Change in activity of catalysts for the oxidation of tritium during a fire event

火災事象時のトリチウム酸化触媒の活性度変化

岩井 保則; 佐藤 克美; 山西 敏彦

Iwai, Yasunori; Sato, Katsumi; Yamanishi, Toshihiko

核融合プラントにおける安全性確保のため、異常事象発生時においてもトリチウムを酸化する触媒の性能は維持する必要がある。火災時には電気ケーブル等から有機ガスが発生し、トリチウム酸化触媒の性能を阻害する可能性が指摘されてきた。これを踏まえて、白金アルミナ触媒及び原子力機構が企業と共同開発した疎水性白金触媒H1Pの二種につき、火災時の触媒の活性度変化を実験的に検証した。火災模擬試験から、火災時に発生する主要有機ガスはエチレン,メタン,ベンゼンであることを明らかとした。触媒温度423Kでは試験した二種の触媒とも火災による活性度低下は見られなかった。293Kでは火災初期に有機ガスの燃焼により、触媒の水素酸化反応速度の向上が見られた。H1Pは水分影響で反応速度が一時的に低下するものの、最終的にはもとの反応速度に戻り、火災により不可逆的な触媒性能の低下は生じないことを明らかとした。

The catalytic performance should be maintained in any off normal events. Fire accident is the typical off normal event. In the fusion plant, typical combustibles are evaluated to be polymeric low-halogen cables. Produced gases from burned low-halogen cable may affect the activity of catalysts for the oxidation of tritium. We experimentally demonstrated the influence of produced gases from burned low-halogen cable on the activity of catalyst using tritium gas. Our analyzed result showed that ethylene, methane and benzene were major produced gases. The activity of catalysts for the oxidation of tritium during a fire event was evaluated using two types of commercial Pt catalysts which are the hydrophilic Pt/AlO and the new type hydrophobic catalyst named TKK-H1P especially developed for the room temperature conversion of tritium to tritiated vapor. The temperature of catalytic reactor was selected to be 423 or 293 K. At 423 K, no considerable decrease in catalytic activity was observed for both catalysts even in the presence of produced gases from burned low-halogen cable. At 293K, considerable increase in catalytic activity was initially observed for both catalysts due to the effect of produced hydrogen. Then the temporary decrease was observed, however the catalytic activity was gradually recovered to be the original activity. Consequently, the irreversible decrease in activity of the catalysts during a fire event was not observed.