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Application of glow discharges for tritium removal from JT-60U vacuum vessel

グロー放電によるJT-60Uプラズマ対向表面からのトリチウム除去への適用

中村 博文; 東島 智; 磯部 兼嗣; 神永 敦嗣; 堀川 豊彦*; 久保 博孝; 宮 直之; 西 正孝; 小西 哲之*; 田辺 哲朗*

Nakamura, Hirofumi; Higashijima, Satoru; Isobe, Kanetsugu; Kaminaga, Atsushi; Horikawa, Toyohiko*; Kubo, Hirotaka; Miya, Naoyuki; Nishi, Masataka; Konishi, Satoshi*; Tanabe, Tetsuo*

核融合炉における有効で簡便なトリチウム除去方法を確立するために、壁調整用放電洗浄法の1つであるグロー放電洗浄(GDC)のJT-60U真空容器からのトリチウム除去への適用を目的として、ヘリウムと水素を用いたGDCによるJT-60Uプラズマ対向面からの水素同位体放出挙動を調べた。その結果、水素同位体の放出挙動は、3種類の時間に対する単純指数減少関数の組合せで表せることを見いだした。解析の結果、水素GDCがヘリウムGDCよりも水素同位体除去に優れていることが判明し、これは、水素の放電に起因する化学スパッタと放電水素とタイル表面水素同位体との同位体交換反応の相乗効果等の化学的な反応によるものと推測される。本結果で得られた放出特性に基づけば、573Kにおける連続的な水素GDCによりJT-60Uの表面水素同位体濃度を1/2に低減させるのに数日程度を要することが示唆された。

In order to establish the effective and conventional in-vessel tritium removal method, glow discharge methods, usually used as wall conditioning, have been applied and examined in vacuum vessel of JT-60U for tritium removal characteristics and kinetics. Release rates of all hydrogen isotopes as well as hydrocarbons from JT-60U vacuum vessel induced by Glow Discharge Cleaning (GDC) with He and H$$_{2}$$ were measured. Release characteristics of hydrogen isotopes were classified into three different release processes each of which is well described by a simple exponential decay with time. It was found that H$$_{2}$$ GDC showed the superior hydrogen isotope release characteristics than the He GDC, probably because chemical processes, such as isotope exchanges assisted by the chemical sputtering process between discharged hydrogen and hydrogen isotopes plasma facing carbon tiles are enhanced by the H$$_{2}$$ glow discharge. Based on the release kinetics observed in the present work, it is estimated that it will take several days to reduce tritium inventory in the surface area of JT-60U to a half by continuous H$$_{2}$$ GDC at 573 K.

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パーセンタイル:76.58

分野:Nuclear Science & Technology

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