United States Nuclear Regulatory Commission - Protecting People and the Environment

Methodology for Low Power/Shutdown Fire PRA – Draft Report for Comment (NUREG/CR-7114)

This NUREG-series publication was issued for public comment, and the comment period is now closed.

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Publication Information

Manuscript Completed: December 2011
Date Published: December 2011

Prepared by:
Steven P. Nowlen, Tara Olivier

Sandia National Laboratories
Risk and Reliability Analysis Department
P.O. Box 5800
Albuquerque, NM 87185

Hugh Woods, NRC Project Manager

NRC Job Code N6592

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

This document presents a probabilistic risk assessment (PRA) method for quantitatively analyzing fire risk in commercial nuclear power plants during low power and shutdown (LPSD) conditions, including the determination of core damage frequency (CDF) and large early release frequency (LERF). Future updates will be made to this document as experience is gained with LPSD quantitative risk analyses of both internal events and fires.

This LPSD fire PRA method is intended to be used in combination with an at-power fire PRA performed using the method documented in Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) publication NUREG/CR-6850 and Electric Power Research Institute (EPRI) publication TR-1011989, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities." This LPSD fire PRA method directly parallels that at-power fire PRA method with respect to the structure and objectives of its technical analysis tasks, addressing those aspects of the at-power fire PRA that require unique treatment in the context of low-power or shutdown conditions. This LPSD fire method also requires an LPSD internal events PRA; that is, both the at-power fire PRA and the LPSD internal events PRA are needed as starting points for conducting an LPSD fire PRA using the method described in this document.

The NRC developed this LPSD fire quantitative risk method so analysts would be able to use a quantitative approach for estimating fire risk during LPSD conditions. While current LPSD safety analyses for fires under National Fire Protection Association Standard 805 (NFPA 805) focus on qualitative, defense-in-depth methods, it is envisioned that applications in the future may evolve to be more quantitative. At present, this method can provide an alternative for the analysis of LPSD fire risk in situations where qualitative methods are not appropriate, or where activities such as planning for an outage could benefit from risk reduction insights that could be gained from a quantitative analysis. It could also prove essential for the analysis of situations involving unusual, complex plant operating states (POSs).

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