Engineering UO2 Thin Films to Investigate Nuclear Fuel Behaviour

: (in- and ex- operando)

Abstract

Understanding the fundamental behaviour of nuclear fuel materials, is an essential element for improving efficiency, reliability and safety throughout the nuclear fuel cycle. Nuclear fuel material research typically adopts one of two strategies: exploration of real world scenarios through complex experimental investigations; or conversely via fundamental theoretical studies of idealised model systems. To further advance our understanding of nuclear fuel
behaviour it is essential that these approaches are reconciled. In this regard, thin films systems offer a unique opportunity, providing highly versatile, idealised surfaces on which fundamental, single parameter studies can be conducted, to experimentally test theoretical models. This thesis begins with the fabrication of epitaxial thin films via reactive DC magnetron sputtering, with further characterisation measurements demonstrating these engineered samples
to have structural and chemical properties representative of bulk fuel materials. Utilising these idealised systems, fundamental studies have been conducted to explore the thermal properties and corrosion behaviour of uranium dioxide. Grazing incidence in-elastic x-ray scattering experiments have enabled phonon measurements of He2+ irradiated epitaxial UO2 thin films, providing a means to explore the fundamental mechanism responsible for the degradation of thermal
conductivity in UO2 as a function of irradiation. Additionally, UO2 thin films have been utilised to investigate dissolution at a fuel / water interface; a primary concern for the long-term storage of spent nuclear fuel. This was achieved through the development of a source-probe synchrotron technique, enabling a radiolytic dissolution study to be conducted for (001), (110) and (111)
epitaxial UO2 thin films. In conclusion, this thesis demonstrates the potential of thin film systems to bridge the gap between complex experimental work and fundamental modelling studies. Using this approach, advancements can be made to build a more fundamental understanding of nuclear fuel behaviour throughout the nuclear fuel cycle.

Date of Award	16 Jan 2018
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ross S Springell (Supervisor), Thomas Bligh Scott (Supervisor) & Ross S Springell (Supervisor)