Document: NRC Regulatory Guide
Document ID: 82659041-98b0-4721-b25d-c4fb2ea394d0
Document Type: regulatory_guide
Title: An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1635/ML16358A153.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.174
CFR Part: 
CFR Title: 

Content:
feat the redundancy, independence, and/or diversity of the layers of defense, fission product barriers, and the design, operational, or maintenance aspects of the plant. The evaluation of the proposed licensing basis change should demonstrate that the change does not result in a significant reduction of existing CCF defenses or introduce new CCF dependencies. DG-1285, Page 21 Two general approaches exist for defending against CCF: (1) defend against the failure cause or event and (2) defend against the CCF coupling factor. A combination of both approaches may be employed. The licensee should determine that the proposed licensing basis change does not reduce existing defense strategies or introduce a new cause, event, or coupling factor. To evaluate this factor, the licensee should determine whether the proposed licensing basis change could: • Introduce a new potential CCF cause or event for which a defense is not in place. • Increase the probability or frequency of a cause or event that could cause simultaneous multiple component failures. • Introduce a new coupling factor for which a defense is not in place. • Weaken or defeat an existing defense against a cause, event, or coupling factor. It is recognized that the PRA model explicitly models some types of CCF so that the risk assessment provides some insights into this factor for evaluating defense-in-depth. However, the licensee should also qualitatively evaluate whether the change has adversely impacted any of the three areas above to judge whether this factor has been met. 5. Maintain multiple fission product barriers. The proposed licensing basis change should not significantly reduce the effectiveness of the multiple fission product barriers. The evaluation of the proposed licensing basis change should demonstrate that the change does not: • Create a significant increase in the likelihood or consequence of an event that simultaneously challenges multiple barriers. • Introduce a new event that