The Micro-Optical Ring Electrode : A Sensor for Multiple Actinide Ions

Linnett, Gary and Andrieux, Fabrice (2022) The Micro-Optical Ring Electrode : A Sensor for Multiple Actinide Ions. PhD thesis, UNSPECIFIED.

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Abstract

This thesis researches the development of the Micro-Optical Ring Electrode (MORE) for the analysis of trans-uranium elements in aqueous mixtures. The MORE is a photoelectrochemical device based on a ring microelectrode that uses the insulator interior to the ring as a light guide. This single device exploits the unique photophysical and electrochemical properties of multiple analytes present in mixtures to quantify them. This study aims to develop a protocol for the analysis of ions of uranium, neptunium and plutonium. These elements are most relevant to the nuclear industry, especially in the areas of decommissioning and fuel-reprocessing, where speedy and safe identification of radioactive contaminants is essential. Non-radioactive surrogates were used to test whether the MORE could generate photocurrents from ions with similar chemical properties to their radioactive counterparts. The results obtained by the successful generation of photocurrents were compared to the mathematical model proposed by (Andrieux, Boxall and O’Hare, 2006a). Depleted uranium was used as a surrogate for active uranium whilst nonradioactive surrogates vanadium and cerium was used for neptunium and plutonium. Upon successful detection of a photocurrent from the surrogates the optimum parameters to give the largest photocurrent magnitude possible were established. For uranium these parameters were an illumination wavelength of 410 nm, a working electrode potential of 0.7 V and the electron acceptor ethanol at a concentration of 200 mmol dm-3 . For vanadium these parameters were an illumination wavelength of 350 nm, a working electrode potential of 0.5 V and the electron acceptor iron (III) chloride at a concentration of 100 mmol dm-3. No photocurrents were generated for cerium. A preliminary study into the ability of the MORE to detect photocurrents generated by individual ions in a mixture of uranium and ruthenium was also carried out. The surface finish at the tip of the MORE was shown to influence the magnitude of the generated photocurrents with a rougher finish resulting in larger photocurrents.