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:
rom the application by requantifying the base PRA model so that the potential effects of originally truncated events can be accounted for should they become important as a result of an application. If the licensee did not requantify the model, or if the application depended on the risk ranking of SSCs from a pre-solved equation, reviewers should use the guidelines provided below. Reviewers should be assured (either by documentation provided in the licensee's submittal or by an independent staff analysis) that cutset or scenario truncation did not introduce errors into the application results or the logic of the PRA that affects the application. Staff review could also involve performing (or reviewing) sensitivity studies where the truncation limit is lowered for the dominant sequences and event initiators, and studying the resultant cutsets or scenarios to see if there are any hidden dependencies or unusual/unexpected event combinations (esl:,ecially if these involve components affected by the proposed application). Staff review could also include comparing a list of the events affected by the application that is in the final truncat:ed cutset equations to the list of application-specific basic 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 w-iere 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 ,)- human dependencies are considered. c. Evaluation Findings Reviewers should verify that the information provided and review activities conducted support the