Compositional and temperature dependence of void swelling in model Fe–Cr base alloys irradiated in the EBR-II fast reactor

A series of annealed and aged Fe–xCr, Fe–12Cr–yC and Fe–12Cr–0.1C–zMo model alloys were irradiated in EBR-II at eight temperatures between 400°C and 650°C and dose levels ranging from 35 to 131 dpa. Swelling-induced density changes observed in the binary alloys generally peaked at mid-chromium levels, with the chromium and temperature dependence expressed primarily in the duration of the transient regime. The steady-state swelling rate at the lower irradiation temperatures was much higher than previous estimates, reaching ∼0.2%/dpa and possibly still climbing at higher neutron exposures. The dependence of swelling on molybdenum and carbon was more complex, depending on whether the temperature was relatively low or high. At temperatures of 482°C and above, the effect of carbon additions was very pronounced with swelling of Fe–12Cr jumping dramatically from near zero at 0.002% C to 6–10% at 0.1% C. This indicates that the major determinant of the composition and temperature dependence probably lies in the duration of the nucleation-dominated transient regime of swelling and not primarily in the steady-state swelling rate as previously envisioned. This raises the possibility that significant swelling may occur earlier in fusion and spallation neutron spectra where high gas generation rates may assist void nucleation.