Interaction Between Metal Fission Products and TRISO Coating Materials: A Study of Chemical Bonding and Interdiffusion: 2nd Quarter Report, 2005

The goal of our project is to investigate interface corrosion processes in TRISO nuclear fuel particles. For this purpose, we are undertaking a detailed study of the interface formation between potential candidates for metallic fission products (Pd, Ag, and Cs), likely to diffuse from the kernel of the TRISO particles, with the TRISO coating layers. As a starting point, we are investigating the Pd/SiC interface and will extend our studies to Ag/SiC during our current summer research campaign. The experimental approach comprises the preparation of metal/SiC interfaces in-situ in our ultra-high vacuum system by electron-beam deposition. In order to understand the impact of the SiC surface on the interface formation properties, we employ a variety of surface preparation and modification schemes. In the past quarter, we were able to obtain a specialized low-energy ion source as a long-term loan from the Hahn-Meitner-Institute, Berlin, Germany. Accomplishments this quarter include: • Further optimization of the experimental set-up: commissioning and optimization of the UPS mode, installation of a low-energy ion source, optimization of communication between electron spectrometer and measurement electronics • Experimental campaign at the Advanced Light Source, Lawrence Berkeley National Laboratory (3 graduate students, one undergraduate student, PI) • Implementation of fit routines for data analysis, in particular the Doniach-Sunjic line profile for metal photoemission peaks • Presentation of results at two conferences (G. Gajjala) and one international symposium (PI

Interaction Between Metal Fission Products and TRISO Coating Materials

This project focuses on the chemical bonding and interface formation of metal fission products with the coating materials used in tri-isotropic (TRISO) fuel particles for gas-cooled reactors. By combining surface- and bulk-sensitive spectroscopic and microscopic methods, intermediate chemical phases at the interface, intermixing/diffusion behavior, and the electronic interface structure for different coating materials and metals are examined. In detail, the project studies the interface formation of Pd, Cs, and Ag with SiC and pyrolytic carbon. Using SiC single crystals and highly-ordered pyrolytic carbon (HOPG) as substrates, interfaces are prepared under controlled conditions in an ultra-high vacuum environment and are studied with a combination of experimental methods, including Photoelectron Spectroscopy, Auger Electron Spectroscopy, X-Ray Emission Spectroscopy, and X-Ray Absorption Spectroscopy. In the past year, emphasis was placed on a detailed analysis and description of the Cs/SiC and Cs/HOPG interface formation processes

Interaction Between Metal Fission Products and TRISO Coating Materials: A Study of Chemical Bonding and Interdiffusion: 1st Quarterly Report, 2006

This project is devoted to an in-depth study of the chemical and electronic impact of metal fission products on the coating layers in TRISO nuclear fuel. In particular, there is a focus on the investigation of Pd, Cs, and Ag and their interface formation with SiC and carbon-based substrates. A variety of surface and near-surface bulk sensitive probes that investigate the occupied and unoccupied electronic states of the substrate and the metal overlayer have been utilized. By a controlled and stepwise deposition of the metal overlayer, it is possible to gain substantial insight into the formation of interfaces and their intermixing behavior. In the past quarter, there has been a focus on a detailed analysis and description of the Pd/SiC interface formation process

Interaction Between Metal Fission Products and TRISO Coating Materials

The goal of this project is to elucidate the chemical bonding and interface formation of metal fission products with the coating materials used in state-of-the-art TRISO fuel particles. Particular emphasis is placed on an analysis of intermediate chemical phases at the interface, the intermixing/diffusion behavior, and the electronic interface structure as a function of material choice (metal and coating materials), temperature, and external stress. Furthermore, the chemical state of some of the metal fission products will be assessed. This project studies the interface formation of Pd, Ag, and Cs with SiC and pyrolytic carbon. Using the TRISO coating materials (and single crystal references) as substrates, interfaces will be prepared under controlled conditions in an ultra-high vacuum environment and will be studied with a variety of different spectroscopic and (when applicable) structural methods. In addition, realistic microstructures will be studied. The research objectives of this project are as follows: To give valuable information about failure mechanisms of TRISO particles and fission product transport. To give, through simulating experiments, indications for optimized irradiation testing and post-irradiation examinations within the AFCI effort at ORNL. To derive strategies to tailor the interface properties for an optimization of TRISO particles in terms of, e.g., chemical and long-term stability

Understanding and optimizing surfaces and interfaces in energy conversion devices

This inaugural event is dedicated to showcasing the renewable/sustainable energy projects of UNLV faculty, staff, students, and collaborators, as well as other external projects underway statewide and nationally. The development and utilization of new technologies to protect the environment, achieve energy independence, and strengthen the economy will be explored. Speakers and poster-session presenters will provide further insight to many ongoing projects and innovative research ideas. Organized by UNLV’s Office of Strategic Energy Programs, the event offers participants the opportunity to learn about energy projects and will encourage networking and collaboration. This symposium is intended for researchers, educators, students, policy makers, public and private-sector energy and environmental professionals, and citizens

