PNNL

Abstract

We have developed a specialized microfluidic cell that enables in-situ investigations of the electrochemical corrosion of micro-gram quantities of solid uranium dioxide (UO2). We have confirmed that we can obtain electro-chemical measurements from these devices that match the experiments at the bulk-scale. By decreasing the amount of material in an individual electrochemical experiment, we reduce hazards and wastes associated with working with radioactive materials. The Cyclic Voltammetry was used to monitor the UO2 oxidation-reduction cycle; from the formation of hexavalent uranium (U(VI)), U3O7 reduction to UO2+x, and interfacial water decomposition. The reaction progress was studied in-operando with Scanning Electron Microscopy. We deduced from X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) that we had formed a uranyl alteration phase on the surface of the electrode. The penetration depth of surface oxidation was quantified with Scanning Transmission Electron Microscopy. With AFM, we also showed that the U(VI) phase underwent dehydration and volume loss over time. Electrochemical experiments with micro-fluidic in-situ cells could be used to make quantitative comparisons between different nuclear fuels.