Precursors to potential severe core damage accidents: 1993, A status report. Volume 19: Main report and appendices A--D

Sixteen operational events that affected sixteen commercial light-water reactors during 1993 and that are considered to be precursors to potential severe core damage are described. 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 1993 licensee event reports from commercial light-water reactors to identify those that could potentially be precursors. Candidate precursors were then selected and evaluated in a process similar to that used in previous assessments. Selected events underwent engineering evaluated that identified, analyzed, and documented 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 and regional offices to ensure that plant design and its response to the precursor were correctly characterized. This study is a continuation of earlier work, which evaluated 1969--1981 and 1984--1992 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 events. This document is bound in two volumes: Volume 19 contains the main report and Appendixes A--D; Volume 20 contains Appendixes E and F. Contents include: Selection criteria and quantification and results; Appendix A: Precursors; Appendix B: Containment-related events; Appendix C: ''Interesting'' events; and Appendix D: Potentially significant events considered impractical to analyze