中性子照射した純鉄および圧力容器鋼の磁気特性と照射欠陥の関係

摘要

Development of nondestructive evaluation (NDE) techniques for neutron irradiation embrittlement of reactor pressure vessel (RPV) steels is of global interest for the aging management of existing nuclear power plants. Magnetic measurement is one of the promising NDE techniques because of its sensitivity to various types of lattice defects. To establish such a technique, it is important to clarify the relationships between irradiation defect structures, and the mechanical and magnetic properties. Specimens of pure iron and A533B-type RPV steel were neutron-irradiated up to 5×10~(19) n/cm~2 (E>1MeV) at 563K. During irradiation, magnetic hysteresis curves were continuously measured. Vickers hardness and Charpy impact tests were conducted before and after irradiation. Coercive force of pure iron increased with increasing neutron fluence, whereas that of RP V-steel showed different behavior. These phenomena were explained by the difference of defect structures observed by TEM.%中性子照射中の純鉄と任力容器銅の連続磁気計測に成功した。純鉄の場合、保磁力は照射とともに増加したのに対して、圧力容器鋼の場合、増加と減少挙動を示し2つの変化機構が存在することが明らかになった。TEM 観察により、圧力容器鋼にもともと存在した転位の近傍で微細欠陥クラスターが形成していることを確認した。照射に伴う保磁力の減少は、転位まわりの応力場の減少に反映していると考えられる。