DEVELOPMENT OF MUD-CRUSHING METHODS FOR FARMLAND-DERIVED CLAYEY SOIL AND THEIR APPLICATION TO PARTICLE-SIZE SEPARATION FOR DECONTAMINATION OF CESIUM-CONTAMINATED SOIL

The volume of radioactive cesium-contaminated soil being removed during the cleanup process after the explosion of Fukushima nuclear power plant 1 is estimated to be 13 million m 3 . Soil contaminated with more than 20,000 Bq/kg of radioactivity is targeted for decontamination by the particle-size separation method to pass the criteria for reuse in Japan. Because more than 80% of the targeted soil is composed of fine silt and clay derived from farmland, a system was developed to increase the amount of recyclable soil by a combination of mud crushing and fine-particle separation with the classification point set lower than about 20  m. Mud crushing is one of the key technologies for effective decontamination because clay forms aggregates due to the presence of organics such as humus. Four types of mud-crushing equipment were examined on site, followed by pebble milling or ultrasonic dispersion, both of which showed promising results. Using the selected equipment, the proposed soil-size separation was carried out. Overall, the proposed system was proven effective by the results of radioactivity reduction ratio and volume of soil for recycling. Furthermore, lab-scale pebble mill tests using a pot-type wet mill were carried out to confirm the basic characteristics of mud crushing for organic