Advanced thermal reactor “FUGEN” is a heavy water-moderated boiling light water-cooled pressure tube-type reactor. Because tritium had been generated in the heavy water during the reactor operation, the heavy water system and helium system were contaminated by tritium.

The chemical form of the tritium was water molecule in FUGEN. For the drying treatment of heavy water contaminated by tritium, air-through drying and vacuum drying were applied to the system drying. The air-through drying has an advantage that can reduce the risk of tritium leakage, because the drying equipment can be constructed as closed-circuit. On the other hand, the vacuum drying can dry the whole system because dead end of piping can be aspirated. Helium system, heavy water purification system and rotary type dehumidifier were chosen for the object in this study.

It was demonstrated that both methods were effective for drying treatment of heavy water in system. Helium system, low-contamination and non inclusion, could finish the vacuum drying rapidly. However, Heavy water purification system needed long period for drying treatment. The result showed that it needed long period to dry up if the objects include the adsorbent of water such as alumina pellet, resin and silica gel. But it can be accelerated by replacement absorbed heavy water to light water from the result of drying treatment of the rotary type dehumidifier.

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