Document: NRC Regulatory Guide
Document ID: cde52d5a-adf9-49be-9d1f-59449dfca895
Document Type: regulatory_guide
Title: TRIAL - Acceptability of Probabilistic Risk Assessment Results for Non-Light Water Reactor Risk-Informed Activities
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2123/ML21235A008.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.247
CFR Part: 
CFR Title: 

Content:
fication), o analytical approaches using plant- and location-specific seismic demand information, and o walkdowns or the evaluation of available data and findings of investigations of the plant design and operations information for plants that have not started construction or do not have enough construction complete to allow physical walkdowns. • Plant walkdowns (or the evaluation of available data and findings of investigations of the plant design and operations information for plants that have not started construction or do not have enough construction complete to perform physical walkdowns) are performed for all applicable POSs and include but are not limited to walkdowns of anchorage, lateral seismic support and potential seismic system interactions. • Uncertainties related to the seismic fragility are identified and characterized. The objective of the seismic plant response analysis is to determine the plant response to and radiological consequences of a seismic event for each POS by combining the plant logic model for each POS with the corresponding component fragilities and the seismic hazard estimates. Usually, the analysis is based on the internal events PRA model for each POS. Unique aspects of the seismic event are incorporated by adding basic events for seismic-induced failures for each POS to the corresponding internal events PRA model. Some portions of the internal events PRA model for a POS that do not apply or that can be screened out based on the impact on the base seismic PRA should be eliminated. For example, near-term recovery of offsite power is highly unlikely after a large earthquake, and therefore, portions of the internal events model related to offsite power recovery can often be eliminated. The seismic PRA model for each POS includes all applicable significant seismic causes, initiating events, and seismic-induced SSC failures, as well as significant non-seismic failures and human errors. All POSs should be evaluated for differences in