In this project the chemical bonding and interface formation of metal fission products with the coating materials used in TRISO fuel particles is investigated. The interface formation of Pd, Cs, and Ag with SiC and pyrolytic carbon is studied in detail. Using the SiC single crystals and TRISO coating materials as substrates, interfaces are prepared under controlled conditions in an ultra-high vacuum environment and are studied with a photoelectron spectroscopy, Auger electron spectroscopy, Inverse Photoemission, X-ray emission spectroscopy, and X-ray absorption spectroscopy. Recent additions to the experimental approach include microscopic techniques (Transmission Electron Microscopy, