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:
tives and the characteristics and attributes of the event sequence quantification 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 quantification analysis PRA element is to develop a frequency estimate of event sequences and event sequence families at any stage of the plant life cycle, while ensuring that all risk-significant contributors are represented and understood. This element should address all dependencies and demonstrate a complete understanding of PRA uncertainties and assumptions and their impacts on the PRA results. Event sequence quantification integrates the accident progression models and source term evaluation to estimate the frequency of radionuclide releases that can be expected following the accidents. The quantitative evaluation reflects the different magnitudes and timing of radionuclide releases. The characteristics and attributes needed to achieve the objectives of the event sequence quantification analysis are as follows: • The analysis integrates individual modeling items including the event sequences, system models, event progression phenomena, barrier failure modes, data, HRA elements, dependencies, and recovery actions, and accounts for all functional, physical, and human dependencies. • The event sequences are quantified using appropriate models and codes and a truncation limit sufficiently low to show convergence of the PRA results. RG 1.247, Page 44 • The analysis addresses the identification and elimination of circular logic, identification of mutually exclusive event combinations, the use of flag events and modules, and the use of system successes. • The analysis identifies the risk-significant contributors to the frequency of each risk-significant event sequence and event sequence family. • Uncertainties in the quantification results are characterized and quantified. C.1.3.16 Mechanistic Source Term