the subject area. 

2.3.2.2 Power Circuits 

Typical safety-related power cables used in NPPs are applied at nominal operating voltages 

from 120 V to 4.16 kV. These cables are single-conductor or multi-conductor (Triplex) cable 

with three spirals wound individually insulated conductors and may include an uninsulated 

grounded drain conductor. Each conductor’s size is 12 AWG or larger. 

The most likely types of power cable faults (shorts to ground) typically lead to a loss of primary 

motive power to plant equipment or devices as a result of overcurrent protective device 

actuation. Continuously operated components such as pumps, fans, and motors will stop 

and/or be unable to start. Intermittent operating devices, such as MOVs, would be unable to 

move or would cease moving if they were moving when the cable failed. Devices that require 

continuous power to maintain position, such as a solenoid operated valve, would revert to the 

de-energized state or maintain the de-energized state if not energized at the time of fault. 

Loss of primary motive power could result from several types of power cable failure modes, 

such as: 

• Single or multiple phase-to-ground short circuits 

• Phase-to-phase or three-phase short circuits. 

In each case, the cable failures would, for a properly designed power system, lead actuation of 

circuit overcurrent protective features (e.g., breakers and/or fuses opening). Given the many 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-17

ways that power cable failures might engender an open circuit fault, the loss of motive power 

will be the predominant fault mode subsequent to the fire-induced failure of power cables. 

Finally, the PIRT panel decided not to include the power circuits in their evaluation process 

similar to the control circuits. Instead, they considered the following two power circuit fault 

modes (as described in Section 4): 

• Three-phase proper-polarity hot short (ac) , and 

• Multiple proper-polarity hot shorts leading to spurious operation of DC motors. 

2.3.2.3 Instrument Circuits 

Instrument circuits (also known as instrumentation and control circuits) can typically use single 

twisted shielded pair conductor cables or much larger multi-conductor cables consisting of 50 or 

more conductors. Each instrument conductor typically is size 16 AWG or smaller. These 

cables frequently enclose several “twisted/shielded pairs” of conductors contained within a 

protective outer jacket. The shielding blocks external sources of electrical “noise” generated by 

other plant equipment. 

Instrumentation circuits are typically low-voltage (0-5 volts) or low-current loops (typically 4-20 

milliamps) connecting various types of sensors to remote monitoring equipment (e.g., control 

room indicators) and actuation devices (e.g., interlocks and trip units) that automatically control 

plant equipment. 

The PIRT panel discussed instrument circuits in detail. However, due to a lack of fire test data, 

the parameters influencing hot short-induced spurious operations could not be identified and 

ranked in the same manner as for the control circuits. Therefore, the PIRT panel recommended 

undertaking more research and testing in this area. 

Based on some limited earlier cable-failure testing of instrument circuits at SNL (Ref. 21), the 

following circuit failure characteristics were noted: 

• Instrument cables failed earlier than co-located control cables during the tests 

• TP cable failed early and the instrument signal was lost abruptly 

• TS cables experienced degradation and subsequent failure over a more extended period 

than did other cables, typically several minutes 

• The behavior of an instrument circuit with specific degradation is predictable based on a 

simple circuit analysis. 

The loss of instrument readings, and false or corrupted signals, may cause a loss of function for 

the system and may or may not have been identified as a part of the plant shutdown model in 

the Fire PRA. Therefore, the PIRT panel recommends further testing to identify the types of 

instrument systems that may be susceptible to fire-induced spurious operations. Section 5 

reports the PIRT panel’s discussions of these issues and their recommendations for testing 

several analog current loop systems. 

2.3.2.4 Ancillary Electrical Circuit Issues 

The electrical expert PIRT panel evaluated several known issues or concerns associated with 

deterministic fire-induced safe-shutdown analyses that often form the basis for treating issues or 

concerns in Fire PRAs. The evaluations for these issues were considered as part of this 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-18 

project’s ancillary objectives. The PIRT considered it appropriate to address these issues to 

ensure treatment within both deterministic and risk-informed analyses for the failure modes in 

question is consistent with the risk posed. They may or may not be associated with hot shortinduced spurious operations; some have been categorized as legacy issues since the Browns 

Ferry fire accident in 1975, and subsequent regulatory guidance. The PIRT panel was asked to 

consider each of the following cases from their phenomenological- and electrical-engineering 

perspectives and provide their technical positions: 

• Multiple high impedance fault (MHIF) on a common power supply (ac/dc) 

• Open circuited secondary of current transformers (CTs) 

• DC control power impact on common enclosure/common power supply 

• Control power transformers (CPTs) 

• Kapton-insulated cables 

• Panel wiring 

• High conductor count trunk cables 

Section 6 of this report discusses the PIRT panel’s technical positions on each of these issues. 

2.4 PIRT Panel Evaluation Process for Control Circuits 

The PIRT panel considered the following when evaluating the control circuits. The control 

circuit may be a motor-operated valve (MOV), a solenoid-operated valve (SOV), or a breakercontrol circuit. The connected conductors within the circuit configuration can be TS- or TPinsulated and located on electrical tray raceways or in conduits. Section 2.3.1 lists the 

parameters that could influence a control circuit of concern or that are associated with the fire 

characterization. A description is given next of the process used to rank the identified 

parameters by the PIRT panel as possibly influencing the failure mode and duration of hot shortinduced spurious operations after fire damage to electrical cables. The individual parameters 

were ranked according to their applicability, importance, ease of conducting research on them, 

and current state of knowledge. 

“Parameter Applicability” considers if the particular influencing parameter is representative of 

existing cable configurations in NPPs. “Research Ease” addresses the ease of conducting any 

additional needed research to better understand the effect of this parameter on the hot shortinduced spurious operation. The PIRT panel scored these two columns before evaluating the 

impact of each influencing parameter on this spurious operation. Then, they assessed and 

scored the following first two bullets (for AC circuits) or first three bullets (for DC circuits) for the 

modes of hot shorts (i.e., intra-cable, inter-cable, and inter-cable with ground plane interaction) 

and the last bullet for the duration of hot short-induced spurious operation: 

• Effect of Parameters on the Likelihood – Intra-Cable Hot Short-Induced Spurious Operation 

• Effect of Parameters on the Likelihood – Inter-Cable Hot Short-Induced Spurious Operation 

• Effect of Parameters on the Likelihood – Inter-Cable Ground Equivalent Hot Short-Induced 

Spurious Operation 

• Effect of Parameters on the Duration – Hot Short-Induced Spurious Operation 

In the early stages of the project, each panel member used a “Number Scheme” for scoring for 

statistical analyses among all panel members, retaining it until the final consensus scores were 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-19

determined, as presented in Appendix B. However, the final scoring scheme was converted to 

an equivalent “Letter Scheme” before the results are presented in Tables 3-1 and 3-2. 

The AC and DC control circuits were evaluated in two separate MICROSOFT ® EXCEL 

worksheets. The panel first discussed the importance of each influencing parameter on the 

circuit’s failure mode (i.e., hot short-induced spurious operation). For each influencing 

parameter apposite to the cable configuration in an NPP, the panel members completed the 

stages of assessment as described in Tables 2-1 through 2-4, which illustrate the “Letter 

Scheme” and the “Number Scheme.” 

Table 2-1 on ranking parameter-applicability and Table 2-2 on research ease are applicable to 

each influencing parameter, irrespective of any of the hot short phenomena identified above 

(i.e., intra-, inter-, inter-cable ground-fault equivalent, or duration). 

Table 2-1. Parameter Applicability Ranking 

High (H or 3) The specific physical configuration of the parameter exists in many US 

nuclear power plants 

Medium (M or 2) At least one example of the physical configuration of the parameter exists 

in US nuclear power plants 

Low (L or 1) No such physical configuration of the parameter are known to the panelist 

in US nuclear power plants 

Table 2-2. Research Ease Ranking 

High (H or 3) Data needed readily is obtainable based on existing experimental 

capabilities 

Medium (M or 2) Data is obtainable but would require moderate, readily attainable 

extensions to existing capabilities 

Low (L or 1) Data is not readily attainable and/or would require significant 

development of new capabilities 

During the next stage of the assessment, the PIRT panel ranked the parameter importance and 

the state of knowledge of each specific phenomenon. Table 2-3 describes this ranking with 

respect to the two figure-of-merits discussed in Section 1.3 of this report. Table 2-4 describes 

the criteria that the panel used to rank the state of knowledge. 

Table 2-3. Parameter Importance Ranking 

High (H or 3) First order importance to figure of merit 

Medium (M or 2) Secondary importance to figure of merit 

Low (L or 1) Negligible importance to figure of merit. 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES 

2-20 

Uncertain (U or 0) Potentially important. Importance should be explored through reliable 

analyses and/or experimentally 

Table 2-4. State of Knowledge Ranking 

High (H or 3) Plant-specific or testing database exists, or a highly reliable assessment 

can be made from existing knowledge. Data readily is available to 

support the parameter and its vulnerability to spurious operations. 

Medium (M or 2) Existing plant-specific or testing database moderately support the 

parameter and its vulnerability to spurious operations. Moderately reliable 

assessments can be made from existing knowledge. 

Low (L or 1) No existing plant-specific or testing database could support the parameter 

and its vulnerability to spurious operations. Reliable assessments cannot 

be made from existing knowledge. 

Uncertain (U or 0) The panel is unaware of any existing state of knowledge about this 

parameter 

One primary objective of the PIRT panel was to identify cable configurations that would be 

vulnerable to hot short-induced spurious operation of certain end devices. The PIRT panel’s 

ranking of these influencing parameters was used to aid in identifying the various control circuit 

configurations that are most vulnerable to hot short-induced spurious operations. 

2.5 Technical Challenges 

During the PIRT discussions on the influencing parameters, the panel faced several technical 

challenges described below: 

• The EPRI/NEI and CAROLFIRE cable-fire tests on AC circuits used MOV control circuits 

without mechanical/electrical interlocks in their Surrogate Circuit Diagnostic Unit (SCDU) 

monitoring system; all DESIRE-Fire tests used interlocked MOV-circuits. Hence, analysis of 

the data from these tests must be interpreted appropriately when comparing the results of 

AC tests with DC tests. 

• All AC tests used an MOV control circuits, and therefore, additional insight may be 

necessary when using these data to determine the effects on other AC-powered end 

devices or equipment. 

• There are limited test results for power and instrument circuits. The PIRT panel used their 

experience and expertise to arrive at a technical position for certain power circuit failure 

modes and in developing recommendations for instrument circuits. 

• No test data is available for panel wiring and trunk cables. Since these are common 

configurations at plants (e.g., panel wiring is present throughout the plant), the panel 

recognized that this situation posed a gap in knowledge. Additionally, both panel wiring and 

trunk cables often involve the close proximity of multiple conductors from different circuits. 

The potential interactions and effects of such configurations are not well understood. 

• Fire testing undertaken by Duke Power included armored cables; however, even though 

some members of the panel were knowledgeable of the test results, the test documents are 
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES

2-21

proprietary, and therefore, not available for public use. Their knowledge of these findings 

was a factor in the PIRT panel’s position on certain parameters; however, the test data did 

not get the same scrutiny as did other test data received. 

• There are very limited test results for ungrounded AC circuits, even though several plants 

use ungrounded AC for control circuits. 

• Knowledge of the effect of the following influencing parameters on hot short-induced 

spurious operations is inadequate (ranked “Low” in ranking sheets): 

- Conductor count 

- Fire exposure 

- Cable aging 

- Cable coating 

- Fuse/Breaker size 

- Drain or shield wire 

- Voltage level 

- Conductor size 

- Fire suppression 

To resolve some of these technical challenges and to better understand the impact of certain 

influencing parameters on the hot short-induced spurious operation of certain end devices, the 

PIRT panel offered several recommendations for several future research areas, documented in 

Section 7 of this report. 

3-1 

3

PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

One mode of failure of control circuits is hot short-induced spurious operation the behavior of 

which may be dynamic and transient, changing its state throughout the course of a fire event. 

As the fire continues, multiple cables may fail at discrete times, and multiple circuit hot shorts 

may become part of the circuit failure. This pattern could entail the simultaneous behavior of 

two or more circuits experiencing concurrent spurious operations. With an adequately 

protracted fire exposure, conductor-to-conductor shorts are likely to transition into shorts to 

ground that eventually actuate an overcurrent protective device (i.e., blow fuse or trip breaker). 

During the first PIRT meeting, the PIRT panel developed ranking worksheets in MICROSOFT ® 

EXCEL involving all the influencing parameters listed in Section 2.3.1 for all three circuit types 

(i.e., control, power, and instrument), with separate worksheets for AC- and DC-power supply 

(i.e., six worksheets ). The panel also agreed upon a scoring scheme commensurate with the 

objectives of this project and the figures-of-merit. Thereafter, the PIRT panel initially ranked the 

influencing parameters and then forwarded the worksheets to BNL for analysis. The analyses 

of these independent panel-member’s rankings using the “Number Scheme” revealed that each 

person had considerable difficulty in interpreting the ranking scheme. Also, most encountered 

problems in filling out these worksheets for power and instrumentation circuits due to lack of 

adequate test data, and the inapplicability of many parameters to power and instrumentation 

cabling. During the second PIRT meeting, the panel discussed these drawbacks, and agreed to 

abandon the PIRT process for power and instrument circuits. For control circuits, the PIRT 

panel applied the PIRT process. However, because of the extreme difficulty in analyzing the 

raw data in the test reports, they decided that both the CAROLFIRE and DESIREE-Fire test 

results must be analyzed and organized such as to allow a clearer interpretation of the effects of 

each influencing parameter. They also combined the results of the EPRI/NEI tests in the overall 

data analysis; this action is documented in NUREG-2128 (Ref. 20). 

As shown in Figure 2-1, the PIRT panel followed Steps 7 through 9 to identify those control 

circuits that would be vulnerable to hot short-induced spurious operations. To identify the most 

significant influencing parameters, the members first highlighted all plausible influencing 

parameters and ranked them to assess their impact on hot short-induced spurious operation 

and duration. During meetings, the panel discussed each influencing parameter in great detail 

and selected some of the significant ones to include in the control circuit characterization. 

Furthermore, they derived various circuit characteristics (such as the power source variations, 

hot short modes of failure) from fire tests (in Step 4) and from their past experience on the 

subject. Finally, the panel identified those simplified control circuit electrical diagrams typically 

used in NPPs to control certain end devices, specifically, the MOV, SOV and circuit-breaker 

circuits. The final control circuit configurations they selected included six with a single contact 

(or break) and seven with double contacts (or breaks). 

3.1 Impact Assessment of Influencing Parameters 

The PIRT panel spent a considerable time debating the impact of the influencing parameters on 

hot short-induced spurious operation of control circuits. Tables 3-1 and 3-2, respectively, 

present their consensus ranking of all influencing parameters for AC- and DC-control circuits. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-2 

The panel made the baseline assumption that AC control circuits are grounded, and DC control 

circuits are ungrounded (see footnote 7 on page 2-3). In addition to individual scores for the 

subgroups associated with each influencing parameter, an overall score (in bold) is shown for 

the impacts of this parameter on the likelihood of spurious operation and its duration. 

The following is a summary explanation of the PIRT panel’s ranking given Tables 3-1 and 3-2. 

The column headings are described in Section 2.4. The following apply to both tables. 

1. Conductor Count

Control cables typically contain 3, 7, or 11 conductors. Some trunk cables that are used for 

multiple control circuits contain as many as 37 or more conductors. While the number of 

conductors can influence the likelihood of spurious operation, the PIRT panel did not consider it 

to be a primary influencing parameter because the wiring configuration has a higher influence 

on the likelihood of spurious operation. Therefore, the number of conductors was considered a 

secondary factor in the wiring configuration parameter because of its effects on some of the 

wiring configuration’s sub-categories (i.e., the number of sources, targets, and mitigating 

conductors (e.g. grounded or return)). Hence, the PIRT panel determined that conductor count 

could be ranked “Low” as an influencing factor, but its overall importance ultimately would be 

reflected in the wiring-configuration parameter (see item 12 below). 

2. Fire Exposure Condition

A range of data was reviewed for direct flame impingement, plume, and hot gas layer (HGL) 

exposures. All Penlight10 tests performed at SNL were subjected to radiant heating, a usage 

that closely simulated the presumed HGL behavior of the fire. However, the Penlight 

temperature profiles were designed to assure cable damage and the conditions for thermal 

exposure were significantly higher than that would be expected for an actual HGL in an NPP. 

Often the test temperature of the Penlight shroud was high enough to exhibit thermal conditions 

similar to plume- or flame-fire zones. 

One surrogate for the exposure conditions explored in the data analysis was time to damage. 

Since the initial cable damage and subsequent degradation of the conductor’s insulation occurs 

more rapidly for cable in the flame and more slowly for a cable in the HGL, the potential was 

evaluated of fire exposure conditions to affect the duration of hot short-induced spurious 

operation. Plots illustrating their effects are included in the data analysis NUREG-2128 (Ref. 

20). The assumption is that the cable’s behavior under fire more closely simulates that in the 

HGL condition may be accurate for comparing the thermal conditions, but the failure-mode data 

in Figures 2-5 and 4-9 of Ref. 20 does not show this relation. Rather, the data indicates that 

modes of fire-induced cable failure do not follow this assumption of simulating the HGL 

condition, and specifically, that the likelihood is that the radiant-failure mode is similar to the 

conditions of exposure to the plume and flame conditions. The PIRT panel determined that the 

fire exposure conditions seemingly play some role in the likelihood of spurious operation 

(ranked Medium), and a relatively strong role in the duration of spurious operation (ranked 

“High”). 

 

10 Penlight are small-scale tests involving one to six lengths of cable exposed to grey-body radiant 

heating in a cylindrical exposure chamber in the CAROLFIRE and DESIREE-Fire test programs (Refs. 9 

and 10) performed at SNL. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-3 

Table 3-1. Panel Consensus Ranking of Influencing Parameters for AC Control Circuits 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

1 Conductor Count L L NA L  a. 1/C M NA NA NA L M L M  b. 2-6/C H H L M L M L M  c. 7-9/C H H L H L H L H  d. 10-15/C H H L M L M L M  e. >15/C H H L L L L L L 2 Fire Exposure Condition M M NA H  a. Flame H H M H M H H H  b. Plume H H M H M H H H  c. Hot Gas Layer M H M H M H H H  d. Time/Temperature L H M L M L H L 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Table 3-1: Panel Consensus Ranking of Influencing Parameters for AC Control Circuits (Cont’d.) 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

3 Cable Routing/Raceway L L NA L  a. Cable Tray Vertical H H L M L M L M  b. Cable Tray Horizontal H H L H L H L H  c. Conduit Horizontal H H L H L H L H  d. Conduit Vertical H H L M L M L M  e. Air Drop M H L M L M L M  f. Tray Type (Ladder/Solid) H H L L L L L L 

g. Panel Wiring* H M H H L H H L NA H H L 

4 Cable Raceway Fill L M NA M  a. Maximum Loading H H L M M M M L  b. Intermediate Loading H H L H M H M M  c. Minimum Loading H H L H M H M H 

d. Bundles* H H M M H M M H NA M M H 

3-4 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Table 3-1: Panel Consensus Ranking of Influencing Parameters for AC Control Circuits (Cont’d.) 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

5 Conductor Insulation Material H H L L H H H H NA L L H 6 Cable Aging H H L L L L L L NA L L L 7 Cable Jacket Insulation Material 

a. Material* H H L L H M M H NA L L H b. Coating* H H L L L L L L NA L L L 

8 

 Time-Current  Characteristics -  Fuses/Breaker Size 

H L L L L L L L NA H H L 

9 Cable Grounding Configuration H H NA M  a. Ground or Drain Wire L H H M H M M L  b. Shield Wrap M H H L H L M L 

3-5 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Table 3-1: Panel Consensus Ranking of Influencing Parameters for AC Control Circuits (Cont’d.)

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

10 Power Supply Voltage L L NA L  a. <100 V L M L L L L L L  b. 120 V H H L H L H L H  c. >150 V L M L L L L L L 11 Armor Grounded versus Ungrounded Circuit H H H H L H H L NA M M L 12 Cable Wiring Configuration H H NA H  a. Number of Sources H H H M H M H M  b. Number of Targets H H H M H M H M 

c. Locations of Sources & 

Targets H H H M H M H M 

d. Number of Grounds/ 

Neutrals H H H M H M H M 

13 Conductor Size H H L L M L L M NA L L L 

3-6 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Table 3-1: Panel Consensus Ranking of Influencing Parameters for AC Control Circuits (Cont’d.)

NOTES: H – High; M – Medium; L – Low; U – Uncertain; N/A – Not Applicable 

 * PIRT Panel Ranked Separately from the Group 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

14 Fire Suppression L-M L-M NA U  a. Water Spray H H L-M L L-M L U L  b. Hose H H L-M L L-M L U L 15 Latching versus Non- latching Device L L NA H  a. Latching MOV H H L L L L H H  b. Non-latching MOV H H L H L H H H 16 Grounded versus Ungrounded Circuit M H L L M H H M NA M M L 

3-7 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control Circuits 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

1 Conductor Count L L L L  a. 1/C M NA NA NA L M L M L M  b. 2-6/C H H L M L M L M L M  c. 7-9/C H H L H L H L H L H  d. 10-15/C H H L M L M L M L M  e. >15/C H H L L L L L L L L 2 Fire Exposure Condition M M M H  a. Flame H H M H M H M H H H  b. Plume H H M H M H M H H H  c. Hot Gas Layer M H M H M H M H H H  d. Time/Temperature L H M L M L M L H L 

3-8 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control Circuits (Cont’d.) 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

3 Cable Routing/Raceway L L L L  a. Cable Tray Vertical H H L M L L L L L L  b. Cable Tray Horizontal H H L H L H L H L H  c. Conduit Horizontal H H L H L M L M L M  d. Conduit Vertical H H L M L L L L L L  e. Air Drop M H L M NA NA NA NA L L  f. Tray Type (Ladder/Solid) H H L L L L L L L L 

g. Panel Wiring* H M H H L H H L M M L H H L 

4 Cable Raceway Fill L M L L  a. Maximum Loading H H L M M L L L L L  b. Intermediate Loading H H L H M H L H L H  c. Minimum Loading H H L H M H M H M H 

d. Bundles* H H L L H M M M M M M M M M 

3-9 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control Circuits (Cont’d.) 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

5 Conductor Insulation Material H H L L H H H H L L M M M H 6 Cable Aging H H L L L L L L L L L L L L 7 Cable Jacket Insulation Material 

a. Material* H H L L H M M H L L H L L H b. Coating* H H L L L L L L L L L L L L 

8 

 Time-Current  Characteristics -  Fuses/Breaker Size 

H H L L L L L L L L M H H H 

9 Cable Grounding Configuration** NA NA NA NA 10 Power Supply Voltage NA NA NA NA 11 Armored versus Unarmored Cable M H L L L H H L H H L M M L 

3-10 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control Circuits (Cont’d.) 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

12 Cable Wiring Configuration H H H H  a. Number of Sources H H H M H M H M H M  b. Number of Targets H H H M H M H M H M 

c. Locations of Sources & 

Targets H H H M H M H M H M 

d. Number of Grounds/ 

Neutrals H H H M H M H M H M 

13 Conductor Size H H L L M L L M L L M L L L 14 Fire Suppression L-M L-M M U  a. Water Spray H H L-M L L-M L M L U L  b. Hose H H L-M L L-M L M L U L 15 Latching versus Non- Latching Device L L L H  a. Latching MOV H H L L L L L L H H  b. Non-latching MOV H H L H L H L L H H 

3-11 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Table 3-2. Panel Consensus Ranking of Influencing Parameters for DC Control Circuits (Cont’d.) 

NOTES: H – High; M – Medium; L – Low; U – Uncertain; NA – Not Applicable 

* PIRT Panel Ranked Separately from this Group 

** Items 9 and 16 are marked “N/A” since the PIRT panel assumed that all DC control circuits at US NPPs are 

ungrounded 

Identification 

Influencing Parameter 

Parameter Applicability 

Research Ease 

Effect of Parameters 

on the Likelihood - 

INTRA-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters 

on the Likelihood - 

INTER-CABLE GROUND 

FAULT EQUIVALENT 

HOT SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

Effect of Parameters on 

the DURATION - HOT 

SHORT-INDUCED 

SPURIOUS OPERATION 

Parameter Importance 

State of Knowledge 

16 Grounded versus Ungrounded Circuit** NA NA NA NA 

3-12 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-13

3. Cable Routing/Raceways

The state of knowledge for configurations other than cable trays and horizontal conduits is 

weak. In particular, no tests have been completed using panel wiring. Additionally, no tests 

have compared variations in tray type (e.g., no solid bottom trays have been tested). Also, 

there are very few tests of vertical-raceway orientations. The data analysis revealed, at most, a 

weak correlation between the routing configuration and the likelihood of spurious operation. For 

intra-cable shorting, there appeared to be no discernible effect. For inter-cable shorting, there 

was an indication that raceway type will have some effect, but since only a few spurious 

operations have been attributed to direct cable-to-cable shorting, i.e., inter-cable shorting, the 

findings from testing are inconclusive. 

The PIRT panel determined that the parameter cable routing/raceways could be ranked “Low” 

as an influencing factor. One exception was panel wiring that has several unique characteristics 

that limited the PIRT panel’s ability to use their expert knowledge to extrapolating a position via 

existing test data. This low state of knowledge about panel wiring, coupled with the PIRT 

panel’s concern about the possible importance of panel wiring for locations, such as the Control 

Room, lead them to rank panel wiring as “High” to assure that it would be given adequate 

consideration for future research. A separate write-up on panel wiring was completed, with 

recommendations for further testing in Section 6.6. The PIRT panel discussed at great length 

whether hot shorts in conductor bundles should be treated as either intra-cable or inter-cable 

hot shorts. This discussion also appears in Section 6.6. 

4. Cable Raceway Fill

The relative number of cables in a raceway is not expected to significantly affect the likelihood 

of spurious operations caused by intra-cable shorts; however, the number of cables determines 

the number of opportunities for inter-cable shorting; accordingly, it would impact the chance of 

spurious operation due to inter-cable shorts. More cables generally increase the likelihood of 

inter-cable shorting, while fewer lower it, or even preclude them entirely (e.g., via maintained 

spacing or single cables in conduit). 

The exception to cable raceway multi-layer cable fill appears to be cables bundled together, 

such as trunk cables or panel wiring with tie-wraps (e.g., nylon zip ties). In the CAROLFIRE 

tests, bundled cables were used commonly to form well-defined thermal targets to support the 

objectives of fire modeling. These bundles seemingly experienced a higher number of spurious 

operations than did unbundled cable rows lying on a cable tray. The bundling arrangement is 

thought to have put additional pressure on the cables and conductors, so entailing more 

conductor-to-conductor shorts. Similar conditions to the bundled arrangement could exist at the 

bottom of a heavily loaded cable tray. However, overall the PIRT panel ranked the cable 

raceway fill as a “Low-Medium” influencing. 

5. Conductor Insulation Material

The test data encompasses cables insulated with thermoset (TS) materials that include XLPE, 

EPR, SR and Kerite-FR, while thermoplastic (TP) cable insulation includes PE, PVC, and TEF. 

These materials commonly are found in the control cable’s insulation and jacket materials used 

in US NPPs electrical cables. 

The insulation type (i.e., TS vs. TP) and specific insulation material had very little effect on the 

likelihood of intra-cable shorts entailing spurious operation. However, strong effect seemingly is 

apparent on the likelihood of inter-cable shorts leading to spurious operation. In particular, all 

test cases causing a spurious operation due to direct cable-to-cable shorting involved cables 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-14

with TP insulation. No such cases were noted with TS insulated cables, although there were 

indications of hot short-induced voltages. There have been instances of TS cables producing a 

spurious operation on a TP cable, but none of TP cables generating a spurious operation on a 

TS cable. We note that the PIRT panel considers the critical factor is the type of insulation, not 

the jacket type, which is ranked separately. 

Kerite-FR cable-insulation displayed a unique failure mechanism during fire-exposure tests (Ref. 

24). The material is a thermosetting polymer, but when experiencing high-temperature electrical 

failure (from as low as 247 o

C) it displays a failure threshold more typically associated with 

thermoplastic cable-insulation materials. While the thermal failure threshold of Kerite-FR is 

relatively low for a thermoset material, the mechanism of its failure does not appear to affects 

the relative likelihood of hot short-induced spurious operations compared to other thermoset 

cable insulations. Hence, the PIRT panel concluded that the conditional probability, given cable 

failure, of a hot short leading to spurious operation would be the same for a Kerite-FR insulated 

cable as for other thermoset cable insulations. 

The CAROLFIRE project (Ref. 9) drew the following conclusions: 

Bin 2 Item A – Inter-cable shorting for TS cables: 

“Inter-cable shorting between two TS-insulated cables that could 

cause hot shorts and the spurious operation of plant equipment 

was found to be a plausible failure mode, although the likelihood 

of this failure mode is low in comparison to intra-cable short 

circuits leading to spurious operation. While no detailed statistical 

analysis has been performed, it appears that the conditional 

probability (given cable failure) of spurious operations arising from 

this specific failure mode is small in comparison to that previously 

estimated for spurious operations from intra-cable shorting.” 

Bin 2 Item B – Inter-cable shorting between TP and TS cables: 

“Inter-cable shorting between a TP-insulated cable and a TSinsulated cable that could cause hot shorts and the spurious 

operation of plant equipment was found to be a plausible failure 

mode, although the likelihood of this failure mode is low in 

comparison to intra-cable short circuits leading to spurious 

operation. While no detailed statistical analysis has been 

performed, it appears that the conditional probability (given cable 

failure) of spurious operations arising from this specific failure 

mode is very small in comparison to that previously estimated for 

spurious operations from intra-cable shorting.” 

While these were the conclusions from CAROLFIRE, the PIRT panel arrived at different ones 

from their review. Specifically, the PIRT panel determined that an inter-cable hot short-induced 

spurious operation between two TS cables was implausible, and an inter-cable hot shortinduced spurious operation in a TS cable by an aggressor TP cable was an incredible event 

(see Section 3.3.2). 

In conclusion, the PIRT panel determined that the insulating material of cable conductors can 

influence the likelihood of inter-cable failures modes (ranked ”High”), but had little effect on the 

likelihood for intra-cable mode and for duration (ranked “Low-Medium”). 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-15

6. Cable Aging

The PIRT panel considered a limited set of test data on the damageability of aged and un-aged 

cables. The PIRT panel also discussed the mechanisms of cable aging and their potential 

impact on shorting behavior. The state of knowledge on this topic is low. Only one study 

investigating the effect of thermal aging on cable damageability was identified, and it did not 

cover fire-induced spurious operations. With the exception of one different opinion, the 

importance of this factor was considered to be low. 

During the PIRT panels discussions related to the affect aging has on the likelihood of electrical 

cables spurious actuation as a result of fire damage, the panel did not reach unanimous 

consensus on this ranking. Six of the eight members opinion was that aging should have 

relatively little effect on the likelihood of spurious operation, given cable failure. This was based 

on their review of experimental data and expert judgment. They noted some changes in 

damage threshold, but this change was minimal and their opinion was that cable aging would 

not affect the failure mode likelihood. 

One member believed that this parameter should have a similar level of importance to insulation 

type, i.e., between “Medium and high.” This member believed that the effect of aging on 

spurious operation likelihood was, at best unknown, and likely important. This member judged 

that since aging clearly affects the properties of cable insulation (Ref. 25), this factor should 

have a similar level of importance to insulation type, i.e., between “Medium and High.” 

Specifically, the member expressed their views as follows; 

I disagree with an importance rating of “Low” for this factor. Since aging 

affects the properties of both the cable jacket and cable insulation (cite 

Equipment Qualification (EQ) experience as a technical basis), it is 

unclear what the overall effects of aging will have on the probability of 

spurious operations. However, ranking this parameter as one of Low 

significance gives an unverified conclusion that aging effects have no 

significance. 

My overall contention is that both the jacket material and the conductor 

insulation properties can change significantly due to ageing effects. It 

appears inconsistent to rank conductor insulation effects on the likelihood 

of “Inter-Cable Hot Short Induced Spurious Operations” as High and then 

rank Ageing effects on the likelihood of “Inter-Cable Hot Short Induced 

Spurious Operations” as Low. My belief is that this factor will become a 

more important parameter as plants continue to age with license renewals 

and cables approach their end of life due to a combination of normal 

ageing and harsh environmental conditions. My recommendation is to 

conduct testing. 

Another member was uncertain to the importance of this parameter on the likelihood of fireinduced spurious operations. This member believed that for several cases the effects of aging 

should have little to no effect on the fire-induced spurious operation likelihood. However, this 

member also believed that there are certain scenarios (e.g., inter-cable interactions) where 

aged cables may behave differently than the test data supports, due to the loss of insulation 

fillers and additives that volatize during the life of the cable. Therefore, this member could not 

generically say aging has no effect on spurious operation probability. This member also 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-16

supported conducting additional research on the effects of aged cable to the likelihood of 

spurious operation and other fire related aspects (e.g., thermal damage threshold, flame spread, 

ignition, etc.). 

7. Cable Jacket Material

This influencing parameter included the cable jacket’s material and coatings. Testing has 

involved a range of jacket types, but there are only limited data from tests on cable coatings. 

Accordingly, the assessment of test data analysis was changed from considering the jacket 

material alone to an evaluation looking at the available combinations of insulation-jacket 

polymer type. This assessment created three bins of cables with (1) TP insulation and TP 

jacket, (2) TS insulation and TS jacket, and (3) TS insulation and TP jacket (mixed cable type). 

In addition, the PIRT panel noted that the NRC’s preliminary study of cable coatings is 

underway at SNL. Since the physical configurations may be different, the PIRT panel 

separately scored the two subgroups, jacket material and coatings. 

The PIRT panel concluded that the jacket material would have little or no effect on the likelihood 

of intra-cable shorts leading to spurious operation. They ranked the effect on inter-cable shorts 

as ‘Medium’ because so few direct cable-to-cable hot short-induced spurious operations have 

been tested; however, the PIRT panel believed that the jacket material could affect the 

probability of spurious operations. 

Cable coatings or electrical raceway fire barrier systems (ERFBSs) were expected to have no 

effect on intra-cable shorting and, at most, a small effect on inter-cable shorting (ranked “Low” 

influence). Coatings are applied to the outside of the cable or group of cables so the impact on 

the cable itself is minimal. The most significant effect that might occur is a delay of the onset of 

damage. In addition, coatings may alter the effective exposure mode or the time/temperature 

relationship. 

Publically available Duke Test data concluded that removing the jackets quickened the effects 

of fire damage but made no significant change to the number of spurious operations. 

8. Time-current Characteristics – Fuses/Breaker Size

Effect of CPTs

The original ranking tables and spurious operation likelihood estimates contained in Section 10 

of NUREG/CR-6850, EPRI TR 1011989 (Ref. 12) included a subcategory for circuits powered 

from a control power transformer (CPT). However, after reviewing all available data the PIRT 

panel elected to remove the distinction between circuits with and without a CPT. The reasoning 

and basis for this decision is detailed in Section 6.4 of this report. 

Effect of Fuses/Breakers (on Duration) 

The reasoning used for AC control circuits can also be applied to DC control circuits, as the 

same engineering principles apply. However, fault behavior for DC circuits is predictably 

different due to higher available fault currents and a wider range of fuse/breaker sizing for DC 

circuits. Additionally, DC control circuits are used in nuclear power plant applications to support 

emergency operations under loss of AC power conditions; thus, overcurrent protective devices 

tend to be larger so as to provide a bias toward power continuity in lieu of equipment protection. 

For the DC test configuration, even with complete cable failure, larger size control fuses (e.g., 

15A or larger) did not clear. Instead, repeated short-lived but relatively high-energy arcing faults 

are possible which may physically sever the conductors of the arcing cable. In several cases 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-17

involving these larger fuses, localized arcing resulted in conductors becoming severed in a short 

period of time (a few seconds or less). This left the conductors fully separated but still 

energized. The DC testing also showed some spurious operation signals that persisted for a 

much longer duration than any observed in the AC testing. 

Because of the characteristics of cable failure, the PIRT panel felt that fuse/breaker size and 

timing characteristics would have a minimal effect on the chances of a hot short inducing a 

spurious operation (ranked “Low”); however, the PIRT panel did believe that once the spurious 

operation occurred, the actual duration of the spurious operation could be affected substantially 

by available fault current, fuse/breaker size, and time-current characteristics (ranked “High”). 

Most AC control circuit tests to date have been conducted with relatively small fast-blow fuses 

(i.e., 3 ampere). In the case of CPTs the fusing has always been applied on the CPT secondary 

side. In other possible configurations (e.g., larger fuses, and fused primary but un-fused 

secondary) spurious operations may persist for a longer duration. 

9. Cable Grounding Configuration (For grounded AC only)

This influencing parameter refers specifically to the potential impact on the likelihood and 

duration of spurious operations given cable failure for: 

(a) a drain wire (i.e., an un-insulated grounded conductor) or

(b) a grounded shield wrap of substantial physical characteristics (e.g., a zinc or copper spirally 

wound tape rather than an aluminized Mylar overwrap). 

