Document: NRC Regulatory Guide
Document ID: 22ccfd5e-c5d8-4615-a02c-32369aa9f533
Document Type: regulatory_guide
Title: Acceptability of Probabilistic Risk Assessment Results for Risk-Informed Activities (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1930/ML19308B636.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.200
CFR Part: 
CFR Title: 

Content:
nt-specific based on actual current conditions of the SSCs in the plant, as confirmed through a detailed walkdown of the plant. The fragilities of all the systems modeled in the accident sequences are included. DG-1362, Page 25 Seismic Plant Response Analysis calculates the frequencies of severe core damage and radioactive release to the environment by combining the plant logic model with component fragilities and seismic hazard estimates. The analysis is usually carried out by using the internal events PRA model as the foundation and adding basic events for seismically-induced failures to the internal events PRA model. Some portions of the internal events PRA model that do not apply or that can be screened out based on the impact on the base seismic PRA should be eliminated. For example, 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. Further screening of out of low-probability, non-seismic failures and human-error events may also be possible, although significant non-seismic failures and human errors must be included. Therefore, the seismic PRA model is usually adapted from the internal events, at-power PRA model to incorporate unique seismic related aspects that are different from the at- power, internal events PRA model. In some cases, instead of starting with the internal events model and adapting it, a special seismic model is created from scratch. In this case it is especially important to check for consistency with the internal events model regarding plant response and the cause-effect relationships of the failures. In any case, the seismic PRA model includes all significant seismic causes initiating events and seismic induced SSC failures, as well as significant non-seismic failures and human errors. The model reflects the as-built and as-operated plant. In meeting the technical characteristics and attributes for the seismic