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:
y to operate the plant or respond to off-normal conditions and accidents, errors committed during test and maintenance, and other plant staff performing an incorrect action. Human errors can result in the degradation or failure of a system to perform its function, thereby significantly reducing the effectiveness of one of the layers of defense or one of the fission product barriers. The plant design and operation includes defenses to prevent the DG-1285, Page 17 occurrence of such errors and events. These defenses generally involve the use of procedures, training, and human engineering; however, other considerations (e.g., communication protocols) might also be important. 7. Continue to meet the intent of the plant’s design criteria For plants licensed under 10 CFR Part 50 or Part 52, the plant’s design criteria are set forth in the current licensing basis of the plant. The plant’s design criteria define minimum requirements that achieve aspects of the defense-in-depth philosophy; as a consequence, even a compromise to the intent of those design criteria can directly result in a significant reduction in the effectiveness of one or more of the layers of defense. When evaluating the effect of the proposed licensing basis change, the licensee should demonstrate that the intent of the plant’s design criteria continue to be met. Evaluating the Impact of the Proposed Licensing Basis Change on Defense-in-Depth It is considered acceptable for a licensee to use the seven defense-in-depth evaluation factors described in Section C.2.1.1.2 to evaluate the impact of a proposed licensing basis change on defense-in- depth. It is presumed that, prior to the implementation of the proposed licensing basis change, the as-built and as-operated plant is consistent with the defense-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