The presence of a substantial, readily accessible ground plane within a cable expectedly will 

increase the likelihood of short-to-ground faults over hot shorts. The PIRT panel considered 

limited data for shield-wrapped cables from the DESIREE-Fire program, and from one older 

NRC study on cable aging (Ref. 25) that involved a cable with a drain wire. Finally, the PIRT 

panel also considered publically available data on testing armored cables. The data from the 

publically available Duke Test of grounded AC circuits concluded that grounded armor and 

control-power source practically eliminates fire-induced spurious operations. Overall, the 

consensus of the PIRT panel is that the presence of these features would substantially reduce 

the likelihood of spurious operations for grounded circuits. Since these cable configurations 

facilitate the shorting of cable conductors to ground, the PIRT panel felt that this type of cable 

also would decrease the duration of any spurious operations that do occur. Therefore, the PIRT 

panel suggested a ranking of “High” for spurious operations, and “Medium” for influence on 

duration. 

10. Power Supply Voltage 

For typical grounded AC control circuits in U.S. plants, the voltage level varies very little. Most 

circuits are based on standard 120 Vac. The PIRT panel recognized the possibility of some 

variation in circuit voltages, ranging from a minimum of 24 VDC (for ungrounded DC circuits) 

and a maximum of 220 VAC for control circuits. Overall, the PIRT panel’s consensus was that 

variation over this range would have no substantive effect on either the likelihood or duration of 

spurious operations after a cable failure. Therefore, the panel assigned a “Low” influence 

ranking to the power-supply voltage. 

11. Armored Grounded versus Ungrounded Circuits

We note that the PIRT panel considered this influencing parameter differently for AC control 

circuits and DC control circuits. As indicated in Tables 3-1 and 3-2, for the former, this 

parameter was assessed based on the grounded versus ungrounded AC control circuits. The 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-18

latter were assessed based on armored- versus unarmored-cable configuration rather than the 

control circuits’ configuration since the US NPP industry does not use grounded DC control 

circuits. 

For grounded AC circuits

For armored cables, whether or not the circuit itself is grounded or ungrounded (i.e., whether or 

not the power source is grounded on the return side) appears to profoundly affect the likelihood 

of spurious operation. The data available is limited to the tests from EPRI/NEI, and insights 

from the Duke Test data set. This information suggests that in a grounded AC circuit, the 

likelihood of spurious operation, given a grounded armor cable, is much lower than for nonarmored cables. This is attributed to the readily available mitigating ground plane via shorts to 

the armor. 

Publically available Duke Test results revealed that the duration of the hot short-induced 

spurious operations of a 37/C armored cable was much longer than that in an 8/C armored 

cable. We note that the 37/C cable contained multiple circuits whereas the 8/C had only one. 

For ungrounded DC circuits

The reasoning about armored cable for DC control circuits parallels that for AC circuits. The 

one unique aspect of the former is that essentially all of the existing DC power supplies (battery 

banks) are ungrounded, whereas most AC power supplies are grounded. Hence, the 

predominant cases for DC versus AC are reversed. Since DC circuits are ungrounded, the 

PIRT panel evaluated this parameter for an armored cable versus an unarmored cable. 

Parameter importance rankings paralleled those for AC control circuits with the exception of 

intra-cable hot short-induced spurious operations that were considered ‘Low’ for DC circuits due 

to the ungrounded configuration of a DC circuit. For AC circuits, this parameter was extremely 

important because grounded armor provided a readily available mitigating ground-plane that 

would blow a fuse in a grounded AC circuit. 

12. Cable Wiring Configuration

We note also that the total number of conductors present in a multi-conductor cable might be a 

factor herein. One special case of this factor is the use of trunk cables that can house four or 

more circuits within a single cable. A separate discussion on this topic appears in Section 6.7. 

The PIRT panel concluded that the wiring configuration was the single most important factor

impacting both the likelihood and duration of fire-induced spurious operations. This 

configuration embodies several factors, including the total conductor count, the number of 

source conductors, the number of mitigating conductors (e.g., grounded conductors for a 

grounded circuit, or circuit return-leg conductors in an ungrounded circuit), and the number of 

spurious-operation target conductors of interest. For example, given more source conductors, 

more opportunities exist for a target conductor to be hit by a hot short. At the same time, if 

those source conductors have common fusing, there are potentially more opportunities for the 

source conductor to short to a mitigating conductor, so blowing a fuse. With more mitigating 

conductors present (grounds or return-leg conductors) the likelihood and duration of spurious 

operation signals both should decrease. Thus, the PIRT panel ranked this parameter effect on 

spurious operation as “High.” 

In section 3.4, the high importance of this parameter is reflected in the different circuit 

configurations and the arrangement of the probability tables. Two of the primary parameters 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-19

considered are associated with wiring configuration: single-break design/configuration, and 

double-break design/configuration. 

13. Conductor Size

Conductor size, within the realm of AC control circuits, varies over a fairly narrow range. 

Generally, control circuit cables would consist of 10 AWG conductors on the upper end of the 

size range, and 16 AWG on the lower end, with 12 and 14 AWG being most typical. Over this 

range, the PIRT panel concluded that the cable conductor’s size is expected to have little or no 

effect on either the likelihood of spurious operation or its duration (ranked “Low”). 

14. Fire Suppression

Water sprays are likely to cause the formation of additional short circuits that may not have 

existed previously. For thermoplastic cables, water sprays might cause melted insulation to 

solidify, potentially "locking-in" conductor-to-conductor shorts. For thermoset cables, water 

sprays likely will disrupt the residual char layer, allowing more conductors to come into contact 

either with each other, with ground or interact electrically due to impurities in the water that 

could create a conductive shorting pathway. 

There is very little evidence of the effects of water spray on the behavior of spurious operations 

in any of the tests. CAROLFIRE included a few tests wherein cables that had not yet failed were 

sprayed with water, at which time they did fail; however, all such cases involved Silicone Rubber 

or the silicone-based Vita-Link cables that proved highly resistant to fire-induced thermal 

damage in the absence of water. In at least one case, the water spray caused the generation of 

a spurious operation signal, while in another case, fuse-blow failures were observed. 

Approximately half of the PIRT panel ranked this factor as “Low” importance, and the other half 

of the PIRT panel ranked it as “Moderate” importance for the likelihood of spurious operation. 

There was little direct evidence to support the PIRT panel’s decision. Overall, the effect of 

water suppression is not considered to be of primary importance to the likelihood of spurious 

operation, but may be of moderate importance for duration because water sprays may mitigate 

previously formed spurious operation failures by inducing ground fault equivalent hot shorts. In a 

practical sense, the PIRT panel also was unable to offer any practical mechanism for 

incorporating the use of fire-fighting water in the estimates of either the likelihood or duration of 

spurious operation since the timing of water application, and whether or not water would be 

applied in any given fire, depends highly on both plant practices and the specific fire event. 

15. Latching versus Non-latching Device

Circuit designs that utilize a latching or seal-in feature require only a momentary signal to lock-in 

the actuation signal. The latching relay itself will maintain the actuation signal until it is either 

interrupted by events related to the control logic (e.g., a limit switch or timer) or there is a loss of 

control power to the coil of the latching relay (that may or may not be independent of the control 

power that activates the latching feature). 

The consensus of the PIRT panel was that the latching feature essentially should have no 

impact on the likelihood of a spurious-operation signal being generated after cable failure 

(ranked “Low”), but that there is a direct, overriding impact on the duration of the resulting 

actuation signal (ranked “High”). The duration is not driven by the modes of cable failure and 

the effects factors that drive other non-latching circuits; rather, it is driven by those circuit design 

features that define the trip behavior of the latching relay coil. Since the behavior of latching 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-20

versus non-latching circuits is independent of the fire damage experienced, this characteristic is 

not addressed any further in this document. 

16. Circuit Grounded versus Ungrounded (For ungrounded AC only)

For a grounded circuit, a single short between an energized source conductor (a "hot" 

conductor) and ground may cause fuse-blow failures that would reduce the likelihood of a hot 

short leading to spurious operation. This also could mitigate hot short signals formed previously 

(i.e., impacting the hot short’s duration). In contrast, for an ungrounded circuit, a single short to 

ground on either the "hot" or "return" side of the circuit will not cause a fuse-blow failure. 

Ground fault equivalent hot shorts (or a direct short between a hot- and return-conductor) are 

required to cause such a failure. 

In grounded circuits with CPTs, the common return of the CPT secondary is grounded. Then, 

two CPTs (similar to two battery banks in DC) that already share a common ground (grounded 

circuits) are considered compatible power sources because a single hot short from one source 

circuit to a second target circuit can actuate the target circuit. For ungrounded circuits, the 

CPTs are not considered compatible power sources in their nominal state. That is, a single hot 

short between circuits cannot trigger a spurious operation. In ungrounded circuits, ground fault 

equivalent hot shorts might cause normally incompatible power sources (e.g., separate CPTs) 

to become compatible power supplies. For example, shorts to ground on the return side of two 

ungrounded CPTs will form a current return path between the two circuits allowing a separate 

single hot short between the circuits to cause an actuation signal. 

The last effect is that ungrounded circuits require direct shorting (i.e., conductor-to-conductor) or 

indirect shorting (e.g., ground fault equivalent hot shorts) between the energized- and returnconductors of the power supply to cause a fuse-blow failure. For grounded circuits, as noted 

above, a single short between an energized conductor and ground can do so. Consequently, 

there may be some secondary effect on the potential duration of any spurious operation signals 

that occur for ungrounded versus grounded circuits. The effect is considered of secondary 

importance because the duration/mitigation of the spurious operation signals appears to be 

dominated by the cascading catastrophic breakdown of the cables; this appears to occur over a 

short time and causes essentially all conductors to short together, and often shorting to ground 

as well. For either grounded- or ungrounded-circuits, a catastrophic cable breakdown will blow 

the fuses. 

For grounded AC control circuits, circuit grounding is considered of primary importance only for 

the inter-cable shorting behaviors (ranked “High”). This is considered to be true since the 

presence of a ground within the control cable is expected more likely to result in a fuse blow 

within the cable prior to an interaction with a target or source conductor in an adjacent and 

separate cable. Several behaviors interact in this case, so complicating the situation. 

3.2 Summary of Influencing Parameters Importance 

In analyzing the results given in Tables 3-1 and 3-2, the PIRT panel developed an overall 

consensus that certain parameters have LOW to MEDIUM impact on the phenomena of hot 

short-induced spurious operation and their duration based on their evaluation of the test data, 

included that from the NRC/SNL and EPRI/NEI tests, along with PIRT panels’ expert judgment. 

Therefore, in identifying the control circuit configurations the PIRT panel did not consider the 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-21

following parameters capable of influencing the vulnerability of hot short-induced spurious 

operations and their duration: 

• Conductor count 

• Fire Exposure Condition (on spurious operation probability) 

• Cable Routing/Raceway (except Panel Wiring) 

• Cable Raceway Fill (except Bundles) 

• Conductor Insulation Material (for Intra-Cable spurious operation probability and duration) 

• Cable aging (with differing views) 

• Cable Jacket Insulation Material 

• Time-Current Characteristics (for spurious operation probability only) 

• Power Supply Voltage 

• Conductor size 

• Fire Suppression 

The above influencing parameters are considered to have a LOW to MEDIUM impact on 

spurious operations and duration for the following reasons: 

(1) The wiring configuration is a surrogate to the conductor count and the PIRT panel’s 

consensus was that the likelihood of a spurious operation was influenced more by the 

configuration of the conductors’ wiring (number of source, targets, and common-powersupply return conductors), rather than the number of conductors. 

(2) Since FIGURE-OF-MERIT 1 assumed that the fire already has damaged the cable, the only 

impact of the fire exposure is associated with the duration of the spurious operation. 

(3) Raceway or routing (i.e., tray, conduit, air drop) has very little effect on hot short-induced 

spurious operation phenomena. 

(4) Raceway fill has little effect on intra-cable hot shorts. However, cables in bundled 

configurations (e.g., panel wiring, bundled cable groups separated within a cable tray) have 

displayed a higher number of spurious operations in fire tests compared with unbundled 

cable in raceway. 

(5) Cable insulation does not affect spurious operations caused by intra-cable hot shorts, but it 

significantly decreases spurious operations caused by inter-cable hot shorts. 

(6) Both CAROLFIRE and AC DESIREE-Fire tests found that the effect of CPTs on spurious 

operations is contrary to the findings of the EPRI/NEI test results. The PIRT panel could not 

determine the reason for this discrepancy but recommended using the data from all test 

programs to develop best-estimate conditional probabilities of spurious operation. 

(7) Limited specific test data was available for the effect of fire suppression on spurious 

operation or duration. Fire suppression may likely have some effect on circuit response but 

those effects are not yet explicitly known. 

(8) The effects of other parameters such as cable aging, power supply voltage, conductor size 

are found to be insignificant. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-22

Parameters that could have HIGH impact on the hot short-induced spurious operation 

phenomena and duration include 

• Fire Exposure Condition 

o For duration 

• Cable Routing/Raceways 

o Panel wiring only 

(NOTE: Due to the limited data on panel wiring, this parameter is not considered in 

the following sections. This parameter was ranked “High” primarily due to the 

sparsity data, and the suspicion of PIRT Panel members that this parameter could be 

important. A high ranking was given to this parameter to assure it was properly 

considered in future research.) 

• Cable Raceway Fill 

o Bundles only for intra-cable hot short induced spurious operations (Note: The PIRT 

panel considered bundles important even though it is ranked Medium) 

• Conductor Insulation Material 

o For Inter-cable hot shorts (TS versus TP) 

• Time-Current Characteristics 

o Fuses/Breaker Size on duration 

• Cable Grounding Configuration 

o Ground or Drain Wire, Shield Wrap 

• Armor Grounded versus Ungrounded Circuit (for AC) and Armored versus Unarmored (for 

DC) 

• Cable Wiring Configuration (Number of Sources, Target, Ground/Neutral and their 

Locations) 

• Latching versus Non-latching devices (e.g., MOVs) for duration 

o This parameter is not considered beyond this point, since the behavior relative to this 

parameter is independent of fire damage. 

• Grounded versus Ungrounded Circuits for AC only 

o For inter-cable spurious operations. 

3.3 Control Circuits Vulnerable to Hot Short-Induced 

Spurious Operations 

This section describes the process that the PIRT panel used to identify electrical control circuits 

that would be vulnerable to hot short-induced spurious operation from fire damage. The 

process included evaluating the results from the PIRT panel’s ranking of influencing parameters, 

the results of fire tests, variations in circuit power supply, and the three typical hot short failure 

modes of concern for control circuits identified from fire tests. The information described is not 

considered exhaustive, but, rather, representative of common configurations found in NPPs. 

3.3.1 Evaluation of Fire Test Results 

Three major test programs have considered fire effects on cables: The EPRI/NEI (Refs. 7 & 11), 

CAROLFIRE (Ref. 9), and DESIREE-Fire (Ref. 10). In all three, a cable’s electrical functionality 

was assessed with two different electrical-monitoring systems. One system, the SNL Insulation 

Resistance Measurement System (IRMS) measured the insulation resistance of individual cable 

conductors (or groups of conductors), so providing a direct measure of the electrical integrity of 

a cable’s insulation. The IRMS can detect the onset of cable degradation and determine the 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-23

specific pattern and timing of shorts occurring among the conductors of one or more cables. The 

second system, the Surrogate Circuit Diagnostic Units (SCDUs)11, involved the control circuit 

simulators wherein a hot short could entail the spurious operation of AC motor-operated valve 

(MOV) circuit-motor contactors. In the DESIREE-Fire tests, eight DC-powered control circuits, 

including the MOV, were monitored using the control circuit simulators. Seven of these 

comprised two reversing MOV circuits, two small pilot SOV circuits, one 1-inch SOV, one valve 

coil for a large direct-acting SOV, and two medium voltage switchgear-breaker units. The eighth 

circuit was a special purpose system built to look for inter-cable hot shorts. We note that the 

MOV circuits used in DESIREE-Fire included an interlock system, whereas both EPRI/NEI and 

CAROLFIRE did not use either electrical- or mechanical-interlocks in their MOV circuits. 

The systematic review of the AC and DC test data (Ref. 20) identified that the insulation material 

(TS versus TP) was an important factor affecting the probability of inter-cable hot shorts and 

that the wiring configuration had an effect on both intra- and inter-cable hot shorts. Other 

parameters, such as fire-exposure conditions, raceway fill, and fuse size greatly can affect the 

duration of the hot short-induced spurious operation. Additionally, the grounding of the circuit 

(increased probability of a blown fuse), or the presence of a ground plane near the source 

conductor(s), can influence the likelihood of experiencing a hot short-induced spurious 

operation. Because of this ground-plane interaction, the parameters of the cable’s construction, 

such as the presence of a drain conductor, shield wrap, or armor, and that of the cable routing 

parameters, such as trays and conduit raceways (assuming that these cable construction- and 

routing-parameters typically are grounded to the plant ground) play a measureable role in 

predicting the likelihood of hot short-induced spurious operations in a control circuit. Finally, the 

PIRT panel concluded that the likelihood of the mode of failures in panel wiring and armored 

cables would differ from the base case of a standard raceway configuration, and therefore, 

should be included in identifying the control circuits to be evaluated. 

The analysis of the test data found only limited information pertaining to fire-induced inter-cable 

failures. Such data is presented in the data analysis report (Ref. 20) for both AC- and DCcircuits. The results show that the likelihood of experiencing these inter-cable hot shorts is 

lower than intra-cable; however, several cases exist in both the EPRI/NEI and CAROLFIRE 

tests where the former were experienced. The data analysis for the DESIREE-Fire tests, on the 

other hand, identified a newly observed (but previously postulated in NUREG/CR-6834 (Ref. 

19)) failure mode wherein multiple shorts to ground cause a DC circuit to spuriously operate. 

This failure mode is referred to as “ground fault equivalent hot shorts” and is the only inter-cable 

failure mode observed in DC circuit testing. This failure mode can impact circuits routed in 

dedicated conduits since this particular phenomenon occurred between cables co-located on 

the same raceway, as well as between cables located on different raceways provided they both 

belonged to the same ungrounded common-power supply. The results from the data analysis of 

the DESIREE-Fire testing now show that these events occurred quite frequently during the 

intermediate-scale testing. 

A similar scenario observed in DESIREE-Fire testing is discussed in Appendix A of NUREG2128 (Ref. 20). Since these tests were performed in Penlight with the cables physically 

 

11 Surrogate Circuit Diagnostic Units (SCDUs) were used in the “Intermediate-scale” open burn test series 

in CAROLFIRE and DESIREE-Fire test programs, and in EPRI/NEI tests to simulate where a hot short 

could lead to spurious operation of an end device such as a motor contactor. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-24

separated from each other, the only route for inter-cable interaction is through the ground via 

the cable tray. 

NUREG-2128 (Ref. 20) examined both AC and DC circuits for concurrent hot shorts (or 

spurious operations). The configurations of the AC test circuits eliminated the possibility of a 

single cable causing multiple concurrent hot shorts affecting multiple circuits, since all AC testinvolved cables were connected to a single MOV circuit. Thus, when reviewing the test results, 

two cables are required to experience a hot short simultaneously to be considered concurrent 

hot shorts. Because of this and the physical arrangement of cables within the SNL 

intermediate-scale testing facility, the concurrence of hot shorting has not been observed in any 

individual AC test. In some cases, the concurrence between two circuits was missed by only a 

few seconds, but adhering to the strict definition of concurrent hot shorts, this phenomenon was 

not observed in any AC circuit testing. This does not rule out the concurrence of spurious 

operations for AC control circuits, but it does point to its low probability. 

Twelve intermediate-scale tests performed in DESIREE-Fire included six to seven DC circuits 

per test. The results were analyzed to identify times when hot short-induced spurious 

operations occurred concurrently. Five different types of DC surrogate circuits were tested, 

namely, a solenoid operated valve (SOV), motor operated valve (MOV), 1-inch valve solenoid, a 

large coil similar in size to a power-operated relief valve, and a medium voltage circuit breaker, 

referred to as switchgear (SWGR). Most of the five circuits were included in every intermediatescale test. Section 4.15 of NUREG-2128 (Ref. 20) denotes that in DC intermediate-scale 

testing, several concurrent spurious operations occurred within the same test. 

3.3.2 Considerations for Defining Control Circuit Configurations 

As discussed in the previous section, the PIRT panel assessed test results on control circuits. 

They employed a very basic circuit model as the base configuration that consisted of a single 

contact and relay for a very basic single-break design, and two contacts and a relay for a 

double-break design. It was felt that these two basic circuits could best illustrate all of the 

different hot short-induced spurious operations. Furthermore, by using a very basic circuit, the 

failure modes and probabilities could easily be extrapolated for more complicated circuits. 

Figure 3-1 presents simplified circuit schematics of a single contract- and double contact-circuit 

powered from a 125 VDC ungrounded (or possibly 120 VAC distribution system) power system. 

Another parameter explored by the PIRT panel was the variations in the power source (i.e., AC 

or DC power supply). They considered both grounded and ungrounded circuits for the AC 

control circuits powered from a CPT and only the ungrounded circuit for the DC control circuits. 

In the discussion of the typical circuit designs and their behavior relative to the three types of 

fire-induced circuit failures that could cause a spurious operation, the information available for 

ungrounded 125 VDC circuits is extrapolated to the case of ungrounded 120 V AC distribution 

circuits (i.e., ungrounded 120V AC circuits that are powered from one or more distribution 

panels). These variations in power source and the three hot short failure modes of concern that 

could lead to a spurious operation are discussed below. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-25

Figure 3-1. Simplified circuit schematics of single and double break circuits: Ungrounded; 

Grounded; Distribution Bus; Powered from CPT. 

Power Source Variations 

The following three different single phase power source configurations of control circuits are 

considered: 

• Grounded AC control circuits, 

• Ungrounded AC control circuits, and, 

• Ungrounded DC control circuits. 

Each involves certain unique characteristics that may impact the likelihood and duration of 

spurious operations after cable failure. Each power source also carries implications relative to 

the modes of cable failure that might lead to spurious operation and the likelihood that those 

modes might in fact occur in an actual fire. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-26

Grounded AC Control Circuits

The first power source considered is grounded AC. Control circuits typically operate at 120 

VAC grounded, and circuit power may be supplied either by a common AC electrical bus (e.g., 

through a breaker distribution panel), or from the electrical bus via a dedicated CPT. Using 

CPTs is common practice in MOV circuits. In this application, the primary (input) side of the 

CPT typically draws power from two phases of the primary power-source (e.g., 480 VAC Bus) 

feeding the MOV’s drive motor, steps that power down to 120 VAC on the secondary (output) 

side of the CPT and feed that power to the control circuit. The common return side of the CPT 

secondary typically is connected to ground for AC-grounded control circuit applications powered 

from a CPT. Thus, the control circuit is parasitic on the primary power circuit that it actually 

controls. 

The CPT is a power-limited device, so placing a hard limit on the total power available to the 

circuit (the product of current and voltage). Hence, as the current flow increases beyond a 

certain point, the voltage begins to decline below the CPTs nominal output voltage. If the 

voltage drops below the minimum pickup voltage for the actuation device (i.e., MOV contactor), 

then no spurious operations could occur. The EPRI/NEI test data show a significantly reduced 

rate of spurious operations for tests where the CPTs were used compared to those without 

them. 

Grounding the common return-side of the power-supply circuit provides an opportunity for power 

to return to the supply source via the ground plane. Hence, when evaluating a given circuit, any 

other grounded AC power source of similar voltage is considered a compatible source. For 

example, any grounded CPT can feed power to any other grounded AC control circuit, even if 

the target circuit normally is powered by a separate dedicated CPT. 

The ungrounded leg of the circuit that is attached to the power supply will be referred to as the 

“hot” leg. With a grounded AC source, a low resistance short between the hot leg and ground 

will trigger circuit-protection features (e.g., trip a circuit breaker trip, or blow a fuse). 

Consequently, a hot short equivalent ground-fault interaction is incredible for a grounded AC 

circuits because hot-leg power cannot be passed from one conductor to another via the ground 

plane without triggering circuit protection. 

Grounded AC circuits have circuit-fault protection in the form of fuses and/or breakers, but their 

configuration can vary. For circuits powered by a common AC bus, a fuse or breaker will be 

located in the circuit’s hot leg. For circuits powered by a CPT, a fuse also will be provided in the 

hot or ungrounded leg of the circuit on either the primary- or secondary-side of the CPT. The 

PIRT panel’s judgment was that fusing on the secondary side was practiced more commonly, 

although cases of primary-side-only fusing are known to exist. Given fusing only on the primary 

side of the CPT, the circuit may be somewhat less sensitive to fire-induced fault currents, 

although a substantive fault current still should cause the fuse to blow. 

Ungrounded AC Control Circuits

Ungrounded AC control circuits are considered less common than grounded AC circuits. The 

PIRT panel identified a few specific applications of ungrounded AC distribution bus at NPPs, 

with all being associated with a battery bank to AC-power inverter systems. While using an 

ungrounded AC distribution bus is infrequent, nevertheless, it was considered in evaluating 

failure modes. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-27

No testing has been undertaken of control circuits powered by an ungrounded AC distribution 

bus; hence, their behavior essentially is unknown. In lieu of actual test data, the PIRT panel 

concluded that an ungrounded AC distribution bus would behave similarly to an ungrounded DC 

one with respect to the likelihood of hot short-induced spurious operations. The reasoning 

underlying this conclusion is that the relative likelihood that the required hot shorts would form 

before circuit protection is triggered is driven more powerfully by the grounding configuration 

than it is by the observed differences in faulting behavior between AC and DC power cables. 

This supposition would tend to imply similar behavior relative to the likelihood of spurious 

operations. 

Concerning the duration of spurious operations, the PIRT panel judged the behavior of circuits 

powered by ungrounded AC distribution buses to mirror that of circuits powered by ungrounded 

DC circuits. This judgment was based on a minimal data set, uncommon configuration, and 

lack of specific circuit design configurations. The PIRT panel judged that using the ungrounded 

DC circuit duration probability would conservatively bound durations for circuits powered from 

ungrounded AC distribution buses. Likewise the PIRT panel judged that the duration for circuits 

powered by an ungrounded AC CPT should mirror that of grounded AC CPT circuits. The 

reasoning for this conclusion is that the duration of an actuation signal would be governed more 

powerfully by factors such as fuse sizing and by the relative energy of the conductor-shorting 

behavior than it would be by the grounding’s configuration. Hence, the duration of a spurious 

operation in an ungrounded AC CPT powered circuit should have more in common with that in a 

grounded AC CPT powered circuit than with that in an ungrounded DC circuit. In summary, for 

those cases involving an ungrounded AC distribution bus, the panel’s recommended treatment 

is to assess likelihood using the corresponding likelihood values developed for ungrounded DC 

circuits. Therefore, to assess the duration of the spurious operation signal involving ungrounded 

AC CPT circuits the PIRT panel suggests using the corresponding values developed for 

grounded AC CPT circuits and to use the values developed for ungrounded DC circuit to bound 

ungrounded AC distribution circuits. 

Ungrounded AC applications at NPPs primarily are associated with CPTs with an ungrounded 

secondary, and the PIRT panel knew of several plants using this configuration. Hence, this 

configuration, ungrounded CPTs, was included in the example circuits in Section 3.4. 

For an ungrounded AC circuit, the two legs of the circuit commonly are referred to as the 

“positive” and “neutral” legs. With an ungrounded source, a single short to ground involving a 

conductor energized to either the positive or neutral legs will not trigger the circuit-protection 

features, but will ground one leg of the power source, at least temporarily. Circuit protection will 

be triggered given direct shorting between the positive- and neutral-legs, or by concurrent shorts 

to ground on both legs. 

One unique aspect of ungrounded AC circuits on separate CPTs is that a single hot short 

cannot feed power between circuits because each CPT has its own electrically independent 

power-return path. For one ungrounded source CPT to activate a target circuit normally 

powered from a separate ungrounded CPT requires concurrent faults involving both legs of the 

source circuit. That is, shorts must connect both the positive- and neutral-legs of the source 

circuit to the appropriate conductors in the target circuit to allow power to flow between them. 

The panel noted that ground fault equivalent hot shorts could be the mechanism for making one 

of these connections. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-28

Ungrounded DC Distribution Systems (also, ungrounded AC distribution systems)

Ungrounded DC battery banks commonly are used in the U.S. nuclear power industry. The 

typical battery voltage is 125 Vdc, but some applications also use 250 Vdc. In all cases known 

to the PIRT panel, involving motors and MOVs, station batteries are ungrounded12. 

Several noteworthy general observations were made during the DESIREE-Fire testing (Ref. 10): 

• The arcing observed in conjunction with the cable faulting was more energetic for DCpowered cables than for this behavior in AC-power cables. Both AC- and DC-powered 

cables displayed arcing, but the arcs formed by the faulting DC-powered cables were more 

substantial, more sustained, and more damaging. 

• Faulting of the DC-powered cables often entailed destructive damage to the cable 

conductors (open circuit/conductor breakage): it was not been observed at this level for ACpowered control cables. 

• In some cases, the DC-powered cables remained energized even after experiencing 

destructive damage as described above. This behavior was commoner for tests with larger 

(15A, 25A, or 35A) fuses. 

• For any given DC-circuit, the two paired fuses (one on the positive leg and one on the 

negative leg) did not necessarily clear simultaneously. Many factors contribute to this 

behavior. For example, the time/current clearing relationship varies somewhat even within a 

single batch of like fuses, so that one fuse may clear more quickly than another after the 

same fault current. Also, some fuse blows resulted from circuit-to-circuit interactions 

through the ground plane (ground fault equivalent hot shorts) so that the two fuses involved 

in the fault might be of different sizes (e.g., the fault currents might be routed through a 10A 

fuse from one circuit, and a 5A fuse from another circuit). Then, the lower amperage fuse 

typically would clear leaving the higher amperage fuse intact. 

• In general, more long-duration hot short-induced spurious operations were observed for the 

DC-powered circuits than for corresponding AC-powered circuits. In at least one case from 

DESIREE-Fire (i.e., Penlight Test # 38, Ref. 10), a spurious operation persisted beyond the 

thermal exposure period and until the DC battery bank was manually isolated from the 

damage cable/circuit, and this behavior had not previously been observed in AC-testing. 

Ungrounded DC circuits are similar in some ways to ungrounded AC circuits. For example, a 

single short to ground involving a conductor energized to either the positive or negative battery 

potential will not trigger circuit-protection features; rather, one side of the battery bank will 

become grounded at least temporarily. Also, the hot short equivalent ground-plane-interaction 

failure mode is possible for DC circuits. The PIRT panel concluded that there are three main 

differences between AC- and DC-power sources that could impact the likelihood and duration of 

spurious operations. 

First, the energy level associated with shorting in DC control circuits is higher than that in AC 

circuits. In testing, the DC shorting behavior observed was far more energetic than were the 

shorts in AC circuits. Both AC and DC circuits generate arcs when short circuits form, but the 

arcs formed during DC testing were substantially more energetic and persisted for longer. The 

 

12 However, there are other DC circuits that are grounded, such as the BWR 24 Vdc +/- nuclear 

instrument batteries that have the center tap grounded. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-29

arcs formed in DC testing often were destructive, damaging the raceways and breaking the 

copper conductors (conductor open circuit failures). 

Second, the same battery bank typically power many DC circuits. Accordingly, we can assume 

that when multiple cables are co-located in a common raceway, there likely will be other cables 

present that are powered from the same bank. Any such cable is considered to be powered by 

a compatible power supply. Hence, under certain conditions, a single hot short can lead to a 

spurious operation. 

Third, DC control circuits may be fused at substantially higher amperages than a similar AC 

control circuit. Using 3 A fuses, for example, is considered quite typical for AC circuits. For DC 

control circuits, typical fusing may range from 5-35 A. Testing demonstrated for DC control 

circuits, larger fuses (e.g., 15 A or more) may not clear, even after severe damage to the cables. 

Several cases were observed where cable conductors had open circuited (broken) due to 

arcing, and yet they remained energized (fuses did not clear). 

Another consideration for DC control circuits involves single- or double-break (or -contact) 

designs. In the former, the control switch that actuates the circuit is only switching the “high” (or 

positive) side of the power circuit; the return (or negative) side of the circuit normally is closed. 

In a double-break design, the control switch opens and/or closes both the circuit’s high- and the 

return-sides. In this design, there is just one target of interest (the SOV solenoid), but with a 

double break design, two hot shorts are required to operate the valve. One side of the solenoid 

must short to the high side of a compatible power source, and the concurrently, the other side of 

the solenoid must short to the return side of that same power source, or another compatible 

one. 

Because ungrounded systems (both AC and DC) do not have a pathway to ground, a return 

path for current always is needed. In other words, current from a different current source cannot 

enter a circuit because there would be no exit path for it to back to the common return to 

complete the circuit. 

Due to this characteristic of ungrounded circuits, the following points should be considered 

whenever evaluating these types of circuits for the effects of an inter-cable or ground-fault hot 

short: 

1. For any spurious operation involving one hot short, the voltage/current source of the 

aggressor cable must be the same as that of the target cable. 

2. For any spurious operation involving two hot shorts of proper polarity (double-break 

design), the positive leg’s hot short and that of the neutral leg both must be connected to 

the same voltage/current source. 

Hot Short Failure Modes Leading to Spurious Operation

There are various cable faults (conductor shorts) that may engender the spurious operation of 

plant equipment. The actual failure modes of interest depend on both the specific circuit-design 

and the cable configuration. The PIRT panel focused on hot short-induced spurious operation 

of electro-mechanical devices. This choice excluded cases wherein a single short (other than a 

hot short) to ground, or a conductor’s open-circuit might cause a device to reposition. It also 

excludes cases involving spurious activation of an indicating light, since this is not considered to 

be an “actuation” of an end device. The analysis of test data identified three primary fire-
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-30

induced failure modes (i.e., electrical conductor shorting behaviors) that may lead to hot shortinduced spurious operations: they are illustrated in Figures 3-2 through 3-4. These figures 

provide an illustration of the various failure modes and are not limited to the specific conductor 

shorts shown. 

1. Intra-cable shorting: Electrical shorting between the conductors of a multi-conductor 

electrical cable (Figure 3-2). The shorting may involve individual conductor pairs and/or 

larger groups of conductors within the cable. More than one shorting pair or group may form 

concurrently. In most cases, the conductors will all belong to one circuit; however, cases 

exist (such as trunk cables) where conductors for multiple circuits are located within one 

cable. 

Figure 3-2. Intra-Cable Hot Short 

2. Direct inter-cable shorting: Direct conductor-to-conductor shorting between electrical 

conductors associated with different electrical cables, independent of the ground plane 

(Figure 3-3). Again, shorting may involve individual conductor pairs, or groups of 

conductors.

 

Figure 3-3. Inter-Cable Hot Short 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-31

3. Ground fault equivalent hot short: Shorting between multiple conductors and ground such 

that energy is transferred from one conductor to another via the ground plane. This mode is 

also referred to as “ground fault equivalent hot shorts.” This is an important AC/DC 

ungrounded circuit fault mode (Figure 3-4).

Bonded 

to plant 

ground 

grid

Raceway

Multiple shorts to ground such 

that power is transmitted via 

the ground plane

Raceway #1 Raceway #2

or

Multiple shorts to ground such 

that power is transmitted via 

the ground plane

Figure 3-4. Inter-Cable Ground Fault Equivalent Hot Short 

Figure 3-4, inter-cable ground fault equivalent hot short, is a complex failure mechanism that 

was observed in DC testing. This case is only applicable to circuits powered by an ungrounded 

source that might include an ungrounded DC battery bank, an ungrounded AC CPT, or an 

ungrounded AC-power distribution source. This case postulates that one leg of the power 

source becomes grounded due to conductor shorting resulting from fire-induced failures, 

allowing power transmission via the common ground plane to another conductor that also is 

grounded. The ground plane may be available via grounded shield-wraps, grounded drainwires, cable armoring, metal raceways (e.g., trays, conduits), or grounded conductors within a 

cable (e.g., grounded spare conductors). All grounds are assumed to be associated with the 

same plant-wide ground plane. 

The successful transmission of power from one circuit to another due to ground fault equivalent 

hot shorts does require a compatible power source to be involved (i.e., one able to activate the 

spurious operation target). A compatible power source must (1) provide nominally the same 

voltage, (2) provide the minimum pickup-power load for the target device, (3) match the target 

circuit relative to AC- or DC-power (i.e., AC power cannot activate a DC device or vise-versa), 

and, (4) allow power flow back to the source via that leg of the power supply remaining 

ungrounded. 

A given circuit may be vulnerable to hot shorts caused by one or more of these failure modes. 

For example, some circuits may spuriously operate due to either intra- or inter-cable fireinduced hot shorts. In some cases a combination of conductor shorting modes must occur 

before triggering a spurious operation. For example, spurious operation in some cases may 

result from multiple intra-cable shorts or from an intra-cable short combined with a concurrent 

inter-cable short. The PIRT panel considered various cases and combinations. 

