Document: NUREG-0800
Document ID: ecf7a8d4-0097-4a93-8609-630545f03f70
Document Type: srp
Title: REGULATORY TREATMENT OF NONSAFETY SYSTEMS FOR PASSIVE
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1308/ML13081A756.pdf
Revision Date: 2023-06
Chapter: 19
Section ID: 19.3
CFR Part: 
CFR Title: 

Content:
arisons of these missions to U.S. Nuclear Regulatory Commission (NRC) goals. An R/A mission is the set of requirements related to the performance, reliability, and availability of an SSC function that adequately ensures the accomplishment of its task, as defined by the focused PRA or deterministic analysis. 2. The designer applies the process to the design to establish R/A missions for the risk- significant SSCs. 3. If active systems are determined to be risk-significant, the NRC reviews the R/A missions to determine if they are adequate and whether the RAP (SRP 17.4) and administrative controls on availability, or simple TSs and limiting conditions for operation (LCOs) can provide reasonable assurance that the missions can be met during operation. 4. If active systems are relied on to meet the R/A missions, the designer imposes design requirements commensurate with the risk-significance of those elements involved. 5. The DC rule does not explicitly state the R/A missions for risk-significant SSCs. Instead, the rule includes deterministic requirements for both safety-related and nonsafety-related design features. The RTNSS process applies broadly to those nonsafety-related SSCs that perform risk significant functions and, therefore, are candidates for regulatory oversight. The RTNSS process uses the following five criteria to determine those SSC functions: A. SSC functions relied on to meet beyond design basis deterministic NRC performance requirements such as those set forth in Title 10 of the Code of Federal Regulations (10 CFR) 50.62 for mitigating Anticipated Transients Without Scram (ATWS) and in 10 CFR 50.63 for Station Blackout (SBO). B. SSC functions relied on to ensure long-term safety (the period beginning 72 hours after a design basis event and lasting the following 4 days) and to address seismic events. C. SSC functions relied on under power-operating and shutdown conditions to meet the Commission goals of a core damage frequency (CDF) of less than