PNNL

Abstract

Pure iron and nickel were irradiated to very high exposures in two fast reactors, BOR-60 and BN-350. It appears that both nickel and iron exhibit a transient-dominated swelling behavior in the range of 2 to 15x10-7 dpa/sec, with the shortest transient at approximately 500 C in nickel, but at less than 350 C for iron. It also appears that the duration of the transient regime may be dependent on the dpa rate. When the two metals are irradiated at 345-355 C, it is possible to obtain essentially the same swelling level, but the evolution of mechanical properties is quite different. The differences reflect the fact that iron is subject to a low-temperature embrittlement arising from a shift in ductile-brittle transition temperature, while nickel is not. Nickel, however, exhibits high temperature embrittlement, thought to arise from the collection of helium gas at the grain boundaries. Iron generates much less helium during equivalent irradiation.