Cable Insulation Material

While the type of cable-insulation material makes little difference in the probability of intra-cable 

hot short-induced spurious operations, it affects the probability of inter-cable hot short-induced 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-32

spurious operations. Because of this, the electrical expert PIRT panel undertook a technical 

evaluation of the credibility of inter-cable failure modes for different insulation types. 

For a single-break design circuit, only one inter-cable hot short of the right polarity would be 

necessary. In an ungrounded circuit containing a “double break” switch design two proper 

polarity hot shorts must occur simultaneously to cause a spurious operation. This proper 

polarity failure mode is also applicable to instances in which: 

• Both positive- and negative-leg fuses blow or are removed, 

• A two-pole circuit breaker opens under fault or is manually opened. 

We note that for the purposes of this discussion, TS and TP refer to the insulation on the cable 

conductors. The PIRT panel discussed four different configurations of cable-to-cable (i.e., intercable) hot shorts as follows: 

1. Thermoset source cable induces a spurious operation in a thermoset target cable

(TS TS): Based upon reviewing the fire-testing research and their expert judgment, the 

PIRT panel concluded that an inter-cable hot short, causing a spurious operation for DC 

ungrounded circuits involving thermoset cables, was implausible. While there was research 

demonstrating the plausibility of the occurrence of an inter-cable hot short among thermoset 

cables, its probability was a very low. Even in the test cases showing some interaction 

between two separate cables, the induced voltage/current was very small and intermittent. 

Because of this, the PIRT panel concluded that an inter-cable, consequential, spurious 

operation between two thermoset cables was implausible. Based on this conclusion, they 

further concluded that a spurious operation caused by two inter-cable hot shorts was 

incredible and need not be considered. 

2. Thermoset source cable induces a spurious operation in a thermoplastic target cable

(TS TP): The CAROLFIRE test data documented a few instances where inter-cable hot 

shorts were caused by a TS-source cable partially energizing a TP-target cable. Although 

no spurious operations were observed under this configuration, the PIRT panel could not 

develop any logic for excluding this configuration from causing spurious operations. The 

physical argument for this configurations possibility was that TP cables typically fail from fire 

damage prior to TS cables (i.e., TS cables typically fail a higher temperatures than TP 

cables) and the failure mode sometimes results in the loss of cable insulation. Once a TP 

cable fails, with its conductors exposed, and becomes de-energized, an inter-cable hot short 

from a TS cable could energize a conductor(s) in the TP cable, thereby possibly causing a 

spurious operation (provided compatible power sources among the cables). Hence, the 

PIRT panel concluded that a TS-source to TP-target inter-cable spurious operation signal is 

plausible, although it would be fairly low in probability. The PIRT panel again used similar 

logic to the discussion for TP-source to TS-target hot shorts (see item 4 below): 

- Thermoplastic cable would be damaged earlier causing the fuses for this cable to clear 

much earlier in the fire. The thermoplastic conductors would be de-energized, but when 

the thermoset cables finally burn to failure, the thermoset cable conductors could cause 

a voltage/current to be induced in the thermoplastic cable conductors should they be 

exposed by loss of insulation capability. 

- Since thermoset tends to char and fail at higher temperatures than thermoplastic cables 

(i.e., TS fail after TP), it makes an inter-cable induced voltage/current much less 

probable. As explained in the following sections, thermoplastic cables would be 

expected to have already become de-energized prior to the failure of the thermoset 

cables. Therefore, thermoplastic to thermoset inter-cable hot shorts are considered to 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-33

be incredible. Additionally, due to the charring characteristics of thermoset cables, 

thermoset to thermoset inter-cable hot shorts are considered to be implausible. In this 

latter case, intra-cable failures are expected to precede inter-cable failures. 

The combination of these factors and the research results made the PIRT panel conclude 

that inter-cable TS-source to TP-target spurious operations are possible, but of low 

probability. Based on this conclusion, they further concluded that a spurious operation 

caused by two inter-cable hot shorts was implausible and need not be considered. 

3. Thermoplastic source cable induces a spurious operation in a thermoplastic target cable

(TP TP): During discussions, the PIRT panel concluded that thermoplastic to 

thermoplastic inter-cable consequential spurious operations were plausible. A small number 

of such cases have been observed in testing during both the EPRI/NEI and CAROLFIRE 

programs. Thermoplastic insulation tends to melt away from the conductors in a 

thermoplastic cable, thereby allowing more direct access to the conductors by external 

cables. The possibility of concurrent inter-cable consequential hot shorts across the 

conductors of two cables producing a spurious operation in an ungrounded circuit is judged 

to be low, but not as low as the probability of spurious operations caused by intra-cable 

shorting for TP TP cases than for TS TS cases. 

4. Thermoplastic source cable induces a spurious operation in a thermoset target cable

(TP TS): Finally, since no instances of thermoplastic cables producing a spurious 

operation on a thermoset cable have been recorded, this type of interaction also was ruled 

as incredible. It should be noted that CAROLFIRE specifically set up test to allow for and 

then monitored for such interactions and none were observed. The PIRT panel speculated 

that this lack of credibility primarily reflected two factors: 

- Thermoplastic cable would be damaged earlier, causing the fuses for this cable to clear 

much earlier in the fire. By the time the thermoset cables burned to failure, the 

thermoplastic cable would no longer have power to its source conductors. 

- Thermoset tends to char rather than melting like thermoplastic. The charred thermoset 

poses an added barrier to inter-cable hot shorts. While induced currents can occur 

across the charred insulation, the current path is not of the same quality as a conductorto-conductor short. As previously mentioned, this results in a much lower probability for 

a consequential hot short failure mode. 

Table 3-3 provides a synopsis of the panel’s evaluation of the inter-cable failure mode. (See 

Section 2.1.3 for the definitions of IMPLAUSIBLE and INCREDIBLE). 

Again, this evaluation considers only the insulation on cable conductors. Since the probability of 

inter-cable hot shorts for TP TS is considered incredible, the PIRT panel did not include this 

insulation combination category in its failure mode consideration in Section 3.4. 

 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-34

Table 3-3. Inter-Cable Failure Mode Categorization 

Conductor Insulation 

Source Target 

Number of Needed 

Inter-Cable Hot Shorts* Possibility 

TS TS 1 IMPLAUSIBLE 

2 INCREDIBLE 

TS TP 1 Possible 

2 IMPLAUSIBLE 

TP TP 1 Possible 

2 See NOTE 

TP TS 1 INCREDIBLE 

2 INCREDIBLE 

*1 - single break (or contact) design; 2 - double break (or contact) design 

NOTE:

Single inter-cable hot shorts involving TPTP interactions were observed in the test 

data. Although multiple concurrent inter-cable hot shorts did not produce a spurious 

actuation in any test, the test circuits were not configured to look for this specific failure 

mode. The possibility of getting concurrent inter-cable hot shorts is considered to be a 

very low likelihood event. The PIRT Panel did not classify the two inter-cable hot short 

TPTP cable interactions as implausible, because it was in their judgment that the 

likelihood of this configuration lie somewhere between a possible and implausible 

classification. Qualitatively the PIRT panel judged the likelihood of TPTP interactions 

higher than the likelihood of TSTP interactions. It is the PIRT panels’ judgment that 

concurrent hot shorts for TPTP cable interactions would be very short lived based on 

the failure characteristics of thermoplastic cable, which involve rapid loss of form (via 

melting of the insulation) and melting away of the insulation. 

3.3.3 Control Circuit Configuration Scenarios 

To qualitatively assess the control circuits for hot short-induced spurious operation, the PIRT 

panel formulated 13 individual base case scenarios (6 with single break or contact circuit 

configurations and 7 with double break or contact circuit configurations) consisting generally of 

the following broad categories of cable’s physical properties and configuration, and cable 

routing configuration: 

• TS-insulated conductors (both source and target conductors), 

• TS- or TP-insulated cable jacket, 

• Nominally a 7-Conductor, unarmored cable, 

• Cables routed on cable trays or in conduits, 

In these 13 cases, the electrical source for the circuit was varied with the individual hot short 

induced spurious operation failure mode (AC grounded, AC ungrounded, or DC ungrounded). 

Grounded AC circuits powered from a CPT (as a target) are susceptible to only intra-cable and 

inter-cable hot shorts. Inter-cable hot shorts via ground equivalent hot shorts, are not possible, 

since a fire-induced fault current due to grounding will cause the fuse to blow or the breaker to 

trip. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-35

For ungrounded AC or DC power supplies, the circuits are susceptible to all three hot short 

failure modes: intra-cable, inter-cable, and ground fault equivalent hot shorts. Thus, three basic 

hot short failure modes are applicable to ungrounded control circuits. 

The following thirteen different hot short induced failure modes that could occur in control 

circuits due to a fire consist of two modes for grounded AC circuits and three modes for 

ungrounded AC/DC circuits requiring a single contact, and five modes for ungrounded AC/DC 

circuits requiring double contacts: 

For AC grounded control circuits (with a single break or contact), conductor-to-conductor hot 

short modes of failure include: 

1. Intra-cable within any raceway configuration 

2. Inter-cable (cable-to-cable) between any two cables within any raceway 

configuration 

For DC (or AC) ungrounded control circuits (with a single break or contact) and proper polarity, 

conductor-to-conductor hot short modes of failure include: 

3. Intra-cable within any raceway configuration 

4. Inter-cable (cable-to-cable) within same raceway cables 

5. Inter-cable (via ground plane) within same raceway cables 

6. Inter-cable (via ground plane) between different raceway cables 

For DC (or AC) ungrounded control circuits (with double breaks or contacts) and proper polarity, 

conductor-to-conductor hot short modes of failure include: 

7. Intra-cable within any cable and Intra-cable within any cable 

8. Intra-cable and Inter-cable (cable-to-cable) within same raceway cables 

9. Intra-cable and Inter-cable (via ground plane) within same raceway cables 

10. Intra-cable and Inter-cable (via ground plane) between different raceway cables 

11. Inter-cable (cable-to-cable) and Inter-cable (cable-to-cable) within same raceway 

cables 

12. Inter-cable (cable-to-cable) and Inter-cable (via ground plane) within same raceway 

cables 

13. Inter-cable (cable-to-cable) and Inter-cable (via ground plane) between different 

raceway cables 

All the above failure modes consider a single target conductor and a single source conductor for 

each contact. 

3.4 Examples of Control Circuits Vulnerable to Hot ShortInduced Spurious Operations 

The first part of this section discusses tables that the electrical expert PIRT panel provided for 

using in the probabilistic assessment of hot short-induced spurious operations. They represent 

the conditional probability categories that the PIRT panel believed important for Fire PRA 

applications. However, it is recognized that these tables ultimately could be changed by the 

expert elicitation PRA Panel to facilitate their portion of this project. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-36

The second part of this section shows figures representing the basic circuit configuration and 

failure modes that the PIRT panel believes should be considered. They give simple 

representations of the circuits to aid in understanding the different hot short-induced spurious 

operations. 

Finally, the last part of this section discusses certain inherent characteristics of cables in the 

control circuit configurations that can limit the probability of hot short-induced spurious 

operations. While not specifically stated in these tables, it is important to recognize that these 

characteristics exist before analyzing deterministic effects and probabilities. Specifically, the 

behavior of AC ungrounded, DC ungrounded, and AC grounded circuits are discussed. 

The control circuit used as the base case for all figures and table sets described in this section 

is considered to be representative of both AOV/SOV and MOV circuits. These types of circuits 

commonly are used in NPPs and they are consistent with the common circuit-configuration 

tested by both EPRI/NEI and NRC/SNL. The circuit provided, because of its simplicity, can 

readily be used to explain the behavior of all hot short-induced spurious operations in NPPs. 

Any differences between the spurious operation probabilities of the AOV/SOV versus the MOV 

circuit that could affect the probability of a fire-induced hot short, spurious operation (i.e., one 

versus two spurious operation targets in the circuit) will be addressed by the follow-on expert 

elicitation PRA panel. 

3.4.1 Control Circuit Configuration Example Sets 

Based upon Section 3.3, several control circuit configuration figures are developed to capture 

the thirteen base cases. Additionally, a number of spurious operation probability tables are also 

given. Three sets of tables are created. The first set of tables addresses the probability of a 

single hot short-induced spurious operation. This set of tables and the resulting probabilities 

can be applied directly to any single contact (single break design). In other words, these tables 

will give probabilities that directly apply to Cases 1 through 6 in Section 3.3. The second set of 

tables takes the results of the first set and combines them to address the remainder of the 

cases in section 3.3 (Cases 7 through 13). Since all of the cases in the second set of tables 

involve two hot short-induced spurious operations, this second set of tables address the double 

break design circuits. 

Additionally, for the first two example sets of tables, since it is determined that the failure 

mechanism for a surrogate ground plane induced hot short is the same whether the aggressor 

cable is in the same raceway or a different raceway as the target cable, the raceway is not 

considered to change the probability of the failure mode itself. However, if the aggressor cable 

is in a different raceway from the target cable, other factors (e.g., the nature of the fire, the 

locations of the two raceways) could greatly affect the probability and duration of a spurious 

operation. Since these factors are plant dependent and not generic, the difference in probability 

would have to be determined on a case-by-case basis. NUREG-2128 (Ref. 20) offers 

information about the number of ground fault equivalent hot shorts that are from conductors 

within the same raceway versus conductors between two different raceways. 

Finally, the third set of tables specifically addresses the duration of a hot short-induced spurious 

operation. 

 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-37

3.4.1.1 Control Circuit Example Set One 

In example set one, three tables are developed. These tables and the associated circuit 

diagrams are organized as shown in Table 3-4, below. 

Table 3-4. Control Circuit Example Set One with Single Break Design 

Figure Control Circuit Power Source Probability Estimation 

3-5 Grounded AC powered from a CPT Spurious Operation 

3-6 Ungrounded AC powered from a CPT Spurious Operation 

3-7 Ungrounded DC (or AC distribution bus) Spurious Operation 

Each table starts (refer to Figures 3-5, 3-6, and 3-7) with a base case control circuit 

configuration and then varies different configuration elements that potentially could affect the 

probability of the failure modes (i.e., hot short-induced spurious operations). The base-case 

cable configuration in a control circuit consists of the following: 

1. Single circuit in a single cable; 

2. Nominally a 7-conductor, unarmored, TS insulation; and 

3. Only one target conductor of interest present (e.g., valve open target). 

The different configuration variables for a cable that are used for the tables are as follows: 

1. Thermoplastic insulated target cable; 

2. Cable with a grounded metal foil shield wrap; 

3. Cable with an un-insulated grounded drain wire; and 

4. Armored 7/C cable. 

The PRA panel will use these tables to estimate the probability of a hot short-induced spurious 

operation. Since there are primarily three hot short failure modes that induce spurious 

operations, i.e., intra-cable-, inter-cable-, and inter-cable ground fault equivalent hot shorts, 

these are included in every table to estimate their probability. Finally, an aggregate of all the 

probabilities of a spurious operation of a control circuit in consideration is provided in the last 

column. 

The ungrounded AC table is applicable to CPT-powered circuits (see Figure 3-6). Ungrounded 

AC distribution circuits should be treated the same as ungrounded DC circuits. A single groundfault-equivalent hot short is not considered in the table for ungrounded AC CPT circuits because 

no return current path is available. It also was not considered for a grounded AC circuit 

because a ground on the source of the aggressor circuit would cause a blown fuse (see Figure 

3-5). 

The PIRT panel believed that the probability of spurious operation could be greatly affected in 

the panel-wiring’s configuration; however, little data was available to support this premise. 

Consequently, the PIRT panel determined that this parameter should not be included in the 

tables, but recommended it as a high priority for future research. 

One additional clarification needs to be made regarding the scope of the ground fault equivalent 

hot short column in Figure 3-7, Table 3-6, and Table 3-7. The ground fault equivalent hot short 

phenomena is meant to capture the possibility of conductors shorting to a ground plane 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-38

(raceway, grounded armor/shield, grounded conductors) resulting in a circuit spurious operation. 

During the development of the probability tables it became apparent that this phenomenon 

could be counted in multiple columns (intra- and ground fault equivalent hot short). For 

instance, a conductor shorting to a grounded conductor (intra-cable short) would have the same 

electrical effect as the same conductors shorting to a grounded cable raceway, grounded armor, 

or other grounded medium (other than a conductor). Thus, the question arose, which column 

should account for intra-cable conductor shorts to grounded conductors. To minimize 

confusion, the PIRT panel recommends that the probability of all intra-cable hot shorts should 

be considered in the column labeled “Single intra-cable hot short” in Figure 3-7, and “Intra + 

Intra cable short” in Table 3-6 and Table 3-7. Thus, a scenario which involves an intra-cable hot 

short between a grounded conductor and another conductor, both within the same cable, should 

be considered an intra-cable hot short and not be considered a ground fault equivalent hot 

short. Although the circuit response would likely be the same, this distinction minimizes the 

likelihood of any double counting during the development and application of the conditional 

spurious operation likelihoods. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Grounded AC power source (from a CPT) spurious operation 

probability table.* 

Cable 

Configuration 

Conductor shorting modes of interest

Single intracable hot short 

Single direct 

inter-cable hot 

short 

Aggregate 

result for all 

possible failure 

modes 

Base Case (TS insulated source and target Cables) TP Cable 

TP insulated source and target cables 

TS insulated source and TP insulated target cables 

Cable includes a grounded metal foil shield wrap N/A Cable includes an uninsulated grounded drain wire Armored 7/C Cable N/A *Shaded black cells are considered implausible but not incredible. Cells marked "N/A" are considered incredible or physically impossible.

Figure 3-5. Grounded AC circuit schematics and probability table 

3-39 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Valve Open

Ungrounded AC

Intra-Cable 

Hot Short

CPT

Valve Open

Ungrounded AC

Inter-Cable 

Hot Short

Additional short-toground providing a current return flow path

CPT

Un-grounded CPT AC power source spurious operation 

probability table.* 

Cable 

Configuration 

Conductor shorting modes of interest

Single intracable hot short 

Single direct 

inter-cable hot 

short 

Aggregate 

result for all 

possible failure 

modes 

Base Case (TS insulated source and target Cables) TP Cable 

TP insulated source and target cables 

TS insulated source and TP insulated target cables 

Cable includes a grounded metal foil shield wrap N/A Armored 7/C Cable N/A *Shaded black cells are considered implausible but not incredible. Cells marked "N/A" are considered incredible or physically impossible.

Figure 3-6. Ungrounded AC circuit schematics and probability table 

3-40 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

Un-grounded DC power source spurious operation probability 

table (also applies to ungrounded AC distribution bus) 

Cable 

Configuration 

Conductor shorting modes of interest 

Single intracable hot short 

Single direct 

inter-cable hot 

short 

Ground fault 

equivalent hot 

shorts 

Aggregate 

result for all 

possible failure 

modes 

Base Case (TS insulated source and target Cables) TP Cable 

TP insulated source and target cables 

TS insulated source and TP insulated target cables 

Cable includes a grounded metal foil shield wrap 

N/A 

Armored 7/C Cable N/A *Shaded black cells are considered implausible but not incredible. Cells 

marked "N/A" are considered incredible or physically impossible. 

 Intra cable shorts that mimic the fault mode of ground fault equivalent hot 

shorts are included under the intra-cable short column.

Figure 3-7. Ungrounded DC circuit schematics and probability table (also applies to ungrounded AC distribution bus) 

3-41 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-42

3.4.1.2 Control Circuit Example Set Two 

As previously stated, example set two addresses failure modes involving two hot short-induced 

spurious operations; therefore, this second set of tables addresses the double-break design of 

control circuits. Once the probability for the single-break design tables was determined, the 

probabilities for the hot short across a single contact can be used to derive the combinations 

needed to initiate a spurious operation in a double- contact/break designed circuit. The 

following hot short-induced combinations were considered: 

1. Intra-cable + Intra-cable; 

2. Intra-cable + Inter-cable; 

3. Inter-cable + Inter-cable; 

4. Intra-cable + Ground fault equivalent hot shorts; 

5. Inter-cable + Ground fault equivalent hot shorts. 

We note that “Ground fault equivalent hot shorts” in combination with another “Ground fault 

equivalent hot shorts” does not exist because it would result in a blown fuse. Additionally, since 

cable-to-cable interactions were being considered, three rows representing different cable 

insulation material types from the base case [TS (intra) and TS TS (inter)] were included: TP 

(intra); TS TP (inter); and TP TP (inter). Figures 3-8 through 3-11 show the associated 

tables and figures. 

Example set two encompasses two different tables. Grounded AC control circuits were excluded 

because the panel members were unaware of any applications of a double-break design for a 

grounded circuit. This primarily is because a grounded AC target does not need two hot shorts 

to produce a spurious operation. Instead, in this case, it would be caused by a single hot short 

on the upstream side (positive) of the relay, and a ground on the other side. However, the case 

of a grounded AC circuit causing a spurious operation on an ungrounded AC circuit was 

included as a possibility for causing a spurious operation in an ungrounded AC circuit design. 

The tables are organized as given in Table 3-5 below. 

 

Table 3-5. Control Circuit Example Set Two with Double Break Design 

Table/Figure Control Circuit Power Source Probability Estimation 

Table 3-6 & 

Figure 3-8 Ungrounded AC powered from a CPT Spurious Operation 

Table 3-7 & 

Figure 3-9 

Ungrounded DC (or AC distribution 

bus) Spurious Operation 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-43

Table 3-6. Double break ungrounded AC probability table 

Double Break Ungrounded AC Powered from a CPT* Cable Configuration 

Conductor shorting modes of interest 

Intra + Intra 

cable short 

Intra + Inter 

cable short 

Inter + Inter 

cable short 

Intra + ground 

cable short 

Inter + ground 

cable short 

Aggregate result 

for all possible 

failure modes 

Base Case (TS 

insulated source and 

target Cables) 

N/A N/A 

TP 

Cable 

TP insulated 

source and 

target cables 

TS insulated 

source and 

TP insulated 

target cables 

 

Cable includes a 

grounded metal foil 

shield wrap 

N/A N/A  N/A 

Armored 7/C Cable N/A N/A  N/A 

*Shaded black cells are considered implausible but not incredible. Cells 

marked "N/A" are considered incredible or physically impossible. 

 Intra cable shorts that mimic the fault mode of ground fault equivalent 

hot shorts are included under the intra + intra cable short column. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Figure 3-8. Double break ungrounded AC schematics 

3-44 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-45

Table 3-7. Double break ungrounded DC probability table 

Double Break Ungrounded DC* 

Cable Configuration 

Conductor shorting modes of interest 

Intra + Intra 

cable short 

Intra + Inter 

cable short 

Inter + Inter 

cable short 

Intra + ground 

cable short 

Inter + ground 

cable short 

Aggregate result 

for all possible 

failure modes 

Base Case (TS 

insulated source and 

target Cables) 

N/A N/A 

TP 

Cable 

TP insulated 

source and 

target cables 

TS insulated 

source and 

TP insulated 

target cables 

 

Cable includes a 

grounded metal foil 

shield wrap 

N/A N/A  N/A 

Armored 7/C Cable N/A N/A  N/A 

*Shaded black cells are considered implausible but not incredible. Cells 

marked "N/A" are considered incredible or physically impossible. 

 Intra cable shorts that mimic the fault mode of ground fault equivalent 

hot shorts are included under the intra + intra cable short column. 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

Figure 3-9. Double break ungrounded DC schematics 

3-46 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-47

3.4.1.3 Control Circuit Example Set Three 

Finally, example set three contains tables specifically designed to address the DURATION of a 

hot short-induced spurious operation (and the duration of hot shorts). Table 3-8 presents the 

logical arrangement of the duration tables. The PIRT panel indicated that fuse/breaker size 

parameter impacts the duration of DC spurious operations and as such the ungrounded DC 

duration tables identified in Table 3-8 have been split. For circuits with fuses ≤ 10 amps 

duration data exists for both spurious operation and hot shorts, while circuits with fuses > 10 

amps only hot short duration data is available. This is a result of all fuses >10 amps used in 

testing were associated with the circuit breaker which by design only allows for a momentary 

spurious operation. The PIRT panel believed that the hot short and spurious operation duration 

data for ≤10 amps case may support extrapolation for spurious operations in the >10 amp case. 

Table 3-8. Control Circuit Example Set Three for Spurious Operation DURATION 

Table Control Circuit Power Source Duration Estimation

3-9 Grounded AC powered from a CPT Spurious Operation Duration 

3-10 Ungrounded AC powered from a CPT Spurious Operation Duration 

3-11 Ungrounded DC power source ≤10 amp fuse Hot Short Duration 

3-12 Ungrounded DC power source ≤10 amp fuse Spurious Operation Duration 

3-13 Ungrounded DC power source >10 amp fuse Hot Short Duration 

The duration tables are set up differently than the probability tables, since the physical 

influencing factors that most affect spurious operation duration differ from those that affect 

probability. The variables chosen for the tables were based upon the parameters from the 

ranking tables that were determined to be highly important to the duration of a spurious 

operation. Such parameters included the following: 

1. Fire exposure condition; 

2. Panel wiring; 

3. Time-current characteristics – Fuses/Breaker Size; 

4. Cable Wiring Configuration (sources, targets); and 

5. Latching versus Non-latching Device. 

Panel wiring, time-current characteristics, and the configuration of the cable wiring were 

eliminated from consideration in this table set because there were insufficient data to 

realistically determine a number to assign for duration based upon these parameters. 

Latching versus non-latching also was eliminated from the tables because it is considered 

primarily to depend upon the circuit design, and not on the cable’s failure characteristics. This 

parameter is a toggle event with pre-determined results. If the device is latching, the spurious 

operation will continue until the fuse blows. If the device is non-latching, the signal will stay in 

until the spurious operation clears, or the fuse blows. In either case, the fact that the circuit is 

latching or non-latching has little effect on the characteristics of cable damage. The true arbiter 

of the duration of spurious operation is the behavior of the cable and the ultimate time for the 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-48

fuse to blow. Consequently, these tables are constructed with the following variables for fire 

exposure conditions: 

1. Flame; 

2. Plume; and 

3. Hot Gas Layer. 

Furthermore, there are no duration tables that specifically address a single-break or doublebreak design as there is for spurious operation probability. This is because there appears to be 

no way to easily correlate the duration of a single hot short-induced spurious operation with that 

of a spurious operation caused by two concurrent hot shorts. 

The ground fault equivalent hot shorts failure mechanism is represented as “N/A” in the 

grounded AC circuits because it cannot occur without blowing a fuse. 

Additionally, the DESIREE-Fire tests show that for fuses greater than 10 amps in ungrounded 

DC circuits, it may not necessarily blow. Consequently, power would be fed to the source 

conductor for a much longer time. Because of the potential effects this could have on the 

duration of hot short and spurious operation the associated tables are separated into “≤10 amp 

fuses” and “> 10 amp fuses” for ungrounded DC. However, because of the circuit configuration 

for the testing that is conducted using fuses over 10 amp fuses (a circuit-breaker configuration), 

spurious operation data is not available from the DESIREE-Fire testing. For these cases, only 

the hot short duration was measured. Because of this, the electrical expert PIRT panel 

determined that tables would provide the probability of hot short duration for both greater than 

and less than 10 amp fuse sizes. No such table was possible for the former category due to the 

dearth of data. 

Table 3-9. Spurious Operation Duration - Grounded AC Power Source 

Spurious Operation Duration - Grounded AC Power Source Flame Zone Location 

Conductor shorting modes of interest Intra-cable Inter-cable Ground fault equivalent hot 

shorts 

Hot Gas Layer N/A 

Plume Region N/A 

Flame Region N/A 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-49

Table 3-10. Spurious Operation Duration - Ungrounded AC Power Source 

Spurious Operation Duration - Ungrounded AC Power Source Flame Zone Location 

Conductor shorting modes of interest Intra -cable Inter-cable Ground fault 

equivalent 

hot shorts 

Hot Gas Layer 

Plume Region 

Flame Region 

Table 3-11. Hot Short Duration - Ungrounded DC power source 

≤10 Amps Fuse Size

Hot Short Duration - Ungrounded DC Power Source <10 Amps Flame Zone Location 

Conductor shorting modes of interest Intra -cable Inter-cable Ground fault equivalent 

hot shorts 

Hot Gas Layer 

Plume Region 

Flame Region 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS 

3-50

Table 3-12. Spurious Operation Duration - Ungrounded DC Power Source 

≤10 Amps Fuse Size 

Spurious Operation - Duration Ungrounded DC Power Source <10 amps Flame Zone Location 

Conductor shorting modes of interest Intra-cable Inter-cable Ground fault equivalent 

hot shorts 

Hot Gas Layer 

Plume Region 

Flame Region 

 

Table 3-13. Hot Short - Duration - Ungrounded DC Power Source 

>10 Amps Fuse Size

Hot Short Duration Ungrounded DC Power Source >10 Amps Flame Zone Location 

Conductor shorting modes of interest Intra -cable Inter-cable Ground fault equivalent 

hot shorts 

Hot Gas Layer 

Plume Region 

Flame Region 
PIRT PANEL EVALUATION OF CONTROL CIRCUITS

3-51

3.4.2 Control Circuit Configurations for Single and Double Break 

Designs 

The PIRT panel used electrical control circuit diagrams and physical circuit configuration layouts 

to assist with the discussion of numerous issues and in understanding how various parameters 

affect the likelihood of hot short-induced spurious operations. Furthermore, the PIRT panel 

determined that providing these circuit diagrams and physical layout illustrations will be valuable 

for the reader of the report and the follow-on expert elicitation by the PRA panel. These eight 

specific cases of the control circuit configurations for both single and double break designs are 

presented in Appendix C of this report. 

4-1

4

PIRT PANEL TECHNICAL POSITIONS ON POWER 

CIRCUITS 

This section addresses the motive power to AC and DC motors; the control circuits are 

addressed in Section 3. Additionally, for DC systems only DC compound-wound type motors 

were evaluated, since these are the type of motors that exist in US NPPs. The electrical expert 

PIRT panel did not identify applications of interest for either a series- or a shunt-wound DC 

motor configuration. 

4.1 Background 

In general, short circuit behavior for power circuits is relatively well understood and is 

documented in countless industry standards, guidelines, and texts. However, some unique 

failure modes that are considered by the PIRT panel to be legacy issues were evaluated. 

Because of the lack of test data for power circuits, the PIRT panel could not apply the PIRT 

evaluation process to them. Instead, the PIRT panel decided to undertake a separate 

evaluation by providing consensus technical positions. The panel considered that much of the 

data on cable fire test for control circuits provided adequate insights to support the conclusions 

drawn in the consensus technical positions. The two power circuit failure modes that the PIRT 

panel investigated were three phase proper polarity hot shorts in AC power circuits and proper 

polarity hot shorts on DC compound-wound motors. Three phase AC cabling is common 

throughout a nuclear plant, and DC compound-wound motors are used for MOVs in a variety of 

applications. 

During discussions, the PIRT panel unanimously concluded that three-phase power 

consequential hot shorts in AC power circuits are incredible. Additionally, they deemed that 

consequential DC power hot shorts to a DC motor are incredible. The following discussions 

contain the rationale behind the panel’s consensus positions and conclusions for these failure 

modes. 

4.2 Three Phase AC Power Circuit 

For the following reasons, the PIRT panel determined that the potential for a fire to cause a hot 

short on all three phases in the proper sequence and thereby cause a spurious operation of a 

motor is incredible. (Refer to Figure 4-1 for the following discussion). 

For a three-phase short to occur that would cause a motor to spuriously operate, the motor’s 

three-phase cabling would have to impinge upon by another three-phase “aggressor” cable in 

the same raceway. This must occur downstream of the motor control center (MCC) or bus 

powering the motor since the motor’s starting contacts (which are only closed when the motorcontrol circuitry drives the motor) or motor circuit breaker located within the MCC or bus would 

prevent any short upstream of the control device (contactor or circuit breaker). This aggressor 

cable also would have to be one that was supplying a continuously running load; otherwise, the 

aggressor cable normally would be de-energized and, therefore would be inconsequential. 

Furthermore, the aggressor cable would have to be supplying a load of such magnitude that the 
PIRT PANEL TECHNICAL POSITIONS ON POWER CIRCUITS 

4-2

over-current protective relaying (specifically, the time over-current feature) would not trip when 

the valve motor initially started running, since now the upstream power supply would be 

supplying both its normal load, and the considerable starting current of that impinging upon the 

motor. 

Figure 4-1. Typical simplified AC 3-phase motor (power circuit) 

Additionally, to cause the three-phase motor to operate, the aggressor cable would have to 

short all three of its phases to the three phases on the cable for the motor. Furthermore, for a 
PIRT PANEL TECHNICAL POSITIONS ON POWER CIRCUITS

4-3

valve motor, these three phases would have to be shorted to the motor’s power cabling in the 

exact sequence such that the motor’s valve would fail in the undesired position (i.e., open for a 

boundary-isolation valve) position; this scenario has a 1 out of 2 probability assuming three hot 

shorts of diverse phases were to occur. 

The conductors for the three-phase motor, as well as the aggressor’s conductors, also could not 

at any time be shorted to ground or shorted to each other. Since three-phase cabling normally 

is in a triplex configuration (three conductors, each separately insulated, wound around each 

other – similar to rope), for three shorts to occur, the insulation would have to be broken down 

sufficiently on all three phases in both cables such that a direct short would occur; however, the 

rest of the cables would have to be insulated sufficiently such that any other area of insulation 

breakdown would not result in a ground or a short to any of the other conductors within the 

cables. This scenario is deemed to be incredible, regardless of the cable’s type of insulation or 

grounding configuration. For some large motors, single-conductor cable may be used. In these 

cases the cables are usually placed within the tray to provide some separation for heat 

dissipation. In this case the single cables are in direct contact with the raceway. In conduit the 

cable might be touching, but physical limitations on fill in most all cases preclude more than one 

set of three-phase cables per conduit. 

In the cable-fire testing for control circuits, there were very few inter-cable hot shorts. The 

predominant failure mode was a short-to-ground. When hot shorts did occur, an intra-cable hot 

short was the most likely one. Such hot shorts, however, were often, in a finite amount of time, 

followed by a short-to-ground that blew the control power’s fusing. The test data clearly imply 

that the likelihood of a single inter-cable hot short is very low. To postulate the occurrence of 

the multiple inter-cable hot shorts without any intra-cable interaction places the postulated threephase hot short scenario into the incredible category. 

Therefore, based upon the unique characteristics of three-phased cabling and loads, a 

consequential three phase short is considered incredible and need not be considered. 

4.3 DC Compound-Wound Motor Power Circuit 

Similar arguments demonstrate that consequential hot shorts on a 250 VDC reversing motor of 

a motor-operated valve also are incredible. Figure 4-2 illustrates DC compound-wound motors. 

The power circuit of a typical reversing DC compound-wound motor must energize a series 

field, a shunt field, and armature to operate the motor to operate. The polarity of the armature 

determines the direction of the motor’s movement. To move this type of motor, a unique 

combination of an inter-cable and two intra-cable hot shorts would have to occur. For example, 

as shown in Figure 4-2, conductor 1 would have to receive power through an inter-cable short. 

Additionally, conductor 2 would have to short to conductor 3 to put the series winding in series 

with the motor’s armature. Additionally, conductor 4 would have to short with conductor 1 to 

provide the proper parallel voltage to the shunt field’s winding. These hot shorts must happen 

concurrently to cause the motor to run. Furthermore, conductors 2 and 3 could not 

simultaneously hot short to conductors 1 and 4. Also, it is unlikely that these faults could occur 

without conductor grounding causing fuses and/or breakers to open. Because of these unique 

conditions that would have happen, the PIRT panel considered that consequential hot shorts in 

the power circuitry of a DC compound-wound motor is incredible and need not be postulated. 

However, it is noted that this analysis only applies to the power circuit for a DC motor. The 

control circuit should be analyzed similarly to any other DC control circuit subject to fire damage. 
PIRT PANEL TECHNICAL POSITIONS ON POWER CIRCUITS 

4-4

Figure 4-2. Typical Simplified DC Compound-Wound Motor (Power Circuit) 
5-1

5

PIRT PANEL EVALUATION OF INSTRUMENTATION 

AND CONTROL CIRCUITS 

5.1 Background 

Industrial instrumentation and control (I&C) systems are used extensively throughout today’s 

commercial nuclear power plant as a way to provide indications and control of temperature, 

pressure, speed, and other critical parameters. Over the years, many communication standards 

and system architectures have been employed to accomplish this functionality. At a very high 

level, these standards include analog-, and digital-signals and their combinations, also known 

as hybrid signals. Communication protocols vary from mechanical analog (pneumatic, 

hydraulic, mechanical linkage), electrical analog (modulated voltage or current signals) to more 

complex digital signals, such as field bus, RS-232, RS-422, and Transmission Control Protocol 

(TCP) over Ethernet. Note that RS-232 and RS-422 are the traditional names for a series of 

standards used in telecommunication circuits, and TCP is the protocol upon which major 

internet applications rely. 

