INVESTIGATION OF AIR OPERATED VALVE PERFORMANCE BY ACCELERATED LIFE TEST

In nuclear power plants, many valves are operated under harsh conditions such as high temperature - high pressure and radiation environments but high levels of reliability are required from valves for safety operation of the power plant. However, deterioration of valve parts due to power plant aging and the system's transient phenomena due to rapid load shift operation are acting as obstacles that impede securing valve reliability. To secure valve reliability, quality in design/production stages and intended performance under the worst operation conditions shall be assured. Also, it is necessary to meet the reliability level given in the specified environment conditions and to perfor m the designed functions throughout its lifetime without failure. Meanwhile, to enhance the safety and the operation of nuclear power plants, it is important to early detect the deterioration of valve performance and take measures quickly. However the mec hanical defects of valves are occurs suddenly in various types and it is very difficult to predict them. Valves which are responsible for the important functions of nuclear power plants are confirmed performance and durability before the installation. Howe ver, the performance degradation and defects of the valve are occurs during plant operating. Therefore, to ensure that the valves perform their designed functions for the requested period without failure, it is important to demonstrate their reliability in all stages such as design, production, and operation. The purpose of this paper is the best preventive maintenance and life cycle management, including comprehensive quality control measures established in the valves. Therefore, the performance verificati on through performance validation tests were performed on air operated valves most commonly used in nuclear power plants. In addition, the leakage and stroke time were measured by performing an accelerated life test (thermal aging, radiation exposure, mech anical cycling) under the operating conditions of the power plants . Results show that the thermal aging of valves has significant effects on the valve seat and stem leakage but it has almost no effect on the actuator leakage and the stroke time. Meanwhile, it is found that the radiation and mechanical aging of valves have no clear effect on the leakage and stroke time of valves