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:
e 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 system being consistently achieved given the same input and system properties (including internal and external conditions). 2. Clause 5.6 of IEEE Std 603-2018 and its sub-clauses deal with Independence requirements including those associated with safety systems and other systems. For programmable digital devices in the safety-related systems of nuclear power plants, RG 1.152 endorses, with clarifications, the communication independence criteria within the normative parts of IEEE Std 7-4.3.2, “IEEE Standard Criteria for Programmable Digital Devices in Safety Systems of Nuclear Power Generating Stations,” (Ref. 45). Furthermore, RG 1.152 endorses, with clarification, the IEEE Std 7-4.3.2 Annex D, “Identification and Control of Hazards,” guidance for identifying and controlling hazards. In addition, when implementing this guidance for digital I&C, all signal processing between or among sensor data input and safety control device actuation is accomplished in a manner that is independent of redundant portions of the safety system or other external systems, such that the required safety function capability remains independent of the performance of any one channel. 3. Clause 5.9 of IEEE Std 603-2018 deals with “Control of Access.” The regulatory guidance on this subject for programmable digital devices in the safety-related systems of nuclear power plants is provided in RG 1.152. For example, the guidance in RG 1.152 Section C, “Staff Regulatory Guidance,” Subsection 1.b.3.4 related to Control of Access states that the use of a hardware-based unidirectional device is one approach the NRC staff would consider acceptable to ensure that safety-related I&C systems do not present an electronic path that could enable unauthorized access to the plant’s safety-