Sodium compatibility of ODS steel at elevated temperature

As oxide dispersion strengthened (ODS) ferritic steels have excellent resistance to swelling as well as superior mechanical strength, they are expected to be used as a long life cladding in the future advanced fast reactor. In this study, sodium environmental effects on the ODS steel developed by JNC were clarified through corrosion and mechanical tests in sodium at elevated temperature. For stagnant sodium conditions, sodium environmental effects were negligibly small. For flowing sodium condition at temperature over 948 K, however, nickel concentration increased at the surface of ODS steel, where phase transformation from α to γ was observed. In the γ-phase ODS steel, an oxide particle distribution is still maintained. From a simulation of the formation of γ-phase at the outer surface of an ODS steel cladding, it is concluded that its tensile strength could not be affected by sodium exposure, even in flowing sodium condition.