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:
nd advanced digital systems arises from the potential effect of the more rapid evolution of digital technology; in particular, the ever-increasing density and complexity of ICs at the wafer level make previously improbable failure mechanisms more significant. For example, at the level of complexity of current very-large-scale integrated (VLSI) circuits, electron migration can become a significant issue where metal interconnects and/or interlevel contacts are commonly designed to carry a current density exceeding 105 amps per cm2 (A/cm2), equivalent to an ordinary household electric wire carrying a current above 4000 A. Reliability tests by VLSI manufacturers typically address this problem by stressing devices at both high temperature and high current density. Synergistic effects of other parameters can precipitate other failure mechanisms, such as dielectric breakdown in semiconductor components. One stressor not previously considered for analog safety system qualification is smoke exposure from an electrical fire. Based on the investigation of smoke susceptibility and the resulting understanding of key failure mechanisms (as discussed in NUREG/CR-6406, NUREG/CR-6476, NUREG/CR-6543, NUREG/CR-6579, and NUREG/CR-6597), smoke clearly has the potential to be a significant environmental stressor that can result in adverse consequences. However, as no practical, repeatable testing methodology is available, it is not feasible to assess smoke susceptibility as part of qualification. DG-1142, Page 6 As a result, the most reasonable approach to minimizing smoke susceptibility is to employ design, construction, installation, and procedural practices that can reduce the possibility of smoke exposure and enhance smoke tolerance. In particular, current fire protection methods focus on a preventive approach, employing isolation and detection practices. In addition, postevent recovery procedures can mitigate the extent of smoke damage. Moreover, certain design choices and