ABSTRACT
The surface morphology characteristics of postenrichment deconversion products in the nuclear fuel cycle are important for producing nuclear fuel pellets. They also provide the first opportunity for a microstructural signature after conversion to gaseous uranium hexafluoride (UF6). This work synthesizes uranium oxides from uranyl fluoride (UO2F2) starting solutions by the wet ammonium diuranate route and a modification of the dry route. Products are reduced under a nitrogen/hydrogen atmosphere, with and without water vapor in the reducing environment. The crystal structures of the starting materials and resulting uranium oxides are characterized by powder X-ray diffraction. Scanning electron microscopy (SEM) and focused ion beam SEM with energy-dispersive X-ray spectroscopy (EDX) are used to investigate microstructural properties and quantify fluorine impurity concentrations. Heterogeneous distributions of fluorine with unique morphology characteristics were identified by backscatter electron imaging and EDX; these regions had elevated concentrations of fluorine impurities relating to the incomplete reduction of UO2F2 to UO2 and may provide a novel nuclear forensics morphology signature for nuclear fuel and U metal precursors.
ABSTRACT
A Phase Field model is developed combining the Orientation Field approach to modeling solidification with the Kim, Kim, Suzuki method of modeling binary alloys. These combined methods produce a model capable of simulating randomly oriented second phase dendrites with discrete control of the solid-liquid interface energy and thickness. The example system of carbon in a liquid uranium (U) melt is used as a test for the model. The formation of uranium carbide within a liquid U melt is simulated for isothermal conditions and compares well with experiments.
