Aging management of nuclear power plants in Japan

In January 2010, Tsuruga-1 reactor was 40 years and 17 units were more than 30 years of service. In Japan nuclear operators are required, before the 30 years and every 10 years afterward, to assess aging effects of the unit and to formulate a long-term maintenance policy based on the assessment results. This long-term maintenance policy is subject to approval of the government as part of the operational safe program. The key equipment subject to aging management include, among others, the reactor pressure vessel, various pipes, and electrical cables. The main phenomena concerned include irradiation embrittlement, stress corrosion cracking, and insulation deterioration. The operators are to ensure the monitoring of deterioration trends be practiced and recorded for each piece of equipment of interest by the use of technical knowledge obtained from the aging evaluations. The operators formulate their respective overall maintenance plans (maintenance methods, items, and frequencies), accordingly. This article detailed reviews of technical assessment of the aging effects, and long-term maintenance policy of Tsuruga-1 reactor. (T.Tanaka)