Development of Selective Hydrogen Pumping Method Using Lithium Films

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Development of a new pumping system where hydrogen isotope fuel (especially tritium) is separately exhausted from helium ash to reuse it has been desired. The present study is aimed at developing an original technique for selective hydrogen pumping with use of lithium panel. The results obtained here are summarized as follows.1. Below the melting point (179ﾟC), lithium does not react with hydrogen molecule but strongly does with hydrogen atom and hydrogen ion to form lithium hydride. This hydrogen absorption takes place at rate of single hydrogen atom per single lithium atom, so that the total amount of hydrogen pumping is proportional to a surface area times thickness of lithium layr, owing to high-speed hydrogen diffusion in bulk lithium.2. Baking of lithium hydride above 400ﾟC leads to decomposition into hydrogen molecule and lithium atom.3. These two properties listed above enable us to construct a hydrogen selective pumping system. Namely, weakly ionized hydrogen discharges or hot-filament induced hydrogen dissociation in pumping ports give rise to selective hydrogen uptake into lithium panel. After saturation of lithium panel with hydrogen, heating the panel up to 400ﾟC induces hydrogen molecule desorption which is exhaused by a conventional pump, recovering the lithium panel to the initial state.4. Special care should be payd to keep lithium surface clean since it easily react with such residual gases as H_2O,O_2 and CO,to form lithium compounds.5. Base materials where lithium films are deposited are preferably metal rather than graphite which chemically reacts with lithium.