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:
es that were unknown, or re veal additional characteristics of known tectonic struc tures. Generally, based on past licensing experience in the CEUS, the discovery of such features will not re quire a modification of the seismic sources provided in the LLNL and EPRI studies. However, initial evidence regarding a newly discovered tectonic structure in the CEUS is often equivocal with respect to activity, and additional detailed investigations are required. By means of these detailed investigations, and based on past licensing activities, previously unidentified tec tonic structures can usually be shown to be inactive or otherwise insignificant to the seismic design basis of the facility, and a modification of the seismic sources provided by the LLNL and EPRI studies will not be re quired. On the other hand, if the newly discovered fea tures are relatively young, possibly associated with earthquakes that were large and could impact the haz ard for the proposed facility, a modification may be required. Of particular concern is the possible existence of previously unknown, potentially active tectonic struc tures that could have moderately sized, but potentially damaging, near-field earthquakes or could cause sur face displacement. Also of concern is the presence of structures that could generate larger earthquakes within the region than previously estimated. Investigations to determine whether there is a pos sibility for permanent ground displacement are espe-' cially important in view of the provision to allow for a 1.165r38 combined licensing procedure under 10 CFR Part 52 as an alternative to the two-step procedure of the past (Construction Permit and Operating License). In the ~j past at numerous nuclear power plant sites, potentially significant faults were identified when excavations were made during the construction phase prior to the is suance of an operating license, and extensive additional investigations of those faults had to be carried out to properly