A review on operating experiences of containment isolation systems in Korea

Abstract

Wide experience, on the order of 50 reactor-years, in operating containment isolation systems has been accumulated in Korea since 1978, necessitating a review of the operating data to confirm the integrity of containments and to establish the future direction to the containment test program. The objectives of the present work are to collect, consolidate and assess the operational data relevant to containment isolation systems, and then to identify types of isolation valve failures, dominant leakage paths and factors affecting integrated leakage rate test. Leakage is observed to be the most frequent type of isolation valve failure. The causes of the valve leakage are packing leakage, seat damage due to foreign material, and misadjustment of torque switches. Malfunction and deterioration are also observed to be frequent failure modes. General leakage trends show that more careful surveillance during preoperational test can reduce the containment leakage. Significant leakage paths are found to be through air locks and large valves of six-inch or greater nominal diameter, so that weighted surveillance and inspection on these dominant leakage paths can considerably reduce the containment leakage. Atmospheric stabilization is found to be the most important factor to obtain the reliable integrated leakage rate. In order to achieve a well stabilized atmosphere, temperature and flow rate of compressed air should be kept constant and it is preferable not to operate fan coolers during pressurizing the containment for test. These results are expected to be a guidance for improving the operation of containment system.