Document: NRC Regulatory Guide
Document ID: 26c3e31f-c018-4aee-b926-6db849b72a5a
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:
ty of common-cause failure attributable to environmental stressors is reduced to an acceptable level. Specifically, Section 5.4.1 of IEEE Std. 7-4.3.2 provides criteria for the equipment qualification of computer-based safety systems, including performing testing with the full range of safety-related software functioning. Revision 1 of Regulatory Guide 1.89 (1984) endorses IEEE Std. 323-1974. Regulatory Guide 1.89 specifically limits its scope to compliance with 10 CFR 50.49 “...with regard to qualification of electric equipment important to safety for service in nuclear power plants to ensure that the equipment can perform its safety function during and after a design-basis accident.” Thus, Regulatory Guide 1.89 focuses on the environmental qualification of equipment intended for use in harsh environments that are subject to the effects of design-basis accidents. Nonetheless, a mild environment in a nuclear power plant can encompass extreme environmental conditions that can affect the performance of sensitive equipment, so qualification to demonstrate compatibility with those environmental conditions is necessary in those cases. This requirement provides an assurance of reliable operation throughout the installed life of the equipment under all normal, abnormal, and anticipated operational occurrences as well as accident environmental conditions. Mild-environment qualification of most electrical equipment is accomplished through design analysis, predicting performance under environmental stress based on knowledge of material properties. However, because of the complexity of microprocessor design, such predictive analysis is not currently possible. Therefore, additional guidance is warranted to address qualification for all environmental conditions within a nuclear power plant. The IEEE revised the consensus national standard for qualification, IEEE Std. 323, in 1983, reaffirmed it in 1991 and 1996, and revised it again in 2003. The 2003 version represents the