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:
ention, 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 defense-in-depth considerations should also be used to account for uncertainties. III.2.1.1.1 Preservation of Multiple Barriers for Radioactivity Release Defense in depth can be evaluated on the basis of considerations involving the barriers that prevent or mitigate radioactivity release. Release of radioactive materials from the reactor to the environment is prevented by a succession of passive barriers, including the fuel cladding, reactor coolant pressure boundary, and containment structure. These barriers, together with an imposed exclusion area and emergency preparedness, are the essential elements for accident consequence mitigation. Given these multiple barriers, safety is ensured through the application of deterministic safety criteria for the performance of each barrier and through the design and operation of systems to support the functional performance of each barrier. In maintaining consistency with the defense-in-depth philosophy, the proposed license amendment should not result in any substantial change in the effectiveness of the barriers. Consequently, reviewers should consider the following objectives to ensure that the proposed change maintains appropriate safety within the defense-in-depth philosophy: • The change does not result in a significant increase in the existing challenges to the integrity of the barriers. • The proposal does not significantly change the failure probability of any individual barrier. • The proposal does not introduce new or additional failure dependencies among barriers that significantly increase the likelihood of failure 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