GENERAL COMMENTS

The Panel believes that the draft report is a basis for a useful final product that has the potential to advance the process of Probabilistic Seismic Hazard Analysis (PSHA). However, the Panel feels that the introduction to the report must be expanded to make clear the purpose and scope of the report, and specifically to state what the report is not. As it stands, the report implies that the methodology is applicable to a broader range of facilities than can be justified. The full range of alternative approaches is not discussed, let alone taken into account.

From the discussions, it appears that there may be a conflict between the expressed needs of the USNRC for a single unified, fully prescribed regulatory method of seismic hazard analysis (SHA) and the attempt by SSHAC to produce a general consensus methodology. The USNRC wants a prescribed procedure that is based on what has been learned from past PSHA experiences. The USNRC recognizes that the way in which input from experts was obtained is a main reason for the discrepencies between the analyses made by Lawrence Livermore and EPRI.

The Panel recognizes the strengths of the report and the significant contributions it offers to PSHA. As applied to nuclear regulations the SSHAC report breaks new ground in its discussion of the Technical Integrator (TI)/Technical Facilitator Integrator (TFI) approaches. However, as discussed in detail below, the presentation of these ideas needs to be made more clear to eliminate some apparent contradictions and advise the users of the report when the full TFI treatment is called for. The TI/TFI approach has the potential to overcome some aspects of past PSHA applications that have led to objections by critics of the whole process.

Because the focus of the report is on process for PSHA, rather than on the underlying earth science, the detailed attention to the treatment of uncertainty is appropriate. However, as discussed below, the motivation for this careful treatment of uncertainty and the way in which the results will be applied are not made clear to the potential user.

Again without yet having the benefit of full discussion of the subject, the Panel feels that the recommendation that behavioral aggregation of expert input be employed is sound, because mechanical aggregation algorithms, if used as “black boxes,” may lead to poor results.



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