Document: NUREG-0800
Document ID: 1877a6e5-f5a2-4394-bd63-c323831e96d0
Document Type: srp
Title: INTRODUCTION - TRANSIENT AND ACCIDENT ANALYSES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2231/ML22319A149.pdf
Revision Date: 2023-07
Chapter: 15
Section ID: 15.0
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case variations of AOOs, and postulated accidents presented to verify that the applicant or licensee has identified the limiting cases. The reviewer evaluates applicants’ or licensees’ claims that individual AOOs, and postulated accidents are limiting or nonlimiting, or bounded by other AOOs and postulated accidents, with particular attention to the bases used for comparison. For example, in some cases, qualitative comparison of an AOO of one type to another AOO of the same type may be readily justified (e.g., all else being equal, an event involving a valve with a faster closure time may result in a larger peak pressure). On the other hand, considering the potential for complex phenomenological and system interactions, a qualitative disposition that an AOO of one type bounds a postulated accident of another type requires closer scrutiny and more justification from the licensee. 15.0-6 Draft Revision 4 – July 2023 2. Analysis Acceptance Criteria. The NRC’s acceptance criteria for safety analysis recognize that the risk of an event is derived from both the event’s frequency of occurrence and the severity of its consequences. The design of a plant should be such that all the AOOs and postulated accidents produce about the same acceptably low level of risk (i.e., the risk is approximately constant across the spectrum of AOOs and postulated accidents). This approach is reflected in the GDC, which generally require plant design to preclude relatively frequent events (AOOs) from resulting in serious consequences. For relatively rare events (postulated accidents), the GDC achieve this acceptably low level of risk by requiring mitigation of potentially serious consequences using less restrictive acceptance criteria than those applicable to AOOs. For example, with respect to fuel performance, the fuel cladding fission product barrier must be maintained for all AOOs; however, for initiating events categorized as postulated accidents, a loss of fuel cladding