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:
and without the need for a detailed PRA model. Regulatory Position C.1.3.11 provides additional guidance on screening and conservative analyses that can be performed to this end. A hazard that is not categorized under the internal events, internal flood, internal fire, seismic, high wind, or external flood hazards groups is commonly referred to as an “other hazard.” Regulatory Position C.1.3.14 provides additional guidance on the modeling of such hazards. An “other hazards” PRA is performed when a screening analysis cannot screen out other hazards. Appendix B to this RG provides a listing and general description of the internal and external hazards that should be considered during the development of a PRA. Initiating events are perturbations to the steady-state operation of the plant that challenge plant control and safety systems and could lead to plant damage states of interest, radioactivity release, or both. They also include failures of plant control and safety systems that may cause perturbation to the steady-state operation of the plant that could lead to these same outcomes. Initiating events may be caused by internal hazards such as equipment failure, operator actions, or a flood or fire internal to the plant or by external hazards such as an earthquake, external flood, or high wind. The risk perspective is based on a consideration of total risk, which includes risk contributions from both internal and external hazards. C.1.2 Level of Detail of a Probabilistic Risk Assessment The level of detail of a PRA is defined in terms of the resolution of the modeling used to represent the behavior and operations of the plant. A minimum level of detail is necessary to ensure that RG 1.247, Page 18 the impacts of designed-in dependencies (e.g., support system dependencies, functional dependencies, and dependencies on operator actions) are correctly represented. This minimum level of detail is implicit in the elements making up the PRA and their associated