疎水性白金触媒の電子線照射によるトリチウム酸化活性の向上

Increase in activity of hydrophobic platinum catalyst for oxidation of tritium by irradiation with electron beams

岩井 保則

Iwai, Yasunori

トリチウム処理に不可欠な貴金属触媒の大幅な反応活性向上手法を開発した。貴金属触媒はトリチウムの環境放出抑制を担う安全システムの中核触媒のほかに、トリチウム水濃縮・分離処理の中核触媒としての使用が見込まれる。高濃度水蒸気に晒された際の失活を防止するため、疎水性高分子を担体とする特徴がある。今回、疎水性のスチレンジビニルベンゼンを担体とした白金触媒(Pt/SDB)、および、より疎水性を強化したターシャルブチルスチレンジビニルベンゼンを担体とした白金触媒(Pt/ASDB)の二種につき、電子線を照射した場合の触媒活性の変化を実験的に精査した。両方の触媒とも線量の増加とともに疎水性白金触媒の触媒活性は向上し、500から1000kGyにてトリチウム酸化における総括反応速度係数はピーク値を示した。総括反応速度係数のピーク値は未照射触媒の6倍の値を示した。この結果は照射済触媒の使用で触媒を充填する装置の規模を大幅に低減できることを示しており、システムの大幅な合理化が見込まれる。

Hydrophobic platinum catalysts have been widely applied in the field of nuclear fusion such as to the exchange reactions of hydrogen isotopes between hydrogen and vapor and to the oxidation reactions of tritium. Hydrophobic platinum catalysts are hardly susceptible to water mist and water vapor. Hydrophobic platinum catalysts are produced by supporting platinum directly on hydrophobic polymer beads. For the hydrophobic polymer, styrene divinyl benzene (SDB) has been applied in Japan. It can be pointed out that the betterment in catalytic activity of hydrophobic catalyst is expected to downsize the catalytic reactor based on a hard look at a large increase in flow rate in future. The acute change in catalytic activity of two types of commercial Pt/SDB catalysts was found when they were irradiated with electron beams. After irradiation with electron beams, the catalytic activity was evaluated by means of overall reaction rate constant for the oxidation of tritium. The overall reaction rate constant increased as increase in dose. The constant showed the peak value in the dose between 500 to 1000 kGy. After the peak, the constant decreased as increase in dose. The overall reaction rate constant at the peak was 6 times larger than that evaluated with unirradiated. The mechanical strength of irradiated Pt/SDB kept sound until 1500 kGy. The irradiation is a promising method to the betterment in catalytic activity of Pt/SDB catalyst.