Volume Reduction of Radioactive Concrete Wastes by Thermal and Mechanical Treatments

Abstract

The decommissioning of nuclear facilities produces a large amount of radioactive wastes and most of them are concrete waste. In Korea, two decommissioning projects such as the decommissioning of the retired research reactors (KRR-1 & 2) and a uranium conversion plant (UCP) at the Korea Atomic Energy Research Institute (KAERI) has been carried out. By dismantling KRR-2, more than 260 tons of radioactive concrete wastes were generated among the total 2,000 tons of concrete wastes and more than 60 tons of concrete wastes contaminated with uranium compounds have been generated for the UCP decommissioning up to now. The volume reduction and recycling of the wastes is essential to reduce the waste management cost with expectation that an approximate disposal cost for the low level radioactive waste will be more than 5,000 US dollars per 200 liter waste drum in Korea. Therefore, we have developed the volume reduction technology applicable to an activated heavy weight concrete generated by dismantling KRR-2 and the uranium contaminated light weight concrete produced from the UCP decommissioning. We have investigated the characteristics of a separation of the aggregates and the distribution of the radioactivity into the aggregates from the volume reduction point of view using an activated heavy weight concrete taken from the KRR-2 and uranium contaminated light weight concrete from the UCP. It could be concluded that the radioactivity is mainly concentrated in the porous fine cement powder below the size of 1mm and the appropriate heating temperature for the treatment of concrete waste is in the range of 450°C to 500°C. The volume reduction rate could be achieved above 70% by a heating followed by a mechanical separation process. A fine cement radioactive produced during the course of the mechanical treatment process was immobilized and reduced in volume by a slagging using a direct current graphite arc melting system which resulted in a volume reduction factor of about 3.4.