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:
for each POS. The model for each POS is adapted from the corresponding internal events PRA model to incorporate unique flood analysis aspects that are different from the internal events PRA model. The external flooding PRA model for each POS includes all applicable significant external flooding causes, initiating events, and external flooding-induced SSC failures, as well as significant non-seismic failures and human errors. All POSs should be evaluated for differences in the external flooding plant response analysis PRA analysis element. It is important that the walkdowns evaluate the differences between the different POSs that impact the plant response analysis. The characteristics and attributes needed to achieve the objectives of an external flood plant response analysis PRA analysis element are as follows: • The external flood PRA model for all POSs— o includes all significant external flood-caused initiating events, o includes other significant failures (both those that are caused by the flood and those that are random failures) that contribute to external flooding risk and radiological consequences, o is adapted from the internal events PRA model for all modeled POSs and radiological sources, o incorporates unique external flood analysis aspects that are different from the internal events PRA model, and o reflects the as-designed or as-to-be built and as-to-be operated or as-built and as-operated plant being analyzed. • Quantification of risk metrics for each POS integrates the following: o the external flooding hazard analysis, o the external flooding fragility analysis, and o the plant response logic analysis. • The analysis identifies and characterizes uncertainties. The external flooding PRA model reflects the as-built and as-operated plant or the as-designed or the as-to-be built and as-to-be operated plant, as applicable in each stage. Assumptions used in external flood plant response analysis (e.g., screening out external flood initiators and