Precursors to potential severe core damage accidents: 1987

Forty-eight operational events ranking 1.0 times 10-6 or higher and 16 lesser events, reported in 3490 licensee event reports (LERs) and revisions and occurring at commercial light-water reactors during 1987, are considered to be precursors to potential severe core damage. These are described along with associated significance estimates, categorization, and subsequent analyses. This study is a continuation of earlier work, which evaluated the 1969--1981 and 1984--1986 events. The report discusses (1) the general rationale for this study, (2) the selection and documentation of events as precursors, (3) the estimation and use of conditional probabilities of subsequent severe core damage to rank precursor events, and (4) the plant models used in the evaluation process