ML24304A855

Technical Presentation at the Fall 2024 IEEE Pes ICC Subcommittee D Technical Session, Electrical Cable Damage and Ignition Characteristics Under Severe Thermal Exposure

ML24304A855
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Issue date:	10/30/2024
From:	Gabe Taylor NRC/RES/DRA/FXHAB
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ELECTRICAL CABLE DAMAGE AND IGNITION CHARACTERISTICS UNDER SEVERE THERMAL EXPOSURE -

RESULTS OF THE HIGH ENERGY ARCING FAULT (HEAF)

PROGRAM Gabe Taylor, P.E.

Senior Fire Protection Engineer Presented at the Fall 2024 IEEE PES ICC Meeting Technical Presentation Subcommittee D Bonita Springs, FL

TEAM ACKNOWLEDGEMENT

OUTLINE I N T R O D U C T I O N N O N - H E A F C A B L E D A M A G E / I G N I T I O N N E E D F O R N E W M E T R I C D ATA J U D G E M E N T F I N A L R E S U LT S & TA K E AWAY S

INTRODUCTION

WHAT IS A HEAF?

HIGH ENERGY ARCING FAULT A FA U LT T H AT R E S U LT S I N T H E R A P I D R E L E A S E O F E L E C T R I C A L E N E R G Y I N T H E F O R M O F H E AT, V A P O R I Z E D M E TA L, A N D M E C H A N I C A L F O R C E.

S W I T C H G E A R S, L O A D C E N T E R S, A N D B U S B A R S / D U C T S ( 4 4 0 V A N D A B O V E ) A R E S U B J E C T T O T H I S FA I L U R E M O D E.

FA U LT S O F T H I S T Y P E A R E C O M M O N LY R E F E R R E D T O A S H I G H E N E R G Y, E N E R G E T I C, O R E X P L O S I V E E L E C T R I C A L E Q U I P M E N T FA U LT S O R F I R E S.

Ref. NUREG-2262

WHY DO WE CARE?

REPRESENTS A HAZARD TO NUCLEAR SAFETY AND HAS UNIQUE CHARACTERISTICS FROM CLASSICAL FIRE PROTECTION AND FIRE RISK ASSESSMENT METHODS.

ZONE OF INFLUENCE (ZOI)

H E A FS D I F F E R F R O M T H E R M A L F I R E S N E E D TO B E T R E AT E D A C C O R D I N G LY P R E V I O U S Z O I S W E R E D E T E R M I N E D F R O M L I M I T E D O P E R AT I O N A L E X P E R I E N C E E V E N T S T H AT O C C U R R E D AT U S N P P S

WHAT DO HEAFS LOOK LIKE

WHY THE LONG DURATION ?

Unit-connected designs No Generator Circuit Breaker (~80%)

15 second decay

WHAT IS AT RISK CABLES & EQUIPMENT RELIED ON FOR SAFE SHUTDOWN HEAF heat flux range from 10s of kW/m2 to several MW/m2 Prevent Detect &

Suppress Ensure Safe Shutdown DEFENSE-IN-DEPTH

CABLE DAMAGE

CLASSICAL FIRE EXPOSURES 12

CLASSICAL THERMAL FRAGILITY CURVES Electrical functionality determines failure Ignition is assumed concurrent with electrical failure Fire propagation follows simple empirically derived rules Thermoset (TS) : 330 °C 11 kW/m2 Thermoplastic (TP) : 205 °C 6 kW/m2 Ref. Taylor 2012 The PROBLEM for HEAF : INSTANT DAMAGE 13

THE QUESTION W H AT I S T H E TA R G E T F R A G I L I T Y ( D A M A G E A N D I G N I T I O N T H R E S H O L D S )

F R O M A H E A F E X P O S U R E ?

NEED FOR A NEW METRIC

NEED

• Existing HEAF PRA methodology does not specify fragility

• HEAFs present a much shorter, higher energy source term, the effects of which are not as well characterized as other fire phenomena

• New metric needed to determine the level at which HEAF exposures cause equipment failure and ignition 16

DATA

APPROACH Literature review identified work done by Stan Martin could serve as reference point for developing an experimental program Developed lumped-material model for high heat flux conditions Helped focus the test parameters Flux Fluence Multi-phase process following design of experiment approach to support program efficiencies 18

TEST FACILITY - SOLAR FURNACE Solar Furnace was used to provide thermal exposure environment Heliostat using flat mirrors (Figure 1-4) with total reflective surface of 55m2 to reflect light through an attenuator onto a large reflective parabolic dish (Figure 1-5), which concentrates sunlight to target using 228 individually aligned mirrors.

