COMPREHENSIVE INVESTIGATION OF SELECTED URANIUM COMPOUNDS WITH APPLICATION FOR CLEAN ENERGY
The focus of this thesis mainly revolves investigation of the thermal properties of triuranium octoxide (U3O8), uranium di-aluminide (UAl2), U3O8-Mo, and U3O8-Al nuclear fuels. They have significant importance in the nuclear industry related to their fuel applications for research and test reactors. This study is carried out mainly using density functional theory (DFT) based calculations within the first principles framework to bring an insight into the molecular level contribution to their heat transport. Furthermore, an experimental evaluation is performed with U3O8, U3O8-Mo, and U3O8-Al, and these results are compared with the theoretical predictions. The theoretical calculations on U3O8 reveal that the strong anharmonicity in the Grüneisen parameter is the origin of its low thermal conductivity. Furthermore, the directional dependence of the group velocity triggers the anisotropic nature of its thermal conductivity. This work experimentally demonstrated a significant thermal conductivity enhancement in U3O8 with added Al or Mo. The experimental band gap measurements and the DFT-based computational predictions on the electronic and optical properties proved U3O8 to be a semiconductor with an indirect bandgap. The structural and mechanical properties and the time-dependent thermal conductivities of UAl2 are assessed computationally. The research findings reveal that both the acoustic and optical modes of the phonon vibrations give a considerable impact on total thermal conductivity. Furthermore, the electronic contribution to the total thermal conductivity in UAl2 is shown to be getting more robust with increasing temperature.
Thermal properties, DFT, SPS, nuclear materials
Doctor of Philosophy (Ph.D.)
Physics and Engineering Physics