Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
CFR Part: 
CFR Title: 

Content:
c events used in the fault tree and event tree models. This yields a list of events that did not make it pass the truncation process. Documentation should be available to enable reviewers to determine the reason truncated events are not important to risk. Finally, in PRA models where common cause failures and human dependencies are incorporated at the sequence level after a truncated set of minimal cutsets has been obtained, reviewers should verify that the truncation criteria used in the PRA do not lead to cutsets involving application- specific components being truncated that could be important if common cause failures or human dependencies are considered. c. Evaluation Findings Reviewers should verify that the information provided and review activities conducted support the following conclusions: • The change is appropriately modeled and is properly quantified. • The licensee has satisfactorily established that conclusions are not adversely affected by truncation either because (i) the change in risk from the application was calculated by the requantification of the base model, or (ii) if model requantification was not performed, or if the application depended on the risk ranking of SSCs from a pre-solved cutset equation, the following apply:  The truncation criterion is sufficiently low to ensure stable results, that is, the magnitude of the CDF or release frequency will not change as a result of lower truncation limits, and the grouping of SSCs into risk categories will not be affected.  The components affected by the application are, for the most part, not truncated out of the model. In cases where they are, a qualitative assessment can demonstrate the reasons why they are unimportant to risk. SRP 19-A21 A.10 Modeling of Containment Response and Changes in Large Early Release Frequency a. Areas of Review The purpose of this section is to provide guidance for use in reviewing the licensee’s evaluation of changes in LERF stemming from proposed changes to