A fire directly affecting the cabling associated with low-energy I&C systems may cause open 

circuits, conductor-to-conductor bolted or resistive hot shorts (inter-cable or intra-cable), or 

shorts to ground. The effects of these failure modes may drive the process variable downscale 

(zero), upscale (span), or may produce values (steady or varying) between zero and span. This 

unpredictability in the failure state of the process variable may elicit undesired automatic- or 

human-responses that possibly might complicate or compromise the overall response to the 

effects of the fire (shutdown or safe and stable). 

For I&C circuits, the electrical expert PIRT panel discussed the different types of control circuits 

and the potential failure mechanisms during a fire event. Because of the limited amount of 

testing undertaken, the panel decided to concentrate on identifying potential plausible failure 

modes of high significance for the prevalent instrumentation configurations throughout the 

industry. They then recommended future research in the areas where the configurations were 

common and the consequences of fire-induced failures could be very high. 

5.2 Instrumentation and Control Circuit Evaluation 

The PIRT panel discussed several different types of instrumentation control circuits during their 

discussions, ruling out a number of them for further consideration/research for several reasons. 

Table 5-1 gives a synopsis of the different types of circuits that the panel evaluated. The table 

briefly describes the configuration of each instrument control circuit, its usages in the nuclear 

industry, and the panel’s recommendations for future research. 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

Table 5-1. Different Types of Instrumentation Circuits 

No. 

Instrumentation 

Control 

System Type 

Description Usage in the Nuclear Industry PIRT panel Recommendation 

1 Current Loop In a current loop instrumentation 

control-system, the current produced by the loop’s power supply is sent around the loop, flowing through every device and load resistor in the circuit. Variations in the loop current are determined by changes in the process parameter, as measured by the instrument. The transmitter produces the output signal, either in the form of a 4-20 mA or a 10-50mA current that can be used for indication, operation, and other functions. 

Current loops are used throughout the industry in a variety of control applications. The most common instrument loops in the nuclear industry are the 4-20 mA ones. 

Since the 4-20 mA current loop is prevalent in the industry, and the signal is transmitted through an electrical cable, very little prior testing has been conducted on the effects fire on the cables. Therefore, the PIRT panel highly recommended undertaking further research. Testing on the 10-50mA current loop, although not as prevalent at NPPs, was also recommended. 

2 Full Pneumatic Full pneumatic-control systems 

utilize mechanical transducers to convert the process variable into a pneumatic signal for transmission around the plant via pneumatic tubing. Control pressures generally are 3-15 psig but can be amplified via mechanical amplifiers to greater pressures and volumes for the purposes of opening valves. 

Used before the advent of the current loop (pre1950s). Found later in some commercial nuclear power plants for the trip logic of the emergency diesel generator. 

Since these systems do not use electrical wiring, the PIRT panel did not recommend their future testing. 

5-2 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

Table 5-1. Different Types of Instrumentation Circuits (Cont’d.)

No. 

Instrumentation 

Control 

System Type 

Description Usage in the Nuclear Industry PIRT panel Recommendation 

1 Current Loop In a current loop instrumentation 

control-system, the current produced by the loop’s power supply is sent around the loop, flowing through every device and load resistor in the circuit. Variations in the loop current are determined by changes in the process parameter, as measured by the instrument. The transmitter produces the output signal, either in the form of a 4-20 mA or a 10-50mA current that can be used for indication, operation, and other functions. 

Current loops are used throughout the industry in a variety of control applications. The most common instrument loops in the nuclear industry are the 4-20 mA ones. 

Since the 4-20 mA current loop is prevalent in the industry, and the signal is transmitted through an electrical cable, very little prior testing has been conducted on the effects fire on the cables. Therefore, the PIRT panel highly recommended undertaking further research. Testing on the 10-50mA current loop, although not as prevalent at NPPs, was also recommended. 

2 Full Pneumatic Full pneumatic-control systems 

utilize mechanical transducers to convert the process variable into a pneumatic signal for transmission around the plant via pneumatic tubing. Control pressures generally are 3-15 psig but can be amplified via mechanical amplifiers to greater pressures and volumes for the purposes of opening valves. 

Used before the advent of the current loop (pre1950s). Found later in some commercial nuclear power plants for the trip logic of the emergency diesel generator. 

Since these systems do not use electrical wiring, the PIRT panel did not recommend their future testing. 

5-3 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

Table 5-1. Different Types of Instrumentation Circuits (Cont’d.)

No. 

Instrumentation 

Control 

System Type 

Description Usage in the Nuclear Industry PIRT panel Recommendation 

3 Electro-Pneumatic Electro-pneumatic control systems 

use an electrical process variable signal and convert it to a proportional pressure signal via an electro-mechanical transducer. 

Used extensively for valve control. 

Electrical portion is similar to the current loop in that a 4-20 ma signal is transmitted through a cable. Future research recommended by the PIRT panel is addressed in number 1 above under Current Loop. Since the pneumatic portion does not employ electrical cabling, the PIRT panel did not recommend this type of system for future testing. 

4 Electro-Hydraulic Electro-hydraulic systems employ a 

standard electrical control system via transducers. A typical example would be the conversion of an electrical process variable into a proportional hydraulic pressure for moving valves such as in the turbine control system. 

Electro-hydraulic controls are found throughout the nuclear industry in the turbine control system and in the control system for many turbine driven pumps. 

Electrical portion is similar to the current loop; therefore, future research is recommended by the PIRT panel and is addressed in number 1 above, Current Loop. Since the hydraulic portion does not employ electrical cabling, the PIRT panel did not recommend this type of system for future testing. 

5-4 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

Table 5-1. Different Types of Instrumentation Circuits (Cont’d.)

No. 

Instrumentation 

Control 

System Type 

Description Usage in the Nuclear Industry PIRT panel Recommendation 

5 Digital Control Digital-control systems employ highorder communication protocols, 

often with complex error-checking and loop-regeneration capabilities. In general, the cabling is shielded, twisted pair, or more recently, specialty cabling that can carry power and other signals within the same cable. Sophisticated isolationand synchronizing- capabilities often ensure seamless transfer when a fault is detected on a cable. Some protocols support the programming of loops so that they enter a “hold last state” mode upon loss of communications. 

While digital-control systems are frequently used in non-nuclear industrial applications, they are not as common in the nuclear industry. This is primarily due to the complexity of the systems, and as a result, the uncertainty of, and vulnerability to, commoncause failures due to software related problems. Digital systems primarily are used in nonsafety and important- tosafety applications, such as feedwater-control and turbine-control systems. (use same type as in rest)

Because of the many variations of standards, protocols, cable media, adaptability, and programmability, a bounding testing- configuration for digital systems would be difficult to establish. Additionally, error- checking schemes are employed by digital- control schemes that largely decrease the likelihood of fireinduced cable faults. Consequently, the PIRT panel does not recommend testing the cabling of digital- control systems . However, overheating effects of digital devices due to a fire may be a concern. It is important to understand the potential effects of exceeding the temperature ratings of the digital devices and the ultimate effects to the system that is being controlled. This is discussed in Section 5.3.2 of this report. 

6 Combination Analog 

and Digital 

In this control system, digital data is carried over the same wires that the analog loop utilizes for control purposes with the digital signal riding in the carrier analog signal. Generally, the digital data is used to convey data such as system/device health, and environmental information. 

While this type of device is “state-of-the-art” and often used in the nonnuclear industry, the PIRT panel was not aware of any nuclear plant that presently employs this type of system. 

Since this type of system is rarely, if ever, used in the nuclear industry, the PIRT panel do not recommend further research. 

5-5 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

5-6

5.3 Specific Concerns involving Instrument Current Loops 

The PIRT panel determined that testing of instrument current loops was extremely important 

considering the potential consequences of fire-induced failures. The panel also was primarily 

concerned that the failure modes and effects on instrument circuits could be substantially 

different than those on control circuits. 

5.3.1 Instrumentation Cabling 

Although the general state of knowledge of the mechanisms of cable failure is fairly 

comprehensive, testing has focused on cables carrying control circuit energy levels rather than 

on cables carrying the very low energy-levels found in instrumentation circuits. The low 

energies of instrumentation circuits could cause them to perform and fail differently under fireinduced fault conditions than those of higher energy control circuits. For instance, while control 

circuits progress relatively quickly through fault states due to arcing-fault energies, this same 

progression may not be experienced as readily in the lower-energy instrumentation circuits. 

The time required before a fault state occurs in the circuit and its duration may differ 

substantially from that of control circuits. Furthermore, various wiring methods, circuit designs, 

and the use of shielding (tied to ground or to the power-supply neutral) may be the dominating 

influences over the failure modes and effects seen as a fire damages the cable. 

In an instrumentation circuit, a fire-induced change in the process variable may have cascading 

effects that trigger varied reactions; including changing the valve’s position, initiating automatic 

function, and indicating incorrect process variables. Based upon knowledge of Equipment 

Qualification (EQ) testing and fire testing on instrument cabling, various modes of failure could 

exist. (NOTE: The instrument-cable fire testing – NUREG/CR-6776 (Ref. 21), Cable Insulation 

Resistance Measurements Made during Cable Fire Tests - was not conducted on actual 

applications of nuclear-power-plant instrument circuits; nevertheless, it afforded some insight 

into the potential failure-modes of this type of cabling as discussed in Section 2.3.2.3 of this 

report). Specifically, there is the possibility that instead of an instrument failing in only two 

functional failure-modes, e.g., either indicating high or low, it might fail in an intermediate mode 

before complete failure. This would result in a false reading that could cause an operator to 

make an incorrect diagnosis, or it could mask an indication of a problem in the plant. This 

potential human-factors effect, if proven to be a likely concern, has not been well analyzed. 

Figure 5-1 shows a simple 4 mA to 20 mA, 2-wire input control loop with power supply, pressure 

transmitter and pressure indicator. Wire-to-wire shorts between the combinations of nodes 1 

through 4 on the figure may cause the loop to fail high state, low state, or in an intermediate 

state that could provide a “false-normal” indication. Because of the low energies involved in 

instrumentation circuits, it may be possible for failure states to exist for a prolonged, and 

possibly, indefinite period of time. 

Some of the panel's specifically identified instrumentation concerns on cable failure concerns 

are listed below: 

1. If the power for the loop is provided by a power supply that is physically independent of the 

loop’s transmitter, a conductor-to-conductor short across the transmitter possible could drive 

the loop current high (20+ mA). The effect of this failure mode is contrary to the belief that 

loop currents cannot be driven high by intra-cable shorting. 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

5-7 

4-20mA 

Transmitter 

Operating Voltage: 24-40VDC 

Min. Operating Current: 3.5 mA

Typical 2-Wire Input Control Loop

 - PT modulates loop current 

 - Input device has a 250 Ohm resistor to 

 convert 4-20mA signal to 1 to 5 VDC. 

Short between 1 and 2 could cause current passing through input device to vary between 4mA and ~144mA 

depending upon the output o the transmitter and the quality of the short. 

Short between any other point could cause current passing through input device to vary between 0mA and <20mA, 

depending upon the output of the transmitter and the quality of the short. Exception: Points 3 and 4 are at the same 

potential with respect to ground.

Figure 5-1. Typical 2-Wire Input Control Loop 

2. Depending upon the electrical relationship of the shield with respect to the signal 

conductors, it may be possible for leakage current to occur between the two. This may 

occur as a result of intra-cable shorts, or a combination of intra- and inter-cable shorts. It 

even may be possible to re-reference a shield, via an inter-cable short, to allow the flow of 

current from one loop to another through the shield or ground plane. This failure mode 

would challenge the concept that the shield will protect the target loop from the influences of 

external loops. 

3. The leakage of signal current could be induced by intra-cable short(s) between the signal 

conductors within a shielded twisted pair cable. Due to the low- energy characteristics of 

instrumentation circuits, a prolonged short condition might be established, producing an 

erroneous signal, fixed or variable, that is in the high-, low-, or midscale-range. This failure 

mode would be contrary to the concept that internal shorting is always of low impedance, 

and will quickly drive the circuit to a single-failure state. 
PIRT PANEL EVALUATION OF INSTRUMENTATION AND CONTROL CIRCUITS 

5-8

5.3.2 Instrumentation Circuit Electronic Devices 

Fire-induced effects on the electronic devices in instrumentation circuits (e.g., transmitters, 

input/output modules, process modules may be extremely detrimental to the instrumentation 

circuit’s functionality. Specifically, as these devices are exposed to the heat of the fire, the 

ability of the device to properly handle input-to-output relationships may become unpredictable 

due to the heating effects on its electronic components. Although the effects of heating 

individual electronic components has been well documented (e.g., changing resistance values, 

component catastrophic failure, and microprocessor instability), the effects of these component 

failure modes on the device’s function is not as well understood. 

For digital circuits, while it is safe to assume that a fire-induced failure (hot short, open circuit, 

short to ground) of an Ethernet cable will not produce properly sequenced communication 

packets in accordance with the communication protocol, it may not be safe to assume that this 

situation would pertain when the sending or receiving device itself is exposed to the fire. 

Additionally, in many cases, redundant digital controllers for important to safety-control systems, 

such as the feedwater control system, are located in the same fire area and zone. This type of 

configuration allows fire-induced heat-up of the room to have a common-mode adverse effect to 

redundant controllers. Since most digital controllers have a specific temperature rating, it is 

important to understand the potential effects on the controllers, and ultimately on the system 

that is being controlled, should a fire cause this limit to be exceeded. 

5.4 Summary of Research Recommendations 

Due to the low state of knowledge and potentially high consequence of fire-induced failure on 

instrumentation current loop circuits, additional testing is recommended 

The PIRT panel considered that the following circuits should be included in the testing: 

• 10 mA to 50 mA instrumentation circuits 

• 4 mA to 20 mA instrumentation circuits 

• 1 VDC to 5 VDC instrumentation circuits. 

Even though the PIRT panel did not recommend testing fire-induced effects on the components 

of instrumentation circuits, such as transmitters, power supplies, and indicators, the state of 

knowledge in this area is low and the potential effects could be highly significant. Therefore, it is 

essential that fire-induced effects on the instrument loop’s components should be adequately 

evaluated when addressing spurious operations. This statement also applies to digital controls. 

While ultimately there may be value in such testing, the PIRT panel concluded that more 

immediate need for testing lay in the area of instrumentation cabling. 
6-1

6

PIRT PANEL TECHNICAL POSITION ON ANCILLARY 

CIRCUIT ANALYSIS RELATED ISSUES 

The electrical expert PIRT panel evaluated several known open issues or concerns associated 

with deterministic fire-induced safe-shutdown analyses. These issues are considered as legacy 

issues related to safe-shutdown circuit analyses; however, the failure modes in question do in 

some cases impact the Fire PRA since they can affect the cable selection processor impacts 

due to associated circuits. The PIRT panel evaluated each of these cases in great detail from 

the perspectives of both fire protection and electrical engineering. They developed technical 

positions on each issue that were evaluated as part of the expert elicitation process by the PIRT 

panel. Their technical positions are detailed in this section for the following technical issues: 

• Multiple High-Impedance Faults (MHIFs) 

• Open Circuit Secondary of Current Transformers (CTs) 

• DC Control Power Common Enclosure/Common Power Supply 

• Control Power Transformers (CPTs) 

• Kapton-Insulated Cables 

• Panel Wiring 

• High Conductor Count Trunk Cables 

6.1 Multiple High-Impedance Faults 

6.1.1 Background 

The Multiple High-Impedance Faults (MHIFs) circuit failure mode is a variation of the concern 

with common power supply associated circuits (see Figure 6-1). A MHIF exists when multiple 

circuits powered from the same distribution bus experience circuit fault conditions resulting in a 

short-to-ground, or conductor-to-conductor hot short, where residual resistance in the faulted 

connection maintains the fault current level below the long-term set point of the component’s 

circuit breaker but the summation of the multiple faults is high enough to trip the feeder breaker 

to the distribution bus (Ref. 16). Such a circuit is considered to pose a risk to safe-shutdown if a 

fire-induced fault on a non-safe-shutdown circuit causes the loss of a safe-shutdown power 

supply due to inadequate electrical-coordination between upstream and downstream 

overcurrent protective devices (e.g., relays, circuit breakers, fuses). 

A Coordination Study is the accepted method for evaluating the potential impact of commonpower-supply associated circuits. It involves reviewing the tripping characteristics of the 

protective devices associated with the electrical power-distribution equipment of concern, in this 

case, the post-fire safe-shutdown or Fire PRA power supplies. The protection devices are 

considered to “coordinate” if the downstream (feeder or branch circuit) device trips before the 

upstream one (supply circuit) over the entire range of possible fault current. In conducting a 

traditional coordination study, each circuit fault is evaluated as a single event. 
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6-2

The concept of MHIFs deviates from baseline assumptions associated with conventional 

electrical coordination. The MHIF failure mode is based on presuming that a fire can cause 

short circuits that generate abnormally high currents below the trip point of the individual 

overcurrent-interrupting devices for the affected circuits. Faults of this type are defined as high 

impedance faults (HIFs). Under the assumed conditions, circuit overcurrent-protective devices 

will not detect and interrupt the abnormal current flow. It follows that if several circuits 

experience a HIF, the cumulative current flow could exceed the trip setting of the supply breaker 

or fuse, causing it to trip. Figure 6-1 depicts the MHIF concern. 

6.1.2 PIRT Panel Recommendations on MHIF 

The panel discussed relevant characteristics of cable faults, as observed during the various fire 

tests, and concluded that the generic methodology for “Analysis of Fire-Induced Multiple High 

Impedance Faults” provided in NEI 00-01, Rev. 2, Appendix B.1, “Justification for the 

Elimination of Multiple High Impedance Faults,” (Ref.13) provided a technically sound basis and 

conclusion regarding the probability of MHIFs. Specifically, the analysis determines that the 

probability of MHIFs developing during a fire “is sufficiently low such that they do not pose a 

plausible risk to post-fire safe-shutdown when certain criteria are met.” The PIRT panel agreed 

with the arguments and reasoning given in this analysis. A summary of that reasoning is given 

in the next section. 

Safe-shutdown components A-1 

and B-1 are redundant, as are A-2 

and B-2. A fire in Fire Area B is 

assumed to render B-1 and B-2 

inoperable, and thus A-1 and A-2 

are credited as available for safeshutdown. Circuit Breakers 4 – 7 

supply non-safe-shutdown 

equipment via circuits that traverse 

Fire Area B. The fire is assumed 

to create high impedance faults on 

several of these circuits 

simultaneously. The nature of the 

faults is such that an abnormal 

current is produced in each circuit, 

but in each case the current is not 

sufficient to cause the affected 

branch feeder breaker to trip. The 

cumulative effect of the fault 

current flowing in each branch 

causes the incoming supply 

breaker (Circuit Breaker 1) to trip 

before the downstream breakers 

are able to isolate the individual 

faults. The safe-shutdown power 

supply is de-energized, causing a 

loss of power to the credited safeshutdown equipment, A-1 and A-2. 

Figure 6-1. MHIF Example 

Non-Safe Shutdown Equipment

Safe Shutdown

Equipment

A-1 A-2

Safe Shutdown

Power Supply

Safe Shutdown

Equipment

B-1 B-2

Safe Shutdown

Power Supply

Fire Area A Fire Area B 3-Hour Barrier

1

2 3 4567
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6-3 

6.1.3 Summary of Technical Analysis on MHIF 

The technical validity of MHIFs is based primarily on the premise that the insulation in a cable, 

during a fire, can degrade to a point such that low-level fault currents will be produced. Since 

this occurs on multiple cables, this phenomenon implies that a low-level fault would not 

ultimately cascade into a complete failure of the cable’s insulation, and that the electrical 

protective device for the affected circuit would not trip. Additionally, if arcing faults, which have 

higher impedances than bolted faults, are considered to be type of HIF and thus a contributor to 

the probability of the MHIF phenomena, then it would have to be assumed that the arcing 

condition would remain as a relatively constant condition for a prolonged period of time. Both of 

these assumptions were analyzed and demonstrated to be contrary to the observed behavior of 

fire-induced faults for voltage levels at or greater than 110 V. 

Cable Insulation Behavior during a Faulting Condition

For 120 VAC systems, when the insulation resistance of a cable and the resulting leakage 

current reaches a certain level, the fault will cascade such that the rate of degradation of the 

insulation’s resistance increases significantly, causing fault resistance to drop rapidly, and 

leakage current to rise quickly. This ultimately leads to a complete failure of the cable, thereby 

opening the upstream protective device. For thermoplastic insulated cables, this failure occurs 

within seconds, and although the cascading failure appears to take slightly longer for thermosetinsulated cables, it is still rapid from the perspective of a growing fire. Should the leakage 

current never reach the level needed to cause this cascading effect, the current will be 

sufficiently low such the distribution feeder device (upstream of the protective device for the 

cable in the fire) could not be tripped provided the devices meet conventional coordination 

criteria. 

For systems operating at or above 480 V, high impedance faults manifest themselves as arcing 

faults. For 125 VDC systems, the cable insulation breakdown behavior was amplified in 

comparison to the 120 VAC since DC power is more energetic and constant (non-sinusoidal) 

thereby delivering more energy to the developing fault. Accordingly, the 125 VDC circuits failed 

rapidly and often produced significant localized damage. It is also noteworthy that 125 VDC 

often experienced arcing faults in short bursts, typically 1-2 seconds in duration. 

Arcing Fault Behavior

For 480 VAC and above systems, the energy level is high enough to sustain an arcing fault. 

The minimum plausible fault current produced by these faults will be detected by an adequately 

designed protective scheme and the fault will be cleared. The energies produced by arcing 

faults for this class of power system cannot be sustained by the hardware for extended periods 

before physical destruction of the conductor, insulating materials, and surrounding equipment 

result in wide spread catastrophic damage. 

For 125 VDC and 250 VDC circuits, expectedly either the protective device will clear, or the 

conducting material in the cable will vaporize due to intermittent but highly destructive arcing, 

thereby resulting in an open circuit at the fault location. Either way, the high impedance fault 

condition will not exist for any appreciable length of time. 
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6.1.4 Applicability 

The PIRT panel determined that the MHIF phenomenon does not need to be considered as long 

as certain criteria are met. Of critical importance is using certain robust design criteria outlined 

in NEI 00-01, Rev. 2, Appendix B.1, “Justification for the Elimination of Multiple High Impedance 

Faults,” (Ref. 13) that ensure high impedance faults do not persist in an electrical system for 

extended periods of time. These criteria include the use of properly coordinated protective 

devices as outlined in IEEE STD 242 (Ref. 27), “IEEE Recommended Practice for Protection 

and Coordination of Industrial and Commercial Power Systems (Buff Book),” and the use of 

proper protective devices that are designed and constructed according to applicable industry 

standards and applied within their vendor ratings. 

Additionally, the PIRT panel felt it important to highlight that appropriate testing and 

maintenance be performed on these protective devices. Periodic maintenance and testing 

ensures that breakers/relays are operating within expected tolerances and can perform their 

intended design function. This is achieved by, as a minimum, following accepted industry 

guidelines and specific vendor recommendations for maintenance and testing of the 

breakers/relays. If the vendor did not provide maintenance and/or testing recommendations or 

the recommendations are outdated due to vintage, then an accepted industry consensus 

standard for testing and maintenance is considered acceptable. 

Finally, Regulatory Guide (RG) 1.189, Revision 2 (Ref. 16), Section 5.5.2, states “Information in 

NEI 00-01, Appendix B.1, may be used to address multiple high impedance faults when used in 

a manner consistent with this guide.” Section 5.5.2 of RG 1.189 applies to Alternative or 

Dedicated Safe-shutdown methodologies. However, if the technical concepts in NEI 00-01, 

Appendix B.1 are valid for alternative and dedicated safe-shutdown, the same concepts are 

considered valid for all fires, regardless of the shutdown methodology. The consensus position 

of the electrical expert PIRT panel was that the guidance in NEI 00-01, Rev. 2 (Ref. 13), 

Appendix B.1, can be safely applied to fire safe-shutdown methodologies throughout the plant. 

6.2 Open Circuit Secondary of Current Transformers 

Current transformers (CTs) represent a theoretical fire safety concern should the secondary 

side of the current transformer suddenly become open circuited. When under load, an open 

circuit on the transformer’s secondary will produce a voltage transient that can potentially 

exceed the dielectric strength of the CT insulating materials or connected components, which 

could result in failure of the CT and potentially initiate a secondary fire. 

6.2.1 Background 

CTs are used throughout the electrical distribution system to monitor current levels at select 

locations and provide signals to metering and overcurrent protection circuits. CTs are physically 

located at the primary electrical conductor (i.e., bus bar or cable) and provide a signal from their 

secondary winding that is proportional to the current flowing through the main (primary) 

conductor. CTs measure the primary current through magnetic coupling and thus do not have a 

physical connection to the primary circuit they are monitoring. 

Current transformers are designed to transform high primary current into low secondary current, 

which is more suitable to delicate instrument circuits. As an example: 
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6-5 

 CT Ratio: 800:5 

 Primary Current: 240A 

 Secondary Current: 240A x (5/800) = 1.5A 

The CT transforms current in the primary windings by producing an electromagnetic flux in the 

transformer coil that, in turn, causes a current to flow in the secondary windings. The primary 

current, when transferred to the transformer’s core, consists of a magnetization current that 

generates the core flux and a core-loss current. These two currents combine to make up the 

transformer’s “excitation current.” During normal CT operation, current flowing through the 

secondary winding produces an opposing flux. 

A rise in CT excitation current will entail a proportional rise in the secondary current. However, 

when the excitation current increases to a certain level, the CT core reaches saturation, and no 

longer behaves proportionally. Then, a rise in the excitation current produces a significantly 

smaller increase in the secondary current. 

Conversely, the voltage of the secondary depends upon the secondary current, and the 

impedance (burden) of the meter and relaying circuitry. Since the secondary current primarily is 

a function of the CT turns-ratio and excitation current, as the CT burden increases, the 

secondary voltage rises. Theoretically, the secondary voltage is as high as needed to maintain 

a constant primary-to-secondary current ratio. A sudden opening of the secondary circuit can 

cause high voltages in the current transformer secondary side as the CT attempts to maintain 

the voltage and current relationships dictated by the transformer turns ratio. This condition can 

potentially generate voltages that exceed the dielectric strength of the current transformer 

materials or connected components. 

Brookhaven National Laboratories (BNL) raised the concern about CT secondary circuits in a 

letter to the NRC date July 21, 1983 (Ref. 39). The BNL letter postulated a scenario in which 

potentially high voltages induced on the secondary winding of a CT as a result of open circuiting 

the CT secondary due to fire ultimately causes the CT to fail in a manner that could start a 

secondary fire or damage safe-shutdown equipment in the immediate vicinity. 

6.2.2 Current Transformer Characteristics with an Open Circuit 

Secondary 

Devices such as current coils of meters or relays are constructed of a few turns of relatively 

large wire. As a result, they have low impedance (burden) and effectively act as a short circuit 

across the CT secondary. Thus, during normal operation, CTs effectively operate with their 

secondary shorted. It is for this reason that short circuit type faults are not of concern in this 

evaluation. It is not, however, intended that CTs operate with the secondary side open when 

primary current is present. Under open circuit conditions, the primary current becomes solely 

exciting current, which in turn raises the core flux density of the CT to saturation and induces a 

high voltage in the secondary. Electricians are cautioned to ensure that the secondary winding 

of a CT is either closed through the instrument circuit or that it is shunted (short-circuited) at the 

terminals. 

The operating characteristics of a CT are such that the voltage at the secondary terminals of a 

CT remains low as long as the secondary circuit is closed. When a CT secondary is opencircuited (analogous to an infinite burden), the current flowing in the primary winding becomes 
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6-6

the only exciting current. Without a secondary-side opposing flux, the transformer core may be 

driven into saturation on alternate half cycles. The flux form approaches a square wave, having 

amplitude equal to the saturation flux of the core with a 180° reversal of the flux each time the 

core is driven from saturation in one direction to that in the other direction. The time rate of 

change of flux (dØ/dt) during these reversals induces high voltage spikes into the secondary 

windings. In each half cycle, there is a relatively high voltage crest that endures for a short 

portion of the half cycle. The magnitude of this voltage crest increases with rising primary 

current, but its duration decreases accordingly (Figure 6-2). 

 

Figure 6-2. Voltage Waveform with Open Secondary 

Although the voltage peak may be significantly high, very little power is available as explained 

below: 

1. The governing power equation is P(t) = V(t) x I(t). Until the circuit arcs or faults, there is no 

significant power output; power is expended in the CT only as core losses. 

2. The instant the circuit arcs or faults, an opposing flux produced by the current in the 

secondary limits the voltage peak. A generalized description of the circuit is that voltage 

declines as current rises. 

3. As the current approaches the CT rating, the voltage profile also approaches the normal CT 

value. The power waveform will appear as a spike with an overall average power 

approximately equal to the maximum power of the CT during normal operation. 

The turns-ratio of a CT affects the amplitude of the voltage spike during open-circuit conditions. 

The higher this ratio, the greater the voltage spikes. Normally, CTs can withstand the maximum 

expected voltage, including the abnormal voltages expected with an open-circuit secondary. 

CTs with a lower turns-ratio (1200:5 or lower) are not expected to be damaged by an open 

circuit, while those with a high one (greater than 1200:5) may experience insulation damage and 

conceivably could fail. Failure, in this case, would most likely involve breakdown of the 

insulation, the secondary windings to short to the core. Thereupon, the open-circuit condition is 

removed and the high voltage terminated. Even though this case is the most likely outcome, the 
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6-7 

PIRT panel could not rule out the possibility of catastrophic failure for CTs with higher turns 

ratios. 

6.2.3 Plausibility of CT Induced Secondary Fires 

For secondary fires to occur due to an open-circuited CT, a combination of damages would 

need to occur. These effects are listed below: 

1. The fire would have to produce an open circuit in the cable carrying the CT secondary 

conductors. 

2. The open circuit in the CT secondary conductors would need to occur before the power 

cable associated with the CT shorted and caused the circuit’s breaker to open. In this case 

no primary current would flow; hence there is no risk of voltage spikes even if the CT 

conductors open. 

However, for the case where the open circuit condition would need to occur rapidly such that 

no arcing or transient current flowed in the circuit at the point of fire-induced failure. The 

voltage transient then would cause arcing or catastrophic failure of the CT. 

3. The resulting arcing or catastrophic failure of the CT would have to cause a secondary fire. 

Each of these factors is addressed below: 

1. Fire Induced Open Circuit

For a fire to produce an open circuit in the secondary, it first must burn through the associated 

cable jacket and insulation, and then burn open one or more of the copper conductors (melting 

temperature of approximately 1980°F) without creating any type of short circuit. An open circuit 

also could be caused by falling debris or some other event resulting from the fire. Regardless of 

the mechanism, intuitively, the jacket and insulation of the cable first must be damaged before 

the conductors lose continuity. While a fire can cause open-circuit conditions, the likelihood of 

this is low. 

2. Arcing or Catastrophic Failure of the CT

Once the CT conductors open, a high voltage is assumed to exist. Since the fire has removed 

or severely damaged the cable’s insulation fire at the open-circuit location, this is the most likely 

point of least resistance in the circuit. Since any arcing that may result from the high voltage is 

assumed to occur at the point of least resistance, the most probable location for arcing is where 

the cable is damaged. Because the open circuit location is by definition within the area of 

damage, arcing damage at the open circuit is presumed captured by the deterministic or PRA 

analysis and does not pose a threat beyond that already assumed. 

As soon as an arc forms at the location of cable damage, the CT circuit voltage will drop 

because of the development of secondary flux opposing the primary current. As the voltage 

drops, the arc will be extinguished, allowing the process to be repeated. This faulted condition 

will continue until the CT’s associated load is de-energized and primary current ceases to flow. 

A majority of the CTs installed at the plant have a turns ratio of 1200:5 or lower. For the low 

ratio CTs, the induced voltage arising from an open circuit on the secondary side is not 

expected to cause damage to the CT or connected components. And, if the high voltage was to 
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6-8

cause arcing, it would most likely do so at the fault location, as described above. High ratio CTs 

at the plant are primarily associated with the main generator, switchyard, and differential 

schemes. In the extreme case, the higher ratio CTs could potentially experience insulation 

damage or failure because of the secondary open circuit voltage. If the insulation fails, the most 

likely location of that damage would be the insulation between winding turns, which in turn is 

expected to cause the CT secondary to short to the core, effectively terminating the high voltage 

condition as described previously. The CT secondary is expected to short to the core, 

effectively terminating the high voltage condition as described previously. If the CT shorts 

through its insulation to the core, the end result is that the CT is non-functional but is effectively 

shorted as desired. Other than internal CT damage, no further adverse effects are expected to 

occur as a result of the open circuit condition. 

Finally, a series of CT failure tests was sponsored by a utility in 1982. The tests were 

conducted by a 3rd party laboratory, Electrical Test Laboratory, Inc. (Ref. 28). These tests 

provide evidence that secondary open circuits in lower turn ratio CTs (up to and including 

1200:5) do not damage the CT. Specifically, the report concluded that while the CT would pose 

a danger to personnel, the CT itself would not be damaged by the open circuit voltage. The 

bounding test case was a 1200:5 CT with 1200A simulated primary current. This case 

produced a crest voltage spike of 850 V, which did not damage the CT or connecting cables. It 

is observed that this voltage is well below the typical breakdown voltage for low-voltage cabling 

and components. 

It is noteworthy that open-circuited CTs concern the electrical industry; however, the concern is 

primarily for personnel safety and not catastrophic failure of the CT. It is due to the large 

number of CTs that are left in an open-circuit condition both during and after maintenance work. 

For this personnel hazard to exist, the open-circuit condition would have to occur without the CT 

failing. 

3. Secondary Fire

If an open circuit in the secondary of a CT were to cause the CT to fail, that failure still would 

have to produce a secondary fire. Since CTs are located inside electrical enclosures, this 

means that the effects would have to extend beyond the enclosure. This is not impossible, but 

is judged to be of low likelihood given the low energies involved and the general construction 

features of switchgear. 

Operating Experience Review

The PIRT panel spent considerable effort researching nuclear and non-nuclear sources for any 

evidence of open circuits on CT secondary initiating a fire. The PIRT panel reviewed the NRC 

Licensee Event Report (LER) based fire event database and identified 10 events related to CTs. 

A more detailed evaluation of these events did not identify any instances where CT open circuits 

(from a fire or other source) resulted in a fire. Concurrent with the NRC review of CT events, 

EPRI staff also performed a similar search using its fire events database. The results of the 

EPRI efforts also did not identify any fires caused by open circuits in the secondary of a CT. 

The electric power industry continues to endorse a policy of extreme caution not to open circuit 

the secondary side of an energized CT. It is helpful to understand that this policy is primarily 

intended to protect personnel and delicate instruments from dangerous voltages. Catastrophic 

failure and fire initiation do not surface as a credible concern. In this context, General Electric’s 

Manual of Instrument Transformers, GET-97D (Ref. 29), states 
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“Although the insulation of most transformers will, in general, withstand open-circuit 

conditions, the resulting voltages are dangerous.” 

Other anecdotal information was identified during the research effort, including input from 

several switchgear manufacturers: 

1. In a November 1984 NRC memo to Auxiliary Systems Branch (ASB) personnel (Ref. 30), 

the ASB Chief states in Section 2.2.4 of the memo: 

“In October 1982. BNL identified a problem with open-circuit operation of current 

transformers (CT) which could exacerbate the consequences of a control room fire. The 

concern stems from the fact that a control room fire could result in a breakdown of the 

power feeder insulation and cause a second fire. Attachment 7 contains the detailed 

description of the problem along with the applicant response to a PSB question on the 

subject. The Power Systems Branch has reviewed this concern and concluded that the 

BNL concerns were overly conservative and recommended no further action on this 

issue. Therefore, the ASB reviewer should be aware of this concern; however, no other 

action is required.” 

2. Bechtel Power Corporation stated in an October 16, 1984 letter (Ref. 31): 

“...the subject concern (CT open circuit causing a fire) is not credible... This conclusion is 

based on the CT manufacturer’s information that the maximum open-circuit secondary 

voltages will not exceed CT insulation rating with full load current flowing through the 

primary winding.” 

3. Brown Boveri stated in an October 22, 1984 letter (Ref. 28): 

“In over 35 years of experience with current transformer design, test and application, the 

writer cannot recall a single incident wherein a fire was caused by an open-circuited current 

transformer. This experience, plus analysis of the rather particular circumstances necessary 

to allow such a fire to start, supports a stand that a fire caused in this fashion is unlikely.” 

4. Additionally, other industry experts with a vast amount of experience in this area have also 

confirmed that they have not known of a CT-induced fire (Ref. 32). 

6.2.4 PIRT Panel Recommendations 

All information considered, it was the judgment of the PIRT panel that the concern of a 

secondary fire resulting from an open circuited CT secondary is more theoretical than real. 

