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:
ts of the SSC’s failure. 2.1 Safety-Significance Determination For the purposes of this BTP, a safety-significant function is one whose degradation or loss could have a significant adverse effect on defense in depth, safety margin, or risk. For example, because immediate responses are needed for certain adverse reactor conditions, the reactor trip system (RTS) and engineered safety features actuation system are generally deemed more critical than those systems that perform auxiliary safety functions not directly credited in the accident analysis. Consequently, a CCF assessment for an RTS should generally be more 6 The use of the term “critical safety functions” goes back to American National Standards Institute/American Nuclear Society-4.5-1980, “Criteria for Accident Monitoring Functions in Light-Water-Cooled Reactors,” and IEEE Std 497-1981, “IEEE Standard Criteria for Accident Monitoring Instrumentation for Nuclear Power Generating Stations.” The most important safety functions may not always be called “critical safety functions.” BTP 7-19-14 Revision 9 — May 2024 rigorous than, for example, a CCF assessment for a safety-related MCR heating, ventilation, and air conditioning (HVAC) chiller. While the HVAC chiller is a safety-related system, maintaining a certain temperature and humidity in the MCR to allow equipment and personnel to operate properly, a failure of this system is not as significant as an RTS failure, because personnel have operating procedures or diverse means to control MCR temperature and humidity and can shut down the plant for this purpose if necessary. Therefore, the reviewer should evaluate the applicant’s safety-significance determination for the SSC subject to the D3 assessment. The reviewer should consider whether the applicant used risk insights from site-specific PRAs, if available, to support its determination. The reviewer should confirm that the application documents the basis for the safety-significance