Effects of dpa rate on swelling in neutron-irradiated Fe–Cr and Fe–Cr–Mo alloys

Data are presented on the void swelling of three model Fe–Cr ferritic alloys following irradiation in TEM packets in FFTF–MOTA over the range 373–600 °C and a wide range of dpa rates. It is shown that raising the chromium level decreases the steady-state swelling rate at ∼420 °C. Addition of Mo to the Fe–12Cr alloy does not change the swelling rate significantly but does lead to an apparent swelling of ∼3% that arises from the radiation-accelerated formation of Chi phase. Swelling tends to decrease with increasing irradiation temperature for all three alloys. It is shown that the sensitivity of swelling to dpa rate expresses itself not at the various packet positions in FFTF, each with their characteristic nominal dpa rates, but also in response to variations in dpa rate along the length of the packet containing the specimens. The latter introduces second-order uncertainties in determination of the dpa levels and dpa rates, but these are not sufficient to obscure the major conclusion concerning dpa rate and composition.