Based on the availability of objective test data for CTs with a turns ratio of 1200:5 and below, 

the panel determined that the unique combination of low probability events makes this failure 

mode (secondary fire caused by a CT secondary open circuit) incredible for CTs with low turns 

ratios (1200:5). 

The PIRT panel also judged the likelihood of secondary fires from higher ratio CTs to be very 

low. However, in the absence of test data along with the concern becoming more pronounced 

as turns-ratio increases, the panel concluded that the failure mode could not be classified as 

incredible. To permanently resolve the concern, the PIRT panel recommends that additional 

testing be performed. 
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The panel also simplified that the assessment applies to CTs used in medium voltage and low 

voltage switchgear typically installed in NPPs, but does not apply to extremely high ratio 

pedestal-style CTs used in high voltage switchyards. 

6.3 DC Control Power Common Enclosure/Common Power 

Supply 

One of the more important uses for DC power is to supply control and/or protective devices in 

high- and medium-voltage switchgear and load centers. These power supplies can be lost as a 

direct result of fire damage to the major DC power-supply components (e.g., batteries, 

chargers,) or to electrical cables. It is noteworthy that the loss of DC control power to 

switchgear or load centers results from fire damage (shorts to ground) and not spurious 

operations. 

The loss of DC control power to switchgear and/or load centers can result in a loss of 

overcurrent protection for protective circuit designs that rely on relaying functions (overcurrent 

protection, circuit breaker coordination, selective tripping) requiring power to actuate the circuit 

breaker trip mechanism. In particular, loss of DC control power directly affects the design 

capability to protect against issues of common power supply and common enclosures (i.e., 

“Associated Circuit” issues for the deterministic rules of Appendix R, “Other circuit issues” under 

the performance-based rules of NFPA 805). It is noted that some breakers contain selfpowered trip units and are thus not susceptible to this concern. 

With a loss of DC control power from fire damage, the ability of the switchgear or load center to 

rectify problems in common power supply is removed. Since the switchgear (load center) no 

longer has power to the trip circuits for the contained circuit breakers, electrical coordination 

within the switchgear is lost. Electrical faults on the load-side of the power circuits supplied from 

that switchgear must be cleared by protective relaying in the upstream power supply, potentially 

resulting in the loss of electrical power to all loads on the switchgear. We note that this will 

occur even if the protective devices on the switchgear are adequately coordinated, i.e., the 

coordination scheme design is satisfactory but there exists no control power to implement the 

desired selective tripping. 

Additionally, the inability of a breaker to clear a faulted circuit on a low-voltage or medium 

voltage three-phase power circuit could lead to cable over-heating and secondary fires, which 

pose a common enclosure concern in the plant during a fire. The PIRT panel determined that 

this could be generic concern for the industry; however, the PIRT panel had no way to 

categorize the safety and risk significance of this issue since it is highly plant specific. 

The PIRT panel acknowledged the switchgear control power issue as a legitimate concern, but 

determined that this area of analysis did not fall within the primary charter for the panel. 

However, since the loss of control power to switchgear is a very real concern with respect to 

preserving the electrical coordination and protection scheme, it is recommended that the 

common power supply and common enclosure concern for switchgear be addressed through an 

appropriate mechanism/forum. 

A related but more general perspective on coordination issues contemplated by the panel 

involved the DC testing in which larger fuses (30 A) did not clear under relatively energetic 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-11 

faults. The panel ultimately concluded that the fault current in these cases could be low enough 

to allow a fault to persist for several seconds, which is sufficiently long to produce significant 

localized damage. The panel ultimately acknowledged that engineering analysis can provide 

design limits for maximum available fault current at locations within a power distribution system, 

but exact predictions of fault current are not realistic given the many variables at play. 

Accordingly, long-standing industry guidelines for assuring coordination over the entire range of 

available fault current are important to maintaining the validity of a coordination scheme. 

6.4 Control Power Transformers 

Control power transformers (CPTs) often are used to supply power to a control circuit, in 

particular for motor-operated valve (MOV) circuits. The CPT places a limit on the total power 

available to the circuit (power is the product of voltage and current). Hence, as the current flow 

increases beyond a certain point, the transformer core enters a saturation condition in which the 

output waveform becomes highly distorted and voltage begins to degrade below the nominal 

voltage; should voltage drops below the minimum pickup level for the actuation devices, then no 

spurious operations can occur. 

The original EPRI/NEI Tests (Ref. 7) indicate that supplying power via a CPT had an effect on 

spurious operation likelihood as compared to a direct connection to a line power source 

(spurious operations were reduced by roughly a factor of two when using a CPT). Of the 18 

tests conducted, eleven tests used the laboratory power supply, two tests used an isolation 

transformer for the inter-cable testing circuit, and the remaining five used CPTs for a total of 20 

MOV circuit trials powered from CPT’s (Ref. 19). 

In explaining the differences between circuit responses powered from a CPT versus the 

laboratory power distribution supply, Section 12.1.5.1 (3rd bullet) of EPRI TR 1003326 (Ref. 7), 

states the following: 

“Differences in power supply characteristics do not appear to 

influence the failure mode. However, significant fewer spurious 

operations occurred for the test circuits powered by CPTs. This 

result is not self evident from the hot short statistics, which show 

an identical rate of hot shorts for the two different types of power 

supplies. Hence, although power supply characteristics do not 

appear to influence the likelihood of hot shorts, they do 

significantly affect the likelihood that a hot short will produce a 

spurious operation.” 

The theory behind these observations is that when a cable is damaged, the ensuing hot short 

development involves several conductors and paths to ground. The summations of these 

leakage currents suffice to either degrade the CPT’s voltage output so that there is insufficient 

voltage available to energize an actuation device, or the upstream protective devices (fuses) 

could clear due to the elevated current. This effect was not present when using a laboratory 

power supply. The phenomenon behind this effect was apparent in the test data and involved a 

rapid voltage collapse as parasitic current leakage paths developed. The spurious operation 

probability values developed by the EPRI expert panel (Ref. 11) and, in turn, cited in 

NUREG/CR-6850, EPRI TR 1011989, for a circuit powered by a “properly sized CPT” are based 

on this set of test results. 
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One of the research follow-up items identified in RIS 2004-03 (Bin 2 Item D) (Ref. 8) was to 

clarify what a “properly sized CPT” would be in the spurious actuation context. The 

CAROLFIRE project (Ref. 9) investigated this question and reached the following conclusions: 

Bin 2 Item D – Presence of CPT in the Power Source “... derived 

from one aspect of the NEI/EPRI testing where a substantial 

reduction in the spurious actuation likelihood was observed given 

the use of control power transformers (CPTs) compared to the 

case with effectively unlimited power available to the control 

circuit. The CPTs used by NEI/EPRI were sized at 150 VA which 

represented 150% of the nominal power required to actually 

operate the simulated MOV control circuit in its normal mode of 

operation. 

The CAROLFIRE tests evaluated a range of relatively larger CPTs 

ranging from 166% to 333% of the nominal design load required to 

operate the circuit. In these tests, there was no observed effect on 

spurious actuation likelihood, and as noted previously, roughly 

70% of the cable failures led to spurious actuations signals of at 

least momentary duration. The CAROLFIRE tests did experience 

some cases of voltage decay prior to fuse blow, but in most such 

cases a prior spurious operation had been observed. No cases 

were explicitly noted where voltage decay appears to have 

prevented a spurious operation from occurring. The differences 

between these two programs cannot be fully explained, and this 

may be an area that is worthy of further investigation.” 

Follow-up testing was also included as a part of the DESIREE-Fire project (Ref. 10) using even 

lower output CPTs than those used in CAROLFIRE in a further attempt to reproduce the voltage 

collapse effect. As in CAROLFIRE, the tests failed to reproduce the voltage collapse effect 

observed in the NEI/EPRI tests. Some cases of voltage degradation were observed, but in no 

case was a spurious operation avoided because voltage collapsed to below the end device pickup voltage. 

Figure 6-3 (Ref. 20, Figure 2-22), along with Tables 6.1, presents the EPRI/NEI and NRC/SNL 

AC test results that were compiled and evaluated comparing circuit failure modes for test trials 

using CPTs and those test trials without CPTs. Since the CPT size used in EPRI/NEI tests is 

unknown, the group of data labeled as “Unknown Size” represents the EPRI data set. The first 

four bar chart sets and part of the last “None” bar chart sets represent NRC/SNL test results 

between circuits using CPTs of various sizes (i.e., 75VA, 100VA, 150VA, and 200VA). 

Comparing the findings for these four sizes does not reveal any variations in spurious 

operations, each denoting above 50 - 68%, which can be considered statistically as the same. 

However, the EPRI/NEI test results indicate that the likelihood of spurious operation with a CPT 

is 18%, while that without one is 50%. 

Based on testing with AC circuits, in particular using control power transformers (CPTs), the 

PIRT panel has concluded that there appears to be no substantial effect on spurious operation 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

ISSUES 

6-13 

likelihood based on the presence or size (i.e., the VA output rating) of the CPT. Therefore, the 

PIRT panel concluded that the presence or size of the CPT has little or no effect on spurious 

operation probability. This conclusion is contrary to the conclusions of the first EPRI circuit 

analysis expert panel. Because of this, the PIRT panel removed the CPT as a subgroup to the 

time-current characteristics in MICROSOFT ® XCEL scoring worksheets. The PIRT panel 

recommended combining both EPRI/NEI and CAROLFIRE test data for AC circuits when 

estimating the impact of this parameter on the likelihood of spurious operation. 

Table 6-1. CPT size - Global Approach 

Global Approach 75VA 100VA 150VA 200VA Unknown 

Size (EPRI) None Total

Fuse Clear 1 5 10 7 10 12 45 

Spurious Operation 1 10 20 9 3 15 58 

Hot Short 1 10 21 10 7 18 67 

HS/SA Possible 2 15 31 17 17 30 112 

Figure 6-3. CPT size - global approach, AC tests 

The PIRT panel spent a substantial amount of time reviewing available test data and other test 

information in an attempt to identify a rational explanation for the difference in test results given 

seemingly identical configurations. The panel discussions ultimately lead to an understanding 

that the phenomenon at work is much more complex than originally thought, and involves the 

full range of dynamic effects relating to the time-current characteristics of a particular circuit. 

The time-current characteristics refer to both electrical power source and circuit protection 

fuse/breaker (size and timing) characteristics, as well as other system parameters such as cable 

characteristics and system X/R ratio13. In combination, these characteristics determine the 

 

13 X/R ratio refers the ratio of reactive impedance to resistive impedance. This ratio can have a 

pronounced effect on the transient magnitude of fault current in AC power systems. X/R ratio is usually 

75VA 100VA 150VA 200VA Unknown Size None

Count

0

10

20

30

40

Fuse Clear 

Hot Short 

Spurious Operation

HS/SO Possible 

100%

100%

100%

65%

100%

100%

100%

50%

50%

50%

33%

67%67%

32%

68%

25%

41%

59%

53%

59%

41%

18%

40%

60%

50%
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-14

nature and intensity of the available short circuit current and the equipment response to the fault 

current (e.g., voltage collapse, fuse let-through current and clearing time, and circuit breaker 

response). These interactions are dynamic and can vary significantly for seemingly identical 

conditions. 

Ultimately, the PIRT panel concluded that CPT size alone, nor indeed the mere presence of a 

CPT as the powering device, is not a predictable and repeatable circuit design parameter that 

reliably yields fewer spurious operations. Rather, CPT size is one of many circuit parameters 

that influence the complex relationship between short circuit current and time. This relationship 

is a dynamic function with many facets that go well beyond the ability to characterize behavior in 

such a way to provide simple go-no go practical binning criteria. These concepts are born out in 

electrical protection theory, which acknowledges the limitations in fully predicting circuit 

response to faults. 

The PIRT panel concluded that the EPRI/NEI test results did not contain an inherent flaw, but 

instead reflected a particular arrangement of devices, system parameters, and protective device 

characteristics that produced the observed results. However, as demonstrated by the inability 

to reproduce in subsequent tests the same results CPT size should not be used as a basis for 

reducing spurious operation likelihood probabilities. The panel further recommended combining 

both EPRI/NEI and CAROLFIRE test data for AC circuits when estimating the impact of this 

parameter on the likelihood of spurious operation. 

6.5 Kapton®-insulated Cables 

The attributes of the unique construction of Kapton-insulated cable complicate its classification. 

The insulation material properties partially are thermoset (TS) and partially thermoplastic (TP). 

The PIRT panel investigated Kapton insulation with the following objectives: 

• Assess the arc-tracking phenomenon observed in Kapton-insulated cable under certain 

conditions to determine if this degradation mode affects the cable’s performance under 

fire conditions, and, 

• Determine how Kapton-insulated cable should be treated for “classification” regarding 

temperature-damage thresholds. 

6.5.1 Background 

The NRC expressed concern that Kapton-insulated conductors might pose a unique 

susceptibility to fire-induced failures based on a degradation mechanism called “Arc Tracking.” 

NRC Regulatory Guide 1.189, Revision 2 (Ref. 16), Section 5.5.2 briefly discusses Kaptoninsulated cables. Arc Tracking is a degradation mode observed in Kapton-insulated conductors 

wherein the insulation either was mechanically damaged (nicked or cut) or degraded by wear, 

and is applied such that the insulation then exposed on a recurring basis to an electrically 

conductive solution. Arc Tracking degradation appears to be limited to Kapton-insulated 

conductors; the mode was discovered in aircraft wiring. The majority of aircraft having 

 

only considered for AC power systems; however, reactive elements in DC circuits can significantly 

influence fault current rise time, which can affect the performance of protective devices. 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

ISSUES 

6-15 

experienced the Arc Tracking failure mode are naval/marine planes flying from aircraft carriers 

at sea. 

Kapton-wire insulation typically is created by winding multiple layers of plastic film in a 

continuous spiral around the conductor (wrapped-tape type construction). The main dielectric 

element in Kapton® is polyimide film (the thermoset material). Du PontTM uses Teflon® 

(thermoplastic material) as an adhesive sintering agent to bind the polyimide to the conductor 

and successive layers of film to each other. A typical system of Kapton wire insulation consists 

of a layer of Kapton film, typically ~1.0 mil thick, which is coated on both sides with a layer of 

0.1 mil Teflon. This multiple layer is wound around the conductor with a ~50% overlap. . A 

second multilayer Kapton/Teflon film is spirally wound in the opposite direction, again with a 

~50% overlap. The wire/insulation assembly then is heated to melt the Teflon so bonding the 

Kapton to the conductor; this process also is called “sintering” the insulation. The unique 

construction process for Kapton, employing both thermoset and thermoplastic materials, create 

ambiguity about the cable’s classification since it has attributes and characteristics of both 

materials. Seemingly, there have been no tests of Kapton-insulated cables in the specific 

context of fire-induced electrical failure/damage. 

Kapton wiring is popular for use in aircraft due to its low weight and very thin insulation. Kapton 

has very high physical strength, high dielectric capabilities, and some products, at least, are 

available with very good thermal properties (high temperature tolerance). Hence, it is light and 

strong. Due to its superior thermal properties, aircraft electrical conductors are designed to 

operate at much higher temperatures and higher ampacities than in other applications. This 

results in wire bundles that are much hotter than typically observed in nuclear plant applications. 

Although Kapton has very good physical strength, aircraft wiring in many applications is more 

susceptible to physical damage due to the tight confines of the wire’s routing (tight bends) and 

the demands of maintenance (wire bundles having to be moved frequently to gain access to 

nearby components). 

Kapton insulation used in nuclear power plants typically is associated with containment 

electrical penetrations or component connection wires (pigtails) where the component must 

meet Equipment Qualification (EQ) requirements. Unlike its use in aircraft, Kapton insulation is 

not typically used as insulation for electrical conductors in single- or multi-conductor cables, but 

at the same time, nothing precludes such use. 

6.5.2 Arc-Tracking Degradation Mode 

The descriptions provided here principally are based on information in EPRI NP-7189 (Ref. 33); 

although there are numerous other references, the EPRI report focuses on nuclear power 

plants, and therefore is the most appropriate one. 

Arc tracking occurs when two conductors have some type of damage to their electrical 

insulation, and a conductive fluid film is present (for naval aircraft, this could be salt water, or 

high pH fluids used to clean the salt deposits off the aircraft), allowing leakage current to flow 

through the conductive fluid. As the electrical current flows, it heats the fluid, causing it to 

evaporate, resulting in a narrowing band of moisture, with a resultant smaller cross-sectional 

area for the current to flow through. The temperature of this narrowing band increases due to 

the higher current density. As the fluid begins to dry out, the temperature of the local Kapton 

insulation becomes high enough to char the insulation. If this wetting cycle is repeated 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-16

constantly, the charred layer eventually will become thick enough to allow conduction through 

the carbon, resulting in an arc. Once created, the arc causes localized damage to other cables 

in the area, resulting in additional charring, so allowing more electrical current to flow. Some 

Arc Tracking events observed in aircraft resulted in significant burning of wire bundles. 

Research also indicates that physical strain on the wire/insulation also may significantly 

increase the tendency to produce Arc Tracks. 

As documented in EPRI NP-7189 (Ref. 33), research performed by the Naval Research 

Laboratories identified five conditions that must be present for Arc Tracking to occur: 

 There must be a fault or radial crack in the conductor on an energized wire, 

 A conductive solution must be present and dripping directly on to the fault, 

 There must be a completed circuit to ground, 

 Substantial voltage and current must be available, and, 

 A specific geometry of wires in relation to ground must exist (e.g., a distance of less than 

3/16 of an inch from a ground electrode). 

An alternative to dripping conductive fluid on the fault is periodic wetting of the two conductors 

with such a fluid. Kapton insulation also is susceptible to degradation by hydrolytic degradation, 

as occurs when the insulation is under significant strain, is at high temperature, and is exposed 

to water for long periods. 

The PIRT panel examined available information to determine if there is any technical rationale 

upon which the arc-tracking phenomenon can be expected to appreciably change the 

characteristics of fire-induced cable failure, as documented in hundreds of fire tests performed 

by industry and NRC. They reached the following conclusions: 

 Arc-tracking is a unique failure-mode not likely to exist for NPP applications. 

 The arc-tracking mechanism should have no impact on the characteristics of cable 

failure with regard to MHIF effects. Once fire has severely damaged the cable’s 

insulation, it will undergo full failure quickly. That is, arc-tracking degradation will not 

cause the cable to establish a long-term high impedance fault under fire conditions. 

 It cannot be ruled out that arc-tracking will reduce the cable’s temperature-damage 

threshold (a similar concern as that observed for Kerite-FR material). The reduced 

integrity of the insulation could hasten the cable’s functional failure. 

6.5.3 Application and Operating Experience at Nuclear Power Plants 

As with the previous section, the information here principally is based on information contained 

in EPRI NP-7189 (Ref. 33). However, this section also includes elements of general industrial 

knowledge. 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-17 

As noted above, Kapton insulation used in nuclear power plants typically is associated with the 

containment’s electrical penetrations or component connection wires (pigtails) where the 

component must meet Environmental Qualification (EQ) requirements for 10 CFR 50.49 (Ref. 

38). Unlike its use in aircraft, Kapton insulation is not typically used as electrical conductor 

insulation in single- or multi-conductor field-routed cables. 

Kapton insulation has experienced electrical failures in nuclear applications. NRC Information 

Notice 88-89 (Ref. 34) reported several failures of Kapton insulation; however, none of them 

appear to have involved Arc Tracking. Experience with EQ testing of Kapton indicates that the 

insulation is susceptible to electrical failure if it is in direct contact with sprays of high pH fluids, 

such as ammonia hydroxide. However, these chemically induced failures have no correlation to 

fire-induced failure. 

Several performance characteristics of Kapton under fire conditions are known: 

 Kapton insulation has demonstrated excellence in flame propagation tests. Kapton 

passed the IEEE STD-383 (Ref. 35) flame propagation test, also passing a 2.4 kVAC 

dielectric withstand test afterwards. Flame propagation testing performed by Du Pont on 

MIL STD W-81381 (Ref. 36) electrical wiring also revealed no problems. 

 Cables insulated with Kapton have not been tested in a fire environment to determine 

the probabilities of attaining electrical failure temperature or of hot short/spurious 

operation. However, based on the usage of Teflon as a bonding agent, it is believed that 

Kapton-insulated wire might exhibit a fire-exposure performance similar to either 

thermoplastic- or thermoset-cable insulation depending on whether failure is driven more 

by the content of the former (e.g., the Teflon sintering agent) or by that of the latter (the 

polyimide film). 

 It is noted that some Kapton products were specifically designed for high-temperature 

use and were qualified for up to 400°C (752°F). 

Unfortunately, there is very little fire test data to help with classifying Kapton®. Classification 

from an academic perspective is not all that important. The fundamental consideration is the 

material’s exhibited properties, in this case, the threshold for temperature damage. It is known 

that some Kapton materials have very good high-temperature characteristics; however, it is not 

clear whether this is valid for all Kapton materials. 

6.5.4 Temperature Damage Thresholds 

Given the uncertainty about the limits of Kapton fire-induced thermal damage, the 

recommended practice relative to its damage thresholds is provided in three parts: 

• If the analyst can establish that the cables in question were certified for use under the 

EQ program, then it is recommended that the cables be assumed to fail consistent with 

other thermosetting cable insulations. Typical EQ qualification would, for example, 

include certification in accordance with the full IEEE STD-383 severe accidentexposure testing standard. We note that compliance with just the flame-spread 

element of the IEEE STD-383 standard is not sufficient for this case. 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-18

• If the analyst can establish and alternate basis for a product/case specific failure 

threshold (e.g., manufacturer or utility testing of the product in question) then the casespecific damage threshold may be assumed. If the failure threshold established is 

below that typical for thermoset cables (i.e., less than 330°C) then it is recommended 

that the cable be treated as a thermoplastic in the spurious operation analysis. If the 

failure threshold established is consistent with typical thermoset insulations (i.e., 

greater than or equal to 330°C) then it is recommended that the cable be treated as a 

thermoset in the spurious operation analysis. 

• If the analyst cannot establish a qualification basis for the cables in question, then it is 

recommended that they be assumed to fail consistent with thermoplastic-insulated 

cable materials. 

6.5.5 Conclusions 

The PIRT panel reached the following conclusions on Kapton-insulated cables: 

Arc-Tracking Effect:

 The arc-tracking mechanism should have no impact on the characteristics of cable 

failure with regard to MHIF effects. Once fire has severely damaged the cable’s 

insulation, it will undergo full failure quickly, just like thermoset- and thermoplastic-cable. 

That is, arc-tracking degradation will not cause the cable to establish a long-term high 

impedance fault under fire conditions. 

 It cannot be ruled out that arc-tracking will reduce the cable’s threshold for temperature 

damage (a similar concern as that observed for Kerite-FR material). The reduced 

integrity of insulation could hasten the cable’s functional failure. 

Temperature-Damage Threshold:

Kapton’s failure thresholds should be assumed consistent with those of thermoplastic (TP)-

insulated cables unless the cable in question was certified for use under the EQ program for 

severe accident-exposure conditions or an alternate basis for a product/case specific thermal 

damage threshold can be established. Cables with EQ-based severe accident certification 

should be assumed to fail consistent with a thermoset (TS) cable-insulation material. Cables 

using an alternate product/case specific basis for the damage threshold should be assumed to 

fail consistent with either a TP or TS material depending on the actual damage threshold 

established (i.e.: if the threshold is less than 330°C treat as TP; if greater than or equal to 330°C 

treat as TS). 

6.6 Panel Wiring 

6.6.1 Background 

The wiring used within an electrical cabinet (panel wiring) is unique compared to the cables 

used in general field-routing applications. Field-routing is dominated by multi-conductor cables. 

In contrast, panel wiring is comprised of both multi-conductor cables, and single conductor 

cables. In a typical configuration, multi-conductor field routing cables enter/exit the cabinet, 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

ISSUES 

6-19 

usually through either its top or bottom , and each conductor (possibly excepting spare 

conductors) is terminated either directly onto a specific end device, to ground, or, quite 

commonly, to a terminal strip mounted within the cabinet. For the conductor termination, a 

section of the multi-conductor cable jacket will be removed (stripped). Single conductor wires 

are commonly used within a cabinet to connect field-wire terminations at a terminal strip to their 

end devices, and for inter-device connections within the cabinet. The configurations used in 

single conductor-panel wiring are expected to be wide ranging and may include individual 

conductors routed somewhat loosely through a panel, conductor bundles routed in metal or 

plastic wire-ways (e.g., Panduit®), bundles of conductors secured with nylon wire ties (zip-ties), 

and bundles secured with rigid metal- or plastic-retaining loop clamps. Figure 6-4 illustrates 

typical panel-wiring configurations. 

 

Figure 6-4. Typical Panel Wiring Configurations 

6.6.2 Discussion 

For those portions of the in-cabinet panel wiring that involve intact multi-conductor cables (e.g., 

field routing cables where the jacket has not been stripped), the PIRT panel concluded that 

spurious operation likelihoods should be calculated in the same manner as for control circuit 

multi-conductor cables in general field-routing applications (e.g., cable tray routing). That is, 

there is no basis for unique treatment just because a multi-conductor cable has entered an 

electrical cabinet so long as the individual conductors have not been stripped out of their cable 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-20

jacket. However, for those portions of the in-cabinet panel wiring that involve single conductor 

cables (including a multi-conductor cable whose jacket has been stripped), a unique treatment 

is needed. 

To understand the PIRT panel’s reasoning, it is important to understand typical practice in 

manufacturing multi-conductor cables. Depending on the total conductor count, the individual 

conductors in a typical multi-conductor cable are arranged in one or more concentric layers. A 

cable with a small conductor count (2-6 conductors) generally has only a single layer. As the 

count increases, the conductors are arranged in layers in the form of a concentric ring. For 

example, a typical 7-conductor cable has a single central conductor and a second layer of 6 

conductors in a ring around the central one. A 12-conductor cable typically has a central core 

layer of three conductors and a second ring/layer of 9 conductors. A 19-conductor cable is 

much like a 7-conductor cable with a third ring/layer of 12 conductors; a 37-conductor cable 

adds a fourth ring/layer with 18 conductors in it. This practice yields finished cables that are 

roughly round. This also means that, while special order products are available in effectively 

any conductor count, most control cables will have one of the more common total conductor 

counts; namely, 2, 3, 5, 7, 9, 12, 19, 37, or 61 conductors. 

One key factor associated with this manufacturing practice is thought to impact the failure 

behavior of multi-conductor cables, and will be absent from single conductor panel wiring. 

Manufacturers lay the conductor rings/layers in an alternating helical spiral pattern. That is, 

each conductor layer is laid as a helical spiral in a geometric pattern, with alternately reversed 

lay direction between the layers. Conductors in each layer maintain their positions relative to 

each other, but spiral (rotate) as a group along the length of the cable, with alternate layers 

spiraling in opposite directions. 

Accordingly, manufacturing leaves some degree of residual tension left in the conductors. It is 

thought that this residual tension may be one factor contributing to the relatively high likelihood 

of intra-cable shorts given electrical failure of the cable. That is, the residual tension may draw 

the individual conductors within the cable together as the insulation begins to degrade and lose 

physical integrity (e.g., melt or burn). Once the conductors are stripped out of the cable jacket, 

this residual tension is absent so that there may be less impetus for the conductors to short to 

each other on failure. Similarly, single conductor panel wiring would lack the residual tension 

associated with multi-conductor cables. A counter-acting effect would be the practice of 

bundling single conductor cables together as they are routed within the cabinet. That is, while 

the residual tension associated with multi-conductor cables is absent, the insulated conductors 

may be routed in relatively tight bundles as noted above. 

6.6.3 Recommendation 

Overall, shorting of conductors in panel wiring conductor bundles could behave similarly to 

either intra-cable or inter-cable shorting depending upon the proximity of the conductors and the 

tightness of their bundles. The PIRT panel believes that the probability of inter-conductor 

shorting within a bundle lies somewhere between the probabilities of an intra-cable and an intercable hot short. This probability is most likely affected by the configuration and tightness of the 

conductor bundles. The lack of test data for panels clearly is problematic when determining the 

true behavior of conductors or components in a panel. Hence, it is important to determine 

bounding characteristics for panel configuration. With this in mind, the PIRT panel strongly 

recommended further testing in this area. Based on the lack of applicable test data and the 
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

ISSUES 

6-21 

potential risk importance of panel wiring, the PIRT panel recommends hot short probabilities 

equivalent to those of an intra-cable hot short be assumed for panel wiring. 

6.7 High Conductor Count Trunk Cables 

6.7.1 Background 

Multi-conductor cables containing more that 12 conductors typically are classified as “trunk 

cables.” The large number of conductors within one cable allow for multiple circuits to be 

contained within one cable and routed to common points within the NPP. Trunk cables are 

typically have with 19/C, 25/C, 37/C and higher conductor-count configurations. Figure 6-5 

shows a photo and illustration of a 37/C trunk cable. The exact number of conductors within a 

trunk cable depends on the geometrical configuration that ensures the cable’s roundness to 

ease installing cables. 

 

Figure 6-5. Photo and Illustration of 37/C Trunk Cable 

6.7.2 Discussion 

The number of conductors in a multi-conductor cable may influence the likelihood that a specific 

pair (or set) of conductors within a cable might short together. That is, the more conductors 

within a cable, the more opportunities for the conductors to short together under severe thermal 

conditions. The proximity of source and target conductors may influence the likelihood of this 

failure mode. 

Fire effects on trunk-cable failure modes were explored by a limited set of experiments 

conducted by Duke Power (Refs. 17 and 18). These results are proprietary to the utility but a 

publically available power-point presentation made at an Institute of Electrical and Electronic 

Engineer (IEEE), Insulated Conductors Committee meeting summarizes the results (Ref. 17). 

In addition, Duke submitted their preliminary test plan to the NRC for review and comment. 

Information from this also gives an understanding of what they proposed to test (Ref. 37). 

Jacket

Insulation

Conductor
PIRT PANEL TECHNICAL POSITION ON ANCILLARY CIRCUIT ANALYSIS RELATED 

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6-22

From this information, the following was noted. The Duke Power cable tests included a 37/C 

armored trunk-control cable enclosing 12 AWG conductors with a flame-retardant XLPE 45 milsthick insulation. Each trunk cable tested included 4 monitored circuits. The findings 

demonstrated that “the speed and temperature intensity of the fire damage to the armored 

cables was not significantly affected, but there was a notable increase in spurious-operation 

activity.” More details of the results of the armored cable test results are not available publically. 

6.7.3 Conclusions 

Because of the large number of conductors in a trunk cable, the electrical expert PIRT panel 

speculated that the greater availability of target and source conductors could have resulted in 

the increase in spurious operations seen in the testing. While this may be plausible, there is no 

way of knowing for certain because the testing did not specifically explore this possibility. Other 

differences of note between the Duke testing and the testing evaluated by the PIRT panel was 

that the former testing was conducted on armored cables and the majority of the latter testing 

was conducted on an ungrounded AC CPT configuration. Because of this lack of 

understanding, future research in this area is warranted. However, since trunk cables are only 

used in a limited set of applications within NPPs, this research would be ranked as medium- to 

low-priority. 
7-1

7

PIRT PANEL RESEARCH RECOMMENDATIONS 

The electrical expert PIRT panel discussed and evaluated an exhaustive number of technical 

issues on hot short-induced spurious operations and other fire damage-related concerns. For 

many of these issues, the PIRT panel made final determinations on the credibility and/or 

importance of the issue. However, for certain technical issues, the PIRT panel could not draw a 

final conclusion, or they formulated a consensus position, but presented it with the caveat that 

more research should be conducted to support that position. In certain cases, there was so little 

information, and the failure modes were so uncertain, that the PIRT panel concluded that more 

research was needed. 

Section 3 discusses the ranking factors that were assigned to influencing parameters for control 

circuitry. In some cases, the PIRT panel assigned an influencing factor of High, and the 

associate parameter “State of Knowledge” was ranked as Low. In these cases, the PIRT panel 

concluded that if there is a lack of knowledge of a parameter that highly influences the likelihood 

or duration of spurious operations, then research should be conducted to find out how much 

effect the parameter truly has. 

Although the PIRT panel recommends additional research, these recommendations do not 

imply that the NRC or EPRI will pursue such efforts. The specific research and associated 

prioritization of that research depends on the internal research planning and budgetary 

constraints of these two organizations. 

This section discusses the research recommendations of the PIRT panel, and then it prioritizes 

those recommendations in terms of their importance. 

7.1 Control Circuit Research 

Most research and testing have been undertaken in the area of control circuitry. Because of the 

availability of data, the PIRT panel was able to evaluate specific control circuit cable parameters 

using test results. However, for certain influencing parameters, testing data did not exist. In 

these cases, the PIRT panel used its expertise and experience to provide a ranking of High (H), 

Medium (M), Low (L), or Uncertain (U) in regard to the influence of that parameter on the 

likelihood of spurious operations or their duration. Parameters that were assigned either a 

ranking of ‘High’ or ‘Uncertain’ as an influencing factor along with a ranking of ‘Low’ in regard to 

the state of knowledge were recommended as candidates for further research. The parameters 

that met these criteria are listed in Table 7-1. Unless stated otherwise, all parameters apply to 

both AC- and DC-control circuits. 

Of the parameters in Table 7-1, all of them, with the exception of panel wiring and fire 

suppression, can be performed using similar testing to that done before. Changing the 

parameters would only require testing of different cable types or circuits. Panel wiring and fire 

suppression, however, would involve a different, potentially more complicated testing setup. 

Conceptually, fire suppression could be tested along with the other five parameters by adding in 

the fire-suppression features for the cables being tested. Therefore, for the purposes of this 
PIRT PANEL RESEARCH RECOMMENDATIONS 

7-2

section, testing of all of these parameters, with the exception of panel wiring, will be 

cumulatively categorized as “control circuit cable testing.” 

Table 7-1. Potential Research Candidates Due to Low State of Knowledge 

Parameter AC DC Likelihood 

Ranking 

Duration 

Ranking 

Fire Exposure Condition (Time /Temp) X X H 

Panel Wiring X X H H 

Time-Current Characteristics - Fuses/ Breaker 

Size 

X H 

Cable Grounding Configuration (Shield Wrap) X H 

Armor Grounded versus Ungrounded Circuit X H 

Armored versus Unarmored X H 

Fire Suppression (Water Spray and Hose) X X U 

The lack of test data for PIRT panels is problematic when attempting to determine the true 

behavior of conductors or components in a panel. Because panels are installed throughout a 

NPP, it is important to determine the characteristics of spurious operations for this configuration. 

The primary concern is the behavior of conductor bundles within a panel. As stated earlier in 

Section 6, the shorting of conductors in panel wiring conductor bundles could behave similarly 

to either intra-cable or inter-cable shorting, depending upon the proximity of the conductors and 

the tightness of the bundles. Therefore, the probability of conductor-to-conductor shorting within 

a bundle lies somewhere between the probabilities of an intra-cable and an inter-cable hot 

short. For deterministic analyses, intra-cable hot shorts would be the conservative assumption. 

Because of this uncertainty about spurious operation behavior in panel wiring configurations, the 

PIRT panel recommended testing in the area of panel wiring. 

7.2 Instrumentation Circuit Research 

The PIRT panel was concerned that the low energies involved in instrumentation circuits could 

cause them to perform and fail differently under fire-induced fault conditions than those of higher 

energy control circuits. While control circuits progress relatively quickly through fault states due 

to arcing fault energies, this same progression may not be experienced as readily in lower 

energy instrumentation circuits. The time required before a fault occurs in the circuit and the 

duration of the fault state may differ substantially from that of control circuits. In addition, 

various wiring methods, circuit designs, and the use of shielding (tied to ground or to power 

supply neutral) may all have dominating influences over the failure modes and effects seen as a 

fire damages the cable. 

Additionally, there is the possibility that instead of an instrument failing in only two functional 

failure modes, high or low, the instrument could potentially fail in an intermediate mode before 

its complete failure. This would result in a false reading that could cause an operator to make 

an incorrect diagnosis, or it could mask an indication of a problem in the plant. Incorrect 

operator actions due to faulty indication potentially can be more adverse to safety during a fire 

than the actual fire damage. 
PIRT PANEL RESEARCH RECOMMENDATIONS 

7-3 

Due to the low state of knowledge and potential high consequences of fire-induced failure on 

instrumentation current loop circuits, the PIRT panel strongly recommended that additional 

testing be performed. The PIRT panel recommended that the following circuits be included in 

the testing: 

• 10 mA to 50 mA instrumentation circuits 

• 4 mA to 20 mA instrumentation circuits 

• 1 VDC to 5 VDC instrumentation circuits. 

7.3 Surrogate Ground Path Research 

The importance of the surrogate-ground-path phenomenon (aka. ground fault equivalent hot 

short) was discovered during the DESIREE-Fire testing. Based upon the results, the PIRT 

panel determined that this would have to be considered as a plausible failure mode along with 

intra-cable and inter-cable shorting. However, with the exception of the DESIREE-Fire results, 

there is little data available on this phenomenon. 

