Feasibility study on vitrification of low-and intermediate-level radioactive waste from pressurized water reactors

Abstract

In order to obtain annual generation volume and composition data for low- and intermediate-level radioactive waste (LILW), characteristics and generation trends for each waste which was produced at nuclear power plants (NPPs) in Korea were investigated. The data were utilized in laboratory scale vitrification experiments and in a technical and economic assessment for LILW vitrification. For technical assessment, four promising melters, which were the cold crucible melter heated by direct induction (CCM), the cold crucible melter heated by vertical electrodes (CCVE), the quantum catalytic extraction process (QCEP), and the plasma torch melter (PT), were selected and evaluated to determine the best available melter. During the performance of laboratory experiments to investigate the vitrification possibility of LILW, pyrolysis/oxidation (PO) for combustibles (e.g. protective clothings and vinyl sheets) and ion exchange resins was first examined to obtain good pyrolysed/oxidized ash which could be contained appropriately in borosilicate glass. PO temperatures of 400–800°C were found to cover the optimal range for converting those wastes into fine powder which could be dispersed and mixed well in molten glass. Later, laboratory cold tests with three types of vitrification equipment were carried out to examine the possibility of vitrification of the ash and dried product of evaporator bottoms. Of the three different types of melters, the platinum crucible was found to be most suitable for the performance of vitrification experiments and hence, was used to help better understand the optimal waste contents in borosilicate glass waste forms with respect to waste types. After the performance of vitrification experiments, compressive strength tests showed that the final waste glass product, containing up to 40 vol% of ash pyrolysed/oxidized at 400–800°C, showed good mechanical stability and homogeneity in the glass matrix. Economical assessment was performed with some considerations given for equipment having already been adopted for LILW treatment in Korea for four treatment strategies with melters selected from a technical assessment. For each strategy, the capital and the operation cost were estimated, and the disposal volume was calculated with reasonably estimated volume reduction factors with regard to waste type and treatment concept. From the analysis of the disposal costs and the results of the technical assessment, the strategy which incorporated a plasma torch melter for the treatment of non-combustibles and a cold crucible melter for the handling of combustibles was found to be the best.