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:
to a sequence, resulting in related components being ranked as low risk contributors. Furthermore, it is not desirable for the categorization of SSCs to be impacted by recovery actions that sometimes are only modeled for the dominant scenarios. Sensitivity analyses can be used to show how the SSC categorization would change if recovery actions were removed. Reviewers should ensure that the categorization has not been unduly impacted by the modeling of recovery actions. Truncation limit: Reviewers should verify that the licensee set the sequence truncation limits low enough so that the truncated set of minimal cutsets or scenarios contains the significant contributors and their logical combinations for the application in question. Depending on the level of PRA detail (module level, component level, or piece-part level), this may translate into a truncation limit from 1012 to 10.8 per reactor year. Multiple component considerations: As previously discussed, importance measures are typically evaluated on the basis of individual SSCs or human actions. One potential concern that arises from this practice is that single-event importance measures have the potential to dismiss all elements of a system or group, despite the system or group having a high importance when taken as a whole. (Conversely, there may be grounds for screening out groups of SSCs, owing to the unimportance of the systems of which they are elements.) * Two potential approaches are used to address the multiple component issue. The first is to define suitable measures of system or group importance. The second is to choose appropriate criteria for categorization based on component-level importance measures. In SRP 19-C3 both cases, it will be necessary for the licensee to demonstrate that the cumulative impact of the change has been adequately addressed. While there are no widely accepted definitions of system or group importance measures, it is likely that some licensees will develop new system or group