USE OF SEISMIC PRA FOR RISK-INFORMED DECISION MAKING BY UTILITIES AND REGULATORY AGENCIES

摘要

The methodology for seismic PRA (SPRA) has existed for over three decades, over which time it has evolved and matured, like the rest of PRA. It has been applied at several dozen nuclear power plants worldwide. SPRA has been used to support risk-informed decision-making to upgrade the safety of existing plants, to help prioritize which proposed backfits are most urgent, to help regulatory agencies like he USNRC and international agencies like the IAEA to develop regulations and regulatory guidance related to seismic risk, to support the prioritization of safety research projects, and to develop insights into the overall seismic risk from an individual plant and from an entire fleet of plants. In this latter role, it has been the principal vehicle for informing decision-makers and the general public about the risk from earthquakes at a typical nuclear plant. What emerges from the ensemble of SPRAs is that typically the seismic part of the overall reactor risk is a major contributor, sometimes dominant, almost always important, although sometimes negligible. However, seismic PRA is subject to a major misconception on the part of some PRA analysts who can be heard continuing to profess the view that SPRA is not mature enough for routine use for risk-informed applications. This view is inconsistent with the current status of the SPRA methodology and its uses in regulatory and plant-specific applications. This paper describes the evolution of the SPRA methodology and its components, and provides examples of some specific applications.