Abstract
The aim of this work is to investigate the microstructure evolution of nuclear materials. Previous studies have highlighted the importance of grain boundary structures that define part of the microstructure of polycrystalline materials. Before assessing properties affected by the presence of grain boundaries, it is fundamental to define structural models to achieve accurate and reliable grain boundary engineering. We further investigate the microstructure evolution of nuclear materials by simulating mixed oxide solutions that usually arise from the nuclear cycle as fission products. Furthermore, the segregation behavior of dopants at the interface can affect macroscopic characteristics and properties, therefore has been investigated.Chapter 1 consists of a literature review focused on the nuclear fuel cycle, fluorite systems and mixed oxide solid solutions. This is followed by a discussion on grain boundary structures, their modelling and the aims of the thesis. In Chapter 2, the computational methodology and the underlying theory used in this work are described in detail including energy minimisation, Molecular Dynamics and Monte Carlo.
Chapter 3 highlights the computational framework used for the structural search for all symmetric independent Coincident Site Lattice grain boundaries in CeO2 based on energy minimisation techniques. 160 grain boundary models have been made and their CSL parameters have been correlated with their formation and cleavage energies. These models will assist experimental characterisation.
Chapter 4 aims to gain an insight into the mixing of (U1-xCex)O2 bulk phases based on Molecular Dynamics and Monte Carlo techniques. The data indicates a different behaviour in terms of thermal expansion coefficient, bulk oxygen diffusivity and stability of the urania-ceria mixed oxide phases.
Chapter 5 expanded this work to grain boundaries and their effect on the segregation of different cation species in the (U1-xCex)O2 mixed oxides. The stability of the different grain boundaries is affected by the concentration of the mixing and temperature.
The thesis ends with Chapter 6, in which conclusions and future work are presented.
| Date of Award | 19 Aug 2024 |
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| Original language | English |
| Supervisor | David Cooke (Main Supervisor) & Marco Molinari (Co-Supervisor) |