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:
e-in-depth philosophy. However, there might be situations where a plant is not in compliance with its design basis or licensing basis or new information might arise indicating that the design basis or licensing basis is deficient. In such cases, the as-built and as-operated plant might not be consistent with the defense-in-depth philosophy prior to the implementation of the proposed licensing basis change. When this occurs, the licensee and the staff should ensure compliance with existing requirements (e.g., regulations, license conditions, orders, etc.) and implement appropriate actions to address any non-compliances. When addressing these deficiencies or non-compliances, consideration should be given to the concepts in this document to help achieve consistency with the defense-in-depth philosophy. Although the guidance is presented separately for each factor, the evaluation of the proposed licensing basis change should be performed in an integrated fashion. The proposed licensing basis change is considered to maintain consistency with the defense-in- depth philosophy if the integrated assessment demonstrates no significant impact on a single factor (i.e., the intent of each defense-in-depth evaluation factor is met). Such an evaluation of the proposed licensing basis change against the seven factors might be qualitative. The seven defense-in-depth evaluation factors could be arranged in a hierarchical manner. For example, the first factor is an overarching high-level description of how defense-in-depth is achieved. Factors two through six might apply to any of the layers of defense to aid the analyst in justifying that the proposed licensing basis change preserves a reasonable balance among the layers of defense. Finally, factor seven helps ensure completeness of the assessment of how the proposed licensing basis change could impact defense-in-depth. Nevertheless, in the interest of completeness, the seven factors should each be addressed for any proposed