Implementation of the SSHAC Guidelines for Level 3 and 4 PSHAs - Experience Gained from Actual Applications

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. Introduction In April 1997, after four years of deliberations, the Senior Seismic Hazard Analysis Committee released its report " Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts " through the U.S. Nuclear Regulatory Commission as NUREG/CR– 6372, hereafter SSHAC (1997). Known informally ever since as the " SSHAC Guidelines, " SSHAC (1997) addresses why and how multiple expert opinions–and the intrinsic uncertainties that attend them–should be used in Probabilistic Seismic Hazard Analyses (PSHA) for critical facilities such as commercial nuclear power plants. Implementation of the SSHAC Guidelines and for Updating PSHAs. " The NRC was interested in understanding and documenting lessons learned from recent PSHAs conducted at the higher SSHAC Levels (3 and 4) and in gaining input from the seismic community for updating PSHAs as new information became available. This study increased in importance in anticipation of new applications for nuclear power facilities at both existing and new sites. The intent of this project was not to replace 2 the SSHAC Guidelines but to supplement them with the experience gained from putting the SSHAC Guidelines to work in practical applications. During the course of this project, we also learned that updating PSHAs for existing nuclear power facilities involves very different issues from the implementation of the SSHAC Guidelines for new facilities. As such, we report our findings and recommendations from this study in two separate documents, this being the first. The SSHAC Guidelines were written without regard to whether the PSHAs to which they would be applied were site-specific or regional in scope. Most of the experience gained to date from high-level SSHAC studies has been for site-specific cases, although three ongoing (as of this writing) studies are regional in scope. Updating existing PSHAs will depend more critically on the differences between site-specific and regional studies, and we will also address these differences in more detail in the companion report. attended by approximately 40 scientists and engineers familiar with hazard studies for nuclear facilities. This company included four of the authors of SSHAC (1997) and four other experts whose contributions to this document are mentioned in …