塩廃棄物の処理に関する基礎試験

The basis examination for the processing of the salt waste

照沼 仁*; 新井 修*

Terunuma, Hitoshi*; Arai, Osamu*

使用済み核燃料乾式再処理法の一つである溶融塩電解法から発生する塩廃棄物を、ガラス固化処理に適用することを目的とし、塩廃棄物の主成分である塩化物を溶融し水蒸気と反応させ、塩素を塩化水素の形態で分離し、塩化物をガラスへの溶解度の高い酸化物に転換処理する方法について基礎検討を実施した。試験は蒸気圧発生法の水分発生器より水蒸気を発生し、模擬塩を溶融、酸化処理する処理容器に通気し、塩化物の酸化転換により発生した塩化水素をガス吸収ビンに湿式回収する試験装置を用いた。模擬塩種、処理温度、水分付加量、酸化促進を目的とした酸化ホウ素の添加の有無をパラメータに試験を実施した。試験中に溶融塩から揮発する塩蒸気が排気系に移行しさらには配管閉塞の原因となり、試験運転に大きな影響を及ぼした。酸化ホウ素を添加することにより酸化物転換効率は数%より50%にまで向上し、処理塩から転換生成した酸化物が確認された。酸化ホウ素添加が塩化物の酸化転換に有効であることが確認できた。しかし酸化ホウ素を模擬塩の塩化物量に対し等モルと大量に添加しているため、処理量の低下、廃棄物の増加を招くこととなり最適添加量の検討が今後の課題となる。

For a purpose of glassification processing of the salt waste generated from the fused salt electrolysis method, one of the nuclear fuel reprocessing methods, a processing method to convert chloride to oxide which has an ability of high solubility to the glass was examined. Chloride, the main ingredient of the salt waste, was fused and reacted with water steam. Then the chlorine was separated as a form of hydrogen chloride. The examination was proceeded by an equipment consists of the following compositions. Water steam is generated from the moisture gas generator by the vapor pressure method. The steam is passed through the processing container where the imitation salt is fused and oxidized. Hydrogen chloride generated from the oxidation conversion of chloride is recovered in wet process by the gas scrubber. This examination was implemented under different conditions of imitation salt, processing temperature, water addition amount and presence of boron oxide addition for the stimulation of the oxidation. Volatilized salt steam switched over from the fused salt to the exhaust system, and it caused the plumbing blockade. This phenomenon exerted a big influence on the examination running. By adding boron oxide, percentage of the oxidation conversion increased from a few % to 50%. The oxide generated from processed salt by conversion could be confirmed. It showed that the addition of boron oxide is effective for oxidation conversion of chloride. However, boron oxide was added as the same amount as a commensurate mole of chloride in the imitation salt, and it causes to decline the processing quantity and to increase the amount of the waste evolution. An investigation of the optimal quantity of boron oxide addition will be a next problem to be solved in the future.