Alternatives to the Maroni Process for Tritium Recovery in Fusion Reactors: Avoiding Volatile Hydrogen Fluoride and High-Temperature High-Speed Rotating Machinery
Fusion reactors now on the drawing table, including LLNL’s LIFE reactor, require liquid lithium blankets for cooling and breeding tritium fuel. The tritium fuel must be continuously removed from the blanket so that it can be returned to the reactor for burning, via target manufacturing in the case of LIFE. The baseline process for accomplishing this in the LIFE reactor is the well-known Maroni process which uses high-temperature molten mixed alkali-metal halide salts (LiCl:LiF:LiBr at 530°C) as an extraction solvent. With the generation of hydrogen isotopes, liquid and gaseous acids such as HCl, HF and HBr (and the deuterium and tritium analogs) form in the salt phase, making these solvents very corrosive, with other problems due to volatility. Following extraction of lithium tritide from the molten lithium, the tritide anion must undergo electrochemical oxidation in a high-temperature electrochemical cell to form tritium gas, which can then be separated by stripping in a stream of inert gas such as xenon or helium. The volatility of hydrogen chloride or the tritium analog (HCl or TCl), hydrogen fluoride or the tritium analog (HF or TF) and hydrogen bromide or the tritium analog (HBr or TBr) complicate this separation. An alternative electrolytic process for the conversion of lithium tritide to tritium gas and metallic lithium is based upon the use of a benign lithium hydroxide (LiOH) or lithium carbonate (Li 2 CO 3 ), which is an extremely attractive alternative to the very volatile and corrosive lithium halide electrolyte. The separation of the molten lithium and molten chloride salt phases requires numerous high-temperature (530°C) high-speed centrifugal separators, with bearings and seals exposed to the highly corrosive fluids. Currently, centrifugal contactors are proposed to contact the liquid lithium in which the tritium is bred with a molten salt extraction solvent. These high-speed centrifugal contactors must operate at high temperature for prolonged periods of time without failure. Such rotating machinery, with a highly corrosive molten salt electrolyte, and a liquid lithium phase threatening liquid metal embrittlement is a source of substantial concern. The invention disclosed here is a non-centrifugal contactor capable of operating without any moving parts.