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Title: The combined electrochemical and microstructural characterisation of the electrochemical reduction of uranium dioxide to uranium metal in molten lithium chloride-potassium chloride eutectic
Author: Brown, L. D.
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2015
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The electrochemical reduction of uranium (IV) oxide to metallic uranium has been studied in lithium chloride-potassium chloride eutectic at 450°C using electrochemical and advanced material characterisation techniques. Electrochemical characterisation identified a single reduction peak occurring at -2.57V with respect to the Ag|Ag+ reference electrode. Sweep voltammetry has identified that the electroreduction of uranium dioxide to metallic uranium occurs via a single, 4-electron transfer, process. The electrochemical reduction has also been observed to be dependent on the activity of O2- ions: An increase in the bulk activity of the oxygen anion impeded the electroreduction process. This phenomena was thermodynamically predicted using Littlewood diagrams produced for the system. In addition, in situ energy dispersive X-ray diffraction investigations were carried out on the I12 JEEP beamline at the Diamond Light Source which resulted in the direct observation of the formation of uranium metal when a uranium dioxide electrode was exposed to electroreduction potentials. No intermediate phases were observed which supports the electrochemical characterisation of this process occurring in a single step. Moreover, microstructural characterisation has been performed on micro-bucket electrodes and metallic cavity electrodes. A coral-like structure was identified after reduction of uranium dioxide and has been attributed to the volume change associated with the reduction. Microstructural reconstructions were performed on four separate sub-volumes in the direction of propagation of the electroreduction process. The porosity was seen to decrease significantly from 16% to 4%. The pore connectivity was also observed to decrease from 93% to 18%. This drastic change in porosity and pore connectivity is reflected in the pore tortuosity which is seen to increase to infinity. This microstructural evaluation is concluded to impede the diffusion of O2- ions out of the electrode resulting in an increased probability of impediment of the electrochemical reduction process.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available