Hydrogen Fuel Cells and Storage Technology (FCAST) Project

The 2008 UNLV Renewable Energy Symposium was presented by the Office of Strategic Energy Programs and co-sponsored by the Division of Research and Graduate Studies on August 20, 2008 on the UNLV campus. The event focused on renewable energy production in Nevada, the US Southwest, and renewable research projects nationwide. It was a great opportunity for anyone working on renewable projects to collaborate with others in this field and exchange information. Over 230 individuals attended the event this year

Investigations of the Fundamental Surface Reactions Involved in the Sorption and Desorption of Radionuclides

Models for describing solution- and surface-phase reactions have been used for 30 years, but only recently applicable to complex surfaces. Duff et al., using micro-XANES, found that Pu was concentrated on Mn-oxide and smectite phases of zeolitic tuff, providing an evaluation of contaminant speciation on surfaces for modeling. Experiments at Los Alamos demonstrated that actinides display varying surface residence time distributions, probably reflective of mineral surface heterogeneity. We propose to investigate the sorption/desorption behavior of radionuclides from mineral surfaces, as effected by microorganisms, employing isolates from Nevada Test Site deep alluvium as a model system. Characterizations will include surface area, particle size distribution, x-ray diffraction (XRD), microprobe analysis, extractions, and microbiology. Surface interactions will be assessed by electron spectroscopy (XPS), x-ray absorption fine structure spectroscopy (XAFS), X-ray emission spectroscopy, transmission electron microscopy (TEM) and Scanning electron microscopy (SEM). Desert Research Institute (DRI), University of Nevada, Reno (UNR), and University of Nevada, Las Vegas (UNLV) researchers will collaborate to enhance scientific infrastructure and the understanding of contaminant behavior on surfaces, with broader implications for the management of DOE sites

Ambient-pressure ozone treatment enables tuning of oxygen vacancy concentration in the La1−x_{1− x}Srx_{x}FeO3−δ_{3− δ } (0 ≤ x ≤ 1) perovskite oxides

Oxygen vacancies in metal oxides can determine their properties. However, it is difficult to reduce the oxygen vacancy concentration in metal oxides without annealing them under high pressure. In this work, we develop a facile approach to control oxygen vacancy content via an ozone treatment under ambient pressure during cooling. This approach is demonstrated for the synthesis of La$_{1−x}$Sr$_{x}$FeO$_{3−δ}$ (0 ≤ x ≤ 1, 0 ≤ δ ≤ 0.5x) perovskite oxides – an important class of energy-related materials due to their wide range of non-stoichiometry, mixed ionic and electronic conductivity, and the presence of a rare Fe(IV) oxidation state. A series of La$_{1−x}$Sr$_{x}$FeO$_{3−δ}$ compounds was initially synthesized using a polymerized complex method. The concentration of oxygen vacancies and Fe(IV) were determined by redox titration, and the crystal structures were derived by analyzing X-ray diffraction patterns using Rietveld refinement. Significant amounts of oxygen vacancies were found in the as-synthesized compounds with x ≥ 0.8: La$_{0.2}$Sr$_{0.8}$FeO$_{3−δ}$ (δ = 0.066) and SrFeO$_{3−δ}$ (δ = 0.195). The ambient-pressure ozone treatment approach was able to substantially reduce the amount of oxygen vacancies in these compounds to achieve levels near the oxygen stoichiometry of 3 for La$_{0.2}$Sr$_{0.8}$FeO$_{3−δ}$ (δ = 0.006) and SrFeO$_{3−δ}$ (δ = 0.021). The oxygenation/deoxygenation kinetics can be tuned by the cooling rate after annealing. As the oxygen vacancy concentration decreases, the structure of SrFeO$_{3−δ}$ evolves from orthorhombic to cubic, demonstrating that the crystal structures in metal oxides can be highly sensitive to the number of oxygen vacancies. The ozone treatment approach developed in this study may thus offer a robust means to tune the properties of a wide variety of metal oxides

Using the Inelastic Background in Hard X-Ray Photoelectron Spectroscopy for a Depth-Resolved Analysis of the Cds / CU(In,GA)SE \u3c Inf \u3e 2 \u3c / Inf \u3e Interface

The inelastic background of hard x-ray photoelectron spectroscopy data is analyzed to paint a depth-resolved picture of the CdS/Cu(In,Ga)Se2 (CdS/CIGSe) layer structure. The CdS/CIGSe interface is the central component in next-generation chalcopyrite thin-film photovoltaic devices. By analyzing both, the (unscattered) core-level peaks and the inelastic background, and by varying the excitation photon energy from 2.1 up to 14 keV, we can derive photoemission information over a broad range of electron kinetic energies and, hence, sampling depths. With this complementary information, the CdS film thickness of a CdS/CIGSe interface can be accurately determined as a function of the CdS deposition time. For the thinner CdS films, the film thickness can be shown to vary laterally. Furthermore, small amounts of Se and process-related Rb can be detected in a thin (∼2 nm) surface layer of all investigated CdS films