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Electrochemical reduction of metal oxides in molten salts for nuclear reprocessing

Abdulaziz, R; (2016) Electrochemical reduction of metal oxides in molten salts for nuclear reprocessing. Doctoral thesis , UCL (University College London). Green open access

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Abstract

This thesis examines the electrochemical reduction of metal oxides in molten salts for nuclear reprocessing applications. The objective of this research is to characterise and understand the direct electrochemical reduction of UO₂ to U metal in a LiCl-KCl molten salt eutectic, as part of the nuclear pyroprocessing scheme, following a similar approach to the FFC Cambridge for the reduction of TiO₂ to Ti metal. The voltammetric behaviour of reduction processes of metal oxides were evaluated using electroanalytical techniques such as cyclic voltammetry and chronoamperometry on different precursor types, such as thermally grown thin oxide films, metallic cavity electrodes, and ‘a fluidised cathode’, a novel process that was developed within this work. Material was characterised before and after the electroanalytical experiments using scanning electron microscopy, X-ray energy dispersive spectroscopy and X-ray diffraction. Predominance phase diagrams, using recent thermodynamic data, for metal-molten salt systems, relating the potential to the negative logarithm of the activity of O²⁻ ions (E-pO²⁻), were produced for the range of spent nuclear materials in both LiCl-KCl and NaCl-KCl. The bulk of this research was on investigating the electrochemical reduction of WO₃ to W metal. Tungsten was selected as a chemical surrogate for uranium to investigate specific process parameters. Nonetheless, tungsten is an important and desirable refractory metal, and the electrochemical route for producing it of high purity might prove viable. The electrochemical reduction of UO₂ to U metal using the fluidised cathode process was investigated. Voltammetry studies were conducted, and alongside a predominance diagram that was constructed, the reaction path-way was studied, and a Faradaic efficiency was established. The fluidised cathode is a robust, three-phase, high efficiency process. It was studied here for the electrochemical reduction of WO₃ and UO₂, however, it is likely applicable for other spent fuel oxides, and in the production of refractory metals.

Type: Thesis (Doctoral)
Title: Electrochemical reduction of metal oxides in molten salts for nuclear reprocessing
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Molten salts, Spent nuclear material, Pyroprocessing, Predominance diagrams, Electrochemical reduction, Fluidised cathode
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: http://discovery.ucl.ac.uk/id/eprint/1512997
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