Document: NUREG-0800
Document ID: 7916b088-fb90-4163-84fe-027bd315bcc5
Document Type: srp
Title: REVIEW OF RISK INFORMATION USED TO SUPPORT PERMANENT PLANT-
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0717/ML071700658.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.2
CFR Part: 
CFR Title: 

Content:
that could result in multiple failures of SSCs. c. Evaluation Findings Reviewers should verify that information provided and review activities conducted support the following conclusion: Dependencies between system and operator interactions have been properly accounted for in the evaluation of the proposed change. Where appropriate, these dependencies have been included in the accident progression models (event trees) and the system analysis models (fault trees). A.5 Determination of Success Criteria a. Areas of Review Guidance in the PRA policy statement and in Regulatory Guide 1.174 stipulates that realistic analysis should be used in PRA implementation. The following discussion is intended to sort out what is meant by "realistic" analysis of success criteria by reference to SAR analysis. In order to fulfill its intended purpose, SAR analysis 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 initiating 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 codes 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