Current research results on the technical basis for environmental qualification of safety-related digital I&C hardware in nuclear power plants

This paper presents progress to date of an NRC-sponsored confirmatory research program initiated to address hardware issues associated with the use of safety-related digital instrumentation and control (I&C) hardware in nuclear power plants. In particular, the potential vulnerability of digital technology to environmental stress effects and means for establishing environmental compatibility for digital I&C systems were studied. The research approach involved evaluating existing military and industrial guidance, identifying the most significant environmental stressors and, for advanced I&C systems in nuclear power plants, investigating the likely failure modes-both at the integrated circuit and system level-for digital technologies under varying levels of environmental stress. Environmental stressors used in the studies included smoke exposure, electromagnetic and radio-frequency interference (EMI/RFI), temperature, and humidity. The insights gained from these studies are being used to recommend appropriate methods for qualifying safety-related digital equipment in nuclear power plants. To characterize the EMI/RFI environment at current LWRs and to estimate the expected environment at ALWRs, ORNL conducted a long-term survey of ambient electromagnetic conditions at several nuclear power plants. A representative sampling of power plant conditions (reactor type, operating mode, site location) were monitored over extended observation periods (e.g., continuous measurements for up to 5 weeks at a single location) were selected to more completely determine the characteristic electromagnetic environment for nuclear power plants. The results of this study contributed to the technical basis for a Nuclear Regulatory Commission Draft Regulatory Guide (DG-1029) issued for comment in 1998. (C) 1999 Published by Elsevier Science S.A. All rights reserved.