On a Solvent Extraction System for Recycling Used Nuclear Fuel with CyMe4-BTBP and TBP as Extracting Agents

Abstract: In Sweden, as well as in many other countries worldwide, the demand for electricity and electrical energy is high. One solution to satisfy this demand in the long term could be to upgrade the nuclear power plants, including recycling of used nuclear fuel, to Generation IV. The Generation IV concept, currently at the research stage, is based on a closed nuclear fuel cycle that includes both a reactor capable of fissioning considerably more nuclides than the thermal reactors of today and a used nuclear fuel recycling process. Recycling of the used nuclear fuel would increase the energy utilization of the fuel and make the final repository more sustainable. Different types of recycling processes are under development. One of these is the Grouped ActiNide EXtraction (GANEX) process. The Chalmers GANEX process is a solvent extraction process for extracting all of the actinides present simultaneously as a group by combining two extracting agents and a diluent into one single solvent. The original Chalmers GANEX process used cyclohexanone as the diluent, which had some drawbacks such as low flashpoint and exothermic reactions with concentrated nitric acid. In this work the focus has therefore been on a new diluent, phenyl trifluoromethyl sulfone (FS-13). Current studies have shown that a solvent based on FS-13 has several promising features such as good actinide extraction while the fission product extraction remains low, fast kinetics, efficient back-extraction using two stripping steps and high stability against both hydrolysis and radiolysis. Thermodynamic investigations have revealed that the system reacts exothermically during the metal extraction. The system also offers a high solubility of CyMe4-BTBP, creating a possibility to optimise the organic phase according to the used fuel composition. The solvent was found to perform well under plutonium loading conditions, showing great promise for future use in recycling of Generation IV fuels.