Concentrate sunlight on a spot roughly 5 cm diameter 19

PURPOSE OF TESTING PHASES P H A S E 0 P R O V I D E P R E L I M I N A R Y M O D E L D A T A A N D V E R I F Y T H E V I A B I L I T Y O F T H E I G N I T I O N M A P M E T H O D O L O G Y H E A T F L U X R A N G E ( 0. 2 5 -

5 M W / M 2 )

E X P O S U R E D U R A T I O N ( 1 0 -

6 0 S E C O N D S )

P H A S E 0 B E V A L U A T E T H E F E A S I B I L I T Y O F A C H I E V I N G P E R S I S T E N T I G N I T I O N A T T H E S O L A R F U R N A C E S C A L E H E A T F L U X P R O F I L E ( 2. 2 5 M W / M 2 F O R 1 0 S E C O N D S, T H E N 0. 2 5 M W / M 2 F O R 3 0 )

P H A S E 1 D E V E L O P D A T E T O S U P P O R T E V A L U A T I O N O F S U S T A I N E D I G N I T I O N A N D C A B L E F A I L U R E D U R I N G H E A F E X P O S U R E E V A L U A T E S E M I - E M P I R I C A L M O D E L H E A T F L U X R A N G E ( M W / M 2 )

E X P O S U R E D U R A T I O N ( S E C O N D S )

• Photos

• Pre-and post-test

• Camera

• 60 frames per second with filters

• Sample weight

• Pre-and post-test

• Thermocouples

• Sub-jacket

• Electrical monitoring circuit

• Some tests were run to failure (RTF) to develop data for damage INSTRUMENTATION

EXAMPLE OF RESULTS

SOLAR FURNACE TEST

SOLAR EXPERIMENTAL

SUMMARY

AND CONCLUSIONS D I F F I C U LT I E S I N P R O V I D I N G R E L I A B L E A N D R E P E ATA B L E D ATA F O R S U S TA I N E D I G N I T I O N E L E C T R I C A L FA I L U R E W H I L E O B S E R V E D I S U N L I K E LY AT T H E H E A F T I M E S C A L E S D A M A G E T O C A B L E J A C K E T A S A F U N C T I O N O F T O TA L E N E R G Y W A S A M O R E R E L I A B L E M E T R I C

FULL SCALE INSIGHTS

JUDGEMENT

EXPERT JUDGEMENT Objective Develop HEAF target fragility estimates Document the data, process, insights, and conclusions from WG Scope Failure modes Functional failure (i.e., damage)

Ignition Focus on electrical cables Recommended guidance for non-segregated phase bus ducts and electric raceway fire barrier systems (ERFBS) 27

APPROACH Simplified expert elicitation process Compile data Present and discuss Formulate a position Debate Revise Finalized and reach consensus 28

KEY FINDINGS Electrical Failure / Damage Thermoplastic (TP) jacketed cables 15 megajoules per square meter (MJ/m2)

Includes cables in conduits and cable trays Thermoset (TS) jacketed cables 30 MJ/m2 Includes cables in conduits and cable trays 29

PROTECTION FROM CABLE TRAY COVERS/BOTTOMS OR CONDUIT C O N D U I T R A C E W A Y S E N G I N E E R I N G C A L C U L A T I O N S U S E D T O E V A L U A T E C A B L E T H E R M A L E X P O S U R E R E S U L T S I N D I C A T E D T H A T R I G I D M E T A L C O N D U I T

( R M C ) M A Y P R O V I D E S O M E P R O T E C T I O N, H O W E V E R,

I N T E R M E D I A T E M E T A L C O N D U I T ( I M C ) A N D E L E C T R I C A L M E T A L L I C T U B I N G ( E M T ) R A C E W A Y S P R O V I D E S I G N I F I C A N T L Y L E S S P R O T E C T I O N U N C E R T A I N T I E S R E L A T E D T O T H E H E A F E X P O S U R E C O N D I T I O N S A N D N U M B E R O F I N F L U E N C I N G P A R A M E T E R S, T H E W G W A S U N A B L E T O D R A W F I R M C O N C L U S I O N S A B O U T T H E I R E F F E C T I V E N E S S A N D T H U S R E C O M M E N D U S I N G T H E U N P R O T E C T E D C A B L E F R A G I L I T I E S T R A Y S W I T H B O T T O M S A N D C O V E R S S I M I L A R E V A L U A T I O N -

S I M I L A R R E S U L T S

KEY FINDINGS C A B L E S O U T S I D E T H E E N C L O S U R E O F O R I G I N ( B U T W I T H I N T H E Z O I )

N O S U S T A I N E D I G N I T I O N C O N C U R R E N T W I T H H E A F M U S T C O N S I D E R C A B L E I G N I T I O N O U T S I D E T H E E N C L O S U R E O F O R I G I N I F W I T H I N T H E F L A M E,

P L U M E, A N D R A D I A T I O N R E G I O N O F T H E P O S T - H E A F F I R E C A B L E S I N S I D E T H E E N C L O S U R E O F O R I G I N I G N I T I O N I S A S S U M E D ( E. G., I N T E R N A L C A B L E S A N D C O M P O N E N T S W I T H I N S W I T C H G E A R A N D L O A D C E N T E R S )

B A S E D O N O P E R A T I N G E X P E R I E N C E A N D T E S T I N G

RESULTS

SIMULATIONS Incident energy estimates made at many points surrounding the enclosure

DETERMINING THE ZONE OF INFLUENCE (ZOI)

Find maximum exposure vs. distance among all devices for each face Adjust maximum exposure using model bias parameters Determine ZOI from intersection with fragility threshold 1000 10000 100000 1000000 0

0.5 1

1.5 2

2.5 Exposure (kJ/m2)

Distance from Rear Face (m)

FDS Adjusted 15 MJ/m² 30 MJ/m² (1) Maximum Exposure (2) Adjusted Maximum Exposure (50th Percentile)

Target Fragility Thresholds (3) ZOI 35

THANK YOU Gabriel Taylor 301-415-0781 gabriel.taylor@nrc.gov