Document: NUREG-0800
Document ID: 0d034ca5-ee9b-43ca-a6d6-b08e537d605b
Document Type: srp
Title: Determining the Technical Adequacy of Probabilistic Risk
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0625/ML062510220.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.1
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Assessment Results for Risk-Informed Activities INTRODUCTION In their March 1999 report, “Nuclear Regulation: Strategy Needed To Regulate Safety Using Information on Risk,” GAO/RCED-99-95 (Ref. 1), the General Accounting Office (GAO) identified a number of issues that it believed required resolution for the NRC to successfully implement a risk- informed regulatory approach. Among these, GAO indicated that more was needed to “develop standards on the scope and detail of risk assessments needed for utilities to determine that changes to their plants’ designs will not negatively affect safety.” Probabilistic risk assessment (PRA) standards have been developed by the American Society of Mechanical Engineers (ASME) and American Nuclear Society (ANS). On April 5, 2002, ASME issued a standard (Ref. 2) for a full-power, internal events (excluding fire) Level 1 and a limited Level 2 PRA. Addenda A and B to the Standard were issued in December, 2003 and December, 2005 respectively. In December 2003, ANS issued a standard for external events (Ref. 3). ANS is developing Level 1 and limited Level 2 PRA standards for internal fire, and the low power and shutdown modes of operation, and ASME is developing standards for Level 2 and Level 3 PRAs. In parallel, reactor owners’ groups developed a PRA peer review program documented in NEI-00-02, “Probabilistic Risk Assessment Peer Review Process Guidance,” Revision A3 (Ref. 4). Over the course of several years, this peer review program was applied at all the U.S. nuclear power plants. For all but one of the plants, the criteria used to assess the technical adequacy of the PRAs had been developed to some extent independently of the development of the ASME PRA 2 standard. Therefore, the results of the peer review could not be used directly to assess whether the PRA was in conformance with the ASME standard. 3 On August 16, 2002, NEI submitted draft industry guidance for self-assessments (Ref. 5) to address the use of