Current and future technologies for plant life management

It is approximately 30 years since the first commercial light-water reactor went into operation in Japan. The number of plants with operation experience of more than 30 years will be 18 during the next decade. As adequate maintenance or replacement has been implemented based on the results of annual inspections, troubles do not increase in line with plant ageing in Japan. To ensure safe and reliable operation of aged plants, however, the Ministry of International Trade and Industry (MITI) and three electric utilities started the plant life management study (the PLIM study) in 1994 and evaluated the integrity of major plant components assuming 60-year operation. As a result of the study, they compiled additional maintenance programmes for long-term operation in February 1999. In this study, the following ageing degradation phenomena and their countermeasures were discussed: stress corrosion cracking (SCC) of stainless steel and nickel based alloy components; reactor pressure vessel embrittlement; erosion-corrosion of carbon steel components; thermal fatigue; ageing of electric cables, etc. On the other hand, Japanese electric utilities have been engaged in developing repair and preventive maintenance technologies against the above mentioned ageing phenomena and have applied them to their plants. This paper briefly introduces some of these PLIM. technologies mainly related to Japanese BWR plants.