EVALUATION OF FREQUENCY OF TRANSIENTS OCCURRING AT NUCLEAR POWER PLANTS IN JAPAN

摘要

In the present study, the frequency occurrence of transients was evaluated by using the published data in Japan, and the results were compared with US data. Abnormal occurrences at commercial nuclear power plants in Japan are reported by electric utilities to the competent authority, the Ministry of International Trade and Industry (MITI), pursuant to either the laws or the notification by the minister of MITI, and these events are summarized in the annual report edited by MITI. In the annual reports, by elminating non-transient events, 133 events in PWRs and 285 events in BWRs were identified as transients. These events were classified into 41 and 37 transient categories in PWRs and BWRs, respectively, as defined in previous US studies. As a result, the most frequent transient was identified as manual trip or scram in both PWRs and BWRs and the second most frequent event was identified as generator trip in PWRs and electric load rejection in BWRs. It was also found that the frequency of transients in Japan was equivalent to a range of nearly a half to a fortieth the range shown by US data, with the exception of some transients such as steam generator tube leaks in PWRs and trips of one primary loop reciruclation pump in BWRs.