Synthesis and characterization of nanometric powders of UO2+x, (Th,U)O2+x and (La,U)O2+x

This paper describes a new way of preparing nanometric powders of uranium oxide, to fit the needs of studies on UO2 oxidation, through the electrochemical reduction of U(VI) into U(IV). These powders can also be doped with radionuclides if necessary. The precipitation of oxides occurs in reducing and anoxic conditions. This original method makes it possible to synthesize nanometric UO2 powders with a calibrated size, as well as the Th- and La-doped UO2 powders with a predefined composition. The powder characterization by the X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron Microscopy shows the formation of spherical crystallites of UO2+x, (Th,U)O2+x and (La,U)O2+x phases. The composition can be defined by the initial Th/(Th+U) and La/(La+U) ratios in solution and the particle size can be controlled by varying the pH.