Final Disposal Facilities for Stabilized Fly Ash Generated from Thermal Treatment of Radioactively Contaminated Incineration Residue

Abstract

Combustible waste contaminated by radio-cesium（Cs）generated by the Fukushima Daiichi Nuclear Power Plant accident has been incinerated, thermally treated for volume reduction, and stored in an interim storage facility as molten slag and fly ash with high radio-Cs concentration. Since the fly ash needs to be disposed of after interim storage, it is necessary to establish the appropriate design for the final disposal facilities and safety assessment methodology, with particular attention to radio-Cs concentrations and leaching characteristics of the stabilized fly ash. This manuscript reviews the containment structure and safety assessment concept of existing disposal facilities, such as strictly controlled landfills for toxic industrial waste and low-level radioactive waste pit disposal facilities. Based on the review, it recommends that the high affinity to radio-Cs of engineered and natural barriers should be properly incorporated in the barrier system design of disposal facilities to delay transport to the surrounding environment until the radio-Cs is attenuated to a safe level. The authors also review recent studies on the sorption performance of radio-Cs in concrete and soil-bentonite mixture, which are expected to be used as engineered barriers, particularly on the influences of high concentrations of potassium, calcium, and other solutes in the leachate. Finally, technical issues for the appropriate final disposal of the stabilized fly ash are summarized.