A wet chemistry route towards UO2 spherical particles was designed through the hydrothermal conversion of uranium(iv) aspartate. A multi-parametric study led us to point out the conditions leading to monodisperse and size-controlled particles in the 400–2500 nm range. This simple protocol paves the way to applications in various scientific areas.

Early stages of various uranium oxides sintering were monitored in situ through High Temperature Environmental Scanning Electron Microscopy. Systems composed of two UO 2+x microspheres were heated up to 900-1200°C under P O 2 ranging from 10-10 to 25 Pa. The oxide phases stabilized were assessed through thermodynamic calculations and powder X-ray diffraction. In all the conditions tested, the formation and the development of a neck was evidenced and image processing led to quantitative data describing the morphological changes. The evolution of the sintering degree was fitted using an exponential law and allowed the evaluation of the activation energy. When P O 2 led to stabilize hyper-stoichiometric UO 2+x oxides, the values obtained increased with x, typically in the 200-400 kJ•mol-1 range. Under air atmosphere, the stabilization of U 3 O 8 led to E A = 260 ± 40 kJ•mol-1. Finally, the main diffusion mechanism driving neck formation was found to be volume diffusion, independently from the oxide stoichiometry.