Evaluation of plane strain fracture toughness of neutron-irradiated A533B steels in nuclear reactor vessel surveillance test

In structural integrity assessment for nuclear reactor technology, one of the most important subject is to develop an estimation procedure of the cleavage controlled fracture toughness K_IC from standard Charpy V surveillance test data for neutron-irradiated pressure vessel steels. This paper proposes an empirical representation of K_IC fracture toughness transition curve for both unirradiated and irradiated A533B steels. The fitting curves derived are written in forms such as, K_IC(C_v))=138(C_v-us)/C_v-1)^-0.45+25(MNm^-3/2), K_IC(C_v) <= 165MNm^-3/2, K^Id(C_v)=44.7(C_v-us)/C_v-1)^-0.33+20(MNm^-3/2), K_Id(C_v) <= 108MNm^-3/2, where K_IC(C_v) and K_Id(C_v) mean the plane strain fracture toughness parameters characterizing an onset of the cleavage instability under static and dynamic loading conditions respectively, C_v is a value of standard Charpy V absorbed energy at a test temperature concerned and C_v-us is a upper shelf energy for the unirradiated steel. It is here demonstrated that the estimated values of K_IC(C_v) and K_Id(C_v) show a good agreement with valid K_IC and K_Id determined experimentally for both unirradiated and irradiated steels. (author)