Uranium-Molybdenum (U-Mo) alloys are of interest to the nuclear engineering community for their potential use as reactor fuel. The addition of molybdenum serves to stabilize the gamma phase of uranium, as well as increasing the melting point of the fuel. Thermal properties of U-Mo alloys have not been fully characterized, especially within the area of partial phase decomposition of the gamma phase of the alloy. Additional data was acquired through this research to expand the characterization data set for U-Mo alloys. The U-Mo alloys used for this research were acquired from the Idaho National Laboratory and consisted of three alloys of nominal 7, 10, and 13 percent molybdenum by weight. The sample pins were formed by vacuum induction melt casting. Once the three sample pins were fabricated and sent to the Fuel Cycle and Materials Laboratory at Texas A&M University, the pins were homogenized and sectioned for heat treatment. Several heat treatments were performed on the samples to induce varying degrees of phase decomposition, and the samples were subsequently sectioned for phase verification and thermal analysis. An Electron Probe Microanalyzer with wavelength dispersive spectroscopy was used to observe the phases in the samples as well as to characterize each phase. The density of each sample was determined using Archimedes method. Finally, a light flash analyzer was used to determine thermal diffusivity of the samples up to 300 degrees C as well as to estimate the thermal conductivity. For U-10Mo, thermal diffusivity increased with increasing phase decomposition from gamma to alpha +U2Mo while U-7Mo saw a flattening of the thermal diffusivity curve with increased phase decomposition.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19093号 / エネ博第317号 / 新制||エネ||64 / 32044 / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 木村 晃彦, 教授 星出 敏彦, 教授 今谷 勝次 / 学位規則第4条第1項該当

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19093号 / エネ博第317号 / 新制||エネ||64(附属図書館) / 32044 / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 木村 晃彦, 教授 星出 敏彦, 教授 今谷 勝次 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

This thesis represents a small contribution to our understanding of metastable patterns in various stochastic models from physics and biology. By a \emph{metastable pattern}, we mean a pattern that appears to persist in a regular fashion on some timescale, but disappears or undergoes an irregular change on a longer timescale. Metastable patterns frequently result from stochastic perturbations of patterns that are stable without perturbation. In this thesis, we study stochastic perturbations of stable spatiotemporal patterns in several classes of PDE and integral equations. In particular, we address two major questions: \begin{enumerate}[Q1.] \item When perturbed by noise, for how long does a pattern that is stable without noise persist? \item How does the stochastic perturbation affect the average behaviour of a pattern on the timescale where it appears to persist? \end{enumerate} To address these questions, we pursue two lines of inquiry: the first based on the theory of \emph{quasi-ergodic measures}, and the second based on \emph{phase decomposition techniques}. In our first line of inquiry we present novel, rigorous connections between metastability of general infinite dimensional stochastic evolution systems and the spectral properties of their sub-Markov generators using the theory of quasi-ergodic measures. To do so, we develop a novel $L^p$-approach to the study of quasi-ergodic measures. We are then able to draw conclusions about the metastability of travelling waves and other patterns in a class of stochastic reaction-diffusion equations. For instance, we obtain a rigorous definition of the \emph{quasi-asymptotic speed}~of a travelling wave in a stochastic PDE. We moreover find that stochastic perturbations of amplitude $\sigma>0$ cause the quasi-asymptotic speed of certain travelling waves to deviate from the deterministic wave speed by a constant that is approximately proportional to $\sigma^2$. In our second line of inquiry, the dynamics of our (infinite dimensional) stochastic evolution system are projected onto a finite dimensional manifold that captures some property of a metastable pattern. While most previous studies using phase reduction techniques have used the \emph{variational phase}, we take an approach based on the \emph{isochronal phase}, inspired by classical work on finite dimensional oscillatory systems. When the pattern in question is a travelling wave, the isochronal phase captures the position of the wave at a given point in time. By exploiting the regularity properties of the isochronal phase, we are able to prove several novel results about the metastable behaviour of the reduced dynamics in the small noise regime in a very large class of stochastic evolution systems. These results allow us to moreover compute the noise-induced changes in the speed of stochastically perturbed travelling waves and other patterns. The results we obtain using this approach are numerically precise, and may be applied to a very general class of stochastic evolution systems.

Indium nitride has many applications as a semiconductor. High quality films of indium nitride can be grown using Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD), but the availability of precursors and knowledge of the underlaying chemical reactions is limited. In this study the gas phase decomposition of a new indium precursor, N,N-dimethyl-N',N''-diisopropylguanidinate, has been investigated by quantum chemical methods for use in both CVD and ALD of indium nitride. The computations showed significant decomposition at around 250°C, 3 mbar indicating that the precursor is unstable at ALD conditions. A computational study of the surface chemical mechanism of the adsorption of trimethylindium and ammonia on indium nitride was also performed as a method development for other precursor surface mechanism studies. The results show, in accordance with experimental data, that the low reactivity of ammonia is a limiting factor in thermal ALD growth of indium nitride with trimethylindium and ammonia.