(IT/P1-18) Studies on Behavior of Tritium in Components and Structure Materials of Tritium Confinement and Detritiation Systems of ITER

K. Kobayashi1), K. Isobe1), Y. Iwai1), T. Hayashi1), W. Shu1), H. Nakamura1), Y. Kawamura1), M. Yamada1), T. Suzuki1), H. Miura1), M. Uzawa1), M. Nishikawa2), T. Yamanishi1)
1) Japan Atomic Energy Institute, Tokai-mura, Ibaraki-ken, Japan
2) Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan

Abstract.  The confinement and removal of tritium are the key subjects for safety of ITER. The ITER buildings are confinement barriers of tritium. In a hot cell building, tritium is often released, as vapor and is in contact with the inner walls. Also those of an ITER tritium plant building will be exposed to tritium in an accident. However, the data are scarce, especially on the penetration of tritium into the concrete of the wall materials. The tritium released in the buildings is removed by the Atmosphere Detritiation Systems (ADS), where the tritium is oxidized by catalysts and is removed as water. Special gas of SF6 is used in ITER, and is expected to be released in an accident such as fire. Although the SF6 gas has the potential as a catalyst poison, the performance of ADS with the existence of SF6 has not been confirmed yet. Tritiated water is produced in the regeneration process of ADS, and is subsequently processed by the ITER Water Detritiation System (WDS). One of the key components of WDS is an electrolysis cell. The electrolysis cell is made of organic compounds, and there is no data on the durability of the cell exposed to tritium. To overcome these issues in a global tritium confinement, a series of experimental studies have been carried out as an ITER R&D task: 1) tritium behavior in concrete; 2) effect of SF6 on performance of ADS; and 3) tritium durability of electrolysis cell of ITER-WDS. 1) The tritiated water vapor penetrated into the concrete up to 2 cm from the surface only in two months’ exposure. The penetration rate of tritium in the concrete was thus appreciably large, so that it is required to evaluate the effect of the lining on the penetration rate quantitatively from the actual tritium tests. 2) The SF6 gas decreased the detritiation factor of ADS. Since the effect of the SF6 depends on its concentration closely, the amount of SF6 released into the tritium handling area in an accident should be deduced by some ideas of the arrangement of components in the buildings. 3) It was expected that the electrolysis cell of ITER-WDS could endure 3 years’ operation under the ITER design conditions. Measuring the concentration of the fluorine ions could be a promising technique for monitoring the damage of the electrolysis cell.

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