THERMODYNAMIC ANALYSIS OF URANIUM-GADOLINIUM FUEL STABILITY AT HIGH TEMPERATURES

摘要

Using the most accurate measurements of the liquidus temperature in the UO_2-Gd_2O_3 system up to 30 mol.% of Gd_2O_3, thermodynamic models of the melt and cubic solution GdO_(1.5) in UO_2 are constructed. The equilibrium phase diagram of the system UO_2-GdO_(1.5) in the interval 1900-3200 K is calculated in the entire composition range and the metastable diagram is calculated assuming that no cubic solid solutions are formed. The upper and lower boundaries of the melting onset temperature (solidus) of uranium-gadolinium fuel are presented. The phase composition of the pellets made from such fuel and, ultimately, the technology determine the melting onset temperature uniquely.