The spent electrolyte arising from pyroprocessing should be recycled to reduce the volume of high-level radioactive waste. To establish the spent electrolyte process by a phosphate conversion method, a preliminary experiment that followed a thermodynamical approach and used an electric furnace under argon gas atmosphere was carried out. The results obtained are that most thermodynamic properties of target phosphates acquired by the CALPHAD method were good in agreement with the experimental result; lithium and rare earth elements (REEs) tend to form the precipitate as orthophosphates, but other alkali metal (AL) and alkaline earth metal elements do not form the orthophosphate particles; and some elements such as ALs could form insoluble double salts with REEs.

The development of separation techniques of insoluble and soluble fission product elements will be the next challenge.