Document: NRC Regulatory Guide
Document ID: cfc61809-5745-460f-8a26-13c168659924
Document Type: regulatory_guide
Title: Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motion
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740084.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.165
CFR Part: 
CFR Title: 

Content:
ypotheses can also be used to evaluate the sensi tivity of the hazard to the uncertainties in the significant parameters and to identify the relative contribution of each seismic source to the hazard. Reference 9 provides guidance for conducting a PSHA. The following steps describe a procedure that is ac ceptable to the NRC staff for performing a PSHA. The 1.165-6 .- details of the calculational aspects of deriving control ling earthquakes from the PSHA are included in Ap pendix C. / 1. Perform regional and site geological, seismologi cal, and geophysical investigations in accordance with Regulatory Position I and Appendix D. 2. For CEUS sites, perform an evaluation of LLNL or EPRI seismic sources in accordance with Appendix E to determine whether they are consistent with the site-specific data gathered in Step 1 or require updating. The PSHAshould only be updated if the new information indi cates that the current version significantly un derestimates the hazard and there is a strong technical basis that supports such a revision. It may be possible to justify a lower hazard esti mate with an exceptionally strong technical ba sis. However, it is expected that large uncertain ties in estimating seismic hazard in the CEUS will continue to exist in the future, and substan tial delays in the licensing process will result in trying to justify a lower value with respect to a specific site. For these reasons the NRC staff discourages efforts to justify a lower hazard es timate. In most cases, limited-scope sensitivity studies should be sufficient to demonstrate that the existing data base in the PSHA envelops the findings from site-specific investigations. In general, significant revisions to the LLNL and EPRI data base are to be undertaken only peri odically (every 10 years), or when there is an important new finding or occurrence. An over all revision of the data base would also require a reexamination of the acceptability of the refer ence probability discussed in