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:
s 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 licensing basis change. If the proposed licensing basis change has no impact on a given factor, the licensee should state as much including a brief justification. Licensees should structure their discussion of how the proposed licensing basis change impacts defense-in-depth by explicitly addressing the seven factors. Such an approach would facilitate the licensee’s analysis as well as make for a more efficient review by the NRC staff. It is important to note that the focus here is on the effect of the proposed licensing basis change on defense-in-depth. The seven defense-in-depth evaluation factors presented in Section C.2.1.1.2 are not intended to define how defense-in-depth is implemented in a plant’s design but are intended to help licensees assess the impact of the proposed licensing basis change on defense-in-depth. DG-1285, Page 18 The following discussion provides guidance on how to evaluate the proposed licensing basis change for each of the defense-in-depth evaluation factors: 1. Preserve a reasonable balance among the layers of defense. The proposed licensing basis change should not significantly reduce the effectiveness of a layer of defense that exists in the plant design prior to the implementation of the proposed licensing basis change. The evaluation of the proposed licensing basis change should consider insights based on traditional engineering approaches; insights from risk assessments might be used to support engineering insights but should not be the only justification for meeting this factor. To evaluate this factor, the licensee should address each of the layers of defense in turn. A reasonable balance among the layers of defense is preserved if the proposed licensing basis change does not significantly reduce the effectiveness of a layer of