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
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Content:
importance measures, and should provide qualitative information (e.g., minimal cutsets) adequate to support defense-in-depth findings. • There should be an inventory of plant response capability for probabilistically significant operating modes and initiating event categories (internal, external, flood, fire, seismic, etc.). Given a full-scope Level 2 PRA, this requirement could be satisfied by an inventory of event tree success paths, with an indication of the mission success criteria, systems, and SSCs involved in each path. Lacking a full-scope Level 2 PRA, surrogate information should be developed for unanalyzed areas, along the lines described in Subsection III.2.2.2 of this SRP section. This requirement is necessary in order to show the safety functions performed by SSCs (or other plant elements) affected by the application. 19.2-71 June 2007 • Causal models (determination of cause-and-effect relationships) should be developed to support an evaluation (qualitative or quantitative) of the change in risk as a function of the application. This is necessary in order to relate the application to actual risk indices. Documentation of inputs to the decisionmaking panel should be part of the process. Reviewers should verify the scope and depth of the information base, especially information supplied regarding modes and/or classes of initiators unanalyzed in the PRA. Treatment of SSCs Not Modeled in the PRA PRAs do not model all SSCs involved in performance of safety functions for various reasons. However, this should not imply that unmodeled SSCs are not important in terms of contributions to plant risk. For example, SSCs are omitted in some cases because the analysts take credit for programmatic activities that ensure a low failure frequency for that item or a short fault exposure time in the event that it does fail. In such cases, even though the PRA results will not reflect the SSC at all, it would be inappropriate to conclude that the programmatic activity is