Document: NUREG-0800
Document ID: e32f0820-4e33-476e-aa36-4ca8c2c64af0
Document Type: srp
Title: Use of Probabilistic Risk Assessment in Plant-Specific, Risk-Informed Decisionmaking:
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0119/ML011940192.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.0
CFR Part: 
CFR Title: 

Content:
lysis is ordinarily based on a set of assumptions containing :significant embedded conservatisms. SAR analysis also reflects a postulated single active failure, in addition to whatever event initiated the sequence. When an SAR analysis shows a successful outcome, there is good reason to believe that (apart from beyond-single-failure scenarios) the system will meet or exceed performance requirements for the initieting event considered. Applying the SAR mission success criterion in a PRA would be conservative, in the sense that the probability of failure to meet this performance standard would be greater than probability of failure to meet a more realistic performance standard. However, re-analyzing event sequences with conventional SAR tools would be too burdensome to apply to the large number of scenarios that are defined in the course of a PRA. In addition, the rather specialized computer coces used in SAR analysis may not be appropriate in beyond-single-failure scenarios. Traditionally, development of mission success analyses in PRAs has ranged from the use of faster running models that might not have the same level of quality assurance as the conventional SAR tools, to the extrapolation of results from analyses performed on similar plants. In order to satisfy the Commission's guideline, then, reviewers should find that the licensee has not distorted the PRA insights by using a systematically conservative bias in mission success criteria, and that mission success criteria used to justify changes to the plant's design or operations have a sound technical basis. b. Review Guidance and Procedures When it is determined that the results and conclusions of a risk-informed application are especially sensitive to the choice of mission success criteria, or if the modeling is particularly controversial, reviewers should evaluate the relevant success criteria and the basis for each. If the basis is analytical, ii: may be appropriate to evaluate of the code and the input data