CHARACTERIZATION OF NUCLEAR TRANSMUTATIONS IN MATERIALS IRRADIATION TEST FACILITIES

This study presents a comparison of nuclear transmutation rates for ca ndidate fusion first wall/blanket structural materials in available fi ssion test reactors with those produced in a typical fusion spectrum. The materials analyzed in this study include a vanadium alloy (V-4Cr-4 Ti), a reduced activation martensitic steel (Fe-9Cr-2WVTa), a high con ductivity copper alloy (Cu-Cr-Zr), and the SiC compound. The fission i rradiation facilities considered include the EBR-II (Experimental Bree der Reactor) fast reactor, and two high flux mixed spectrum reactors: HFIR (High Flux Irradiation Reactor) and SM-3 (Russian reactor). The e stimated transmutation and displacement per atom (DPA) rates in these test reactors are compared with the calculated transmutation and DPA r ates characteristic of a D-T fusion first wall spectrum. In general, p ast work has shown that the displacement damage produced in these fiss ion reactors can be correlated to displacement damage in a fusion spec trum; however, the generation of helium and hydrogen through threshold reactions ((n,x alpha) and (n,xp)) are much higher in a fusion spectr um. As shown in this study, the compositional changes for several cand idate structural materials exposed to a fast fission reactor spectrum are very low, similar to those for a characteristic fusion spectrum. H owever, the relatively high thermalized spectrum of a mixed spectrum r eactor produces transmutation rates quite different from those predict ed for a fusion reactor, resulting in substantial differences in the f inal composition of several candidate alloys after relatively short ir radiation time. As examples, the transmutation rates of W, Ta, V, Cu, among others, differ considerably when the irradiation is performed un der a mixed spectrum reactor spectrum and under a fusion first wall sp ectrum. The out-of-core positions in mixed spectrum reactors can be pa rtially shielded against low energy neutrons, e.g. by hafnium, to redu ce the transmutation rates, but the displacement rates at these positi ons are much lower than those for the core positions. Fast reactors (E BR-II) provide the only possibility for obtaining high damage rates wi thout producing significant compositional effects in vanadium alloys, ferritic steels and copper alloys.