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:
bability increasing as a result of proposed changes, licensee actions to ensure operator performance at the level credited in the risk analysis should also be a part of the change request. Ensure that appropriate justification is provided when the licensee takes credit for post-accident recovery of failed components (repair or other non-proceduralized manual actions, such as manually forcing stuck valves to open). Reviewers should also ascertain whether the identified recovery action is an obvious, feasible (given the time and physical constraints), and supportable by plant programs such as training. Ensure that the licensee assessed whether the conditions under which the human actions are to be performed have changed significantly so that the HEP should be modified. Reviewers should also be aware that the impact of the change can be obscured if the accident sequences which do not contain affected SSCs are artificially increased in value by HEPs that are too large. These cases will impact applications involving risk categorization by lowering the relative contribution of the affected SSCs. An understanding of these effects can be obtained from sensitivity analyses performed by removing the pertinent HEPs or by using more realistic values for the HEPs. Another consideration associated with the potential masking of important SSCs is that the SSCs might not be included in the model used to perform the evaluation of risk. This can happen in several ways: SRP 19-A17 Cutsets or scenarios containing the SSCs may be truncated because HEPs in the same cutset or scenario are too low. Such truncation should only be a concern if the logic model was not re-solved to determine the change in risk (for example, in applications that depend on SSC risk ranking using a pre-solved equation). The preferred resolution to this would be a request for re-solution with the appropriate changes made to all affected SSCs. Section A.9 of this SRP chapter discusses this in more detail. SSCs may