Development of Pyrometallurgical Partitioning of Actinides from High-Level Radioactive Waste Using a Reductive Extraction Step

Abstract

High-level radioactive waste (HLW) from reprocessing (Purex) light water reactor spent fuel contains a small number of long-lived nuclides, mainly actinide elements, having half-lives of longer than one million years. If actinide elements could be separated from HLW and transmuted to short-lived nuclides, not only would waste management be much simpler but also public support for nuclear power generation might be easier to obtain. Central Research Institute of Electric Power Industry (CRIEPI), Japan, has proposed a pyrometallurgical process to separate actinides from HLW. When the solvent used in the Purex process is reclaimed by NaCO{sub 3} and NaOH, a waste stream containing sodium with fission products and actinides is produced also. The focus of CRIEPI is the disposal of HLW from both the Purex and the solvent rinse processes. In this concept, HLW is converted to chlorides, the actinides as molten chlorides are reduced by lithium metal and extracted into liquid cadmium, and finally, the actinides are purified by electrorefining. However, in the extraction of actinides into liquid cadmium, some of the rare earth elements are expected to be recovered together with the actinides because of their chemical similarity. Thus, it is necessary to obtain thermodynamic data of the actinidesmore » and rare earth elements in molten chlorides and liquid cadmium. The distribution coefficients for uranium, neptunium, and rare earth elements are determined in molten LiCl-KCl eutectic salt/liquid cadmium (LiCl-KCl system) and molten LiCl-NaCl salt/liquid cadmium (LiCl-NaCl system) systems. The equilibrium distribution of uranium, neptunium, and rare earth elements is also calculated based on the Gibbs energies of formation of the metal chlorides and their activity coefficients in molten salts and cadmium.« less