Seismic hazard analyses—a utility perspective

Abstract

Seismic hazard analyses represent a rational framework for the incorporation of new information and contending hypotheses such that the licensing process for nuclear plants or other critical facilities can be stabilized. Stabilized in the context that the present licensing process under Appendix A is sensitive to changes of official position (Charleston earthquake issue) or the occurrence of future earthquakes. Results of seismic hazard analyses can be used in several ways. For example, results can be used for: 1. (1) Resolution of the Charleston earthquake issue. 2. (2) Quantification of a plant's seismic design basis. 3. (3) Probabilistic seismic risk assessments. 4. (4) Evaluation of the stability of the licensing basis of existing plants. 5. (5) Licensing of future plants. Insights with respect to these issues are directly handled using probabilistic methods. For some of these issues, the relative change in seismic hazard, based on the sensitivity of the results to variation of an input parameter, such as upper bound magnitude, is sufficient to give decision-makers substantial insight into the importance of an issue. For other issues, such as probabilistic risk assessments, absolute measures of seismic hazard are needed to quantify the risk due to earthquakes. Lastly, for issues such as evaluating the stability of the licensing process, relative measures are informative, yet must not be viewed in isolation, and should be framed within the context of absolute probabilities.