Document: NRC Regulatory Guide
Document ID: 0df18aa6-42a8-4990-aa7e-3df6d0907f3f
Document Type: regulatory_guide
Title: Criteria for Safety Systems (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2511/ML25114A021.pdf
Revision Date: 2025-11
Chapter: 
Section ID: RG-1.153
CFR Part: 
CFR Title: 

Content:
6 due to Latent Design Defects in Digital Instrumentation and Control Systems,” (Ref. 30) and the Design Review Guide, “Design Review Guide (DRG): Instrumentation and Controls for Non-Light-Water Reactor (Non-LWR) Reviews” (Ref. 31) as applicable. Further, regarding the last paragraph in Clause 5.16, if a determination concludes that the consequences of a CCF are low or a determination concludes that the CCF has a very low likelihood of occurrence, that conclusion could be credited in a plant-specific analysis toward justification of the proposed safety system design in an overall risk-informed D3 approach on a case by case basis. However, a risk-informed approach requires that risk insights are considered together with other factors to establish requirements that better focus licensee and regulatory attention on design and operational issues commensurate with their importance to public health and safety, consistent with SRM-SECY-98-144, “Risk-informed and Performance Based Regulation,” (Ref. 32) and SRM-SECY-22-0076. Finally, the NRC staff agrees that each identified source of CCF should be evaluated, but also addressed, on a case-by-case basis. Data Communications Independence DI&C architectures may employ data communications between safety systems, between redundant portions of a safety system, and between systems of different safety classes. One of the more significant regulatory implications is maintaining not only physical, functional, and electrical independence but also data communication independence, thereby ensuring that faults from data communications do not propagate and adversely affect safety functions. Otherwise, fault propagation can lead to undesired behavior of I&C systems, which could create hazards that challenge plant safety. Hazards may result from lost independence because of interconnectivity or functional relationships among DI&C systems through their data communications. These hazards may be more difficult to identify and