SUBJECT: Ph.D. Dissertation Defense
BY: Jacob Startt
TIME: Wednesday, March 25, 2020, 10:00 a.m.
PLACE: Boggs, 3-47
TITLE: Atomistic studies of structure-property relationships in actinide and transition metal alloys
COMMITTEE: Dr. Chaitanya Deo, Chair (NRE)
Dr. Hamid Garmestani (MSE)
Dr. Farzad Rahnema (NRE)
Dr. Yan Wang (ME)
Dr. Preet SIngh (MSE)
Dr. Stephen Raiman (ORNL)


In this thesis, four nuclear materials-based projects will be presented and discussed. Each project presents a unique problem within the field of nuclear materials engineering and can demonstrate the application of computational methods in support of existing experimental framework or in the guidance or suggestion of new experimental investigation. The first project seeks to understand the atomic ordering behavior in U-Zr, an alloy under investigation for use as a metallic fuel in advanced fast reactors. In these metals there is a potential for phase decomposition and a redistribution of fissile U atoms and so a complete understanding of the atomic ordering behavior in U-Zr is therefore needed. Density Functional Theory (DFT), a first-principles electronic structure modelling framework, is employed to investigate this ordering behavior. In the second project, point defect formation energies in Th and Th-U metal are modeled using DFT. These defects often have a large effect on a material’s mechanical properties. The third project investigates Cr depletion in Ni-Cr surfaces in molten salt reactors. The depletion of Cr atoms in the surface regions of these materials has been observed as the dominant form of corrosion but the underlying mechanisms and driving forces are not well understood. In this project, DFT is used to model the segregation behavior of Cr in fcc Ni surfaces. The oscillatory nature of the segregation energy profile is then discussed in terms of charge transfer and lattice distortion effects. In the fourth project, DFT is again used to extend the investigation of Cr segregation behaviors, with a focus aimed at understanding the effects of adsorbed salt atoms on segregation behavior near the surface of a Ni-Cr alloy. An emphasis is placed on the relative effects of cations and anions in the molten salt, and on the relative effects of natural salt components versus salt impurities.