CHARPY IMPACT TEST-RESULTS FROM LOW ACTIVATION ALLOYS IRRADIATED TO 10 DPA AT 365-DEGREES-C

The effect of irradiation on Charpy impact properties has been determined for six low activation ferritic alloys irradiated in FFTF/MOTA to 3 x 10(22) n/cm2 (E > 0.1 MeV) or 10 dpa at 365-degrees-C. Compositions Fe-2Cr-1.5V, Fe-12Cr-6Mn-1V and Fe-12Cr-6Mn-1W develop unacceptably large shifts in ductile to brittle transition temperature (DBTT) due to irradiation, Fe-9Cr-1V develops a small shift and Fe-9Cr-1W and Fe-7.5Cr-2W develop negligible shifts. There is little effect on upper shelf energy (USE) in all cases. Fractographic examinations revealed a change in fracture mode from transgranular cleavage to intergranular failure at prior austenitic boundaries due to irradiation for four of the six alloys. The cause is ascribed to Mn additions in the alloys. Alloy development of low activation ferritic alloys should concentrate on the Fe-7.5 to 9Cr range.