Document: NUREG-0800
Document ID: 96afb1d6-6ce9-41e4-b4ec-1fc7747bc0b2
Document Type: srp
Title: Revision 8 – January 2021
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2033/ML20339A647.pdf
Revision Date: 2023-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
tial effects 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 to detect the onset of adverse reactor conditions, trip the reactor, and quickly reach a safe, stable state, systems that perform protection functions (e.g., RTS and ESFAS) are deemed more critical than those that perform auxiliary safety functions that are not directly credited in the Chapter 15 analysis in the FSAR. Consequently, a CCF assessment for an RTS should be more rigorous than one 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. The reviewer should consider whether the applicant used risk insights from site-specific probabilistic risk assessments (PRAs), if available, to support its determination. The reviewer should confirm that the application documents the basis for the safety-significance determination, including any use of risk insights. The reviewer should also determine whether the use of risk insights is reasonable. System Integration and Interconnectivity System integration and interconnectivity can introduce additional CCF vulnerabilities. If there is integration (e.g., through combined design functions, shared resources, or digital interconnectivity), the system should be assessed using the methods appropriate for the highest