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:
Std 603-2018 states, “The safety system design and development shall address common-cause failures (CCF) that create a potential to degrade or defeat the safety system function.” This statement is consistent with the NRC’s policy in Staff Requirements Memorandum (SRM)-SECY‑22-0076, “Expansion of Current Policy on Potential Common-Cause Failures in Digital Instrumentation and Control Systems,” (Ref. 29) on CCF and has been incorporated into 10 CFR 50.55a(h). The NRC staff considers the remainder of Clause 5.16 (i.e., after the first sentence) as guidance on how CCF could be addressed. The methods included in Clause 5.16 may be acceptable for licensees or applicants to address CCF as part of their overall defense-in-depth and diversity (D3) analyses, in appropriate circumstances; however, the list is not comprehensive and does not include flexibilities the Commission recently directed the NRC staff to incorporate into its licensing reviews. In its direction to the NRC staff in SRM-SECY‑22-0076, the Commission approved expanded acceptance of risk-informed approaches in performing the D3 assessment and in determining the adequacy of design techniques, prevention measures, and mitigation measures other than diversity, to address a postulated digital I&C (DI&C) CCF. This policy provides additional flexibility in addressing CCFs beyond the methods described in Clause 5.16. Therefore, licensees or applicants may use the methods described in Clause 5.16 and other methods referenced in this draft guidance in their overall D3 analyses. The NRC staff would review such applications on a case-by-case basis using the guidance in Branch Technical Position (BTP) 7-19, “Guidance for Evaluation of Defense in Depth and Diversity to Address Common-Cause Failure DG-1251, Page 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