Fusion Science and Technology / Volume 52 / Number 3 / October 2007 / Pages 711-715
Technical Paper / The Technology of Fusion Energy - Tritium, Safety, and Environment
To obtain performance data of atmosphere detritiation system at the off normal events such as SF6 release for the safety of ITER, the detritiation experiment was planned and performed at Tritium Process Laboratory (TPL) in Japan Atomic Energy Agency (JAEA) using a small scaled detritiation system for the oxidation performance test which can process gas flow rate of 0.06 m3/hr in once through. The detritiation system consists of two oxidation catalyst beds (473K and 773K) for converting hydrogen isotopes and tritiated methane in compounds to water vapor and a bubbler for removing water vapor. SF6 gas is used as an electric insulation gas of Neutral Beam Injection system (NBI) in ITER, and is expected to be released in an accident such as fire. In this time, the performance of oxidation catalyst bed of the detritiation system for hydrogen under existence of SF6 which are released from NBI was investigated.
The SF6 gas was notably decomposed in the case of the catalyst bed temperature higher than 623K. In addition, when 0.05% or more of SF6 was introduced with 1% of hydrogen, a part of the water produced by the 473K catalyst bed was reduced to hydrogen due to the reaction with the decomposed gas in SF6. Consequently, the detritiation factor (D.F.) of the detritiation system was decreased to less than 50 from > 10000 of its initial value. Since the effect of SF6 depends on its concentration closely, the amount of SF6 released into the tritium handling area in an accident should be reduced by some ideas of the arrangement of components using SF6 in the buildings.