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Ferritic steels have been selected as candidate materials for first-wall applications in fusion reactors because of their high resistance to swelling and low thermal expansion coefficient. To characterize the fracture behavior of these materials influenced by both displacement damage and transmutation produced helium at levels relevant to fusion reactor irradiation conditions, the fracture toughness of HT9 and 9Cr-1Mo irradiated to 10 to 20 dpa at 50°C was evaluated using electric potential, single-specimen techniques. Circular compact tension specimens were tested at temperatures ranging from room temperature to 450°C. The single specimen method was employed to minimize the number of specimens required to save irradiation space and to meet the requirements for testing samples with a prototypic component thickness. Specimens of HT9 doped with 1 and 2% nickel to increase helium production during High Flux Isotope Reactor (HFIR) irradiation were also tested.
The results showed that the fracture toughness of the alloys was reduced after HFIR irradiation. The degradation of irradiation toughness resistance was more severe for 9Cr-1Mo than it was for HT9. The reduction in fracture toughness for both steels arising from irradiation in HFIR appeared to be more significant than that from irradiation in the Experimental Breeder Reactor-II (EBR-II). In addition, no major influence of nickel on the fracture toughness of HT9 was observed. Specimen thickness criteria for valid
fracture toughness, ferritic steels, low irradiation temperature, irradiation effects, data validity, fusion reactor
Senior scientist, Westinghouse Hanford Company, Richland, WA