Redesign of Low-Activation Vanadium Alloys Based on Impurity Control for Fusion Reactor Applications

Vanadium alloys are highly promising as structural materials of fusion reactor blanket, owing to their excellent high-temperature strength, and good compatibility with liquid metal lithium, which functions as both a coolant and a fuel tritium breeder material. Chemical composition of V-4Cr-4Ti has been selected as the primary candidate after systematic investigations into its neutron irradiation properties. Since V and Cr do not produce long-lived radioactive isotopes emitting high-energy gamma rays even under intense neutron irradiation conditions, low-activation characteristics are primarily governed by Ti and detrimental high-activation impurities, such as Co, Cu, Fe, Mo, Nb, and Ni. Very early material recycling, such as remote recycling within ten years, and re-use even in the same fusion reactor is achievable through effective impurity removal and minimization of Ti concentration. This paper discusses the progress in and mechanisms of vanadium metal refining. Additionally, the present paper reviews recent results and current status of redesign efforts for the Cr and Ti concentration balance to identify a new high-Cr and low-Ti composition, maintaining various attractive properties of the V-4Cr-4Ti alloy.