United States Nuclear Regulatory Commission - Protecting People and the Environment

A Framework for Low Power/Shutdown Fire PRA – Final Report (NUREG/CR-7114)

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Publication Information

Manuscript Completed: May 2013
Date Published: September 2013

Prepared by:
Steven P. Nowlen, Tara Olivier, Jeff LaChance

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

Felix Gonzalez, 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) framework 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). It is expected that 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 framework 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 framework 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 framework also requires a 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 a LPSD fire PRA using the framework described in this document.

The NRC developed this LPSD fire quantitative risk framework as a first step in providing analysts with the methods needed to support 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 framework 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). The framework has been exercised via a tabletop involving two volunteer power plants, but a full implementation of the methods described here has not yet been undertaken. The document also serves as a “gap analysis” highlighting areas of technical challenge that will likely be encountered in an actual implementation and identifying methodology development needs to fill out the framework into a full methodology.

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