Thermal studies on fluorite type ZryU1−yO2 solid solutions

Solid state reactions of UO2 and ZrO2 in mild oxidizing condition followed by reduction at 1673 K showed enhanced solubility up to 35 mol% of zirconium in UO2 forming cubic fluorite type ZryU1−yO2 solid solution. The lattice parameters and O/M (M = U + Zr) ratios of the solid solutions, ZryU1−yO2+x, prepared in different gas streams were investigated. The lattice parameters of these solid solutions were expressed as a linear equation of x and y: a0 (nm) = 0.54704 − 0.021x – 0.030y. The oxidation of these solid solutions for 0.1 ⩽ y ⩽ 0.2 resulted in cubic phase MO2+x up to700 K and single orthorhombic zirconium substituted α-U3O8 phase at 1000 K. The kinetics of oxidation of ZryU1−yO2 in air for y = 0–0.35 were also studied using thermogravimetry. The specific heat capacities of ZryU1−yO2 (y = 0–0.35) were measured using heat flux differential scanning calorimetry in the temperature range of 334–860 K.