Accession Number:



Digital I&C Systems in Nuclear Power Plants. Risk-Screening of Environmental Stressors and a Comparison of Hardware Unavailability With an Existing Analog System

Descriptive Note:

Technical rept.

Corporate Author:


Personal Author(s):

Report Date:


Pagination or Media Count:



In this report, we present a screening study to identify environmental stressors for digital instrumentation and control IC systems in a nuclear power plant NPP which can be potentially risk-significant, and compare the hardware unavailability of such a system with that of its existing analog counterpart. The stressors evaluated are temperature, humidity, vibration, radiation, electro-magnetic interference EMI, and smoke. The results of risk-screening for an example plant, subject to some bounding assumptions and based on relative changes in plant risk core damage frequency impacts of the stressors, indicate that humidity, EMI from lightning, and smoke can be potentially risk-significant. Risk from other sources of EMI could not be evaluated for a lack of data. Risk from temperature appears to be insignificant as that from the assumed levels of vibrations. A comparison of the hardware unavailability of the existing analog Safety Injection Actuation System SIAS in the example plant with that of an assumed digital upgrade of the system indicates that system unavailability may be more sensitive to the level of redundancy in elements of the digital system than to the environmental and operational variations involved. The findings of this study can be used to focus activities relating to the regulatory basis for digital IC upgrades in NPPs, including identification of dominant stressors, data-gathering, equipment qualification, and requirements to limit the effects of environmental stressors.

Subject Categories:

  • Nuclear Power Plants and Fission Reactor Engineering

Distribution Statement: