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:
ors for Evaluating the Impact of the Proposed Licensing Basis Change on Defense- in-Depth Any one or more of the layers of defense discussed above might be adversely impacted by the proposed licensing basis change. The NRC has identified seven factors that should be used to evaluate the impact of the change on defense-in-depth. These are discussed in detail below. Section C.2.1.1.3 discusses guidance on how to apply these factors in more detail. The NRC finds it acceptable for a licensee to use the following seven factors to evaluate how the proposed licensing basis change impacts defense-in-depth. 1. Preserve a reasonable balance among the layers of defense. A reasonable balance of the layers of defense-minimizing challenges to the plant, preventing any events from progressing to core damage, containing the radioactive source term, and emergency preparedness, helps to ensure an apportionment of the plant’s capabilities between limiting disturbances to the plant and mitigating their consequences. The term reasonable balance is not meant to imply an equal apportionment of capabilities. The NRC recognizes that aspects of a plant’s design or operation might cause one or more of the layers of defense to be adversely affected. For these situations, the balance between the other layers of defense becomes especially important when evaluating the impact of the proposed licensing basis change and its impact on defense-in-depth. 2. Preserve adequate capability of design features without an overreliance on programmatic activities as compensatory measures. Nuclear power plant licensees implement a number of programmatic activities including, for example, programs for quality assurance, testing and inspection, maintenance, control of transient combustible material, foreign material exclusion, containment cleanliness, training, and so forth. In some cases, activities taken as part of these programs are used as compensatory measures, that is measures taken to compensate for