Document: NRC Regulatory Guide
Document ID: 086612c4-a8a7-4f50-a166-6f1cb05bcdaf
Document Type: regulatory_guide
Title: Guidelines for Environmental Qualification of Safety-Related Computer-Based Instrumentation and Control Systems in Nuclear Power Plants
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0630/ML063040591.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.209
CFR Part: 
CFR Title: 

Content:
ore, 10 CFR 50.55a(h) requires that safety systems shall meet the requirements of IEEE Std. 603-1991 and the correction sheet dated January 30, 1995, or IEEE Std. 279-1971, contingent on the date that the NRC issued the related construction permit. The design- basis criteria identified by those standards or by similar provisions in the licensing basis for such facilities include the range of transient and steady-state environmental conditions throughout which the equipment shall perform during normal, abnormal, accident, and operational events. In addition, in Appendix B to 10 CFR Part 50, Criteria III, XI, and XVII establish practices to confirm that a design fulfills its technical requirements. Furthermore, 10 CFR 50.49 requires licensees to establish an environmental qualification program for all (safety-related) equipment that is relied on to remain functional during and following design-basis events.1 The use of COTS computers and microprocessor-based technology in safety systems poses potential environmental compatibility issues. These issues result from functional as well as hardware characteristics. One unique characteristic of digital systems that should be considered in verifying design by qualification arises from the higher functional density that is possible with computer-based I&C systems. Because of expanding single-chip capabilities, many safety-related implementations involve replacing multiple functional modules with a multifunction microprocessor-based module. Therefore, failure of a single module for a computer-based I&C system can affect numerous functions. Another characteristic that should be considered in verifying design by qualification involves the sequential function execution that typifies computer-based I&C systems in contrast to the essentially parallel function execution of analog modules. The effect of this behavior can be compounded for distributed implementations that rely on either successful completion of digital data