Because of the importance of the surrogate-ground-path phenomenon in DC ungrounded 

circuits, the PIRT panel strongly recommended further research focusing on the effects and 

probability of this type of failure mechanism. Also, since the phenomenon depends on the 

circuitry being ungrounded, ungrounded AC circuits should be included as a sub-set in any such 

testing. 

7.4 Current Transformer Research 

The PIRT panel could only definitively concluded that secondary fires were not a credible risk 

for CTs with turns-ratios 1200:5 and lower. For CTs with higher turns-ratios, the PIRT panel felt 

that the risk to fire safety was low, but there were no test data to support their position. While 

there are only a limited population of CTs in NPPs that have these high turns ratios, the PIRT 

panel felt that testing was warranted for the entire range of turn ratios so that this issue finally 

can be resolved. 

7.5 Conclusions and Prioritization of Future Research 

Because there was a lack of knowledge in all of the aforementioned areas, prioritization was 

based upon the importance of the configurations to plant operations during a fire, and the 

potential consequences of mal-operation or fire damage. Additionally, consideration was given 

to the lack of a clear technical consensus on the characteristics of spurious operation. For 

instance, many of the control circuit parameters could at least be categorized as having a high 

influence on either the likelihood or duration of spurious operations. This knowledge primarily 

was based upon the knowledge of cable characteristics during testing. However, in the case of 

instrumentation, it was difficult to come to any conclusions on spurious operation characteristics 

because there was so little information. 

Prioritization of research is presented below, with highest priority listed first: 

1. Instrumentation and Control Circuits [highest priority] 

2. Panel Wiring 

3. Surrogate Ground Path 

4. Control Circuit Cable Testing (Influencing Parameters given in Section 7.1) 
PIRT PANEL RESEARCH RECOMMENDATIONS 

7-4

5. Current Transformers 

6. High Conductor Count Trunk Cables (discussed in Section 6.7) [lowest priority] 

Importantly, items 3 and 4 can most likely be accomplished through the same testing program. 

Instrumentation was chosen as the number one priority because there is little information about 

fire-induced failures to instrumentation circuitry and because of the overall importance of 

instrumentation circuitry to the safe operation of a NPP. 

Trunk cables are another special type of multiconductor cables (with 12 or larger number of 

conductors) often used with multiple identical circuit wiring between the main control room 

panels and the relay rack room before being routed to the field end devices. It is discussed in 

detail in Section 6.7 where the PIRT panel ranked the recommended testing to be low or 

medium. 
8-1

8

SUMMARY AND CONCLUSIONS 

The objective of this PIRT exercise was to identify the phenomena (electrical circuit 

configurations) that can affect the circuit failure modes from fire-induced cable damage. Using 

the results from recent fire tests performed by the EPRI/NEI in 2002 and the NRC/SNL 

(CAROLFIRE in 2008 and DESIREE-Fire in 2010), the electrical expert PIRT panel identified 

and ranked the parameters that could influence the hot short-induced spurious operations in 

electrical circuits. Utilizing these parameters, the findings from cable fire tests, expert judgment, 

and operating experience, the PIRT panel indentified and developed circuit configurations that 

would be vulnerable to hot short circuit failure modes of concern that can cause certain end 

devices to operate spuriously. 

This PIRT investigated such fire-induced spurious operations of plant components, evaluating 

both alternating current (ac) and direct current (dc) types of circuits. The PIRT panel’s focus 

encompassed three specific types of electrical circuits, i.e., power, control, and instrument 

circuits. Their primary emphasis was upon the control circuits (e.g., 120 VAC and 125 Vdc) 

because fire-induced damage of these types is considered to pose a higher risk to plant safety 

than does the other types of circuit. Accordingly, the majority of test data from industry, along 

with the NRC’s tests, was related to low-voltage control circuits. Due to the limited test data 

available for instrument circuits, the PIRT could not undertake a complete parametric treatment 

of this type. Available failure modes for power circuits are well understood, except for a few 

unique cases. For certain types of power circuits (for example, three-phase power cables), 

there were no available findings from specific testing by industry; therefore, the PIRT panel’s 

technical recommendations rested upon their expert judgment involving engineering principles 

and physical configurations for power cables and power-cable installations. In other instances, 

such as the PIRT panel’s considerations of open circuits in the secondary circuits of current 

transformers (CTs), their recommendations were based upon available open-circuit test data, 

manufacturers’ input, operating experience (nuclear and non-nuclear), and expert judgment. 

The PIRT panel ranked the following parameters “as having a” HIGH impact on the likelihood of 

hot short-induced spurious operations, and the duration of a spurious operation: 

• Spurious Operation

o Wiring Configuration (number of sources, target, ground/neutral, and their 

locations) - An increase in the number of source and target conductors was 

deemed to add to the potential for a spurious operation, whereas an increased 

number of ground conductors was concluded to lead to an increased potential for 

a blown fuse that could either prevent a spurious operation or reduce its duration. 

o Conductor Insulation Material Type [for inter-cable hot shorts (thermoset (TS) 

versus thermoplastic (TP))] - For intra-cable hot shorts/spurious operations, the 

type of insulation did not contribute to the potential. However, for inter-cable hot 

shorts/spurious operations, the type of insulation was a contributing factor, since, 

for example, by the time the char layer on a TS conductor is worn away by the 

effects of the fire; it will have interacted with an adjacent conductor in the same 

cable before interacting with a conductor in an adjacent cable. 
SUMMARY AND CONCLUSIONS

8-2

o Grounding Configuration - The ground condition for a specific cable will 

contribute greatly to that cable’s ability to reach grounds, to open the circuit 

protective device (i.e., fuse, breakers), and remove the voltage potential from the 

circuit. The latter process eliminates the circuit’s ability to hot short with any 

adjacent conductors. The following parameters could influence the grounding 

configuration of a circuit: 

 Cable-grounding configuration (e.g., ground or drain wire, shield wrap) 

 Armor Grounded versus Ungrounded Circuit (for grounded AC circuits), 

and, Armored versus Unarmored (for ungrounded DC circuits) 

 Grounded versus Ungrounded Circuits (for inter-cable hot-shorts). 

o Cable Routing/Raceway – Panel Wiring (ranked as HIGH due to a lack of 

available test data, and the belief that testing this parameter is important for 

assessing its impact on post-fire safe shutdown). 

o Cable Raceway Fill – Bundles (Note: The PIRT panel considered this important 

even though they ranked it medium) - The additional cable-to-cable pressure 

exerted by bundling appeared to make somewhat of a difference (i.e., an 

increase) in the propensity for spurious operations. 

• Duration

o Fire Exposure Conditions (flame, plume, hot gas layer) - The slower the 

progression of fire damage to the cable, the longer will it take fully to erode the 

insulation from the conductors and thereby ground the cable. The grounding of 

the cable and the opening of the cable’s protective device is the mechanism for 

stopping the spurious operation. Longer times to reach ground are related 

directly to longer spurious operations. 

o Time-Current Characteristics – fuses/breaker size. Larger fuse/breaker sizes are 

expected to take longer times to clear that, in turn, entail longer durations of 

spurious operations. Additionally, in some ungrounded DC circuits, larger fuse 

sizes did not clear immediately. Extended periods of arcing occurred. 

o Wiring Configuration (number of sources, targets, ground/neutrals and their 

locations) - The PIRT panel concluded that whilst an increased number of source 

and target conductors would add to the potential for a spurious operation, more 

ground conductors would lead to a higher potential for a blown fuse that could 

either prevent a spurious operation or reduce its duration. 

o Cable Routing/Raceway – Panel Wiring (ranked as HIGH due to a lack of 

available test data and the belief that testing of this parameter is important for its 

impact on post-fire safe shutdown). 

o Cable Raceway Fill – Bundles (Note: The PIRT panel considered this important 

even though they ranked it as medium) - The additional cable-to-cable pressure 

exerted by bundling appeared to make somewhat of a difference (i.e., an 

increase) in the propensity for spurious operations. 
SUMMARY AND CONCLUSIONS

8-3 

o Latching Circuit Design (e.g., motor operated valves) - This parameter is a 

specific design-feature of a control circuit that will cause the effects of the hot 

short to lock-in in a very brief time. This feature in the control circuit design will 

extend the duration of the spurious operation, but it is not directly related to 

specific aspects of a cable’s fire robustness. 

Taking all these factors into consideration and using their expert judgment and experience, the 

PIRT panel identified thirteen different base cases that represent control circuit cable 

configurations vulnerable to hot short-induced spurious operations. Based on this assessment, 

the PIRT panel presented several example cases that currently are used in nuclear power 

plants and are considered in the safe-shutdown circuit analysis documented in fire protection 

programs. 

In addition to reviewing and evaluating the spurious operation of the control circuits and its 

duration, the PIRT panel provided technical recommendations on other aspects of fire-induced 

circuit failures associated with control and power circuits in the analyses of post-fire safeshutdown circuits. Specifically, the PIRT panel concluded the following: 

• The spurious operation of a three-phase AC motor due to proper polarity hot shorts on 

three-phase power cabling is incredible. 

• The spurious operation of DC compound-wound motor due to proper polarity hot shorts 

in the motive/power cabling is incredible. 

• The ignition of a secondary fire from an open circuited CT secondary circuit with a turnsratio of 1200:5 or less is incredible. 

• The guidance given in Nuclear Energy Institute, NEI 00-01, Rev. 2 (Ref. 13), Appendix 

B.1, can be applied safely to fire safe-shutdown methodologies throughout the plant in 

resolving concerns associated with Multiple High-Impedance Faults (MHIFs). (Note: 

Appendix B.1 of NEI 00-01, Rev. 2 offers a basis for concluding that MHIFs need not be 

considered, provided there exists breaker coordination for any circuits damaged by the 

fire that previously should have been assessed for the effects of MHIFs and appropriate 

testing and maintenance is performed). 

• The spurious operation likelihood reduction factor of “two” provided in the Fire 

Probabilistic Risk Assessment (Fire PRA) methods when a control power transformer 

(CPT) is the derived energy source for a circuit, does not accurately reflect the entirety of 

the test data; no credit should be taken in the Fire PRA for their use in a CPT-powered 

control AC circuit. (Note: The revised probability in Volume 2 of this NUREG/CR will be 

based on a composite of all testing undertaken, and, hence, the probability offered for 

using with both CPT and non-CPT circuits may be increased by a factor less than 2). 

• Kapton® cable, a polyamide stable from -271 to +400 o

C, should be treated as a 

thermoplastic (TP) material for assessment of circuit failures, including risk-informed 

applications, unless an alternate basis can be established for the specific cable being 

analyzed based either on full equipment qualification certification of a cable produce or 

on other tests (e.g., manufacturer or utility testing of the cable product) that establish a 

failure threshold. The treatment relative to failure behavior is then assumed consistent 

with the established failure threshold (see Section 6.5.4 for details). 
SUMMARY AND CONCLUSIONS

8-4

• Spurious operation caused by shorting conductors through a surrogate ground path in 

ungrounded circuits as a result of fire induced damage, is a failure mode that occurred 

during the DESIREE-Fire Testing; it is referred to as “Ground Fault Equivalent Hot 

Short.” The probability of this failure mechanism for cable-to-cable hot shorts is such 

that it warrants consideration for including in future testing programs and, subsequently, 

in analyzing post-fire safe-shutdown conditions. 

Additionally, the PIRT panel recommended future research in several areas. The 

recommendations were based upon a lack of knowledge (and available test data) therein, and 

the importance of the configurations to plant operations during a fire and the potential 

consequences of faulty operation to certain electrical devices. The PIRT panel recommended 

considering the following areas in future research: 

1. Instrumentation and Control Circuits (Discussed in Section 5) [highest priority] 

2. Panel Wiring (Discussed in Section 6.6) 

3. Surrogate Ground Path Hot Short (Discussed in Section 7.3) 

4. Control Circuit Cable Testing (Influencing Parameters given in Section 7.1) 

5. Current Transformers (Discussed in Section 6.2 & 7.4) 

6. High Conductor Count Trunk Cables (Discussed in Section 6.7) [lowest priority] 

Finally, based upon the findings of the PIRT panel, BNL will conduct a follow-on expert 

elicitation via a PRA panel to determine the best-estimate conditional probability (or likelihood) 

of failure, given fire-induced cable damage. Their findings will be documented in Volume 2 of 

this NUREG/CR report. These probability estimates represent an advancement of the state-ofthe-art for assessing the likelihood of circuit failure and could be used for revising, directly 

replacing, or creating new probabilities for Table 10-1 through Table 10-5 of NUREG/CR-6850 

for conducting Fire PRAs. 
9-1

9

REFERENCES 

1. 10 CFR 50.48 (Title 10 of the Code of Federal Regulations, Part 50, Section 50.48), “Fire 

Protection.” 

2. 10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities.” 

3. 10 CFR Part 52, “Licenses, Certifications, and Approval for Nuclear Power Plants.” 

4. 10 CFR Part 50, Appendix A, “General Design Criteria for Nuclear Power Plants,” GDC 3, 

“Fire Protection.” 

5. 10 CFR Part 50, Appendix R, “Fire Protection Program for Nuclear Power Facilities 

Operating Prior to January 1, 1979.” 

6. NFPA 805, “Performance-Based Standard for Fire Protection for Light-Water Reactor 

Electric Generating Plants,” 2001 Edition, National Fire Protection Association. 

7. EPRI TR-1003326, “Characterization of Fire-Induced Circuit Faults: Results of Cable Fire 

Testing,” Electric Power Research Institute, Palo Alto, California, December 2002. 

8. Regulatory Issue Summary 2004-03, “Risk-Informed Approach for Post-Fire Safe-Shutdown 

Circuit Inspections,” Revision 1, December 29, 2004. 

9. NRC. NUREG/CR-6931, “Cable Responses to Live Fire (CAROLFIRE),” SAND2007-

600/V1, V2, and NISTIR 7472 Vol. 3, April 2008. 

10. NRC. NUREG/CR-7100, “Direct Current Electrical Shorting in Response to Exposure Fire 

(DESIREE-Fire) - Test Results,” SAND2012-0323P, April 2012. 

11. EPRI TR-1006961, “Spurious Operation of Electrical Circuits Due to Cable Fires – Results of 

an Expert Elicitation” Electric Power Research Institute, Palo Alto, California, May 2002. 

12. NRC. NUREG/CR-6850 and EPRI TR-1011989, “EPRI/NRC-RES Fire PRA Methodology 

for Nuclear Power Facilities,” Volumes 1 and 2, September 2005. 

13. NEI 00-01, “Guidance for Post Fire Safe-shutdown Circuit Analysis,” Revision 2, May 2009. 

14. NRC. NUREG/CR-6923, “Expert Panel Report on Proactive Materials Degradation 

Assessment,” February 2007. 

15. NRC. NUREG/CR-6978, “A Phenomena Identification and Ranking Table (PIRT) Exercise 

for Nuclear Power Plant Fire Modeling Applications,” SAND2008-3997P, November 2008. 

16. NRC Regulatory Guide 1.189, “Fire Protection for Nuclear Power Plants,” Revision 2, 

October 2009. 
REFERENCES

9-2

17. Graham, S.P., “Fire-Induced Spurious Actuation Testing of Armored-Cable Control Circuits,” 

122nd Insulated Conductor Committee Meeting, Scottsdale, Arizona. November 2007. 

http://www.pesicc.org/iccwebsite/subcommittees/subcom_d/Presentations/Fall07/D3.Graha

m.pdf 

18. Barrett, H., “Fire Research-Integrating Research into Practical Applications,” RIC 2007, 

March 2007. 

19. NRC. NUREG/CR-6834, “Circuit Analysis – Failure Mode and Likelihood Analysis,” 

September 2003. 

20. NRC. NUREG-2128, “Electrical Cable Test Results and Analysis during Fire Exposure 

(ELECTRA-FIRE) – A consolidation of the three major fire-induced circuit and cable failure 

experiments performed between 2001 and 2011,” Draft Report for Comments, April 2012. 

21. NRC. NUREG/CR-6776, “Cable Insulation Resistance Measurements Made During Cable 

Fire Tests,” June 2002. 

22. IEEE STD. 100-1998, “IEEE Standard Dictionary of Electrical and Electronics Terms,” 4th 

Edition, Institute of Electrical and Electronics Engineers. 

23. Generic Letter (GL) 81-12, “Fire Protection Rule (45 FR 76602, November 19, 1980),” 

February 20, 1981, and Clarification Letter, March 1982. 

24. NRC. NUREG/CR-7102, “Kerite Analysis in Thermal Environment of Fire (KATE-Fire) Test 

Results,” SAND2011-6548P, December 2011. 

25. NRC. NUREG/CR-5546, “An Investigation of the Effects of Thermal Aging on the Fire 

Damageability of Electric Cables,” May 1991. 

26. IEEE STD 242, “IEEE Recommended Practice for Protection and Coordination of Industrial 

and Commercial Power Systems (IEEE Buff Book),” 2001. 

27. NRC Generic Letter 86-10, “Implementation of Fire Protection Requirements.” 

28. Letter from Mr. R. A. McMaster of Brown Boveri Electric, Inc. to Mr. Carl Hurty of Bechtel 

Power Corporation with attachment of Section V, Attachment 4, May 28, 1982. 

29. GE Manual of Instrument Transformers, Operation Principles and Application Information, 

GET-97D, superseded GET-97C. 

30. NRC Memo to ASB Members from Mr. Olan D. Parr, Chief, Auxiliary System Branch, 

Division of Systems Integration on “Fire Protection Review Guidance,” November 30, 1984. 

31. Letter from Mr. R. W. Fosse of Bechtel Power Corporation to Mr. R. L. Steele of Trojan 

Nuclear Plant, BP-11866, Dated October 16, 1984. 

32. Edan Engineering Corp. Telephone Call Report, ELD-057-95, with Ray Thomas of Siemens 

(Allis-Chalmers), December 1, 1995. 
REFERENCES

9-3 

33. EPRI NP-7189, “Review of Polyimide Insulated Wire in Nuclear Power Plants,” 1991. 

34. NRC Information Notice 88-89, “Degradation of Kapton Electrical Insulation,” November 21, 

1988. 

35. IEEE STD 383, “IEEE Standard for Type Test of Class 1E Electric Cables, Field Slices, and 

Connections for Nuclear Power Generating Stations,” 1974. 

36. Military Specifications, MIL STD MIL-W-81381. 

37. Graham, S.P., “Duke Power Nuclear Generation Test Plan For Evaluation of Fire-Induced 

Spurious Actuations in Armored-Cable Control Circuits,” August 2005. ADAMS Accession 

No. ML052900252. 

38. 10 CFR 50.49, “Environmental qualification of electric equipment important to safety for 

nuclear power plants.” 

39. Brookhaven National Laboratory (BNL) Letter from Mr. E. A. MacDougall to Mr. Nicholas S. 

Fioravante of NRC, dated July 21, 1983. 

A-1

APPENDIX A

PANELIST AND FACILITATOR RESUMES 

Harold Barrett, NRC

TITLE/POSITION: Senior Fire Protection Engineer Years of Experience: 37 

SUMMARY

Mr. Barrett has provided a wide range of engineering and management services for the nuclear 

industry. His experience includes nuclear plant regulation, engineering, maintenance and 

operations, plant technical support, procedure development, site emergency plan participation 

and direction, shift supervision, training, start-up testing and design reviews. Mr. Barrett has 

extensive expertise in the day-to-day operation of various U.S. nuclear power plants. In 

addition, he has provided extensive engineering support in the areas of fire protection, safeshutdown analysis, valve engineering, motor operated valves (MOVs) and air operated valves 

(AOVs). 

Mr. Barrett is currently the lead technical reviewer for NFPA 805 License Amendment Requests 

in the U. S. Nuclear Regulatory Commission’s Office of Nuclear Reactor Regulation (NRR). 

EDUCATION/TRAINING

BS, Marine Nuclear Science, State University of New York Maritime College at Fort Schuyler, 

1975 

PROFESSIONAL AFFILIATIONS/CERTIFICATIONS

U. S. NRC Qualified Technical Reviewer 

Society of Fire Protection Engineers (SFPE) – Member Grade 

NEI Fire Protection Working Group NFPA 805 Task Force 

NEI Fire Protection Working Group 

NEI Fire Protection Rule Making Task Force 

Senior Reactor Operator (SRO), U.S. Nuclear Regulatory Commission (NRC) 

Second Assistant Engineer, Steam Vessels of Any Horsepower, U.S. Coast Guard 

Third Assistant Engineer, Motor Vessels of Any Horsepower, U.S. Coast Guard 

EXPERIENCE

Senior Fire Protection Engineer

U. S. Nuclear Regulatory Commission 

Office of Nuclear Reactor Regulation 

Division of Risk Assessment 

Washington, DC 20555-0001 

4/07 to present 
PANELIST AND FACILITATOR RESUMES 

A-2

Lead technical reviewer of NFPA 805 License Amendment Requests for the Fire Protection 

Branch (AFPB) in the Division of Risk Assessment. Responsible for reviewing fire protection, 

nuclear safety assessment (post-fire safe-shutdown including circuit analysis), fire modeling, 

non-power operations, radioactive release, monitoring program, programmatic, and 

performance-based, risk-informed, changes. 

Worked closely with the Office of Nuclear Regulatory Research (RES) on fire testing of Direct 

Current (DC) electrical circuits performed as part of the DESIREE-Fire testing program. 

Technical Project Manager and lead reviewer for the first NFPA 805 pilot plant, Shearon Harris. 

Provided technical oversight of the technical review and development of the first NFPA 805 

safety evaluation. 

Provided significant technical input to NRC’s NFPA 805 infrastructure (Regulatory Guide 1.205, 

Standard Review Plan Chapter 9.5.1.2, Safety Evaluation Template) and interfaced with 

industry through the NFPA 805 Frequently Asked Question (FAQ) process. 

Principal Engineer

Duke Power Company 

Oconee Nuclear Station 

Seneca, SC 

Dates: 4/99 to 4/07 

Project Manager and corporate lead engineer for the NFPA 805 Transition Project. Responsible 

for program cost, schedule and quality. This program transitioned the fire protection program 

for all three Duke nuclear sites from deterministic requirements to a Risk-Informed, 

Performance-Based Program under 10CFR50.48(c) and NFPA 805. Oconee was granted Pilot 

Plant status during the transition. This required significant coordination and interface with both 

internal and external groups, including NRC regulators. 

Lead engineer for the development and performance of fire testing of armored cable in 

simulated, representative circuits in both AC and DC configurations. 

Responsible for the Appendix R Reconstitution Project at Oconee. This project is reconstituting 

the post-fire safe-shutdown analysis, including component selection, cable selection and 

analysis, fire zone/area analysis and compliance assessments. 

Engineering Support Program (application, performance, problem resolution and maintenance) 

for Power Operated Valves (AOVs or MOVs). Responsibilities included program management, 

maintenance of design basis calculations, diagnostic testing and analysis, performance 

trending, troubleshooting and root cause analysis, problem resolution as well as equipment 

failure analysis (root cause analysis processes); component monitoring and trending; valve 

specification, selection, application; Minor Modification development and support; procedure 

development; generation and review of calculations. 

Senior Engineer

Duke Engineering & Services, Inc. 

Charlotte, NC 

Dates: 11/97-4/99 
PANELIST AND FACILITATOR RESUMES

A-3 

Lead Systems Engineer on an Appendix R reanalysis project to reduce the overall reliance on 

electrical raceway fire barrier wrap for the Salem Nuclear Generating Station. Responsible for 

development of System and Component Logic, development and population of the Safeshutdown Equipment List, circuit selection and analysis and resolution of safe-shutdown 

compliance issues and safe-shutdown procedures development. Responsible for update of 

licensee configuration documents and generation of the Appendix R Safe-shutdown Analysis 

Report. 

Senior Consultant

HGP, Inc. 

Greenville, SC 29615 

Dates: 10/94-10/97 

Provided engineering, technical and management consulting services to a variety of clients 

ranging from nuclear utilities to law firms. Performed a Probabilistic Risk Assessment (PRA) of 

a petrochemical production plant and performed due diligence reviews of nuclear utilities in 

support of merger and acquisitions. In support of expert testimony in a major litigation case, 

analyzed management effectiveness and schedule delays related to an extended outage at a 

large, late model dual unit pressurized water reactor (PWR) in the southwest. Analyzed heat 

loads to support several real-time temperature transient analyses of nuclear power plant 

heating, ventilating and air conditioning (HVAC) systems, including loss of ventilation during 

station blackout and loss of coolant accident (LOCA). 

Mechanical Engineer IV, Nine Mile Point Unit 1 

Niagara Mohawk Power Corporation

Nine Mile Point Nuclear Station 

Lycoming, NY 13093 

Dates: 10/92-10/94 

Managed the technical aspects of the Generic Letter 89-10 Motor Operated Valve (MOV) 

Program for Nine Mile Point Unit 1. Defined the MOV program scope, developed maximum 

expected operating conditions and MOV sizing calculations for all GL 89-10 MOVs. Performed 

cable voltage drop and DC MOV stroke time calculations. Served as Design System Engineer 

for numerous systems at the plant, including nuclear instrumentation and automatic 

depressurization system. Appendix R program design engineer responsible for maintenance of 

safe-shutdown analysis, transient analysis, inventory loss boundaries, and high and low 

pressure interface maintenance. Provided direct support to operations during fire and control 

room evacuation special operating procedure flow chart development. 

Program Coordinator, Operations Oversight Operations Support 

Nine Mile Point Unit 1 

Niagara Mohawk Power (same address as above) 

Dates: 04/92-10/92 

Provided operations and technical support to the operations branch. Served as a member of 

the Station Operations Review Committee (SORC). Served as procedure owner for all 

operations department procedures. 

 
PANELIST AND FACILITATOR RESUMES 

A-4

General Supervisor, Shift Operations, Nine Mile Point Unit 1 

Niagara Mohawk Power (Same address as above) 

Dates: 10/90-04/92 

Served as SRO providing day-to-day supervision of shift operations. Supervised a staff of 65 

licensed and unlicensed operators, including eight shift supervisors. Responsible for 

compliance to NRC license, as well as protection of public health and safety and maximum 

power generation at the lowest cost. Performed the duties of control room advisor and/or site 

emergency director as part of the Emergency Response Organization. Acted as procedure 

owner for operations department procedures. Served as a member of the Station Operations 

Review Committee (SORC). 

Associate Senior Engineer, Plant Productivity Group 05/90-10/90 

Nine Mile Point Units 1 & 2 

Niagara Mohawk Power (Same address as above) 

Dates: 05/90-10/90 

Served as task manager for resolving reactor feedwater pump testing problems. Managed 

troubleshooting, disassembly, repair, re-assembly and successful testing of reactor feedwater 

pumps at Nine Mile Point Unit 1. Discovered pump impellers were installed backwards on pump 

shafts. 

Consulting Engineer

Compis Services 

Liverpool, NY 13088 

Dates: 11/89-05/90 

Developed safety classification basis documents in accordance with 10CFR50 Appendix B for 

numerous electronic and electrical circuits including 125 VDC ground detector circuits, 

emergency diesel generator voltage regulator and emergency diesel generator governor control 

circuits. 

Senior Engineer/Training Instructor

General Physics Corporation 

Columbia, MD 21046 

Dates: 02/89-11/89 

Implemented systematic approach to training (SAT) -based programs. Developed training 

material on symptom-based emergency operating procedures for Savannah River Site. 

Level III Test Engineer

Newport News Shipbuilding 

Newport News, VA 23607 

Dates: 07/88-02/89 

Performed naval nuclear propulsion plant testing to support new construction. Directly 

supervised new system flushes, hydrostatic testing, and reactor plant system start-up testing. 

Developed, implemented and cleared electrical and mechanical tagouts to support nuclear plant 

testing and construction. 
PANELIST AND FACILITATOR RESUMES

A-5 

Assistant Operations Superintendent

Shift Operations, Nine Mile Point Unit 1 

Niagara Mohawk Power (Same address as above) 

Dates: 07/85-06/88 

Provided technical and management support of day-to-day operations of a commercial nuclear 

station. Directly responsible for symptom-based Emergency Operating Procedure (EOP) 

development and implementation. Represented NMPC on the boiling water reactor (BWR) 

Owner's Group Emergency Procedures Committee. Performed QR reviews of all Instrument 

and Control (I&C) and Maintenance (both Mechanical and Electrical) procedure revisions and 

temporary procedure changes. Reviewed all new design changes and plant modifications for 

Operations. 

Assistant Supervisor, Technical Support 

Nine Mile Point Unit 1 

Niagara Mohawk Power (Same) 

Dates: 10/83-07/85 

Supervised engineers performing plant engineering, operations experience assessment (OEA), 

modifications, pre-operational testing, LERs and inspection report responses. Reviewed 

operational occurrences for reportability and acted as a site operations review committee 

alternate member. Provided technical and operations input into the Limited Scope Probabilistic 

Safety Assessment (PSA) of Nine Mile Point Unit 1. Provided technical and operations input 

into a component level safety classification database or Q-List. 

Senior Technical Assistant, Technical Support Group 

Nine Mile Point Unit 1 

Niagara Mohawk Power (Same) 

Dates: 08/81-10/83 

Performed Operations Experience Assessment (OEA). Performed design review of numerous 

electrical and electronic control systems such as failure modes and effects analysis of feedwater 

control system and 125 VDC control power distribution system. Proposed and performed 

conceptual design, as well as supervised the installation and final pre-operational testing on 

several control system design improvement modifications. Obtained SRO License. Acted as a 

key member of the Appendix R Safe-shutdown Analysis team. Established safe-shutdown 

equipment list, inventory loss paths, and hi/low pressure interfaces. Performed electrical circuit 

analysis for spurious operation as well as developed confirmatory and redundant relay logic 

schemes for protection of safe-shutdown components. Performed conceptual design, 

intermediate design, field installation and final pre-operational testing of electrical design 

modifications implemented to meet 10CFR50 Appendix R. Supervised the installation of two 

Shutdown Supervisory Control Cabinets, two Shutdown Supervisory Distribution Cabinets, 

approximately 60 auxiliary relays, and several thousand feet of control cable. Performed circuit 

analysis of reactor recirculation pump motor generator set tachometer/voltage regulator circuit. 

Designed and developed temporary modifications to substitute a solid state power supply to 

replace the volts/hertz voltage regulator input from the tachometer to prevent premature pump 

trip and prevent loss of electric generation and subsequent risk of reactor scram. 

 
PANELIST AND FACILITATOR RESUMES 

A-6

Nuclear Engineer, GS-11, Code 2340, Test Engineering Group 

Norfolk Naval Shipyard 

Portsmouth, VA 

Dates: 09/80-07/81 

Performed reactor plant testing on naval nuclear propulsion plants. Performed work control, 

technical and operations management activities. Received and provided training on submarine 

PWR reactor plants. 

U.S. Coast Guard Licensed Marine Engineer

Department of the Navy 

Military Sealift Command, Atlantic 

Bayonne, NJ 

Dates: 12/76-05/77 and 08/78-08/80 

Served as a U.S. Coast Guard licensed marine engineer and a third, second and first assistant 

engineer. Operated, maintained and supervised an engineering department on a 16,000 SHP 

Steam Geared Turbine Powered Refrigerated Stores Ship. 

Associate Mechanical Engineer, Haddam Neck Plant 

Connecticut Yankee Atomic Power Company 

East Haddam, CT 

Dates: 06/77-08/78 

Performed plant engineering and supervised the installation and testing of modifications on a 

580 MW 4 Loop Westinghouse PWR. Coordinated and managed the installation of replacement 

pressurizer power operated relief valves (PORVs) including installation of new motor operated 

PORV blocking valves and the associated electrical design, installation and testing. Installed: 1. 

An instrument air system inside primary containment including the associated electrical design, 

installation and testing; 2. Added a new mixed bed demineralizer including the associated 

automated control logic testing; and 3. Installed main turbine moisture separator reheater 

scavenging steam vent chambers. Served as plant engineering group representative on 

backshifts during the plant outage. Represented the plant on a team to alleviate spent fuel rack 

bulging and assisted in developing a spent fuel rack poison cavity venting tool. 

Nuclear Engineer, GS-7, 9, Code 2370, Nuclear Refueling Engineering 

Mare Island Naval Shipyard 

Vallejo, CA 94590 

Dates: 09/75-12/76 

Revised procedures to support reactor refueling activities on Naval Nuclear Propulsion Plants. 

Performed reactor plant shield surveys. Received training on submarine reactor plant refueling 

procedures, equipment, support systems and design. 

 
PANELIST AND FACILITATOR RESUMES

A-7 

David Crane, Pyrolico 

TITLE/POSITION: Vice President 

EXPERIENCE

• Mr. Crane has over 25 years of industrial experience in the commercial nuclear, 

semiconductor, pharmaceutical and automotive industries. 

• Mr. Crane has held engineering and engineering management positions in fire 

protection, life-safety systems, environmental health and safety, instrumentation and 

controls, electrical and bulk gas system distribution systems. 

• Mr. Crane has held technical advisor and/or supervisor roles on three 10CFR50 

Appendix R program enhancements, including Reg. Guide 1.189, as well as one 

NFPA 805 project. 

• Mr. Crane has extensive experience representing industry to regulatory agencies: 

US NRC, US EPA, state and local authorities having jurisdiction. 

• Mr. Crane has led multinational engineering teams for the semiconductor industry in 

the areas of life-safety and industrial control systems. 

• Mr. Crane is skilled in performing OSHA PSM and EPA RMP analysis as well as 

establishing and managing RCRA / Hazardous Waste and SPCC programs. 

• Mr. Crane has designed, installed and maintained life-safety and industrial control 

systems with a combined I/O in excess of 20,000 points. 

EDUCATION

• Bachelor of Science degree in Electrical Engineering from Western Michigan 

University 

• Completed coursework in Environmental Management at the University of Maryland 

University Campus 

• Certification in Industrial Firefighting from Lambton College, Sarnia, Ontario, 

Canada 

• Microsoft Certified System Engineer certificate from Colorado Technical University 

PUBLISHED WORK

Mr. Crane has published numerous semiconductor white papers on plant industrial controls 

integration, and advanced process control.

PANELIST AND FACILITATOR RESUMES

A-9 

Robert Daley, NRC

Engineering Branch Chief – United States Nuclear Regulatory Commission 

PROFESSIONAL HIGHLIGHTS

• Manages electrical, I&C, and fire protection engineers 

• Specialist in the area of 10 CFR 50.59 evaluations 

• Skilled and proficient in the area of fire protection safe-shutdown analysis 

• Certified as an NRC Operator Licensing Examiner for BWR and PWR nuclear plants 

• Manages, plans, and directs present and future efforts in the growing areas of digital 

systems and cyber security 

• Design Electrical Engineer at Grand Gulf Nuclear Plant 

• Technical Specification Coordinator and member of the Technical Specification Task Force 

while at River Bend Station 

• Member of the BWROG Fire-induced Fire-induced Circuit Failures Task Force 

• BWR-6 Senior Reactor Operator Certification 

PROFESSIONAL EXPERIENCE

United States Nuclear Regulatory Commission 2000 - Present 

Engineering Branch Chief 

Supervises engineering inspectors in the implementation of the NRC’s Reactor Oversight 

Program to assure the safety of licensed activities and compliance with requirements. Provides 

administrative oversight of engineering inspectors. 

• Manages technical issues and inspection in the areas of electrical engineering, 

instrumentation and controls, digital systems, fire protection, cyber security, and 10 CFR 

50.59. 

• Manages and schedules all regional team Fire Protection inspections and Modification and 

10 CFR 50.59 inspections. 

• Member of the IMC 0612 (Power Reactor Inspection Reports) and IMC 0620 (Inspection 

Documents and Records) working groups. 

• Organized, led, and facilitated a two day agency-wide Modifications and 10 CFR 50.59 

workshop. 

• Member of the Office of Research PIRT Electrical Expert Panel for fire-induced cable failure 

modes. 

• Led an agency-wide self-assessment of inspection report quality. The assessment team 

consisted of staff from all four regions and NRC headquarters. 

Senior Reactor Engineer 

Led and participated in engineering team inspections at nuclear power plants including the 

Component Design Basis Inspections, Modification and 50.59 Inspections, Fire Protection 

Inspections, and In-service Inspections. 

• Certified as an Operator Licensing Examiner. Qualified to write, review, and administer 

NRC exams for the qualification of Senior Reactor Operators and Reactor Operators for 

BWR and PWR nuclear plants. 
PANELIST AND FACILITATOR RESUMES 

A-10

• Regional contact for engineering modification and 10 CFR 50.59 issues and inspections. 

• Provided significant technical and inspection support during the Davis-Besse extended 

shutdown for reactor vessel head corrosion and for the Point Beach 95003 supplemental 

inspection. 

- Led an electrical issues inspection at Davis-Besse during their extended shutdown. 

- Led the Point Beach CDBI that that was used as a basis for their exit from the 95003 

process. 

• Regional Power Uprate point of contact. 

