Separation of rare earths from nuclear fuel by selective sulfurization

For the recovery of fissile materials from spent nuclear fuel, a novel reprocessing process based on selective sulfurization was examined. This process consists of 1) voloxidation of spent fuel for decladding, 2) selective sulfurization of fission products (FPs) and 3) acid dissolution of sulfurized FPs. Sulfurization behavior of uranium oxides and doped FPs such as rare earth with CS₂ was studied by XRD phase analysis of formed compounds. The sulfurization and acid dissolution behavior of doped cerium into U ₃O₈; was also studied as a chemical analog of plutonium. The acid dissolution of sulfurized FPs and cerium was demonstrated by using radioactive tracer ¹³⁹Ce and ¹⁵²Eu. Results are summarized as follows; 1) UO₂ was oxidized to U₃O₈ by the voloxidation in air at 1000°C, while cerium and europium were reacted with U₃O₈ forming UO₂ solid solution. 2) The doped europium was successfully sulfurized by CS₂ at 500 °C, on the other hand, uranium was scarcely sulfurized but reduced from U₃O ₈ to UO₂ at temperature below 500 °C. 3) The doped cerium was not sulfurized at temperature below 500°C. 4) The sulfurized europium dissolved into 1M nitric acid solution, while uranium and doped cerium were insoluble. From these results, it was indicated that uranium and plutonium in spent nuclear fuel could be recovered as oxides by the selective sulfurization method.