Analytical evaluation of solidus and liquidus temperature on (U,Pu)O fuel

Nagai, Shuichiro

Phase diagram calculation code PD32 for 2 phases-2components and 2 phases-3components systems was developed based on Gibbs Free Energy Minimum Principal under equilibrium condition. Phase diagram calculation of UO-PuO system described by ideal solution model and Ag-Au-Cu system described by regular solution model showed that PD32 gave the reasonable results, that was, the chemical potential of each component had good agreement between two phases. Free energy of solid U-O, Pu-O and (U,Pu)O systems was calculated based on Blackburn's oxygen potential model. For the calculation of free energy of liquid systems, three parameters which modified the equilibrium constants between the metal ions and oxygen pressure in Blackburn model was introduced, and was established to fit the solidus and liquidus line in U-O and Pu-O systems. Calculated solidus and liquidus line and their O/M dependence in (U,Pu)O system agreed well with measured data by Aitken et al. It was confirmed that the solidus and liquidus line between Pu-O and (U,Pu)O systems by Aitken et al was self-consistent.