ゼオライトを主体とした高選択性吸着剤による高汚染水の処理

Treatment of highly contaminated water with highly selective adsorbents mainly composed of zeolites

三村 均*; 山岸 功 

Mimura, Hitoshi*; Yamagishi, Isao

福島第一原子力発電所事故対策を進める上で、50万トン規模の高汚染水が大きな障害となっている。海水が混入した高汚染水の浄化、特にセシウムの選択的除染に対しては、無機イオン交換体充填吸着塔による循環注水冷却システムが稼動しており、冷温停止が達成されているが、運転システムの高度化や二次固体廃棄物の安全管理および処分が課題となっている。ここでは、ゼオライトを主体としたセシウムおよびストロンチウム選択性吸着剤の吸着特性および固化特性を比較評価するとともに、吸着剤の高機能化の試みを紹介する。特に、わが国に豊富に産出する天然産ゼオライトは、セシウムに高い選択性を有すると共に、高温でのガス状セシウムのトラッピング機能および安定固化を実現できる自己焼結機能など優れた特性を有しており、高汚染水の処理および処分において今後重要な役割を果たすものと期待できる。さらに固体廃棄物の安全管理の現状および安定固化技術の開発状況について解説し、将来的な処分に対する課題を整理する。

Massive tsunami caused by the Great East Japan Earthquake attacked the Fukushima Daiichi Nuclear Power Plant and caused the nuclear accident of level 7 to overturn the safety myth of nuclear power generation. The domestic worst accident does not yet reach the convergence, and many inhabitants around the power plant are forced to double pains of earthquake disaster and nuclear accident. At present, large amounts of high-activity-level water over 500,000 tons are stored in Fukushima NPP-1 site, which is a serious obstacle to take measures for the nuclear accident. For the decontamination of high-activity-level water containing seawater, the circulating injection cooling system using packed columns with inorganic ion-exchangers is operated and the cold shutdown is accomplished. However, the advancement of operating system and the safety management of secondary solid wastes are very important subject. In this paper, the adsorption properties and solidification characteristics are compared for Cs and Sr selective adsorbents mainly composed of zeolites and the enhancement of adsorption properties are reported. Especially, naturally occurring zeolites abundant in Japan have high selectivity towards Cs, and also have excellent functions of gas trapping and self sintering for stable solidification. Zeolites are thus expected for the treatment and disposal of contaminated water in future. This paper also reports the present situation of safety management of solid wastes and the development of stable solidification methods, and summarizes the future subjects considering the safety disposal.