Study on the Reaction Characteristics for Sulfurization of Simulated Nuclear Fuel

In order to evaluate the feasibility of selective sulfurization of uranium and rare-earth(RE) oxides, analysis on thermodynamic data, such as M-O-S phase stability diagram and changes of Gibbs free energy for sulfurization of uranium and rare-earth oxides were carried out. RE oxides, such as Nd2O3 and Eu2O3 are sulfurized into RE2O2S or REySx at a range of 400 to 450 .deg. C, while uranium oxides, such UO2 and U3O8 remain unreacted up to 450 .deg. C. Formation of UOS at 500 .deg. C is initiated by sulfurization of uranium oxides. Hence, reaction temperature for the selective sulfurization of the mixture of uranium and RE oxides and RE-doped uranium oxides was selected as a 450 .deg. C. In the case of sulfurization of the mixture of uranium and RE oxides, RE sulfide and RE oxysulfide without reaction between uranium and RE oxides are formed at 450 .deg. C. Selective sulfurization for RE-doped uranium oxides, HOX, and HORXE were not observed, but for HOXRE preferentially reacted due to differential reactivity with sulfurization temperature. The difference of magnetic susceptibility should be larger to increase the separation efficiency. Since UOS has higher magnetic susceptibility than UO2, magnetic susceptibility of RE-rich uranium oxysulfide is expected to be higher than that of UO2