Evaluating the corrosion behaviour of uranium silicide phases

: an advanced technology fuel study

Abstract

Advanced technology fuels (ATFs) are key in the drive to improve the overall performance and safety in the nuclear industry. The intermetallic uranium silicide phases are of significant interest to the nuclear fuel cycle, with three of the stoichiometric phases, U₃Si, U₃Si₂, and U₃Si₅ being highlighted as ATFs. These phases have the potential to offer higher thermal conductivities and uranium densities when compared to the widely used UO₂. For these phases to be implemented into the nuclear fuel cycle, the understanding of these materials must be extended across the entire uranium-silicon phase diagram. This will highlight how inclusions of secondary phases that may form as a result of the bulk fabrication process could alter the behaviour of the main fuel compound. Thin films provide idealised samples that are well suited for single parameter investigations. Epitaxial U₃Si, U₃Si₅, α−USi₂, and USi₃, alongside poly-crystalline U₃Si₂ have been engineered for the first time using DC magnetron sputtering, allowing for novel measurements to be conducted on these materials. Characterisation of these phases using x-ray diffraction and x-ray photoelectron spectroscopy have provided information about the structural and chemical nature of each compound. X-ray photoelectron spectroscopy provided a unique insight into the chemical bonding and stoichiometry of each uranium silicide phase, presenting the metallic nature of these compounds, alongside their unique U:Si ratios using the U-4f and Si-2s core levels. Thin films also provide excellent samples upon which surface sensitive investigations can be conducted. Here, the ambient surface oxidation in air of each compound is presented, from which the results indicated the preferential oxidation of uranium sites, allowing for the formation of silicon-rich phases within the native oxide. The aqueous corrosion of uranium silicides within H₂O and H₂O₂ is also considered. These experiments provided further understanding of the preferential oxidation model, with indication that this mechanism applies to uranium silicides within aqueous environments. Finally, the implications of the results collected from each uranium silicide phase regarding its application as a nuclear fuel candidate are considered.

Date of Award	22 Mar 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ross S Springell (Supervisor) & Thomas Bligh Scott (Supervisor)