Mechanical properties of reduced activation ferritic/martensitic steels after European reactor irradiations

The development of First Wall and Blanket materials which are capable of withstanding many years the high neutron and heat fluxes, is for material scientists a critical path to fusion power. In an energy generating fusion reactor, such structural materials will be exposed to very high levels of irradiation damage up to about 80 dpa. Regarding the radiation damage resistance of the considered Reduced Activation Ferritic/Martensitic steels, e.g. the European EUROFER and the Japanese F82H mod., as international reference material of this kind, broad European reactor irradiation programmes cover several steps from up to 5 dpa for ITER Test Blanket Modules, till up to 80 dpa for First Wall and Blanket of a DEMO fusion reactor. The lower irradiation damage conditions until 15 dpa can be realized in European fission reactors like the HFR at JRC, Petten, but higher damages - in reasonable times - in fast reactors only. For this purpose the fast reactor BOR 60 of the State Scientific Centre of Russian Federation Research Institute of Atomic Reactors, Dimitrovgrad, has been utilized for irradiations up to 80 dpa. Results from the lower damage irradiations like SIENA, MANITU and HFR-Ib, up to 2.4 dpa had been reported in the past frequently. Recent results of mechanical properties, like Ductile to Brittle Transition Temperatures from instrumented impact-V tests with sub size specimens and stress and strain values from tensile tests with miniaturized specimens will be presented from specimens of the HFR Phase-IIb (SPICE) irradiation project up to 15 dpa at different irradiation temperatures between 250 and 450 deg. C. The fast reactor irradiation project ARBOR 1 reached at a temperature ≤ 340 deg. C an irradiation damage of 33 dpa. In the post irradiation instrumented impact-V tests a dramatic increase in the Ductile to Brittle Transition Temperature as an effect of irradiation has been detected. During tensile testing the strength values are increased and the strain values reduced due to irradiation hardening. After first thermal recovery tests with 550 deg.C annealing for three hours it could be demonstrated on EUROFER specimens irradiated at a temperature ≤ 340 deg. C up to 15 dpa, that nearly virgin conditions could be achieved. (author)