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:
Safety System Instrument Channels” (Ref. 44). Documents Discussed in Staff Regulatory Guidance This regulatory guidance addresses the use of a standard developed by the IEEE. This standard contains references to other IEEE standards (“secondary references”). If a secondary reference has itself been incorporated by reference into NRC regulations as a requirement, then licensees and applicants must comply with that standard as set forth in the regulation. If the secondary reference has been endorsed in an RG as an acceptable approach for meeting an NRC requirement, then the standard constitutes a method acceptable to the NRC staff for meeting that regulatory requirement as described in the specific RG. If the secondary reference has neither been incorporated by reference into NRC regulations nor endorsed in an RG, then the secondary reference is neither a legally-binding requirement nor a “generic” NRC-approved acceptable approach for meeting an NRC requirement. However, licensees and applicants may consider and use the information in the secondary reference, if appropriately justified, consistent with current regulatory practice, and consistent with applicable NRC requirements. DG-1251, Page 8 C. STAFF REGULATORY GUIDANCE Supplemental and clarifying guidance for implementing certain criteria in IEEE Std 603-2018 are identified below: 1. Supplement Clause 5.5 of IEEE Std 603-2018 with the following: For the purposes of this clause, “predictable and repeatable” means that: (1) events that support the operation of the system, including the transmission of signals between or among sensor data input and safety control device actuation, that occur at a given time that can be defined in advance through known relationships among the controlled system states. The required responses to those states make them regular or expected at a known frequency such that a given set of input signals will always produce the same output signals; and (2) the output of such a