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Demonstration on endurance of ion exchange membrane immersed in high-concentration tritiated water under the Broader Approach activities

幅広いアプローチ活動における高濃度トリチウム水に浸漬したイオン電解質膜の耐久性実証試験

岩井 保則; 佐藤 克美; 河村 繕範; 山西 敏彦

Iwai, Yasunori; Sato, Katsumi; Kawamura, Yoshinori; Yamanishi, Toshihiko

核融合炉から発生する高濃度トリチウム水はトリチウム水処理システムにて同位体濃縮・電気分解を行ったのち、水素同位体分離システムにて燃料純度にまで高度同位体濃縮を行うことでトリチウムの閉じ込め・再利用を図る。トリチウム水処理システムでは濃縮トリチウム水の電気分解を高分子電解セルにて行う。高分子電解セルのイオン電解質膜は高濃度トリチウム水と長期間接する代表的高分子膜であり、その放射線耐久性は幅広いアプローチ活動における研究項目となっている。本報告ではイオン電解質膜であるナフィオン膜につき1.38$$times$$10$$^{12}$$Bq/kgの高濃度トリチウム水に浸漬させた場合の劣化挙動を調査し、同線量の$$gamma$$線・電子線照射結果と比較することでトリチウム$$beta$$線による劣化の特異性の有無を考察した。高濃度トリチウム水浸漬によるイオン電解質膜ナフィオンの劣化について機械的強度・イオン交換能とも$$gamma$$線・電子線による同線量照射時の劣化度と同一であることを明確に示し、懸念されていたトリチウムに由来する特異的な劣化は生じないことを明らかとした。

The Nafion ion exchange membrane is a key material for electrolysis cells of the water detritiation system. Endurance of ion exchange membrane immersed into high-concentration tritiated water has been demonstrated under the Broader Approach activities, as a R&D on endurance of fuel cycle components at high tritium exposure. Long-term exposure of Nafion ion exchange membrane into 1.38 TBq/kg of tritiated water was conducted at room temperature for up to 2 years. The curves of percent elongation at break vs. dose and tensile strength vs. dose for the Nafion membranes immersed into tritiated water were well consistent with those for Nafion membranes irradiated to an equivalent dose with $$gamma$$ rays and electron beams. The results of ferric Fenton test indicated that the degradation directly by radiation was dominant at room temperature compared with that by reactions with radicals produced from water radiolysis. The curve of ion exchange capacity vs. dose for the Nafion membranes immersed into tritiated water was also well consistent with that for Nafion membranes irradiated to an equivalent dose with $$gamma$$ rays and electron beams. These results showed that the irradiation tests with $$gamma$$ rays and electron beams were effective to predict a degradation behavior of ion exchange membrane immersed into high-concentration tritiated water.

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パーセンタイル:37.15

分野:Nuclear Science & Technology

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