Irradiation embrittlement of pressure vessel steels of the BWR plants in Japan. An analysis of the surveillance data

Surveillance data for pressure vessel steels of the 51 LWR plants in Japan were analyzed to make clear the effect of neutron irradiation on the brittle transition temperature of the steels. The clear difference observed in the rise of the ductile to brittle transition temperature between the normal and accelerated irradiation samples is considered to be due to the effect of neutron flux. The present analysis is discussed in comparison with the result of computer simulation based on the rate equations of the radiation damage process and the recent experiments of APFIM and positron annihilation. (author)