Risk-Informed Fire

ProtectionLecture 8-3

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Key Topics

• Browns Ferry fire

• Fire PRA history

• Risk-informed fire protection

• Current controversies

2

Overview

Resources

• U.S. Nuclear Regulatory Commission, The Browns Ferry Nuclear Plant

Fire of 1975 Knowledge Management Digest,” NUREG/KM-0002, Rev. 1,

February 2014.

• S.P. Nowlen, M. Kazarians, and F. Wyant, “Risk Methods Insights Gained

From Fire Incidents,” NUREG/CR-6738, September 2001.

• N. Siu, N. Melly, S. P. Nowlen, and M. Kazarians, “Fire Risk Assessment

for Nuclear Power Plants,” The SFPE Handbook of Fire Protection

Engineering, 5th Edition, Springer-Verlag, New York, 2016.

• Nuclear Energy Agency, “CSNI Technical Opinion: Fire Probabilistic Safety

Safety Assessment for Nuclear Power Plants: 2019 Update,” Boulogne-

Billancourt, France, in publication.

• N. Siu, K. Coyne, and N. Melly, “Fire PRA maturity and realism: a technical

technical evaluation,” U.S. Nuclear Regulatory Commission, March 2017.

(ADAMS ML17089A537)

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Overview

Other References

• U.S. Code of Federal Regulations, “Fire Protection,” 10 CFR 50.48, June 16, 2004, last amended Aug. 28, 2007.

• National Fire Protection Association, “Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants,” NFPA 805, 2001 Edition, Quincy, MA, 2001. (Available through the NFPA Online Catalog at www.nfpa.org)

• Electric Power Research Institute and U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research, “EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities,” EPRI 1011989 and NUREG/CR-6850, Electric Power Research Institute (EPRI), Palo Alto, CA and U.S. Nuclear Regulatory Commission, Washington, DC, 2005.

• Electric Power Research Institute and U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research, “Fire Probabilistic Risk Assessment Methods Enhancements: Supplement 1 to NUREG/CR-6850 and EPRI 1011989,” EPRI 1019259 and NUREG/CR-6850 Supplement 1, Electric Power Research Institute (EPRI), Palo Alto, CA and U.S. Nuclear Regulatory Commission, Washington, DC, 2009.

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Overview

Other References (cont.)

• M. Kazarians, N. Siu, and G. Apostolakis, “Fire risk analysis for nuclear power plants: methodological developments and applications, Risk Analysis, 5, 33-51, 1985.

• N. Siu, J.T. Chen, and E. Chelliah, “Research Needs in Fire Risk Assessment,” NUREG/CP-0162, Vol. 2, 25th Water Reactor Safety Information Meeting Bethesda, MD, October 20-22, 1997.

• U.S. Nuclear Regulatory Commission, “Perspectives Gained from the Individual Plant Examination of External Events (IPEEE) Program,” NUREG-1742, April 2002.

• Nuclear Energy Agency, “International Workshop on Fire PRA: Workshop Proceedings,” NEA/CSNI/R(2015)12, Boulogne-Billancourt, France, 2015. (Available from: http://www.oecd-nea.org/nsd/docs/indexcsni.html)

• B. McGrattan, et al., “Fire Protection and Fire Research Knowledge Management Digest, 2013,” NUREG/KM-0003, 2013.

• N. Siu, “Fire Risk Assessment for Nuclear Power Plants,” FPE 580R – Fire Risk Assessment and Policy, Worcester Polytechnic Institute, December 2, 2015. (ADAMS ML15301A832)

• N. Siu, “PSA Heterogeneity: Implications for Risk Aggregation,” IAEA Consultancy Meeting on Development of a Methodology for Aggregation of Various Risk Contributors for Nuclear Facilities,” International Atomic Energy Agency, Vienna, Austria, April 10-13, 2017. (ADAMS ML17093A744)

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Overview

Risk-Informed Regulations

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How it started…

• Browns Ferry Nuclear Power

Plant (3/22/75)

• Candle initiated cable tray fire;

water suppression delayed;

complicated shutdown

• Second-most challenging event

in U.S. nuclear power plant

operating history

• Spurred changes in requirements

and analysis

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8.5m 11.5m

3m

Adapted from NUREG-0050

Browns Ferry Fire

Browns Ferry (March 22, 1975)

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Browns Ferry Fire

Fire Protection After Browns Ferry

• Post-Browns Ferry deterministic fire

protection (10 CFR Part 50, App R)

– 3-hour fire barrier, OR

– 20 feet separation with detectors and

auto suppression, OR

– 1-hour fire barrier with detectors and auto

suppression

• Concerns

– Equivalence of protection methods:

what’s best?

– 20-foot criterion: how protective?

– Possible to make win-win trade-offs?

– License by exemption?

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From Cline, D.D., et al., “Investigation of Twenty-Foot

Separation Distance as a Fire Protection Method as Specified in

10 CFR 50, Appendix R,” NUREG/CR-3192, 1983.

Browns Ferry Fire

Professor George Apostolakis, UCLA(UCLA School of Engineering)

Early Fire PRAs

• Early cable spreading room analyses

– WASH-1400

– HTGR PRA

• NRC-sponsored, post-Browns Ferry

R&D at UCLA => fire PRA methodology

– Physical model for fire-induced damage

– Incorporation in PRA via competing

processes model (growth vs.

suppression)

• Used and refined in Zion and Indian

Point PRAs

• Framework and tools for subsequent

analyses (NUREG-1150, IPEEEs)

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Fire PRA/RIDM History

Early Results – Fire Can Be Important Or Even

Dominant Contributor to CDF

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Fire PRA/RIDM History

“Near Misses” – Empirical Support for Results

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Event Summary Description*Browns Ferry(BWR, 1975)

Multi-unit cable fire; multiple systems lost, spurious component and system

operations; makeup from CRD pump

Greifswald(VVER, 1975)

Electrical cable fire; station blackout (SBO), loss of all normal core cooling for 5

hours, loss of coolant through valve; recovered through low pressure pumps and

cross-tie with Unit 2

Beloyarsk (LWGR,

1978)

Turbine lube oil fire , collapsed turbine building roof, propagated into control

building, main control room (MCR) damage, secondary fires; extinguished in 22

hours; damage to multiple safety systems and instrumentation.

