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:
dequate for all hazard groups evaluated within the scope of the PRA. • POS definitions should include consideration of changing plant conditions that may impair or change the effectiveness of hazard barriers, affect propagation pathways, or modify fragilities of SSCs to ensure the appropriateness of the POS definition. • LPSD types of POSs that are subsumed into each other are shown to be represented by the characteristics of the subsuming group. • The duration and number of entries into each POS are determined. • The sources of model uncertainty related to POS definitions and screening are identified and characterized. • The key attributes of the plant conditions for each POS should be clearly documented in a format (e.g., table or chart) to facilitate understanding of the NLWR PRA results by an independent reviewer. C.1.3.2 Initiating Event Analysis Probabilistic Risk Assessment Element This section identifies the objectives and the characteristics and attributes of the initiating event analysis PRA element for an NLWR PRA that addresses all radiological sources, all hazards, all POSs, and all levels of PRA analysis. The objectives of the initiating event analysis are to identify and characterize events that challenge plant operation during any POSs and that require successful mitigation by plant equipment and personnel to prevent or to mitigate a release of radiological material. Events that have occurred at the plant and those that have a reasonable probability of occurring should be identified and characterized. An understanding of the nature of events will facilitate a grouping of events that allows for managing the many events that can potentially challenge the plant. Initiating event groups should be defined in terms of similar system impacts and plant responses, as based on the related success criteria. The characteristics and attributes needed to achieve the objectives of an initiating event analysis are as follows: • The analysis includes