Recent accomplishment for the development of reduced activation ferritic/martensitic steels. Interim report for HFIR phase IV with results of relating activities

Extensive efforts for evaluating the irradiation performances of a reduced activation ferritic/martensitic steel (RAF/M) of F82H and other several RAF/Ms have been made in recent several years. They are, examination of the effects of neutron irradiation on (1) Ductile to brittle transition temperature (DBTT) up to a damage level of 20 dpa to explore lower temperature limit, (2) Enhanced He effect on DBTT shift for Ni/B doped heats (isotopic tailoring method was used for B doping), (3) Susceptibility to environmentally assisted cracking by the slow strain rate tensile tests (SSRT) in a high temperature pressurized water and (4) Flow stress-plastic strain relation obtained by measuring the profile of the specimen during tensile testing, together with the activities of (5) the development of the test methods after neutron irradiation and (6) other supporting researches. Results are summarized in the present report. They clearly indicate the good applicability of RAF/Ms to fusion machines. To prepare design criteria for ITER test blanket module (ITER TBM) and to examine irradiation effects to high irradiation damage levels to explore and to extend the materials limit are the key tasks in the development program of RAF/Ms. Researches of (1), (2) and (6) are oriented for the materials response to high irradiation damage levels, while (1), (3), (4) and (5) are expected to contribute to ITER TBM development. Development program of the RAF/M and the road map for ITER TBM and the blanket for DEMO are briefly introduced. (author)