Study of valve malfunction events in nuclear power plants

It is useful to analyze accident information of nuclear power plants at home and abroad with a view to enhancing the reliability of the plant. The valve plays an important role in safety and efficient operation of the plant, but the valve has many troubles, so an analysis of valve malfunctions has been made. This report analyzes nuclear power plant valve malfunction events from the Japanese and the United States databases, examines relevant documents, and studies measures for preventing recurrence of similar events. First, to help this analysis the Secondary Database for Valve Malfunction Events (SDBVME) has been structured from the Licensee Event Report (LER) in the United States and the accident reports to the Ministry of International Trade and Industry in Japan. By utilizing SDBVME, the causes of each event were analyzed and the importance of valves was evaluated. It became clear that the main valves in the turbine system, (for example, the feedwater regulating valve, the main steam isolation valve) are important because of the influence on the plant power level. On the other hand, motor-operated valves are important because of the influence on plant safety. Based on this analysis, seven measures have been studied to improve facilities and practical operation for the prevention of recurrence of accidents. (author)