Document: NUREG-0800
Document ID: ac43f632-9db1-4857-9f56-bfba45965456
Document Type: srp
Title: * These are modifications to a plant’s design, operations, or other activities that require NRC approval. These modifica
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0232/ML023250195.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19
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CFR Title: 

Content:
ge meets current regulations (unless the change is explicitly related to a requested exemption or rule change); the defense-in-depth philosophy is maintained; sufficient safety margins are maintained; and proposed increases in core damage frequency and/or risk (if any) are small and are consistent with the intent of the Commission’s Safety Goal Policy Statement (Ref. 7). III.2.1 Evaluation of Defense-in-Depth Attributes and Safety Margins Reviewers should assess the licensee’s engineering evaluations to confirm that the principles identified in Section II are not compromised. These evaluations should include not only the traditional design basis accident (DBA) analyses, but also evaluations of the defense-in-depth attributes of the plant, safety margins, and risk assessments performed to obtain risk insights and to quantify the impact of the proposed change. SRP 19-9 III.2.1.1 Defense in Depth Defense in depth is defined as a philosophy that ensures that successive measures are incorporated into the design and operating practices for nuclear plants to compensate for potential failures in protection and safety measures. In risk-informed regulation, the intent is to ensure that the defense-in-depth philosophy is maintained, not to prevent changes in the way defense in depth is achieved. The defense-in-depth philosophy has been and continues to be an effective way to account for uncertainties in equipment and human performance. In some cases, risk analysis can help quantify the range of uncertainty; however, there will likely remain areas of large uncertainty or areas not covered by the risk analysis. Where a comprehensive risk analysis can be performed, it can help determine the approximate extent of defense in depth (e.g., balance among core damage prevention, containment failure, and consequence mitigation) to ensure protection of public health and safety. However, because PRAs do not reflect all aspects of defense-in-depth, appropriate traditional