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Leaching behavior of simulated bituminized radioactive waste form under deep geological conditions

ビチューメン放射性廃棄物固化体の深地層条件下における浸出挙動

中山 真一; 飯田 芳久; 永野 哲志; 秋元 利之

Nakayama, Shinichi; Iida, Yoshihisa; Nagano, Tetsushi; Akimoto, Toshiyuki

ビチューメン放射性廃棄物固化体の地層処分の性能評価に必要な浸出データを得るために、小規模模擬固化体を用いて、地下深部に特有な低酸素濃度条件を中心に浸出挙動を調べた。浸漬液は、セメント接触地下水を模擬するためのアルカリ性水溶液,処分場の沿岸立地を想定した塩水、及び標準としての純水である。NaやCsなど溶解性成分の浸出は膨張したビチューメン固化体内部での拡散に支配され、またBaやNpなど難溶性成分の浸出は、固化体の浸出程度とともに、それらの難溶性成分を含む化合物の溶解度によって抑制された。Npのように酸化還元性環境の変化に敏感な元素の浸出は、大気下のような酸化性雰囲気と地下深部のような還元性雰囲気とでは、存在する安定化合物の化学的特性の違いを反映して、明らかに異なる浸出挙動を示した。

Leaching behavior of synthetic bituminized waste form was studied to inquire data for performance assessment of the geologic disposal. Laboratory-scale leaching tests were performed. The bituminized samples were contacted with an alkaline solution representing cement-contacting groundwater, with a saline solution simulating seawater for a possible repository construction at the coastal area, and with deionized water as reference. The release of soluble components, Na and Cs, was enhanced by the swelling, and considered to be diffusion controlled in the swelled layers of the specimens. The release of insoluble components such as Ba and Np was solubility-limited in addition to control by the progression of leaching. Neptunium, a redox-sensitive element, showed a distinct difference in release reflecting the difference between the anoxic and atmospheric conditions. The concentrations of Pu were below the detection limit ($$2 times 10^{-10}$$ mol/L) under all of the leaching conditions in this study.

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パーセンタイル:38.02

分野:Nuclear Science & Technology

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