PNNL

Abstract

The surface morphology characteristics of post-enrichment deconversion products in the nuclear fuel cycle are important to the production of 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 (ADU) route and a modification of the dry route. Products are reduced under either a hydrogen atmosphere with or without the introduction of water vapor to the environment. The crystal structures of the starting materials and resulting uranium oxides are characterized by powder X-ray diffraction (P-XRD). Scanning electron microscopy (SEM) and focused ion beam SEM (FIB-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 back scatter electron (BSE) imaging and EDX; these regions had elevated concentrations of fluorine impurities relating to incomplete reduction of UO2F2 to UO2 and may provide a novel nuclear forensics morphology signature relating to the production of nuclear fuel and U metal precursors.