Armenia(VVER, 1982)

Electrical cable fire (multiple locations), smoke spread to Unit 1 MCR, secondary

explosions and fire; SBO (hose streams), loss of instrumentation and reactor

control; temporary cable from emergency diesel generator to high pressure pump

Chernobyl (RBMK,

1991)

Turbine failure and fire, turbine building roof collapsed; loss of generators, loss of

feedwater (direct and indirect causes); makeup from seal water supply

Narora(PHWR, 1993)

Turbine failure, explosion and fire, smoke forced abandonment of shared MCR;

SBO, loss of instrumentation; shutdown cooling pump energized 17 hours later

*See NUREG/CR-6738 (2001), IAEA-TECDOC-1421 (2004)

Fire PRA/RIDM History

Risk-Informed Fire Protection (“NFPA 805”)

• Difficulties with deterministic compliance

with Appendix R => exemptions

• Risk-informed approach

– Alternative method for regulatory compliance

– Additional benefits: improved understanding of

sources of fire risk,

• Risk-informed, performance-based fire

protection (10 CFR 50.48(c), NFPA 805)

– Voluntary alternative to Appendix R

– Deterministic and performance-based

elements

– Changes can be made without prior

approval; risk must be “acceptable”

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Fire PRA/RIDM History

“Making Sausage”

Standard and regulatory approach

development

• Consensus process

• Multiple stakeholders, diverse

views (incl. strong PRA critics)

• “Good enough” for immediate

problem

10 CFR 50.48(c)(3)

Fire PRA R&D

• Restarted in 1997

– Better understanding of fire risk

– Improved support of regulatory

activities

– Methods and tools

• Near- and long-term issues, e.g.,

– Multiple spurious operations

– Lessons from operational events

• “Fire risk requantification” task (to

assess impact of methodological

improvements) => guidance

development (joint with EPRI) to

support NFPA 805

• Major disruption: 9/1114

NUREG/CR-6850/EPRI TR1011989

Fire PRA/RIDM History

Fire R&D: The “Laundry List” (c. 1998)

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Fire PRA/RIDM History

Fire PRAs – More Recent Results

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Fire PRA/RIDM History

Fire PRAs – Risk Contributors

17From: K. Voelsing, “EPRI Fire PRA Research Plan,” U.S. Nuclear Regulatory Commission Regulatory

Information Conference, March 15, 2018.

Fire PRA/RIDM History

Recap: Fire PRA/RIDM in the U.S.

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1975 1980 19901985 1995 2000 20102005 2015

Bro

wn

s F

err

y f

ire

(WA

SH

-1400 a

naly

sis

)

Fire PRA R&D

IPEEEs

Industry

Full-Scope PRAs

NUREG-1150/RMIEP

NFPA 805 LARs

NFPA 805, 10 CFR 50.48(c),

RG 1.205, NEI 04-02,

EPRI 1011989/NUREG/CR-6850, …

Fire PRA/RIDM History

A “Heated Debate”

• Is fire PRA mature? Are the results overly conservative?

• Industry concerns– Expense of detailed analyses

– Realism of specific sub-models

– Flexibility in making plant changes

– Implications for other risk-informed applications

• NRC concerns– Technical basis for alternative

models

– Implications for other risk-informed applications

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Current Challenges

RG 1.174, Revision 3

Common View: The Need for Realism

• Excessive conservatism or optimism can

– Inappropriately focus decision maker attention

– Lead to wasteful or even problematic “solutions”

– Mask opportunities for other improvements

– Damage stakeholder confidence

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?

Current Challenges

Current Issues – An Example

• High Energy Arcing

Faults (HEAF) in

cabinets

• Operational events, e.g.,

– Maanshan (2001)

– Robinson (2010)

– Onagawa (2011)

• Potentially important

contributor to fire risk

• Multi-national

experimental program21

Current Challenges

Where are we now?

• Completed transitions to NFPA 805 (> 1/3 fleet)

• Use of fire PRA methods by international organizations

• Cooperative data collection and R&D to address some

issues

• Debates over appropriate R&D for others

• Debates over proper “aggregation” of results from

heterogeneous analyses

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Current Challenges

On “Aggregation”

• Heterogeneity sources in a practical PRA:

– Multiple technical disciplines

• Different states of knowledge

• Different views on what needs to be and what can be reasonably

modeled

• Different views on acceptable modeling approaches

• Different views on treatment of uncertainty

– Limited project resources

• Numerical results need to be provided in context

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Current Challenges

Comments

• Multiple technical cultures with varying/divergent views on appropriate use of risk information + need for expediency =>

– Compromise solutions that might not be “good enough” for other applications

– Different solutions for different technical domains (and technical cultures)

• Personal concern: myopic tactics can have short-term success but also social impacts that hurt fundamental, long-term acceptance (let alone support) of PRA and RIDM

– Sound-bite characterization of issues

– Goal-directed R&D (“reducing conservatism” vs. “improving realism”)

– Marginalization of stakeholders

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