Failure and Maintenance Analysis of Motor Operated Valves of TVO I and II Nuclear Power Plants

The analysis of operating experience, e.g. failure and maintenance data, gives valuable information on components behaviour in its operational environment. This knowledge can be used to reveal weaknesses in component and plan more effective maintenance practices and improve the component reliability. The efficient use of operating experiences requires systematic data collection systems, which are widely used in nuclear industry. For data analyses, both qualitative and quantitative methods are available in reliability engineering. In this paper, we demonstrate an analysis of motor operated valve operating experiences of four safety related systems in TVO I and II. The data consists of nearly 200 failure and maintenance descriptions, which have been reported during the observation period 1.1.1981-31.12.1989. The analyses cover failures of both the valve itself and its electromechanical actuator. Failure mode and effect analysis (FMEA) and maintenance effects and criticality analysis (MECA) are used as operating experience analysis methods. Classifications were made on valve parts, failure modes, causes, effects, detection, and criticality, and recurring failure causes and significant problem areas in valve operability were studied. The failure and maintenance descriptions are documented on particular FMEA and MECA sheets, from which data is easily retrievable and updatable for further analyses. As examples of quantitative studies, statistical analyses concerning repair and unavailability times and failure trends are demonstrated.