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:
RA model, which is modified to include the impact of the identified flood scenarios in terms of causing initiating events and failing equipment used to respond to initiating events. The quantification task specific to internal floods is RG 1.247, Page 25 similar to that for the internal events. Because of its dependence on the internal events model, the internal flood PRA incorporates the elements of Regulatory Positions C.1.3.1 through C.1.3.7 of this RG, as necessary. The internal flood PRA 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; internal flood-induced failure probability of structures, systems, and components (SSCs); the plant response; or a combination of these three as compared to at-power-types of POSs. The objective of internal flood area partitioning is to divide the plant into flood areas that are used as the basis for the analysis. Flood areas are defined on the basis of physical barriers, mitigation features, and propagation pathways. All POSs should be evaluated for differences in the internal flood area partitioning analysis element. The differences in the POSs may impact the flood areas that are used. The characteristics and attributes needed to achieve the objectives of an internal flood area partitioning are as follows: • Flood areas are defined based on plant features that can restrict a flood. • Area definitions are verified through plant walkdowns or by evaluating available data and findings of investigations of the plant design and operations information for plants that have not started construction or do not have enough construction complete to allow physical walkdowns. • Flood areas are based on the physical barriers, mitigation features, and propagation pathways for all POSs. • Sources of