Document: NUREG-0800
Document ID: fe8ec6c2-e960-404c-854f-55c77bde1672
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2400/ML24005A077.pdf
Revision Date: 2024-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
s. Single failures must be addressed by meeting the principal design criteria of the facility or the criteria described in 10 CFR 50.55a(h) (i.e., the safety design criteria in Institute of Electrical and Electronics Engineers (IEEE) Std 279-1971, “Criteria for Protection Systems for Nuclear Power Generating Stations,” or IEEE Std 603-1991, “IEEE Standard Criteria for Safety Systems for Nuclear Power Generating Stations”). Because such failures are likely to occur during the life of the plant, the plant’s design basis needs to include analysis of the possible effects (consequences) of such failures. 3 SRM-SECY-93-087 states, “The staff's position has been modified in essentially two respects: First, inasmuch as common mode failures are beyond design-basis events, the analysis of such events should be on a best-estimate basis…” [emphasis added]. The NRC Glossary defines “beyond design-basis accidents” as follows: This term is used as a technical way to discuss accident sequences that are possible but were not fully considered in the design process because they were judged to be too unlikely. (In that sense, they are considered beyond the scope of design-basis accidents that a nuclear facility must be designed and built to withstand.) As the regulatory process strives to be as thorough as possible, “beyond design-basis” accident sequences are analyzed to fully understand the capability of a design. The design basis of a facility generally addresses certain beyond design-basis events. For example, 10 CFR 50.34, “Contents of applications; technical information,” includes “(i) Mitigation of beyond-design-basis events….” BTP 7-19-4 Revision 9 — May 2024 interdependencies among DI&C systems make it more challenging to identify and evaluate potential consequences of a postulated CCF. Generally, except in a few structures, systems, and components (SSCs) with relatively simple designs, DI&C systems cannot be fully tested, nor can their