• Expertise and specialty areas include: 

- Fire Protection Safe-shutdown Circuitry Analysis 

- 10 CFR 50.59 

- Technical Specifications 

- Electrical and I&C Design 

- Station Blackout 

- Equipment Qualification (EQ) 

- 10 CFR 50, Appendix J 

Entergy Operations, Inc. 1991-2000 

Senior Engineer – Grand Gulf Nuclear Power Station 

Evaluated and resolved electrical system and component design and performance problems. 

Developed electrical engineering specifications/standards, design drawings, and design 

changes. Proficient in protective relaying and fuse/breaker coordination. Design changes have 

included complex control circuitry modifications. 

• Performed electrical system design including fuse/breaker replacement, electrical 

coordination calculations, transformer replacement, and re-design of the airlock door control 

circuitry. 

• Fire Protection Safe-shutdown Engineer. 

• Technical lead for the license basis reconstitution project for Fire Protection, Electrical 

Engineering, and I&C. 

• Member of the fire protection (Appendix R) Safe-shutdown Analysis Owner’s Group 

(BWROG) committee. 

• Entergy’s representative on the BWROG circuit failures task force. 

• Operations Test Coordinator for surveillances and equipment testing during plant outage 

activities. 

Senior Engineer – River Bend Station 

Performed a variety of assignments in the areas of electrical engineering, nuclear licensing, 

nuclear safety assessment, and operations. 

• Served as Technical Specification Coordinator for four years. Coordinated plant activities 

and resolved issues regarding Technical Specifications and the Technical Requirements 

Manual. 

• River Bend representative on the Technical Specifications Task Force (TSTF). 

• Senior Reactor Operator certified. 

• Root Cause Team Leader. Led root cause evaluations for significant plant events. Trained 

and proficient in: 

- Kepner-Tregoe 

- TapRoot 
PANELIST AND FACILITATOR RESUMES

A-11 

- Management Oversight and Risk Tree (MORT) 

• Developed and implemented License Amendment Requests (LAR) and Licensee Event 

Reports (LER). Developed and submitted the first 10 CFR 50, Appendix J, Option B, 

License Amendment in the nuclear industry. 

• Directed and assisted in assessments and analyses of plant processes and adverse 

trends/issues. 

RCA (Thomson Consumer Electronics) 1990 - 1991 

Shift Supervisor 

Supervised two production lines and 43 personnel in the manufacturing of high optical quality 

glass for television screens. Coordinated the technical efforts involved in keeping a high-speed, 

fully automated production line in constant operation. Responsibilities included the 

maintenance and repair of robotics and complex machinery as well as the adjustment of 

equipment to maintain maximum productivity. 

United States Navy Nuclear Officer 1984 - 1989 

Served as a naval officer assigned to the USS Long Beach. 

• Supervised 25 personnel in the daily maintenance of all shipboard electrical distribution 

equipment, electrical machinery and electronic hardware. 

• Supervised and coordinated the operational staff in 2 nuclear power plants as a fully 

qualified Nuclear Reactor Watch Officer and Engineering Duty Officer. 

EDUCATION AND CERTIFICATIONS

US NRC

• Operator Licensing Examiner Certification for BWR and PWR nuclear plant designs 

• GE BWR Technology Series 

• Westinghouse PWR Technology Series 

• Reactor Inspector qualification 

Entergy Operations, Inc. 

• Senior Reactor Operator Certification – River Bend Station 

• Successfully passed the Engineer in Training (EIT) exam 

US Navy 

• Engineering Duty Officer and Engineering Officer of the Watch (USS Long Beach) 

• Surface Warfare Officer Qualification 

• Naval Nuclear Power School and Naval Nuclear Power Prototype School. 

College Level Coursework 

Northwestern University – Bachelor of Science in Electrical Engineering (1984) 

Ohio State University – Finished 1/3 of Master’s Degree in Electrical Engineering (1990) 

Other Pertinent Training 

Team and Meeting Facilitator 

ANSI/ISA-S67.04-2006: Set points for Nuclear Safety-Related Instrumentation 

Protection of Industrial and Commercial Electric Power Distribution Systems – Univ. of 

Wisconsin 

Understanding Power Cable Characteristics - Univ. of Wisconsin 

Ultrasonic Testing, Level I and II 
PANELIST AND FACILITATOR RESUMES 

A-12

ASME Section XI In-Service Inspection 

Fire Protection SDP 

Software Verification and Validation 

ETAP Power System Engineering Workshop 

GE EHC and Turbine Trip and Monitoring System 

RCIC System and Control Circuitry 

GE Neutron Monitoring Systems 
PANELIST AND FACILITATOR RESUMES

A-13 

Daniel Funk, Kleinsorg Group Risk Services

SUMMARY

Mr. Funk is the Manager of Risk Analysis for Kleinsorg Group Risk Services (KGRS). In this 

capacity he directs technical and business operations for the group. The KGRS Risk Analysis 

Group provides consulting services to the nuclear power industry, specializing in all aspects of 

analysis relating plant response to fire and safe shutdown capability. Mr. Funk maintains an 

active technical role in his specific area of expertise – electrical power and control. He has 30 

years of engineering, testing, and management experience, and has held positions as 

engineering manager, principal engineer, engineering supervisor, and project manager. 

Mr. Funk is highly proficient at completing complex, multi-discipline projects on time, within 

budget, and to high quality standards. He is an accomplished project manager and has 

established expertise in the design, analysis, evaluation, testing, maintenance, modification, and 

operation of electrical power systems, instrumentation & control systems, and complex industrial 

equipment. Mr. Funk has extensive experience with nuclear power plants, Department of 

Defense facilities, electrical power distribution systems, industrial power and control systems, 

electrical and fire safety, and codes and standards. 

EDUCATION/CERTIFICATIONS

Registered Professional Engineer: 

 Oregon No. 13734 Electrical and Control Systems 

 Washington No. 30516 Electrical 

 California No. E17744 Electrical 

Bachelor of Science Degree, Electrical & Computer Engineering, Oregon State University, 1981 

Naval Nuclear Power School 

PROFESSIONAL AFFILIATIONS

Institute of Electrical and Electronic Engineers (IEEE) 

National Fire Protection Association (NFPA) 

IEEE Standards Coordinating Committee 29 (1995 – 2003) 

EXPERIENCE

Senior Technical Consultant November 2011 – Present 

Kleinsorg Group Risk Services 

A Hughes Associates Company 

Mr. Funk joined KGRS in November 2011 as a Senior Technical Consultant and Manager of the 

Risk Analysis Group. He oversees the group’s activities and maintains an active technical role 

in projects and nuclear industry research activities. Mr. Funk continues his efforts to advance 

and promote state-of-the-art methods, techniques, and tools for addressing fire risk at nuclear 

plants. Mr. Funk’s primary areas of expertise and recent accomplishments are summarized 

below: 
PANELIST AND FACILITATOR RESUMES 

A-14

Fire Protection – Extensive experience with fire protection requirements and issues for 

electrical systems and equipment at nuclear power plants and hazardous industrial facilities: 

 Specific expertise in the evaluation and analysis of fire-induced circuit failures, spurious 

operations, and associated circuits. 

 Fully versed in all aspects of fire safe shutdown analysis for Appendix R and NFPA 805. 

Serving as project manager and/or lead electrical for numerous Appendix R, NFPA 805, 

Fire PRA, and Multiple Spurious Operation projects. 

 Industry representative for joint NRC/EPRI expert panel for assessment of fire-induced 

circuit failures (Electrical PIRT Panel). Active participant in industry and NRC fireinduced circuit failure tests, including EPRI/NEI, CAROL-FIRE, and DESIREE-FIRE. 

 Providing direction and technical consulting to utilities for major projects involving NFPA 

805 transition, multiple spurious operation analysis, and fire-induced circuit failure 

issues. 

 Co-author of NUREG 6850, with primary responsibility for development of advanced 

analytical methods for the analysis of fire-induced circuit failures. 

 Principal author for report of EPRI/NEI fire-induced cable failure test program (EPRI 

1003326). 

 Member of industry-wide Expert Panel to assess spurious operation likelihood (EPRI 

1006961). 

 Expertise in the use of ARCPlus® and CAFTA software as applied to safe shutdown 

analysis, nuclear safety capability assessment, and multiple spurious operations. 

Developer of the Fire Data Manager (FDM®) module of ARCPlus. 

 Member of project team to develop optimization techniques for fire protection equipment 

maintenance programs at nuclear plants (EPRI 1006756). The performance-based 

techniques developed by the project are being introduced into NFPA codes and 

standards. 

 Conduct fire risk assessments for electrical process equipment as part of U.S. and 

European Union equipment safety certifications. 

Electrical Power Systems – Extensive engineering design and analysis expertise with 

electrical power systems for nuclear power plants, DoD facilities, DoE facilities, and hazardous 

industrial facilities: 

 Conducted numerous full-scope electrical engineering studies, including short circuit, 

power flow, electrical protection and coordination, arc flash, motor starting, and power 

quality. 

 Familiar with design requirements, equipment specifications, codes/standards, and 

construction support for electrical power distribution systems, including medium voltage, 

low-voltage, overhead, and underground distribution. 

 Extensive experience with and knowledge of electrical analysis software, including 

EasyPower®, Etap®, SKM PowerTools, and ArcView/ArcMap® (Geobase software) 

 Directed managed comprehensive master planning studies of electrical distribution 

systems at DoD facilities. Projects typically involve: 100% field walkdown of equipment 

regeneration of one-line and layout drawings  Geobase satellite coordinate 
PANELIST AND FACILITATOR RESUMES

A-15 

determination  characterization of all equipment and development of Geobasecompliant equipment databases  development of electrical software models  full-scope 

electrical analysis  reliability and vulnerability assessment  10-year system plan. 

 Managed all aspects electrical design projects requiring professional engineer 

certification. Prepared designs for projects with construction value up to $50M. 

 Developed operation, maintenance, and training manuals for electrical distribution 

systems. 

 Provide electrical analysis, electrical design, and electrical safety training to engineers 

and electrical linemen. 

 Experienced in the design, analysis, maintenance, and testing of batteries and critical 

DC power systems. Received national recognition for accomplishments in advancing 

techniques for battery performance testing. 

Codes and Standards – Broad knowledge of electrical and fire safety codes and standards, 

including IEEE, ANSI, NFPA, UL, NEMA, NETA, SEMI, IEC, UFC, MIL, and European 

Directives. 

PREVIOUS EXPERIENCE

Principal Engineer 1990 – November 2012 

Edan Engineering Corporation 

Prior to joining KGRS, Mr. Funk was a founder and co-owner of Edan Engineering Corporation. 

As a principal of the company, he directed Edan’s technical and business operations for over 20 

years. Mr. Funk helped build Edan into a solid engineering and test firm with nationally 

recognized expertise in several fields. Edan Engineering recently joined Hughes Associates 

and KGRS, and now operates as a division of Hughes providing specialized electrical 

engineering services to critical government facilities. 

Project Manager 1989 – 1990

Precision Interconnect 

Mr. Funk joined Precision Interconnect as a project manager in charge of product development 

for customized electrical connection systems used in military and aerospace guidance and 

navigation systems. He led a team of engineers and technicians through the development and 

qualification cycle for several unique products. Mr. Funk was instrumental in obtaining 

government approval to allow Precision Interconnect to supply military components under a 

certified quality assurance program. Mr. Funk gained extensive knowledge of military 

specifications and standards, and developed the qualification test plan and procedures for 

component certification. 

Electrical Engineering Manager 1986 – 1989 

Portland General Electric Company 

Mr. Funk joined Portland General Electric Company as an Engineer II working for the Trojan 

Nuclear Plant. Within a 2-year period he was promoted to senior engineer and then to 

supervising engineer. As a supervising engineer, Mr. Funk managed a group of 10 to 14 

electrical engineers. He was accountable for budget, schedule, and technical adequacy of 
PANELIST AND FACILITATOR RESUMES 

A-16

engineering design and analysis activities under his control. Mr. Funk ultimately advanced to 

become the Electrical Engineering Manager, where he managed over 80 engineers, designers, 

and drafters. He managed an annual budget in excess of $20M and was responsible for 

electrical, instrumentation & control, fire protection, and environmental qualification engineering 

activities. 

Navy Submarine Officer 1981 – 1986

US Navy 

Mr. Funk started his career as a naval submarine officer. He rapidly qualified as Officer of the 

Deck and Engineering Officer of the Watch. His assigned duties included Assistant Weapons 

Officer, Damage Control Assistant, Reactor Controls Assistant, and Quality Assurance Officer. 

He received numerous commendations while serving in the Navy and was consistently rated as 

the top junior officer on board. 

PUBLICATIONS

 Air Force Manual 32-1181, Design Standards for Facilities Interior Electrical Systems

 Advanced Circuit Analysis Methods Development for Fire-Risk Analyses, presented at 

2005 ANS Conference 

 NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, September 2005 

 EPRI Report 1003326, Characterization of Fire-Induced Circuit Faults: Results of Cable 

Fire Testing, December 2002 

 EPRI Report 1006756, Fire Protection Equipment Surveillance Optimization and 

Maintenance Guide, July 2003 

 EPRI Report 1969001, Spurious Actuation of Electrical Circuits Due to Cable Failures: 

Results of an Expert Elicitation, May 2002 

 EPRI Report 1006522, Stationary Battery Monitoring by Internal Ohmic Measurements

 EPRI Report 106154, Instrument Monitoring and Calibration Product Guide, October 

2000 

 EPRI Report 106752-R2, Instrument Performance Analysis Software System, July 1999 

 Air Force Pamphlet 32-1186, Valve Regulated Lead Acid Batteries for Stationary 

Applications, January 1999 

 EPRI Report 100249-R1, Emergency Battery Lighting Unit Maintenance and Application 

Guide, June 1997 

 
PANELIST AND FACILITATOR RESUMES

A-17 

Thomas Gorman, PPL 

EDUCATION:

Rensselaer Polytechnic Institute 

Bachelor of Science in Civil Engineering 

Syracuse University 

Masters in Business Administration 

PPL Susquehanna, LLC 

Plant Operations Certification Program 

PROFESSIONAL AFFILIATIONS:

Registered Professional Engineer – Pennsylvania 

Society of Fire Protection Engineers – Member Grade 

BWROG – Chairman of the Appendix R Committee & Fire Protection Sub-Committee of the 

IRIR Committee 

NEI Circuit Failures - Issue Task Force Member 

PROFESSIONAL EXPERIENCE:

Chicago Bridge & Iron Company – 1974 to 1976 – Engineer 

Niagara Mohawk Power Corporation – 1976 to 1982 – Civil Group Supervising Engineer 

PPL Susquehanna, LLC – 1982 to Present – Sr. Staff Engineer 

Mr. Gorman has 38 years of design engineering experience with 35 of the years in the Electric 

Power Industry and 34 in the Nuclear Power Industry. He has specialized in Appendix R postfire safe-shutdown analysis for 28 years. He has been a contributing author to the development 

of the following industry documents: 

• GE-NE-T43-00002-00-03 R01, BWROG Position on the Use of SRVs and Low Pressure 

Systems as Redundant Safe-shutdown Paths, dated August 1999. 

• GE-NE-T43-00002-00-02 R0, Generic Guidance for BWR Post-Fire Safe-shutdown 

Analysis, dated November of 1999. 

• NEI 00-01 Revision 2, Guidance for Post-Fire Safe-shutdown Circuit Analysis, dated 

June of 2009. 

• NEDO 33638, BWROG Assessment of Generic Multiple Spurious Operations (MSOs) in 

Post-Fire Safe-shutdown Circuit Analysis, dated June of 2011. 

PANELIST AND FACILITATOR RESUMES

A-19 

James Higgins, BNL 

TITLE: Group Leader 

FIELD OF EXPERTISE: Nuclear Facility Operations, Fire/Electrical, Human Factors, PRA 

EDUCATION:

1969 - BS, Naval Engineering, Mathematics, U.S. Naval Academy 

1970 - MS, Mathematics, Naval Postgraduate School 

1971 - U.S. Naval Nuclear Propulsion Training 

EXPERIENCE:

1983-Present 

Brookhaven National Laboratory - Provided various types of onsite reviews, analysis and 

research, and technical assistance to the NRC and DOE on various programs including: 

advanced/new reactor reviews, updating of NRC standard review plan, fire protection/safeshutdown, review of soviet reactors, inspection of specific technical issues & allegations at NPPs, 

aging of components and systems, PRA-based inspection prioritization, PRA sensitivity analyses 

on the effect of variation in human performance, value-impact analyses, influence of organizational 

factors, safety policy, upgrades to annunciators and local control stations, and control room human 

factors reviews. Performed safe-shutdown inspection onsite. Group leader responsible for review 

of many triennial fire protection inspections including electrical separation, associated circuits, and 

safe-shutdown. Participated in aging study of motors, nuclear grade battery testing, and diesel 

generator reliability. Performed inspections at vendor sites for all US nuclear grade EDG vendors. 

Knowledgeable in new reactor designs, AP1000, ABWR, EPR and ESBWR. Program manager at 

BNL for the review of university reactor license renewal for the NRC, including review of 8 reactor 

submittals. Performed onsite reviews of research reactors at BNL, ORNL/HFIR, and NIST. 

Developed, administered, and taught training courses and programs for NRC and DOE, including 

work for NRC Regional Offices, HQ, TTC and for DOE. Participated in DOE ORRs for HFIR at 

ORNL and two at Savannah River (for DWPF and CIF). Assisted in the development/teaching of 

DOE Conduct of Ops course, engineering fundamentals course, performance based inspection 

course, and fire protection courses for Russian personnel and NRC inspectors. Participated with 

the International Atomic Energy Agency (IAEA) in missions to RBMK reactor sites in Russia and 

Lithuania. Performed root cause analysis of various failures at these sites and provided 

recommendations for improvements in their operations. Served as Principle Investigator, Group 

Leader and Assoc. Division Head. 

1976-83 

U.S. Nuclear Regulatory Commission - Region-based reactor inspector at operating and 

preoperational BWR and PWR commercial nuclear power plants. Inspected approximately 20 to 

25 different reactor plants. Served as lead inspector for containment testing, pipe supports and 

snubbers, refueling, and in-service testing of pumps and valves. Also inspected plants to review 

responses to major incidents and accidents. Reviewed safe-shutdown facility and procedures. 

Senior Resident Inspector at Shoreham Nuclear Power Station (BWR). Inspected the construction 

and preoperational test phases of the plant and initial reactor fuel delivery. Participated as an 

expert witness during licensing hearings. Reviewed numerous allegations regarding improper 

practices. Section Chief, Region I, responsible for all resident inspectors and the inspection 

program at four operating reactors (PWRs). Author of over 100 NRC inspection reports. 
PANELIST AND FACILITATOR RESUMES 

A-20

1971-76 

U.S. Navy - Division Officer in the Engineering Department of the USS Nathan Hale (SSBN - 623) 

a nuclear powered polaris submarine. Served as the Sonar Officer, Electrical Officer, Reactor 

Controls Officer, and Auxiliary Division Officer. Qualified as Submarine Officer, Engineering 

Officer of the Watch, and as Engineer Officer. Trained in various aspects of handling, repairing, 

and use of nuclear weapons. Served as Division Director and Instructor at the U.S. Naval Nuclear 

Power School. Responsible for course curriculum, exams, and instruction techniques, while 

teaching reactor plant systems and electrical theory courses. Wrote a new course text for the 

Electrical Theory Course. Served as Department Head of the Weapons Department of the USS 

Billfish (SSN - 676), a fast attack nuclear-powered submarine. Responsible for the sonar 

systems, fire control systems, torpedo and missile systems (including a nuclear weapons 

capability), and deck systems. 

SELECTED PUBLICATIONS LIST

• Review of the IEEE Standard for Computerized Operating Procedure Systems, BNL Technical 

Report No. BNL-91087-2010, February 26, 2010, J. O’Hara and J. Higgins 

• SER on Review of the Initial Test Program for the US-APWR, DCD Chapter 14.2. October, 

2008 and August 2009, J. Higgins, W. Gunther and R. Belles 

• Guidance for the Review of Changes to Human Actions, NUREG-1764, Rev. 1, J. Higgins, J. 

O'Hara, et al. September 2007 

• SER on Review of Containment Leak Rate Testing for the US-APWR, Chapter 6.2.6, June, 

08, J. Higgins and R. Deem 

• Evaluation of the WCAP-16555, AP1000 Identification of Critical Human Actions, and Risk 

Important Tasks (TR59), BNL Technical Evaluation Report No. Q4060, J. Higgins & J. 

O’Hara, 2007 

• Evaluation of the ESBWR Operating Experience Review (OER) Plan, BNL TER No. 11094-

2-3/06, James Higgins and John O’Hara, 2007 

• Technical Specification for the Control Room Upgrade for the NBS Reactor at the NIST 

Center for Neutron Research (NCNR), March 4, 2004, D. Danseglio, J. Higgins, and J. O’Hara 

• Adaptation of the NRC Risk-Informed Inspection Notebooks for the Evaluation of Electrical 

Circuit Inspection Findings during Fire Protection Inspections, March 18, 2003, J. Higgins 

• Nine Summary Reports on Risk-Informed Benchmarking Trips for nine (9) nuclear power 

plants’ Significance Determination Process (SDP) 2003 

• Technical Evaluation Report, Human Factors Engineering Review of the Oskarshamn Unit 1 

Modernization Program, prepared for Statens Kärnkraftinspektion (SKI), the Swedish Nuclear 

Power Inspectorate, John O’Hara and James Higgins, October 9, 2002 

• Human Factors Engineering Program Review Model, NUREG-0711, O’Hara, Higgins, et al., 

2002 

• Maintainability of Digital Systems, Technical Basis and Human Factors Review Guidance, 

NUREG/CR-6636, W. Stubler, and J. Higgins, March, 2000 

• Safety Significance of Inadvertent Operation of Motor Operated Valves in Safety-Related 

Piping Systems in Pressurized Water Reactors, BNL report E-2071-T1-12-93, Rev. 1, March, 

1995, C. Ruger, J. Carbonaro, J. Higgins, and W. He 

• Risk Sensitivity to Human Error, NUREG/CR-5319, P. Samanta, J.C. Higgins, et al., April 

1989 

• Reliability Program to Improve and Maintain Emergency Diesel Generator Performance, BNL 

Technical Report A-3817-4-87, S. Karimian, J.C. Higgins, & J.H. Taylor, April 1987 

• PRA Applications, NUREG/CR-4372, J.C. Higgins, January 1986 

• A Review of Emergency Diesel Generator Performance at Nuclear Power Plants, 

NUREG/CR-4440, J.C. Higgins and M. Subudhi, November 1985 
PANELIST AND FACILITATOR RESUMES

A-21 

• Authored over 100 NRC inspection reports for nuclear safety reviews at commercial nuclear 

power plants. Plants included: Beaver Valley 1, Calvert Cliffs 1 & 2, Fitzpatrick, Ginna, 

Haddam Neck, Indian Pt. 2 & 3, Limerick 1 & 2, Maine Yankee, Millstone 1 & 2, Nine Mile Pt. 

1, Oyster Creek, Peach Bottom 2 & 3, Pilgrim, Salem 1 & 2, Shoreham, Susquehanna 1, 

Three Mile Island 1 & 2, Vermont Yankee, Yankee Atomic. 

• Course Text for US Naval Nuclear Power School Electrical Theory for Mechanical Operators, 

1976 

PANELIST AND FACILITATOR RESUMES

A-23 

Steven Nowlen, SNL

CURRENT EMPLOYMENT:

Employer: Sandia National Laboratories 

 Risk and Reliability Analysis Department 6231 

Title/Position: Distinguished Member of the Technical Staff 

Employed Since: October 17, 1983 

Business Address: Mail Stop 0748 

 Albuquerque, New Mexico, USA 87185-0748 

Phone: (505)845-9850 

 Facsimile: (505)844-2829 

 e-mail: spnowle@sandia.gov

EDUCATION AND HONORS:

Appointed to the rank of Distinguished Member of the Technical Staff at Sandia National 

Laboratories, October 2001, an honor reserved for no more than 10% of the SNL 

engineering/science staff. 

Master of Science, Mechanical Engineering, Michigan State University, East Lansing Michigan, 

March 1984. 

DuPont Research Fellow, Department of Mechanical Engineering, Michigan State University, 

1981-1983. 

Bachelor of Science with High Honor, Mechanical Engineering, Michigan State University, East 

Lansing Michigan, December 1980, Graduated Phi Beta Kappa. 

PROFESSIONAL EXPERIENCE:

Since joining Sandia in 1983, I have been active in both experimental and analytical research in 

the fields of nuclear power plant safety with a focus on fire safety and quantitative fire risk 

analysis. I have been Sandia’s technical and programmatic lead for the nuclear power fire 

research programs since 1987. My responsibilities include direct technical contributions, 

technical team leadership, sponsor interactions, program planning and program management. 

The most important application of my research has been in the development and application of 

probabilistic risk assessment (PRA) methods for fires in nuclear power plants; that is, 

quantitative assessments of the impact of fires on nuclear power plant safety and operations. I 

also have experience in harsh environment equipment qualification testing and accelerated 

thermal and radiation aging of materials. 

My experimental work has included the planning, execution, evaluation, and reporting of fire 

safety experiments, as well as the interpretation, evaluation, and application of experimental 

results generated by other researchers. Specifically, I have experience in the testing of fire 

growth behavior, large-scale room fires, enclosure ventilation and smoke purging, cable and 
PANELIST AND FACILITATOR RESUMES 

A-24

electrical equipment fire-induced damage, smoke particulate characterization, fire barriers, 

smoke damage effects on digital equipment, and cable ampacity and ampacity derating. 

As a secondary aspect of my experimental experience, I have also participated in Equipment 

Qualification tests assessing the performance of electrical equipment in the harsh steam and 

radiation environments associated with nuclear power plant severe accidents. This work has 

included both accelerated thermal and radiation aging of electrical cables and the evaluation of 

equipment performance during harsh environmental exposures such as loss of coolant 

accidents. 

Related analytical efforts in the area of fire safety have included the evaluation and validation of 

computer fire simulation models, the review and analysis of actual fire events in nuclear power 

plants, fire risk assessment analytical support work, the development and evaluation of fire risk 

assessment methods, and the development and evaluation of analytical methods for cable 

ampacity and fire barrier ampacity derating assessments. I have also participated as an expert 

consultant in various inspection activities for U.S. Nuclear Regulatory Commission (NRC). 

I have performed training for the NRC staff in the application of the NRC Significance 

Determination Process (SDP) for fire protection inspection findings. I am currently participating 

in an effort to develop and deploy inspector training for application to those NRC licensees 

transitioning to the new risk-informed, performance-based fire protection requirements. I also 

act as technical coordinator and classroom instructor for the annual Fire PRA training course 

offered as a part the NRC Office of Nuclear Reactor Research (RES) and Electric Power 

Research Institute (EPRI) collaboration on fire research. This training course has been 

conducted annually since 2005 and routinely attracts well over 100 participants per year. 

I was a member of the U.S. NRC Senior Review Board for the review of Individual Plant 

Examination for External Events (IPEEE). I am currently a member of the ASME/ANS Joint 

Committee on Nuclear Risk Management Subcommittee on Standard Maintenance. I also cochair the associated working group on fire risk. 

My publication list is available on request and includes 10 journal articles, approximately 30 

formal SNL technical reports, five invited conference papers and over 20 other general 

conference papers. I also co-authored a section of the SFPE Handbook of Fire Protection 

Engineering entitled “Risk Assessment for Nuclear Power Plants.” 

NOTABLE ROLES AND ACCOMPLISHMENTS:

SNL technical area lead and program manager for nuclear power plant related fire research 

(1987-present) 

Voting member of the American Society of Mechanical Engineers (ASME) American Nuclear 

Society (ANS) Joint Committee for Nuclear Risk Management (JCNRM) Subcommittee on 

Standards Maintenance 

Co-Chair of the ASME/JCNRM Standard for Level 1 / Large Early Release Frequency 

Probabilistic Risk Assessment for Nuclear Power Plant Applications Fire Working Group (RASa-2009) 

Leading member of the core writing team for the American Nuclear Society (ANS) Standard on 

Fire PRA methodology (ANSI/ANS-58.23-2007) 
PANELIST AND FACILITATOR RESUMES

A-25 

Lead author and NRC technical team lead for the consensus Fire PRA methodology 

NUREG/CR-6850 which as developed as a collaboration between the NRC and the Electric 

Power Research Institute (EPRI)) 

Technical Coordinator for development of the U.S. NRC Significance Determination Process 

(SDP) for risk-informed fire inspections (2003-2004) 

Technical coordinator and instructor for the annual NRC/EPRI Fire PRA methodology training 

sessions (2004-present) 

Member of the Nuclear Regulatory Commission (NRC’s) Senior Review Board for the review 

and evaluation of licensee submittals under the Individual Plant Evaluation of External Events 

Program (1995-2001) 

Technical advisor to the U.S. NRC staff during development of the National Fire Protection 

Association (NFPA) Performance-Standard for Fire Protection for Light Water Nuclear Reactor 

Electric Generating Plants (NFPA 805) (1995-2001). 

Qualified as an expert witness in nuclear power plant fire safety in U.S. Federal Criminal District 

Court (1995). 

PANELIST AND FACILITATOR RESUMES

A-27 

Andy Ratchford, RDS

SUMMARY

Mr. Ratchford is the President of Ratchford Diversified Services, LLC, an engineering services 

consulting firm providing fire protection and risk management consulting services. Mr. Ratchford 

has more than 27 years of experience in the nuclear field, including 22 years in nuclear power 

plant fire protection. He has provided fire protection and post-fire safe-shutdown technical 

support to more than one half of the nuclear power plants in the United States. He is actively 

involved in industry activities, such as development of risk-informed guidance for fire protection 

(NFPA 805), the implementation guidance for NFPA 805 (development of NEI 04-02), NFPA 805 

transition pilot plant activities, and resolution of major nuclear plant fire protection issues such as 

multiple spurious operations and operator manual actions. 

EDUCATION/TRAINING

B.S., Civil Engineering, Clemson University, 1984 

U.S. Navy Nuclear Power Program 

Cooperative Education Program, Savannah River Site, Aiken, SC, 1981 - 1983 

PROFESSIONAL AFFILIATIONS/CERTIFICATIONS

Registered Professional Mechanical Engineer, State of California 

Member, American Nuclear Society 

Member, Society of Fire Protection Engineers 

Member, National Fire Protection Association (NFPA) 

Member, NFPA Technical Committee on Fire Protection for Nuclear Facilities (alternate) 

Member, NEI NFPA 805 Task Force 

Member, NEI Circuit Failures Task Force 

EXPERIENCE

Principal 09/99-Present 

Ratchford Diversified Services/KGRS Strategic Alliance

Principal of Ratchford Diversified Services, an engineering consulting firm that provides 

technical services to the nuclear industry. He has provided consulting services to a number of 

clients as a subcontractor to a number of engineering consulting firms. He is a leading technical 

contributor to the Strategic Alliance for NFPA 805 Transition, led by Kleinsorg Group Risk 

Services, LLC (KGRS), an alliance of companies involved in the technical direction and support 

of licensees transition their fire protection programs to 10 CFR 50.48(c). 

He is an active participant in the nuclear fire protection community, including participation in 

numerous NRC and NEI workshops and meetings as a member of the KGRS Strategic Alliance. 

He is a member of the NFPA Technical Committee on Fire Protection for Nuclear Facilities and 
PANELIST AND FACILITATOR RESUMES 

A-28

has been actively involved in the development of NFPA 805 and its implementing guidance for 

transition to a risk-informed, performance-based fire protection program (NEI 04-02). He has 

served as an NEI representative in the NFPA 805 pilot plant process and is actively involved in 

the NFPA 805 Task Force meetings, Pilot Observation Meetings, and other pilot activities. He 

has been involved in all aspects of NFPA 805 transition, including lead roles in the resolution of 

industry issues related to multiple spurious operations and operator manual actions. He has 

developed a number of NFPA 805 Frequently Asked Questions (FAQs) in support of pilot plant 

activities. 

He has worked closely with the Fire PRA community in the integration of Fire PRA into the 

NFPA 805 application and resolution of industry issues. This includes technical support and 

reviews of Fire PRA Component and Cable Selection, modeling of spurious operations, and use 

of the Fire PRA in support of change evaluations. He has also participated in Fire PRA Peer 

Reviews, with an emphasis on the Fire PRA Component Selection, Fire PRA Model 

Development, Cable Selection, and Circuit Analysis tasks. He is a participant on the 

Phenomena Identification and Ranking Table (PIRT) panel for fire-induced circuit failures as 

applied to Nuclear Power Plant applications, an activity sponsored by the NRC Fire Research 

Branch. 

He serves in technical oversight and consultant roles on a number of NFPA 805 transition 

projects, including both pilot plants (Harris Nuclear Plant and Oconee Nuclear Station) and fleet 

transition projects for Florida Power and Light and Southern Nuclear Corporation. He was 

instrumental in the development of the pilot plant NFPA 805 License Amendment Requests, 

having worked extensively with Progress Energy, Duke Energy, and NEI on the format, content, 

and level of detail in the submittals. 

He has also been very active in industry efforts in the resolution of fire-induced circuit failures 

using the processes in NEI 00-01. He was an active participant in the NEI Circuit Failures Task 

Force group that developed NEI 00-01, Revision 2. He also a led or participated in 15 Expert 

Panels addressing fire-induced multiple spurious operations and their impact on plant safety. 

In addition to primary roles in the NFPA 805 transition, he also has supported licensees during 

NRC Triennial Fire Protection Inspections and performed and led self assessments addressing 

fire protection, post-fire safe-shutdown, and fire-induced circuit failure issues. 

Fire Protection Manager 08/96-09/99 

Duke Engineering & Services 

Managed the Western Region Fire Protection and Hazards Analysis group. Responsible for 

project quality and business performance, including nuclear and commercial and industrial 

business areas. This included managing fire protection and Appendix R program validation 

projects, self assessments, and resolution of complex technical issues for numerous clients. 

Supervisor 06/94-08/96

VECTRA Technologies 

Supported American Electric Power with an Appendix R Revalidation Project for Cook Nuclear 

Plant (CNP). Was the primary author and project manager for an Appendix R Topical Design 

Basis Document and a Fire Protection Topical Design Basis Document for CNP. Project 

Engineer for a comprehensive Thermo-Lag Fire Barrier Resolution Project for Entergy at River 

Bend Station. 
PANELIST AND FACILITATOR RESUMES

A-29 

Lead Senior Engineer 02/90-06/94

ABB Impell 

Assigned to the Mechanical Engineering Group responsible for support of Diablo Canyon Power 

Plant (DCPP) for Pacific Gas and Electric. He was the project engineer of the comprehensive 

DCPP Fire Protection/ Appendix R Upgrades Project, which included responsibility for all 

technical and financial aspects of this multi-disciplined project. 

Commissioned Officer 02/85-1/90 

U.S. Navy Submarine Force 

He served 5 years in the U.S. Navy as a submarine officer in the Nuclear Propulsion Program. 

This included training and education, as well as a tour of duty as a Submarine Officer. Certified 

as Engineer Officer of Naval Nuclear Power Plants by the Department of Energy and the U.S. 

Navy. 

PUBLICATIONS

Mr. Ratchford has been a principal contributor to many nuclear industry fire protection 

documents. A listing of documents and his level of participation in the development of the 

document is provided below: 

NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric 

Generating Plants, 2001, Code Committee Member, Contributing Author 

NEI 04-02, Guidance for Implementing a Risk-Informed, Performance-Based Fire Protection 

Program Under 10 CFR 50.48(c), Principal Contributor 

NEI 00-01, Guidance for Post-Fire Safe-shutdown Circuit Analysis, Task Force Member, 

Reviewer 

EPRI Technical Report 1010981, Transition Process Pilot Report – NEI 04-02 Guidance for 

Implementing a Risk-Informed, Performance-Based Fire Protection Program Under 10 CFR 

50.48(c), Principal Contributor 

EPRI Technical Report 1001442, A Pilot Plant Evaluation NFPA 805, "Performance-Based 

Standard for Fire Protection for Light Water Reactor Electric Generating Plants," Principal 

Contributor 

NRC. NUREG/CR-6850, EPRI Technical Report 1011989, Fire PRA Methodology for Nuclear 

Power Facilities, September 2005, Independent Reviewer (selected sections) 

Farley Units 1 and 2, 10 CFR 50 Approved Appendix R Exemption, August 16, 2005 (RI-PB 

approaches using NEI 04-02 methods), Principal Contributor 

EPRI Technical Report 1006756, Fire Protection Equipment Surveillance Optimization and 

Maintenance Guide, July 2003, Principal Contributor 

PANELIST AND FACILITATOR RESUMES

A-31 

Mano Subudhi, BNL

CLASSIFICATION: Engineer (Scientific Staff) 

FIELD OF EXPERTISE: Mechanical Engineering: Codes and Standards; Piping and Equipment 

Design and Analysis; Equipment Qualification; Electrical Equipment Aging; Materials Science; 

Structural Engineering; Seismic Analysis 

EDUCATION: 

1969 - B.S., Mechanical Engineering, Banaras Hindu University, India 

1970 - M.S., Mechanical Engineering, Massachusetts Institute of Technology 

1974 - Ph.D., Mechanical Engineering, Polytechnic Institute of New York 

EXPERIENCE: 

1976-Present 

Brookhaven National Laboratory, Currently performing piping design certification reviews for 

ESBWR, APWR and EPR and revising design-specific review standards (DSRSs) for small 

modular reactors. Conducted workshops and classes on various topics associated with NRC 

regulations in FSU countries. 

