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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Content:
yond-design-basis events involve conditions not fully considered in the design process (e.g., the occurrence of multiple, independent failures) because they were judged to be too unlikely. Considering their very low likelihood of occurrence, beyond-design-basis events are typically assessed with best-estimate inputs in lieu of the conservative design-basis assumptions associated with design-basis events. The following are examples of beyond-design-basis events required to be addressed: • Anticipated transient without scram (ATWS) (10 CFR 50.62) • Station blackout (10 CFR 50.63) • Loss of all alternating current (ac) power (10 CFR 50.155) The individual subsections of Chapter 15 of the SRP provide guidance for the review of these specific events, except for loss of all ac power events.1 For new reactor designs, the relevant set of analyzed events and their categorization may differ from the examples above. B. Categorization According to Type. AOOs and postulated accidents are also categorized according to type. The type of AOO or postulated accident is defined by its effect on the plant. For example, one type of AOO or postulated accident will cause the RCS to pressurize and possibly jeopardize RCS integrity. Another type will cause the RCS to depressurize and possibly jeopardize fuel cladding integrity. It is useful to categorize and organize analyses of AOOs and postulated accidents according to type, so that analysts can compare them on common bases, effects, and safety limits. Such comparisons can help to identify limiting events and cases for detailed examination and eliminate nonlimiting cases from further consideration. 1 RG 1.226 provides guidance on methods that the staff considers acceptable for use in implementing 10 CFR 50.155 (Ref. 14). 15.0-5 Draft Revision 4 – July 2023 AOOs and postulated accidents considered in previous licensing reviews for currently operating PWR and BWR designs have been grouped into the following seven types: (1) Increase