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 resea rch program initiated to address hardware issues associated with the use of safety-related digital instrumentation and control (I&C) hardware in nucle ar power plants. In particular, the potential vulnerability of digital tech nology to environmental stress effects and means for establishing environme ntal compatibility for digital I&C systems were studied. The research appro ach involved evaluating existing military and industrial guidance, identify ing the most significant environmental stressors and, for advanced I&C syst ems in nuclear power plants, investigating the likely failure modes-both at the integrated circuit and system level-for digital technologies under var ying levels of environmental stress. Environmental stressors used in the st udies included smoke exposure, electromagnetic and radio-frequency interfer ence (EMI/RFI), temperature, and humidity. The insights gained from these s tudies are being used to recommend appropriate methods for qualifying safet y-related digital equipment in nuclear power plants. To characterize the EM I/RFI environment at current LWRs and to estimate the expected environment at ALWRs, ORNL conducted a long-term survey of ambient electromagnetic cond itions at several nuclear power plants. A representative sampling of power plant conditions (reactor type, operating mode, site location) were monitor ed 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. T he results of this study contributed to the technical basis for a Nuclear R egulatory Commission Draft Regulatory Guide (DG-1029) issued for comment in 1998. (C) 1999 Published by Elsevier Science S.A. All rights reserved.