Effect of a trivalent dopant, Gd 3+, on the oxidation of uranium dioxide

Abstract

The effect of a trivalent dopant, Gd 3+, on the oxidation of doped UO 2 was investigated using thermogravimetry and X-ray diffraction (XRD) analysis. Gd-doped stoichiometric UO 2's of various dopant contents [ y=0–0.29 in (U 1− y Gd y )O 2] were prepared. Weight gains by oxygen with increasing temperature for pulverized specimens were measured to obtain the oxidation kinetic curves. The oxidation kinetic curve for undoped UO 2 shows a two-step reaction: UO 2→U 4O 9 in the first step and U 4O 9→U 3O 8 in the second step. Decrease of the gradients of the oxidation kinetic curves for the first step with increasing content of Gd suggests that Gd dopant slowed down the reaction from (U 1− y Gd y )O 2 to (U 1− y Gd y ) 4O 9. Calculated O/(U + Gd) values from the weight gains and the deflection patterns of final stage of the oxidation revealed that the degree of oxidation from (U 1− y Gd y )O 2 to (U 1− y Gd y ) 3O 8 decreased linearly with increasing content of Gd. Such behavior as the slowdown and the inhibition were interpreted by the chemical states of U atoms in the lattice structures depending on doping of Gd 3+.