CESIUM LEACHING UNDER SEVERE CONDITIONS FOR CEMENT / GEOPOLYMER SOLIDIFIED BODY OF CESIUM ADSORBED MORDENITE

Abstract

Following the accident at the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant, decontamination was conducted, and approximately 140,000 m³ of radioactive waste was generated. For the final disposal, it is essential to establish volume reduction and cesium (Cs) stabilization technology. Combustible waste was incinerated and melted to lower its volume, and soluble Cs became concentrated in the fly ash. Cs in the fly ash is soluble, and the Cs stabilization processes are needed, which could be done by Cs adsorbent like mordenite. This study explores Cs leaching behavior from the solidified body of Cs adsorbed mordenite. Solidified bodies with cement or geopolymer were prepared, and their Cs leaching characteristics were evaluated. In addition, changes in Cs leaching behavior due to freezing and thawing, and contact with seawater were evaluated as an estimated severe condition. As a result, Cs leaching was principally controlled by Cs desorption from the mordenite and Cs diffusion in the solidified bodies. The Cs leaching rate was not affected by freezing and thawing, but increased on immersion in seawater.  While the type of binder (cement or geopolymer) affects the nature of surface precipitates formed, it has only a minor impact on the Cs leaching rate. The Cs leaching ratio was as low as below 0.5% even after 60 days of immersion in seawater, and the leached Cs concentrations were lower than the standard for environmental water. The results indicate that mordenite and its solidification were an appropriate means of final disposal.