UO2 and ThO2 Doped Fuel In the nuclear field, research must advance fast enough to keep pace with the industry’s growing demands and new applications. Safety and high performance needs to be maintained for both fuel and reactor. Major progresses have been made in this matter thanks to the development of a new generation of nuclear fuel. A wide variety of fission products (FP) are formed during the fission chain reaction.Therefore, it is important to delve the understanding of the local phenomena at atomic scale, the crystal chemistry and the type of defect that is formed when a foreign element is accommodated in the UO2 matrix. The First perpose of this research is practical, such as, the improvement of the understanding of the UO2 crystal stability. Secondly, there are structural and fundamental purposes, for instance the research on the coordination and valence state of the foreign elements on the UO2 matrix, as well as the modellingof f-electron interactions. The study of the highly similar ThO2 structure and the behaviour of foreign elements in their latter structure, allow us to use more exact characterization techniques. The complex part is that Thorium remains in its 4+valence state, while Uranium canassume a 4+, 5+ and even a 6+ valence state. In order to reach these goals, UO2 and ThO2 will be synthesized so that they contain non-radioactive FP such as Cerium, Europium, Gadolinium, Zirconium. Two synthesis methodes has been choosen solid state that consistin on the mechanical mixing of UO2 and the dopant oxides and sol gel process in solution,followed by a thermal decomposition of the molecular prcursors. The materials will be sintered in various atmospheres (from highly reducing to moderately reducing) at high temperatures (from 1500 °C to 1750 °C). Under these conditions, solid solutions of the impurity element and the UO2 matrix are obtained (either over the entire mixing domain or up to a certain solubility limit). Our primary interest is the study of the distorted host matrix structure near to the dopant. The resulting compounds will be investigated by X-ray diffraction to determine the influence of the dopant on the crystal lattice parameter. The experimental lattice parameters results will be used for the validation of molecular dynamics (MD) calculations. The homogeneity and microstructure of the doped UO2 or ThO2 pellets will be determined by scanning electron microscopy (SEM) and electron microprobe analysis (EPMA). The doped ThO2 will be characterised by optical absorption and luminescence spectroscopy in order to determine the local structure of the dopants ions in the host matrix. The results from the characterization would depend of the two selected synthesis methods: sol-gel and solid-state.
|Date of Award||5 Jul 2016|
|State||Published - Jul 2016|