Some Observations On Risk-Informing Appendices A & B to 10 CFR Part 50 (NUREG-1755)

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Publication Information

Manuscript Completed: December 2001
Date Published: January 2002

Prepared by:
J.N. Sorensen,
Senior Fellow

Prepared for:
Advisory Committee on Reactor Safeguards
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

This report was prepared for the Advisory Committee on Reactor Safeguards to provide a basis for discussing possible changes to the general design criteria (GDC) of Appendix A to Title 10, Part 50, of the Code of Federal Regulations in order to make them more consistent with a risk-informed regulatory structure. The three broad options identified include (1) changing the scope of the GDC from "important to safety" to "important to risk," (2) modifying individual criteria to address risk more directly, and (3) replacing the GDC with safety goals and risk acceptance criteria. As written, the GDC apply to systems, structures, and components (SSCs) important to safety, which are defined as those SSCs that are required to provide reasonable assurance that there will be no undue risk to public health and safety. If the scope is changed to "important to risk," the GDC can be applied to those SSCs that will have the greatest impact on reducing risk, as measured by risk metrics such as core damage frequency or large early release frequency. Specific changes to improve the risk focus of individual criteria are also discussed. Such changes might involve replacing requirements for redundancy, diversity, and independence with an overall reliability goal for a system or function. Applicability of the GDC to non-light-water reactors (LWRs) is briefly examined, with the conclusion that slightly more than half of the criteria could apply to non-LWRs, but the remainder should be modified or replaced to address phenomena important to the safety of other reactor types. Another brief discussion of the quality assurance requirements of Appendix B to 10 CFR Part 50 concludes that Appendix B has sufficient flexibility to permit less stringent requirements for SSCs that are less important to risk.