Fig. 2-11 A schematic diagram of a tritium removal system using hollow-filament polyimide membranes (the dotted lines show the loops for unit tests) The water vapor component is removed at first after circulation of air in a glove box and permeation through a membrane. Second, the tritium gas is removed from air.

Fig. 2-12 The outside appearance of a gas separation membrane module and cross sectional views of a membrane A bundle consists of 10000 hollow-filaments, each polyimide filament has 0.7 mm in diameter 1.4 m in length, respectively. The total surface area of these membranes are approximately 40m2. The permeation ratio of this membrane for hydrogen/nitrogen is 160 at room temperature.

Deuterium and tritium are used as fuels in fusion reactors. Tritium is a radioactive material emitting a rather weak beta-ray. Therefore tritium should not leak to the environment. So far, tritium is removed by a water adsorbent, where tritium is oxidized in the form of water by a catalyst. Moisture in air is simultaneously adsorbed in this method. This result in a big volume of processing air. This may mean the rather large, complex low reliability in the system. The total tritium quantity in a fusion reactor is significant so that the issue becomes serious. A hollow-filament polyimide membrane has a function to permeate through hydrogen (tritium) gas and water vapor selectively. This function is useful in reducing the volume of processing air by the separation of water vapor. Consequently it is expected to provide a compact reliable tritium removal system (Fig. 2-11). A bundle of 10000 filaments, each filament having approximately 0.7 mm in diameter, 1.4 m in length, is shown in Fig. 2-12. The tritium concentration in a glove box moves a figure two places to the right after the 2 hour operation. The tritium concentration ratio before and after the membrane is 50 that is to say a final volume of tritium removal processing will be reduced 1/50. This method is effective to provide a compact high reliable system for all safety facilities in tritium handling. We have good information for scale-up, and the durability necessary for future safety regulation.

Reference T. Hayashi et al., Gas Separation Performance of a Hollow-filament Type Polyimide Membrane Module for a Compact Tritium Removal System, Fusion Technol., 28, 1503 (1995).

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