August 8, 2024
Vanadium base alloys are leading candidate materials for breeder blanket structures in fusion reactor designs flowing liquid lithium because of their excellent lithium compatibility and superior high-temperature mechanical properties compared to reduced activation ferritic-martensitic steels and other structural materials. Blanket design activities at Tokamak Energy have indicated that a self-cooled liquid lithium blanket without an electrical insulator coating may not be viable due to the magnetohydrodynamic (MHD) pressure drop and the resulting parasitic load. A dual-cooled design with helium as the coolant obviates the need for an insulator coating and provides a more accessible design point. However, vanadium alloys have not been strongly considered for dual-cooled designs because of concerns with oxidation and embrittlement by the uptake of interstitial atoms including oxygen, carbon, nitrogen, or hydrogen. The most studied vanadium base fusion alloy, V-4Cr-4Ti, the prime candidate vanadium alloy previously selected by the U.S. Fusion materials program, has been shown to have unacceptable tensile elongation in oxygen bearing environments, including in high purity helium with < 0.1 vppm O2. Therefore, to enable development of a dual-cooled blanket design with liquid Li as the breeder, a vanadium base alloy with improved oxidation resistance and equivalent or better mechanical properties compared to V-4Cr-4Ti is required. The proposed work scope involves thermodynamic modelling to devise the optimal processing for V-Ti and V-Zr alloys containing between 7 and 15 wt.% Cr. Oxidation, thermomechanical property, and weld testing will be combined with microstructure characterization to evaluate the fabricated alloys. If this project is successful, the development of an advanced vanadium base alloy with improved oxidation resistance could potentially expand the use of these materials to more diverse environments, enable new design avenues, enhance safety under accident conditions, and improve plant efficiency.