Acceleration tests for radiation damage in reactor materials

In nuclear reactor materials, the lowering of ductility, the change of dimensions and other damage occur when they undergo neutron irradiation during the use, and this neutron irradiation damage increases with the amount of irradiation. Actually in the fuel assembly materials of one year service period as well as the structural materials, the life of which exceeds ten years, it is necessary to confirm the radiation endurance, and it is desirable to shorten the test period. In case of light water reactors, the rate of neutron irradiation in the core is relatively low, accordingly it is easy to carry out the acceleration test. But in case of fast breeder reactors, the neutron flux in the core is high, therefore heavy iron accelerators are used for the acceleration test of their core materials. Further in case of nuclear fusion reactors, the neutron energy is higher, and the evaluation of neutron irradiation damage is very difficult. As the materials of fuel assemblies used in the core of fast breeder reactors, the development is carried out so as to endure the use at 2 x 1027 n/m2 and 650 deg C. In case of SUS 316 stainless steel usually used in the core of fast breeder reactors, swelling occurs. The formation of helium due to the (n, α) reaction with fast neutrons affects the swelling. The effect of precipitated phase induced by the neutron irradiation and the embrittlement due to high temperature helium are also problems. The acceleration tests are useful in these cases. (Kako, I.)