Developed SER templates for the new reactor licensing. Moderator and Technical lead for 

expert panel for material degradation PIRT. Served as lead engineer, principal investigator, and 

group leader. Completed engineering projects for NRC, DOE, and other federal agencies. 

Developed qualification guidelines for the dynamic and seismic evaluation of Class 1E 

equipment. Studied alternate procedures for calculating the inertia and pseudo-static responses 

for multiple supported piping systems. Developed the EPIPE finite element computer code for 

benchmarking and confirmatory analyses of several as-built piping systems. Principal 

Investigator for the NRC’s equipment aging research program to develop maintenance practices 

including ISI/IST to mitigate equipment failures. Conducted tests on equipment performance. 

Studied impact of aging on seismic capacity in the event of an earthquake. Evaluating 

environmental qualification procedures for cables. Completed studies and issued reports on: 

NPP EDG performance, reliability, and inspection techniques; snubber performance and 

inspection; risk-based inspection; system performance and aging; and component performance 

and aging. Reviewed relief requests for ISI requirements and applications for license renewal. 

The LR review primarily included reactor coolant system in PWR plants (e.g., ANO1, North 

Anna and Surry, and Catawba and McGuire). Performed LRA audits of reactor coolant system 

at BWR sites (e.g., Brown’s ferry, Brunswick, Oyster Creek and FitzPatrick). 

1975-1976 

Bechtel Power Corp., Mechanical Engineer. Involved in the stress analysis of nuclear power 

plant components subjected to thermal, dead weight, seismic, thermal transients, pressure and 

fatigue loads; special problems including water hammer, flow-induced vibrations, and sudden 

valve closures; and preparation of Nuclear Class I Reports for licensing purpose. Represented 

Bechtel in the interfacing with manufacturers, clients and vendors. 

1974-1975 

Nuclear Power Service, Sr. Stress Analyst. Performed stress analysis of mechanical and 

piping systems according to the requirements of ASME B&PVC, Section III, and ANSI B31.1 
PANELIST AND FACILITATOR RESUMES 

A-32

Code. Applied finite element techniques in the analysis and certification of components, which 

did not meet the code requirements. Have written computer programs for incorporating the 

ASME standards for solving complex stress problems. 

1971-1974 

PINY, Teaching Fellow. Research was based on investigation of a stability criterion to study 

the dynamic response of some complex nonlinear systems. Carried out experiments to 

introduce damping into the materials used in the sporting goods fields. 

1969-1971 

M.I.T., Research Assistant. Developed a yield criterion and an associated flow rule for a 

porous material with the eventual goal of predicting ductile fracture. 

SELECTED PUBLICATIONS: 

"Seismic Evaluation of the Brookhaven High Flux Beam Research Reactor," BNL Technical 

Report, December 1979. 

"Seismic Analysis of Piping Systems Subjected to Independent Support Excitations by Using 

Response Spectrum and Time History Methods," BNL Technical Report No. BNL-NUREG31296, April 1982. Also, Presented at the ASME Summer PVP Conference, Portland, Oregon, 

PVP-Vol. 73, June 1983. 

"The Assessment of Alternate Procedures for the Seismic Analysis of Multiply Supported Piping 

Systems," Proceedings of the 1985 ASME PVP Conference, New Orleans, PVP-Vol. 98.3, June 

1985. 

"Seismic Upgrading of the Brookhaven High Flux Beam Research Reactor," Proceedings of 

DOE Natural Phenomena Hazards Mitigation Conference, Las Vegas, October 1985. 

"Improving Motor Reliability in Nuclear Power Plants," NUREG/CR-4939, BNL-NUREG-52031, 

Vols. 1,2,3, November 1987. Also, Proceeding of the 15th WRSM, October 1987. 

"Age-Related Degradation of Westinghouse 480-Volt Circuit Breaker," NUREG/CR-5280, BNLNUREG-52178, Vols. 1&2, November 1990. 

"Degradation Modeling with Application to Aging and Maintenance Effectiveness Evaluations," 

(Co-author), NUREG/CR-5612, BNL-NUREG-52252, March 1991. 

"Life Testing of a Low Voltage Air Circuit Breaker to Assess Age-Related Degradation", Nuclear 

Technology, Vol. 97, pp.362-370, March 1992. 

“Managing Aging in Nuclear Power Plants: Insights from NRC’s Maintenance Team Inspection 

Reports,” Nuclear Safety, Vol. 35, No. 1, January-June 1994. 

 

“Literature Review of Environmental Qualification of Safety-Related Electric Cables,” 

NUREG/CR-6384, BNL-NUREG-52480, Vols. 1&2, April 1996. 

“RAPTOR Gas Gun Testing Experiment,” (Co-author) Proprietary, CRADA BNL-C-96-01, June 

1998. 
PANELIST AND FACILITATOR RESUMES

A-33 

“IAEA Verification Experiment at the Portsmouth Gaseous Diffusion Plant,” (Co-author), BNL65714, September 1998. 

“Review of Industry Responses to NRC Generic Letter 97-06 on Degradation of Steam 

Generator Internals,” NUREG/CR-6754, BNL-NUREG-52646, December 2001. 

“A Reliability Physics Model for Aging of Cable Insulation Materials,” NUREG/CR-6869, BNLNUREG-73676-2005, March 2005. 

“Application of laser generated ultrasonic pulses in diagnostics of residual stresses in welds,” 

Proc. of SPIE, 2005. 

“Expert Panel Report on Proactive Material Degradation Assessment,” NUREG/CR-6923, BNLNUREG-77111-2006, February 2007. 

PANELIST AND FACILITATOR RESUMES

A-35 

Gabriel Taylor, NRC

EDUCATION

The University of Maryland – College Park, MD 

Masters of Science in Fire Protection Engineering

Graduated: May 2012 

Thesis: Evaluation of critical nuclear power plant electrical cable response to severe thermal fire 

conditions, 2012 

Engineer-in-training (EIT) / Fundamentals of Engineering (FE) certificate 

(Maryland Reg. No. 38236 – Oct 2009) 

The Pennsylvania State University – University Park, PA 

Bachelor of Science in Electrical Engineering

Graduated: December 2004 

EXPERIENCE

U.S. Nuclear Regulatory Commission – Rockville, MD 11/2007–Present 

Fire Protection Engineer Office of Nuclear Regulatory Research (RES) 

 Authored NUREG-2128, Electrical Cable Test Results and Analysis during Fire 

Exposure (ELECTRA-FIRE)

 Authored NUREG-1924, Electric Raceway Fire Barrier Systems in US Nuclear Power 

Plants

 Instruct NRC-RES/EPRI fire PRA electrical circuit analysis training 

 Witnessed fire testing, analyzed results and wrote test reports 

o Duke Armored cable testing 

o Navy Digital I&C testing 

o Progress Penetration Seal Testing 

 International OECD Fire-Events Database and High Energy Arching Fault Task Group 

 International OECD Digital Instrumentation and Control Failure Modes Task Group 

 Managed DOE work on fire-induced failure circuit testing and conducted supplementary 

data analysis 

 Supported NRR and RES meetings and activities and presentations at numerous 

conferences 

 Presented CAROLFIRE research to Advisory Committee on Reactor Safeguards (ACRS) 

2/2008 

U.S. Nuclear Regulatory Commission – Rockville, MD 4/2005–10/2007 

NSPDP General Engineer Office of Nuclear Reactor Regulation 

• Graduate of Nuclear Safety Professional Development Program (NSPDP) Class of 2007 

• DORL: Evaluated proposed changes to license amendments in regards to their effect to 

public safety 

• ACRS: Prepared summary report for committee members and assisted with meeting 

preparations 

• RII/Watts Bar Resident Office: Basic inspector qualified IMC 1245 Appendix A 

 
PANELIST AND FACILITATOR RESUMES 

A-36

The Pennsylvania State University – University Park, PA 8/2003–2/2004 

Undergraduate Research Assistant Semiconductor Spectroscopy Lab Dr. P. M. Lenahan 

• Modified magnet power supply to operate correctly using U.S. power system 

• Designed data acquisition system to signal average ESR and SDR signals using LabVIEW 7 

• Reviewed, ordered, and installed SDR spectroscopy system 

OSRAM Sylvania Inc. – St. Marys, PA 1–3/2005 & 1– 8/2003 

Process Engineer & Engineering Co-Op (R&D, Process, EH&S, Electrical Departments) 

• Developed and conducted tests to examine customer complaints and analyzed the safety of 

products 

• Developed a recycling program to reduce net residual waste and increase gain from 

recyclable goods 

• PLC programming using VersaPro for GE PLC’s (Latter-logic) 

• Designed and constructed electrical cabinet using AutoCAD (ergonomic layout for operator 

and maintenance) 

ACHIEVEMENT, SKILLS, AND AREAS OF PERSONAL STUDY

Eagle Scout – Troup #95, Bucktail Council 

Dean’s List – The Pennsylvania State University (Fall 03, Fall04) 

Eta Kappa Nu (HKN)-Epsilon Chapter–National Electrical/Computer Engineering 

 Honors Society 

Dale Carnegie Program Graduate 

Penn State Conservation Leadership School Graduate 

Rivers Conservation Leadership School Graduate 

Member of IEEE, SFPE, HKN 
B-1

APPENDIX B

MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

The PIRT panel scored the influence parameter rankings using numerical scheme consistent 

with the alphabetical scores presented in Tables 3.1 and 3.2 of this report, as described below: 

Score Letter Number 

 Scheme Scheme

High H = 3 

Medium M = 2 

Low L = 1 

Uncertain U = 0 

Two MICROSOFT ® EXCEL worksheets represent AC and DC control circuits are presented in 

the following pages. 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus

Identification 

INFLUENCING PARAMETERS 

Parameter Applicability 

Research Ease g Rankin Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter Importance 

State of Knowledge 

 1.1 1.2 1.3 

1 Conductor Count 1.1.1 1.00 1.2.1 1.00 1.3.1 1.00 

a. 1 2 N/A N/A N/A 1 2 1 2 b. 2-6 3 3 1 2 1 2 1 2 c. 7-9 3 3 1 3 1 3 1 3 d. 10 - 15 3 3 1 2 1 2 1 2 e. >15 3 3 1 1 1 1 1 1 

2 Exposure Condition 1.1.2 2.00 1.2.2 2.00 1.3.2 3.00 

a. Flame 3 3 2 3 2 3 3 3 b. Plume 3 3 2 3 2 3 3 3 c. Hot Gas Layer 2 3 2 3 2 3 3 3 d. Time/temperature 1 3 2 1 2 1 3 1 

B-2 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter 

Applicability 

Research Ease 

Ranking 

Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter 

Importance 

State of 

Knowledge 

3 Routing / Raceway 

(Excluding g. Panel Wiring)

1.1.3 1.00 1.2.3 1.00 1.3.3 1.00 

a. Cable Tray Vertical 3 3 1 2 1 2 1 2 b. Cable Tray Horizontal 

3 3 1 3 1 3 1 3 

c. Cables in Horiz. Conduits 

3 3 1 3 1 3 1 3 

d. Cables in Vert. Conduits 

3 3 1 2 1 2 1 2 

e. Cables in Air Drop Configuration 

2 3 1 2 1 2 1 2 

f. Tray type 3 3 1 1 1 1 1 1 g. Panel wiring 3 2 3.00 1 3.00 1 3.00 1 

B-3 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter 

Applicability 

Research Ease 

Ranking 

Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter 

Importance 

State of 

Knowledge 

4 Raceway Fill 

(Excluding d. Bundles)

1.1.4 1.00 1.2.4 2.00 1.3.4 2.00 

a. Maximum Loading 3 3 1 2 2 2 2 1 b. Intermediate Loading 

3 3 1 3 2 3 2 2 

c. Minimum Loading (1 or 2 cables) 

3 3 1 3 2 3 2 3 

d. Bundles 3 3 2.00 3 2.00 3 2.00 3 

5 Insulation Type 1.1.5 1.00 1.2.5 3.00 1.3.5 1.00 

Insulation Material 3 3 1 3 3 3 1 3 

6 Aging 3 3 1.1.6 1.00 1 1.2.6 1.00 1 1.3.6 1.00 1 7 Jacket 1.1.7 1.2.7 1.3.7 

a. Material 3 3 1.00 3 2.00 3 1.00 3 b. Coatings 3 3 1.00 1 1.00 1 1.00 1 

B-4 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter 

Applicability 

Research Ease 

Ranking 

Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter 

Importance 

State of 

Knowledge 

8 Time-Current 

Characteristics: 

1.1.8 1.00 1.2.8 1.00 1.3.8 3.00 

Fuse/breaker size and type 

3 2 1 1 1 1 3 1 

9 Grounding Cable 

Configuration 

1.1.9 3.00 1.2.9 3.00 1.3.9 2.00 

a. Drain Wire 1 3 3 2 3 2 2 1 b. Shield wrap 2 3 3 1 3 1 2 1 

10 Voltage level 1.1.10 1.00 1.2.10 1.00 1.3.10 1.00 

a. < 100vac 1 2 1 1 1 1 1 1 b. 120vac 3 3 1 3 1 3 1 3 c. > 150vac 1 2 1 1 1 1 1 1 

11 Armor Grounded vs 

Ungrounded Circuit 

3 3 1.1.11 3.00 1 1.2.11 3.00 1 1.3.11 2.00 1 

B-5 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter 

Applicability 

Research Ease 

Ranking 

Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter 

Importance 

State of 

Knowledge 

12 Wiring Configuration 1.1.12 3.00 1.2.12 3.00 1.3.12 3.00 

a. # of Sources 3 3 3 2 3 2 3 2 b. # of Targets 3 3 3 2 3 2 3 2 c. Locations of S & T 3 3 3 2 3 2 3 2 d. # of Grounds/neutrals 

3 3 3 2 3 2 3 2 

13 Conductor Size 3 3 1.1.13 1.00 2 1.2.13 1.00 2 1.3.13 1.00 1 14 Suppression 1.1.14 1.50 1.2.14 1.50 1.3.14 U 

a. Water Spray 3 3 1.5 1 1.5 1 U 1 b. Hose 3 3 1.5 1 1.5 1 U 1 

15 Latching vs 

Nonlatching Device 

1.1.15 1.00 1.2.15 1.00 1.3.15 3.00 

a. Latching MOV 3 3 1 1 1 1 3 3 b. Non-Latching MOV 3 3 1 3 1 3 3 3 

B-6 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

AC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter 

Applicability 

Research Ease 

Ranking 

Effect of Parameters on the Likelihood -- 1.1 SPURIOUS ACTUATION of AC control circuit - INTRA-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Likelihood -- 1.2 SPURIOUS ACTUATION of AC control circuit - INTER-CABLE short 

Parameter 

Importance 

State of 

Knowledge Effect of Parameters on the Plant Cable Configuration -- 1.5 DURATION of Spurious Actuations 

Parameter 

Importance 

State of 

Knowledge 

16 Circuit Grounded vs. 

Ungrounded 

2 3 1.1.16 1.00 2 1.2.16 3.00 2 1.3.16 2.00 1 

B-7 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

DC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus

Identification INFLUENCING PARAMETERS 

Parameter Applicability 

Research Ease Ranking Effect of Parameters on the Likelihood -- 2.1 SPURIOUS ACTUATION of DC control circuit - INTRA-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.2 SPURIOUS ACTUATION of DC control circuit - INTER-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.3 INTER-CABLE GROUND FAULT EQUIVALENT SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge Effect of Parameters on the Plant Cable Configuration -- 2.4 DURATION OF SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge 

2.1 2.2 2.3 2.4 

1 Conductor Count 2.1.1 1.00 2.2.1 1.00 2.3.1 1.00 2.4.1 1.00 

a. 1 2 N/A N/A N/A 1 2 1 2 1 2 b. 2-6 3 3 1 2 1 2 1 2 1 2 c. 7-9 3 3 1 3 1 3 1 3 1 3 d. 10 - 15 3 3 1 2 1 2 1 2 1 2 e. >15 3 3 1 1 1 1 1 1 1 1 

2 Exposure Condition 2.1.2 2.00 2.2.2 2.00 2.3.2 2.00 2.4.2 3.00 

a. Flame 3 3 2 3 2 3 2 3 3 3 b. Plume 3 3 2 3 2 3 2 3 3 3 c. Hot Gas Layer 2 3 2 3 2 3 2 3 3 3 d. Time/temperature 1 3 2 1 2 1 2 1 3 1 

B-8 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

DC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter Applicability 

Research Ease Ranking Effect of Parameters on the Likelihood -- 2.1 SPURIOUS ACTUATION of DC control circuit - INTRA-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.2 SPURIOUS ACTUATION of DC control circuit - INTER-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.3 INTER-CABLE GROUND FAULT EQUIVALENT SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge Effect of Parameters on the Plant Cable Configuration -- 2.4 DURATION OF SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge 

3 Routing / Raceway 

(excluding f. Panel Wiring)

2.1.3 

1.00 

2.2.3 

1.00 

2.3.3 

1.00 

2.4.3 

1.00 

a. Cable Tray Vertical 3 3 1 2 1 1 1 1 1 1 b. Cable Tray Horizontal 3 3 1 3 1 3 1 3 1 3 c. Cables in Horiz. Conduits 3 3 1 3 1 2 1 2 1 2 d. Cables in Vert. Conduits 3 3 1 2 1 1 1 1 1 1 e. Cables in Air Drop Configuration 2 3 1 2 N/A N/A N/A N/A 1 1 f. Tray type 3 3 1 1 1 1 1 1 1 1 g. Panel Wiring 3 2 3.00 1 3.00 1 2.00 1 3.00 1 

4 

Raceway Fill (Excluding d. Bundles)

2.1.4 

1.00 

2.2.4 

2.00 

2.3.4 

1.00 

2.4.4 

1.00 

a. Maximum Loading 3 3 1 2 2 1 1 1 1 1 b. Intermediate Loading 3 3 1 3 2 3 1 3 1 3 c. Minimum Loading (1 or 2 cables) 3 3 1 3 2 3 2 3 2 3 d. Bundles 3 3 1.00 3 2.00 2 2.00 2 2.00 2 

B-9 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

DC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter Applicability 

Research Ease Ranking Effect of Parameters on the Likelihood -- 2.1 SPURIOUS ACTUATION of DC control circuit - INTRA-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.2 SPURIOUS ACTUATION of DC control circuit - INTER-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.3 INTER-CABLE GROUND FAULT EQUIVALENT SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge Effect of Parameters on the Plant Cable Configuration -- 2.4 DURATION OF SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge 

5 Insulation Type 2.1.5 1.00 2.2.5 3.00 2.3.5 1.00 2.4.5 2.00 

Insulation Material 3 3 1 3 3 3 1 2 2 3 

6 Aging 3 3 2.1.6 1.00 1 2.2.6 1.00 1 2.3.6 1.00 1 2.4.6 1.00 1 7 Jacket 2.1.7 1.00 2.2.7 2.00 2.3.7 1.00 2.4.7 1.00 

a. Material 3 3 1 3 2 3 1 3 1 3 b. Coatings 3 3 1 1 1 1 1 1 1 1 

8 

Time-Current Characteristics: 2.1.8 

1.00

2.2.8 

1.00

2.3.8 

1.00

2.4.8 

3.00

Fuse/breaker size and type 3 3 1 1 1 1 1 2 3 3 

9 Grounding Cable 

Configuration NOT APPLICABLE NOT APPLICABLE NOT APPLICABLE NOT APPLICABLE 

10 Voltage level NOT APPLICABLE NOT APPLICABLE NOT APPLICABLE NOT APPLICABLE 11 Armor vs. 

Unarmored 

2 3 2.1.11 1.00 1 2.2.11 3.00 1 2.3.11 3.00 1 2.4.11 2.00 1

B-10 
MICROSOFT® EXCEL PIRT PANEL SCORING SHEETS 

DC CONTROL CIRCUITS PANEL MEMBER: Panel Consensus (Cont’d.)

Identification INFLUENCING PARAMETERS 

Parameter Applicability 

Research Ease Ranking Effect of Parameters on the Likelihood -- 2.1 SPURIOUS ACTUATION of DC control circuit - INTRA-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.2 SPURIOUS ACTUATION of DC control circuit - INTER-CABLE short 

Parameter Importance 

State of Knowledge Effect of Parameters on the Likelihood -- 2.3 INTER-CABLE GROUND FAULT EQUIVALENT SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge Effect of Parameters on the Plant Cable Configuration -- 2.4 DURATION OF SPURIOUS ACTUATION 

Parameter Importance 

State of Knowledge 

12 Wiring Configuration 2.1.12 3.00 2.2.12 3.00 2.3.12 3.00 2.4.12 3.00 

a. # of Sources 3 3 3 2 3 2 3 2 3 2 b. # of Targets 3 3 3 2 3 2 3 2 3 2 c. Locations of S & T 3 3 3 2 3 2 3 2 3 2 d. # of Grounds/neutrals 3 3 3 2 3 2 3 2 3 2 

13 Conductor Size 3 3 2.1.13 1.00 2 2.2.13 1.00 2 2.3.13 1.00 2 2.4.13 1.00 1 14 Suppression 2.1.14 1.50 2.2.14 1.50 2.3.14 2.00 2.4.14 U 

a. Water Spray 3 3 1.5 1 1.5 1 2 1 U 1 b. Hose 3 3 1.5 1 1.5 1 2 1 U 1 

15 

Latching vs Nonlatching Device 

2.1.15 

1.00 

2.2.15 

1.00 

2.3.15 

1.00 

2.4.15 

3.00 

a. Latching MOV 3 3 1 1 1 1 1 1 3 3 b. Non-Latching MOV 3 3 1 3 1 3 1 1 3 3 

B-11 

C-1 

APPENDIX C

CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE 

AND DOUBLE BREAK DESIGNS 

During the PIRT panel meetings, the use of circuit diagrams and physical circuit configuration 

layouts became more common to be drawn on white boards to assist with the discussion of 

numerous issues and to assist in understanding how various parameters affect the likelihood of 

hot short-induced spurious operations. Furthermore, the PIRT panel determined that providing 

these circuit diagrams and physical layout illustrations to be valuable for the reader of the report 

and the follow-on expert elicitation by the PRA panel. Thus, the following pages provide 

simplified schematic configuration and physical configuration illustrations, along with specific 

notes on the configuration to assists the reader of this report. The list is meant to represent the 

pool of circuit designs that the PIRT panel determined to be important for discussions and 

development of conditional spurious operation probabilities, but is not meant to be exhaustive or 

representative of detailed circuit diagrams common to US NPPs. The diagrams for the eight 

specific cases are presented in the following order: 

Case 1: Single contact Intra-cable hot short-induced spurious operation 

Case 2: Single contact Inter-cable hot short-induced spurious operation 

Case 3: Single contact Inter-cable hot short-induced spurious operation via a ground plane 

interaction from cables in the same or different raceway 

Case 4: Double contact – one Intra-cable and one Inter-cable hot short-induced spurious 

operation 

Case 5: Double contact – two Inter-cable hot short-induced spurious operations 

Case 6: Double contact – two Intra-cable hot short-induced spurious operations 

Case 7: Double contact – Intra (+) and ground fault hot short (-) – induced spurious operation 

Case 8: Double contact – Inter (+) and ground fault hot short (-) – induced spurious operation 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

Valve Open

Valve Open

Ungrounded DC

[or 120 V ac Distribution System]

125 V dc

Ungrounded AC

Valve Open

Grounded AC

Simplified Schematic Configuration – Single Break Control Circuit

Intra-cable hot short

Bonded to plant ground grid

Raceway

Physical Configuration Intra-Cable 

Hot Short

Intra-Cable 

Hot Short

Intra-Cable 

Hot Short

Case 1 – Single Contact Intra-Cable Hot Short – Induced Spurious Operation

Notes:1. Component is energize to open. 2. A fire-induced intra-cable hot short will open the component.

a. If the component is a latching circuit, the component will remain open even if the intra-cable hot short is eliminated, e.g., goes to ground. b. If the component is a non-latching circuit, the component will close when the intra-cable hot short is eliminated, e.g., goes to ground. c. If power is lost to the control circuit by blowing the control power fuses or by a failure of the power supply to the fuses, the component will close regardless of whether or not it is a latching or non-latching circuit.

3. The behavior described on this drawing is typical of an intra-cable hot short from a conductor within the same circuit. Ifthe intra-cable hot short is from a conductor in the same cable, but from a different circuit, the behavior will be governed more by the characteristics described for the inter-cable hot short in Case 2. 

CPT

CPT

(+)

(-)

C-2 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

Valve Open

Valve Open

Ungrounded DC

[or 120 V ac Distribution System]

125 V dc

Ungrounded AC

Valve Open

Grounded AC

Simplified Schematic Configuration – Single Break Control Circuit

Physical Configuration Inter-Cable 

Hot Short

Inter-Cable 

Hot Short

Inter-Cable 

Hot Short

Case 2 – Single Contact Inter-Cable Hot Short – Induced Spurious Operation

Notes:1. Component is energize to open.2. A fire-induced inter-cable hot short will open the component.

a. If the component is a latching circuit, the component will remain open even if the inter-cable hot short is eliminated, e.g., goes to ground. b. If the component is a non-latching circuit, the component will close when the inter-cable hot short is eliminated, e.g., goes to ground. c. If power is lost to the control circuit by blowing the control power fuses on the aggressor circuit or by a failure of the power supply to the fuses in either the primary or aggressor circuit, the component will close regardless of whether or not it is a latching or non-latching circuit.

3. For the case of the ungrounded DC or ungrounded distributed AC circuit, the inter-cable hot short must come from the same battery source. This is required since an inter-cable hot short from a different battery source will not have a current return flow path.4. For the case of the ungrounded AC circuit power from a CPT, the inter-cable hot short must be accompanied by a short to ground on the negative leg of the circuit providing a current return flow path to the power source of the aggressor circuit. If the aggressor circuit is an ungrounded AC source off of a CPT, the aggressor circuit will also require a ground on the negative leg to complete the circuit and cause the spurious operation. 5. For the case of the grounded AC circuit powered from a CPT, if the aggressor circuit is an ungrounded AC source off of a CPT, the aggressor circuit will also require a ground on the negative leg to complete the circuit and cause the spurious operation.

Inter-cable hot 

short

Bonded 

to plant 

ground 

grid

Raceway

Additional short-toground providing a current return flow path

CPT

CPT

(+)

(-)

C-3 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-4 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-5 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-6 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-7 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-8 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-9 
CONTROL CIRCUIT CONFIGURATIONS FOR SINGLE AND DOUBLE BREAK DESIGNS 

C-10 
D-1 

APPENDIX D

SELECTED PRESENTATION VIEWGRAPHS 

During the first PIRT meeting held during November 2010, BNL presented to the PIRT panel the 

results of the EPRI/NEI and the NRC/SNL cable testing programs. In addition, BNL presented 

the project’s overall objectives, and an approach to achieve these objectives in order to start the 

discussion among the PIRT panel members. This appendix includes a selected number of 

these presentations. 

 
SELECTED PRESENTATION VIEWGRAPHS 

D-2 
SELECTED PRESENTATION VIEWGRAPHS

D-3 
SELECTED PRESENTATION VIEWGRAPHS 

D-4 
SELECTED PRESENTATION VIEWGRAPHS

D-5 
SELECTED PRESENTATION VIEWGRAPHS 

D-6 
SELECTED PRESENTATION VIEWGRAPHS

D-7 
SELECTED PRESENTATION VIEWGRAPHS 

D-8 
SELECTED PRESENTATION VIEWGRAPHS

D-9 
SELECTED PRESENTATION VIEWGRAPHS 

D-10 
SELECTED PRESENTATION VIEWGRAPHS

D-11 
SELECTED PRESENTATION VIEWGRAPHS 

D-12 
SELECTED PRESENTATION VIEWGRAPHS

D-13 
SELECTED PRESENTATION VIEWGRAPHS 

D-14 
SELECTED PRESENTATION VIEWGRAPHS

D-15 
SELECTED PRESENTATION VIEWGRAPHS 

D-16 
SELECTED PRESENTATION VIEWGRAPHS

D-17 
SELECTED PRESENTATION VIEWGRAPHS 

D-18 
SELECTED PRESENTATION VIEWGRAPHS

D-19 
SELECTED PRESENTATION VIEWGRAPHS 

D-20 
SELECTED PRESENTATION VIEWGRAPHS

D-21 
SELECTED PRESENTATION VIEWGRAPHS 

D-22 
SELECTED PRESENTATION VIEWGRAPHS

D-23 
SELECTED PRESENTATION VIEWGRAPHS 

D-24 
SELECTED PRESENTATION VIEWGRAPHS

D-25 
SELECTED PRESENTATION VIEWGRAPHS 

D-26 
SELECTED PRESENTATION VIEWGRAPHS

D-27 
SELECTED PRESENTATION VIEWGRAPHS 

D-28 
SELECTED PRESENTATION VIEWGRAPHS

D-29 
SELECTED PRESENTATION VIEWGRAPHS 

D-30 
SELECTED PRESENTATION VIEWGRAPHS

D-31 
SELECTED PRESENTATION VIEWGRAPHS 

D-32 
SELECTED PRESENTATION VIEWGRAPHS

D-33 
SELECTED PRESENTATION VIEWGRAPHS 

D-34 
SELECTED PRESENTATION VIEWGRAPHS

D-35 
SELECTED PRESENTATION VIEWGRAPHS 

D-36 
SELECTED PRESENTATION VIEWGRAPHS

D-37 
SELECTED PRESENTATION VIEWGRAPHS 

D-38 
SELECTED PRESENTATION VIEWGRAPHS

D-39 
SELECTED PRESENTATION VIEWGRAPHS 

D-40 
SELECTED PRESENTATION VIEWGRAPHS

D-41 
SELECTED PRESENTATION VIEWGRAPHS 

D-42 
SELECTED PRESENTATION VIEWGRAPHS

D-43 
SELECTED PRESENTATION VIEWGRAPHS 

D-44 
SELECTED PRESENTATION VIEWGRAPHS

D-45 
SELECTED PRESENTATION VIEWGRAPHS 

D-46 
SELECTED PRESENTATION VIEWGRAPHS

D-47 
SELECTED PRESENTATION VIEWGRAPHS 

D-48 
SELECTED PRESENTATION VIEWGRAPHS

D-49 
SELECTED PRESENTATION VIEWGRAPHS 

D-50 
SELECTED PRESENTATION VIEWGRAPHS

D-51 
SELECTED PRESENTATION VIEWGRAPHS 

D-52 
SELECTED PRESENTATION VIEWGRAPHS

D-53 
SELECTED PRESENTATION VIEWGRAPHS 

D-54 
SELECTED PRESENTATION VIEWGRAPHS

D-55 
SELECTED PRESENTATION VIEWGRAPHS 

D-56 
SELECTED PRESENTATION VIEWGRAPHS

D-57 
SELECTED PRESENTATION VIEWGRAPHS 

D-58 
SELECTED PRESENTATION VIEWGRAPHS

D-59 
SELECTED PRESENTATION VIEWGRAPHS 

D-60 
SELECTED PRESENTATION VIEWGRAPHS

D-61 
SELECTED PRESENTATION VIEWGRAPHS 

D-62 
SELECTED PRESENTATION VIEWGRAPHS

D-63 
SELECTED PRESENTATION VIEWGRAPHS 

D-64 
SELECTED PRESENTATION VIEWGRAPHS

D-65 
SELECTED PRESENTATION VIEWGRAPHS 

D-66 
SELECTED PRESENTATION VIEWGRAPHS

D-67 
SELECTED PRESENTATION VIEWGRAPHS 

D-68 
SELECTED PRESENTATION VIEWGRAPHS

D-69 
SELECTED PRESENTATION VIEWGRAPHS 

D-70 
SELECTED PRESENTATION VIEWGRAPHS

D-71 
SELECTED PRESENTATION VIEWGRAPHS 

D-72 
SELECTED PRESENTATION VIEWGRAPHS

D-73 
SELECTED PRESENTATION VIEWGRAPHS 

D-74 
SELECTED PRESENTATION VIEWGRAPHS

D-75 
SELECTED PRESENTATION VIEWGRAPHS 

D-76 
SELECTED PRESENTATION VIEWGRAPHS

D-77 
SELECTED PRESENTATION VIEWGRAPHS 

D-78 
SELECTED PRESENTATION VIEWGRAPHS

D-79 

BIBLIOGRAPHIC DATA SHEET

(See instructions on the reverse)

NRC FORM 335

(12-2010)

NRCMD 3.7

U.S. NUCLEAR REGULATORY COMMISSION 1. REPORT NUMBER

 (Assigned by NRC, Add Vol., Supp., Rev.,

 and Addendum Numbers, if any.)

NUREG/CR-7150

BNL-NUREG-98204-2012

EPRI 1026424

3. DATE REPORT PUBLISHED

MONTH

October

YEAR

2012

4. FIN OR GRANT NUMBER

JCN N6866

2. TITLE AND SUBTITLE

Joint Assessment of Cable Damage and Quantification of Effects from Fire (JACQUE-FIRE)

Volume 1: Phenomena Identification and Ranking Table (PIRT) Exercise for Nuclear Power

Plant Fire-Induced Electrical Circuit Failure

5. AUTHOR(S)

M. Subudhi and J. Higgins

6. TYPE OF REPORT

Technical

7. PERIOD COVERED (Inclusive Dates)

11/17/2010 - 10/1/2012

8. PERFORMING ORGANIZATION - NAME AND ADDRESS (If NRC, provide Division, Office or Region, U.S. Nuclear Regulatory Commission, and mailing address; if contractor,

Department of Energy, Science and Technology

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, 

Division of Risk Analysis

provide name and mailing address.)

and mailing address.)

10. SUPPLEMENTARY NOTES

Gabriel Taylor, NRC Project Manager

11. ABSTRACT (200 words or less)

Volume 1 of this report documents the results of a Phenomena Identification and Ranking Table (PIRT) exercise that was

undertaken on fire-induced electrical circuit failures that may occur in nuclear power plants when cables are damaged by fires. 

This program was sponsored by the U.S. Nuclear Regulatory Commission's (NRC's) Office of Nuclear Regulatory Research

(RES) and the Electric Power Research Institute (EPRI) under the NRC-RES/EPRI Memorandum of Understanding (MOU)

collaborative research agreement. The electrical expert PIRT panel was comprised of a group of experts sponsored equally by

the NRC and EPRI. Staff from Brookhaven National Laboratory (BNL) facilitated the efforts of the PIRT panel. The objective of

this PIRT was to identify phenomena that can affect the fire-induced failure modes of electrical circuits after cables are damaged

by fire. The PIRT panel used the results from recent fire tests performed by EPRI and NRC, identifying and ranking the

parameters that can influence the hot short failure modes of electrical control circuits. Using these influencing parameters, the

results of cable-fire tests, expert judgement, and operating experience, the PIRT panel developed circuit configurations

vulnerable to hot short modes of circuit failures that can engender the spurious operation of certain end devices. In addition to

completing the PIRT exercise on control circuits, the PIRT panel reached technical consensus on several issues in analyzing fire

protection circuits such as power-cabling consequential hot shorts, open circuits on the secondary of current transformers,

multiple high-impedance faults, and concerns about common enclosure and common power supplies. The PIRT panel noted the

dearth of data on instrumentation circuits to support a structured evaluation of the influencing phenomena and therefore, the

panel suggested conducting further research to advance the current knowledge base.

12. KEY WORDS/DESCRIPTORS (List words or phrases that will assist researchers in locating the report.)

Circuit Analysis, Fire Protection, Fire Hazard Analysis (FHA), Fire Safety, Fire Safe-shutdown, Hot

Short, Nuclear Power Plant (NPP), Phenomena Identification and Ranking Table (PIRT), Performance

Based, Probabilistic Risk Assessment (PRA), Risk-Informed Regulation, Spurious Operation (or

Actuation)

14. SECURITY CLASSIFICATION

13. AVAILABILITY STATEMENT

unlimited

(This Page)

unclassified

(This Report)

unclassified

15. NUMBER OF PAGES

16. PRICE

NRC FORM 335 (12-2010)

Brookhaven National Laboratory

P.O. Box 5000

Upton, New York 11973

Office of Nuclear Regulatory Research

U.S. Nuclear Regulatory Commission

Washington, DC 20555-0001




UNITED STATES 

NUCLEAR REGULATORY COMMISSION

WASHINGTON, DC 20555-0001

--------------------

OFFICIAL BUSINESS
NUREG/CR

-7150,

Vol. 1

Joint Assessment of Cable Damage and Qu

Effects from 

antification of 

Fire(JACQUE-FIRE)