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:
e types of external flood phenomena that should be considered in the analysis are dependent on the site. Both natural phenomena, such as river or lake flooding, ocean flooding from high tides or storm surges, unusually high precipitation, tsunamis, and seiches, as well as human-caused events, such as failures of dams, levees, and dikes, are considered. Because of its dependence on the internal events model, the external flood PRA incorporates the elements of Regulatory Positions C.1.3.1 through C.1.3.7 of this RG, as necessary. The analysis of how the flood pathways and water levels cause the failure of SSCs following ingress into the plant structures is similar to the analysis in the internal flood PRA. The types of PRA analysis elements for an external flood PRA are similar to those for an internal flood PRA and a seismic PRA. The external flood PRAs for at-power and LPSD types of POSs are similar in many ways, differing primarily in plant configuration, including radioactive or hazardous material inventory distribution, or both, and temporary features. These differences can manifest themselves in the flood pathways and water levels, external flood-induced failure probability of SSCs, or the plant response for the LPSD types of POSs as compared to at-power types of POSs. The objective of an external flood hazard analysis is to estimate the frequency of external floods at the site using a site-specific probabilistic hazard analysis that incorporates the available recent site-specific information and uses up-to-date databases. Uncertainties in the models and parameter values are properly accounted for and fully propagated to allow the derivation of a mean hazard curve from the family of hazard curves obtained. It is likely that a specific site would not be identified during the design phase. In such a case, a representative or bounding site can be identified with justification that the site is either representative of or bounding for the anticipated sites for the