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:
is warranted. • Although unmodeled, the item already receives and will continue to receive programmatic attention commensurate with its significance. In cases where reduced commitments are proposed, adequate justification is provided for this reduction. 19.2-72 June 2007 • The item does not currently receive sufficient programmatic attention and may be subject to tighter controls. Reviewers should verify that the safety significance of SSCs not modeled in the PRA (but affected by the proposed application) are appropriately characterized and justified. Addressing Limitations of the Risk Analysis One objective of the integrated decisionmaking process is to overcome certain limitations of the PRA. However, this does not include substituting the analyst's judgment for essential PRA results. One reason for developing PRA models is that the complexity of many facilities makes judgment difficult in many contexts. Generally, if the PRA highlights a plant vulnerability, this should be taken seriously and should not be discounted on the basis of judgment. If the analyst can show that the PRA representation of a vulnerability is invalid, then the PRA should be modified, and the licensee should work with the results of the revised PRA. To address the issue of credit for unmodeled systems that would change a PRA result, the preferred method is to alter the PRA to take the credit. Reviewers should be aware that cases may potentially arise in which credit for an unmodeled system would be seriously complicated by issues of shared support systems, environmental conditions, or other factors such as spatial interaction issues or operator interaction dependencies. To address the issue of making decisions about SSCs that might influence plant response in unmodeled modes or to unmodeled initiators, the acceptable approach is to proceed on the basis of a structured representation of plant response that shows at least qualitatively the initiating events that may pertain, the systems