Palladium-catalyzed oxidative diffusion for tritium extraction from breeder-blanket fluids at low concentrations

Abstract

Oxidative diffusion can extract hydrogen from metal solutions at extremely low partial pressures. The hydrogen diffuses through a metal membrane and is oxidized to water. The oxidation reaction produces the very low downstream pressures that drive the flux. This method is attractive because the flux can be proportional to the square-root of upstream pressure. For fusion reactors with liquid lithium or lithium-lead alloy breeder blankets, permeation windows provide a simple, cheap tritium extraction method. Interdiffusion rates, separation flux, window size, helium contents, tritium holdup costs, and overall costs are calculated for membranes of palladium-coated zirconium, niobium, vanadium, nickel and stainless-steel. For extracting tritium from liquid lithium using the cheapest windows, Zr-Pd, the material and labor cost is 8.0 M$ at 1 wppm, and is inversely proportional to tritium concentration in the lithium. The tritium holdup cost for the windows is 4.8 M$, and for the blanket it is proportional to the blanket volume and concentration. An overall economic optimization suggests that 1 to 1.5 wppm in lithium is optimal. For extracting tritium from 17Li83Pb at 0.26 wppb, the cheapest window is V-Pd; the cost is 2.6 M$, and the tritium holdup is negligible.