Document: NRC Regulatory Guide
Document ID: 8a2332d3-66ca-40af-84e1-507db8b26559
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:
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 reactor, and the seismic hazard analysis discussed above should be applied to that representative or bounding site. Various plant POSs are expected to be evaluated using the same external flood hazard analysis. The characteristics and attributes RG 1.247, Page 40 needed to achieve the objectives of an external flood hazard analysis PRA analysis element are as follows: • Probabilistic flood hazard analysis— o results in frequency of external floods at the site, o is based on site-specific data or data for a justified representative or bounding site, as applicable, and o reflects recent information. • Uncertainties in the models and parameter values— o are properly accounted for, o are fully propagated, and o allow estimation of the mean hazard curve. The objective of an external flood fragility analysis is to perform an evaluation to estimate plant-specific, realistic flood fragilities for those SSCs (or their combination) in each POS whose failure contributes to risk from an external flood hazard. It is likely that a specific site would not be identified during the design phase. In addition, actual current configuration of SSCs in the plant and its confirmation by a detailed physical walkdown of the plant may not be feasible during the design and construction phases. In such cases, assumptions used in the external flood fragility analysis PRA analysis element (e.g., location of flood barriers, SSC configuration and design characteristics) should be clearly identified, documented, and tracked to ensure their continued validity across different stages. Such assumptions include those that are identified or included in virtual layouts of the plant. All POSs should be evaluated for differences in the external flood fragility analysis PRA analysis element. It is