Japan now has about 40 nuclear power plants in commercial operation and the oldest one has been in operation for about 20 years which is regarded as a half of the design life. It is, therefore, required to establish the general procedure for life evaluation of a plant.
In this paper, the technical issues for the life evaluation are summarized concerning the aging phenomena and their causes, the prioritization of each component according to its relevance to plant safety, and examples of failures and troubles of plants in Japan.
Considering the aspects peculiar to Japan like the relatively small number of plants reaching their design lives at the same time and highly sophisticated technological level, the technical issues are explained from the following view points:
(1) Identification of aging phenomena
(2) Management of information on plant and experiences
(3) Technical requirements for monitoring and inspection
(4) Approach to modelling of aging
(5) Establishment of general procedure for life evaluation.
Finally, the aging research program in JAERI is described, which includes the aging evaluation of decommissioned JPDR and test studies on irradiation embrittlement and crack growth of RPV steel and/or concrete.