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
CFR Part: 
CFR Title: 

Content:
re compared to the existing conditions. • The overall redundancy and diversity among the barriers is sufficient to ensure compatibility with the risk acceptance guidelines. In demonstrating that the proposal fulfills the objectives listed above, the staff expects that the proposed change will meet the following guidelines: SRP 19-10 • A reasonable balance is preserved among prevention of core damage, prevention of containment failure, and mitigation of consequences. • The proposal avoids over-reliance on programmatic activities to compensate for weaknesses in plant design. • The proposed change preserves system redundancy, independence, and diversity commensurate with the expected frequency of challenges, consequences of failure of the system, and associated uncertainties. • The proposal preserves defenses against potential common cause failures and assesses the potential introduction of new common cause failure mechanisms. • The proposed change does not degrade the independence of barriers. • The proposed change preserves defenses against human errors. • The proposal fulfills the intent of the General Design Criteria in Appendix A to 10 CFR Part 50. Reviewers can assess fulfillment of the above guidelines by using qualitative or traditional engineering arguments or by using PRA results contained in the accident sequences or cutsets. III.2.1.1.2 Role of PRA in Review of Defense in Depth In addition to the usual quantitative risk indices, PRAs provide important qualitative results, namely, the contributors to accident sequences. For PRAs that use the fault tree linking approach, these contributors are described by the accident sequence minimal cutsets. Each accident sequence minimal cutset is a combination of passive and active SSC failures and human errors that would cause core damage or a release of radioactivity. The cutsets therefore directly show one particular aspect of defense in depth, in that they reveal how many failures must occur in order