Uranyl ammonium carbonate precipitation and conversion into triuranium octaoxide

Uranyl ammonium carbonate (AUC), with the chemical formula UO₂CO₃·2(NH₄)₂CO₃, plays a crucial role in the wet conversion of uranium hexafluoride (UF₆) into uranium dioxide (UO₂) or triuranium octaoxide (U₃O₈) for nuclear fuel production, and is used in commercial and research reactors. In this study, the precipitation of AUC from uranyl fluoride (UO₂F₂) solution and its subsequent conversion into U₃O₈ powder were investigated. AUC precipitation was performed at uranium concentrations in UO₂F₂ solution of 80-120 gL^-1, ammonium carbonate (NH₄)₂CO₃ concentrations of 200-400 gL^-1, and (NH₄)₂CO₃ to U (C/U) ratios of 5-9. The conversion of AUC into U₃O₈ powder was studied and sintering of the U₃O₈ nuclear material derived from ammonium uranyl carbonate (ex-AUC U₃O₈) was conducted at temperatures of 1000-1800 °C. The kinetics of AUC precipitation from the UO₂F₂ solution were studied using fundamental kinetic equations, and the kinetics of AUC conversion into UO₃ were examined using an isoconversion method based on the thermogravimetric analysis of AUC. The final product of U₃O₈ nuclear material was characterized using typical techniques, such as thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. This study provides valuable insights into the production and characterization of AUC and U₃O₈ nuclear materials, which are key materials in the nuclear fuel industry.