Miniaturised impact properties of 2.5 dpa 300oC neutron irradiated RA FM plate, EB and TIG welds. F82H-mod, JLF-1, JLF-1B. Final report subtask SM1.2.2, EBP 95-98 programme

Reduced Activation Ferritic/Martensitic (RAFM) alloys are being developed for application in future thermonuclear fusion reactors by various partners in the fusion community. One of the major issues of these alloys is the low temperature irradiation embrittlement. The irradiation behaviour of the RAFM steel F82H-mod (2 IEA heats) and its EB and TIG welded joints, together with small amounts of related alloys, such as JLF-1 and JLF-1B, were investigated by irradiation experiments in the High Flux Reactor (HFR) in Petten. Miniaturised Charpy-type KLST impact specimens were neutron irradiated to various dose levels at 300C. The current report covers the results from the miniaturised impact tests of specimens irradiated to 2-3 dpa at a temperature of 300C, including a few specimens irradiated to 1-2 dpa at 80C. In the unirradiated condition, minor differences are observed between the 15 and 25 min plate F82H materials. After irradiation however, the induced shift is 50% higher for the 15 mm material. Differences in temper treatment, composition, and irradiation conditions may be the cause of this difference. After irradiation, the DBTT of JLF-IB was shifted by 150C, which is 90C more than the shift observed for JLF-1. The excess helium formed by transmutation reactions is presumably the cause of this larger shift. The fusion zone of EB welded joints has a very high DBTT around room temperature in the as welded, unirradiated, condition. The irradiation shifts the DBTT to very high values, some cases above +250C. Apparently the application of EB welded joints in the as-welded condition is unrealistic and a post-weld heat treatment is mandatory. There is a large variation in impact properties for the TIG welded joint. The limited number of specimens available prevents firm conclusions about the impact properties after irradiation, but the DBTT seems to be in the same range as that of the irradiated plate material. 5 refs