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:
frequency of exceedance for selected ground motion parameters during a specified time interval using a site-specific probabilistic hazard analysis that incorporates the available recent site-specific information and uses up- to-date databases. The analysis involves identification of earthquake sources, evaluation of the regional earthquake history, and an estimate of the intensity of the earthquake-induced ground motion at the site. At most sites the objective is to estimate the probability or frequency of exceeding different levels of vibratory ground motion. However, in some cases other seismic hazards are included, such as fault displacement, soil liquefaction, soil settlement, and earthquake-induced external flood. For all the various hazards the objective is to estimate the probability or frequency of the hazard as a function of its intensity. The complexity of the hazard analysis depends on the complexity of the seismic situation at the site, as well as the ultimate intended use of the seismic PRA. Where no prior study exists, the site-specific probabilistic seismic hazard should be generated. However, in many cases an existing study can be used to develop a site-specific probabilistic seismic hazard. In a probabilistic seismic hazard analysis, an essential part of the methodology is the consideration of both aleatory and epistemic uncertainties, and typically results in generating a set of hazard curves, defined at specified fractile (confidence) levels and a mean hazard curve. Seismic Fragility Analysis estimates the conditional probability of SSC failures at a given value of a seismic motion parameter such as peak ground acceleration, peak spectral acceleration, floor spectral acceleration, etc. Seismic fragilities used in a seismic PRA are realistic and plant-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