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:
o 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 communication or error detection before continuation of discrete functional steps. The confirmation that digital system design accommodates the potentially synergistic effects of environmental stress is an important consideration for qualification of computer-based I&C systems. Hardware characteristics that warrant consideration result from the continuing trend toward higher clock frequencies, faster operating speeds, and lower logic-level voltages. The faster logic families have shown a greater susceptibility to upsets and malfunctions because of the effects of EMI/RFI. Another hardware characteristic is that the ever-increasing density and level of complexity at the wafer level make previously improbable failure mechanisms (e.g., electromigration) more significant. In addition, some MOS devices can fail at relatively low radiation doses on the order of 10 Gy (1 krad). DG-1142, Page 10 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, issued in 1993 and revised in 2003. That standard emphasizes that the application of computers in safety systems needs to address reliability and environmental compatibility. In particular, Annex F.2.3 of IEEE Std. 7-4.3.2 requires the performance of analyses to ensure that the system has a high “correct response probability” and that the probability of common-cause failure is reduced to an acceptable level. Addressing qualification requirements for safety-related computer-based I&C systems is one method of ensuring that the probability 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