Precursors to potential severe core damage applications, 1991. A status report, main report and Appendix A

Twenty-seven operational events with conditional probabilities of subsequent severe core damage of 1.0 x 10-6 or higher occurring at commercial light-water reactors during 1991 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 1969-1981 and 1984-1990 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 mnk precursor events, and (4) the plant models used in the analysis process.