Nuclear Fuel Cycle Chemistry: A Density Functional Study

The nuclear fuel cycle aptly describes the life cycle of nuclear fuel sources such as uranium. From its early forms in naturally bearing ores, to its high-temperature sintering into a fuel pellet, the chemistry uranium experiences throughout the fuel cycle is diverse, driving many experimental efforts towards understanding its chemistry to both improve nuclear technologies and advance the safety and handling of nuclear materials. Computing techniques and methodologies can be used to supplement experimental research and are readily available to researchers interested in utilizing computing-based data to support experimental findings. Density functional theory (DFT) is commonly practiced, reliably predicting the electronic ground states of molecular and crystal structures. The work presented in this thesis utilizes computational modeling for scenarios or simulations related to the nuclear fuel cycle, primarily employing DFT-coded programs to gather data that is then compared to or accompanied with experimental data. The ion-exchange behavior of a simple silicotitanate structure is examined, where the formation energies are compared to determine the favorability of the exchanged ion. A candidate crystal structure for an ammonium fluorouranate species is optimized to gather a theoretical diffraction pattern that is then compared to experimental sources. The optimization of a UO2 structure doped with CsI is replicated experimentally for comparisons of both research methods. Lastly, an early uranium oxide phase found in the fuel cycle is intentionally tagged with transition metals that are compared for their proclivity to imbed in the crystal matrix of the oxide.