Feasibility study on the volume reduction of radioactive concrete wastes using thermomechanical and chemical sequential process

Abstract

This study describes a method to reduce the volume of radioactive concrete wastes generated during the decommissioning process of nuclear facilities. The method involves thermomechanical and chemical treatment processes sequentially to separate the bulk aggregates from the cement binder; the latter of which contain the majority of the radioactive contaminants. The thermomechanical process acted to weaken the chemical bond between the cement and aggregate components in the concrete. Optimal thermomechanical treatment conditions were determined to be as follows: Isothermal pre-treatment at 550 °C for 1 h using crushed concrete followed by rotary mill grinding for 4 h at room temperature with a 75% loading volume. Such conditions were found to be effective at reducing the volume of the concrete waste, but could not remove the contaminants 137Cs and 60Co from the aggregates completely. Applying the chemical process to remove the contaminants using a hydrochloric acid solution, the clearance criteria for 137Cs and 60Co could be attained for the aggregates separated. Therefore, the radioactive concrete waste could be treated for clearance by the sequential treatment process, thus achieving an approximately 75% volume reduction of the radioactive concrete waste and ultimately lowering the cost of decommissioning and waste disposal.