Host: The Japan Society of Mechanical Engineers
Name : The 27th International Conference on Nuclear Engineering (ICONE27)
Date : May 19, 2019 - May 24, 2019
Advanced thermal reactor "FUGEN" is the heavy water moderated, boiling light water-cooled, pressure tube-type reactor. The commercial operation started in March 1979, and terminated in March 2003.Tritium was generated in heavy water as a moderator by absorbing neutron during operation. Heavy water system and Helium system are contaminated by tritium. Tritium has a nature to diffuse easily, so there is a risk of leakage. The tritium decontamination in their system had been carried out to prevent its spreading and to minimize tritium exposure for workers during dismantling work. The tritium decontamination has three steps: draining residual heavy water, removing residual tritiated water by air through drying and vacuum drying, and removing tritium as crystallization water in oxide film by air displacement. The removal of residual tritiated water and tritium were carried out after dividing tritium-contaminated system into several parts. In the removal of residual tritiated water, there were two issues to be solved; (1) the difficulty in applying a huge dehumidifier used a solid adsorbent because decontamination object is located in narrow space, (2) the necessity to estimate the volume of residual tritiated water for managing the removal process. For the first issue, a portable and small dehumidifier with hollow fiber polyimide had been applied. As a result, it was indicated that the dehumidifier allow us to remove residual tritiated water effectively and has the high applicability to tritium decontamination in FUGEN. For the second issue, the volume of residual tritiated water had been tried to estimate by considering heat transfer phenomena. As a result, the volume of residual tritiated water could be estimated with about 80% accuracy.
