Irradiation Programme HFR Phase lib -SPICE : Impact testing on up to 16.3 dpa irradiated RAFM steels

The objective of this work is to study the effects of neutron irradiation on the embrittlement behavior of different reduced activation ferritic/martensitic (RAFM) steels. The irradiation was carried out in the Petten High Flux Reactor (HFR) in the framework of the HFR Phase IIb (SPICE) irradiation project at a nominal dose of 16.3 dpa and at different irradiation temperatures (250-450 °C). The impact properties are investigated by instrumented Charpy-V tests with subsize specimens (KLST-type). The emphasis is put on the investigation of irradiation induced embrittlement and hardening of the European RAFM reference steel for the first wall of a DEMO fusion reactor, EUROFER97 under different heat treatment conditions. The mechanical properties of EUROFER97 are compared with the results on international reference steels (F82H-mod, OPTIFER-la, GA3X and MANET-I) included in the SPICE project. EUROFER97 irradiated up to 16.3 dpa between 250 and 450 °C showed irradiation resistance that is comparable to those of best RAFM steels. Large low temperature (T im ≤ 300°C) embrittlement is seen for all investigated RAFM steels. Heat treatment of EUROFER97 at higher austenitizing temperature led to the reduction of embrittlement at low temperatures (T irr 350°C the DBTTs of the steels remain below -20°C and, hence, are well below the application temperature. Analysis of hardening vs. embrittlement behaviour indicated hardening dominated embrittlement at Tjrr < 350°C with 0.17 ≤ C 100 ≤ 0.53 °C/MPa. Oxygen dispersion hardened ODS EUROFER with 0.5 wt.% Y 2 O 3 has been irradiated at selected irradiation temperatures. ODS EUROFER showed not satisfying impact properties already in the unirradiated condition characterized by low USE =2.54 J and large DBTT = 135°C. Furthermore, the increase of USE for irradiation temperatures below Tjrr ≤ 350°C indicates not optimized fabrication process. At T irr =250°C neutron irradiation induced shift in DBTT is comparable to that of the base EUROFER97 steel. At higher irradiation temperatures, however, hipped ODS EUROFER shows larger embrittlement compared to base metal. He embrittlement is investigated in EUROFER97 based steels, that are doped with different contents of natural boron and the separated 10 B-isotope (0.008-0.112 wt.%). Boron doped steels show progressive embrittlement and reduction of toughness with increasing helium amount. At T irr =250 °C helium induced embrittlement is of hardening nature for low helium contents up to 84 appm. Larger helium concentrations lead to non-hardening embrittlement mechanisms beyond that of hardening embrittlement.