United States Nuclear Regulatory Commission - Protecting People and the Environment

Precursors to Potential Severe Core Damage Accidents: 1998 A Status Report (NUREG/CR-4674, Volume 27)

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Publication Information

Manuscript Completed: June 2000
Date Published: July 2000

Prepared by:
R.J. Belles, J.W. Cletcher, D.A. Copinger, B.W. Dolan1,
J.W. Minarick1, M.D. Muhlheim, P.D. O'Reilly2, S. Weerakkody2,
H. Hamzehee2

Oak Ridge National Laboratory
Managed by UT-Battelle, LLC
Oak Ridge, TN 37831-6285

1 Science Appicatlons Internmatiomal Corporation
Oak Ridge, TN 37831

2 U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared for:
Division of Safety Analysis Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code B0435

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Abstract

This report describes the nine operational events in 1998 that affected eight commercial light-water reactors (LWRs) and that are considered to be precursors to potential severe core damage accidents. All these events had conditional probabilities of subsequent severe core damage greater than or equal to 1.0 x 10-6. These events were identified by first computer-screening the 1998 licensee event reports from commercial LWRs to identify those events that could be precursors. Candidate precursors were selected and evaluated in a process similar to that used in previous assessments. Selected events underwent an engineering evaluation to identify, analyze, and document the precursors. Other events designated by the Nuclear Regulatory Commission (NRC) also underwent a similar evaluation. Finally, documented precursors were submitted for review by licensees and NRC headquarters to ensure that the plant design and its response to the precursor were correctly characterized. This study is a continuation of earlier work that evaluated 1969–1997 events. The report discusses the general rationale for this study, the selection and documentation of events as precursors, and the estimation of conditional probabilities of subsequent severe core damage for the events.

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