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:
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 sufficiently detailed identification and characterization of initiating events. • Initiating events are grouped so that events in the same group have similar requirements for mitigation. • Any individual or grouped initiating events are properly screened. • Initiating event frequency is quantified. • The sources of model uncertainty related to initiating event analysis PRA element are identified. • The initiating event analysis PRA element is fully documented to provide traceability of the work. RG 1.247, Page 21 C.1.3.3 Event Sequence Analysis Probabilistic Risk Assessment Element This section identifies the objectives and the characteristics and attributes of the event sequence analysis PRA element for an NLWR PRA that addresses all radiological sources, all hazards, all POSs, and all levels of PRA analysis. The objective of the event sequence analysis PRA element is to model chronologically (to the extent practical) the different possible progressions of events (i.e., event sequences) that can occur from the start of the initiating event to either successful mitigation or release. The event sequences account for the systems that are used (and available) and operator actions performed to mitigate the initiator based on the defined success criteria and plant operating procedures (e.g., plant emergency and abnormal operating procedures) and training. The availability of a system includes consideration of the functional, phenomenological, and operational dependencies and interfaces between the various systems and operator actions during the accident progression. The characteristics and attributes needed to achieve the objectives of an event sequence analysis PRA element are as follows: • The barriers to radionuclide release and the safety functions necessary