The paper presents the analysis of operational events at nuclear power plants (NPPs) of Ukraine caused by failures and defects of the instrumentation and control systems (I&C systems). The effort contains statistical information about the number and the share of operational events at Ukrainian NPPs due to incorrect performance of analog and digital I&C systems in the general amount of events. The categories of these events according to the international and national classifications have been considered. The paper provides for the brief overview of the recently published EC Joint Research Center Technical Report on digital I&C systems at NPPs of foreign countries based on the information from IAEA and U.S. NRC databases. There are causes of operational events due to defects of the specified systems and main recommendations on their prevention. Using the approach similar to the one in the Technical Report, the paper presents the detailed analysis of direct and root causes, as well as correction measures for the operational events at Ukrainian NPPs from 2013 to 2018 caused by digital I&C systems. The experts considered separately four groups of events due to defects of components in the peripheral part of the digital I&C systems (sensors, actuators), central part of digital I&C systems (software and hardware), cable lines and electronic components of analog I&C systems (built-in components). There is an additional analysis of root causes of events related to digital I&C systems by the types of systems and lifecycle stages (design, mounting, operation) and main sources of occurrences within the systems (software, hardware, cables, etc.).
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