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
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CFR Title: 

Content:
f Federal Regulations defines a mild environment as one “that would at no time be significantly more severe than the environment that would occur during normal plant operation, including anticipated operational occurrences.” However, as a mild environment in a nuclear power plant can encompass environmental conditions that can affect the performance of sensitive equipment, qualification to demonstrate compatibility with those environmental conditions is necessary in those cases. Because Regulatory Guide 1.89 limits its scope to equipment intended for application in harsh environments, additional guidance is warranted to address qualification for mild environmental conditions, as needed for computer-based technologies. IEEE revised the industry guidance for qualification, IEEE Std. 323, in 2003. A particular distinction between IEEE Std. 323-2003, “IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power Generating Stations,” and IEEE Std. 323-1974 is that the current version does not require age conditioning to an end-of-installed-life condition for equipment in mild environments where significant aging mechanisms are not present. The practices in IEEE Std. 323-2003 are sufficiently comprehensive to address qualification for the less severe environmental conditions of typical plant locations where safety-related computer-based I&C systems are generally located. These plant areas are unaffected by design-basis accidents and the most severe conditions to which the equipment is subjected, which arise from the environmental extremes resulting from normal and abnormal operational occurrences. Use of computers in safety systems poses challenges that differ from those associated with analog systems, prompting the development of IEEE Std. 7-4.3.2, “IEEE Standard Criteria for Digital Computers in Safety Systems of Nuclear Power Generating Stations,” issued in 1993 and revised in 2003. This standard emphasizes that the application of computers in safety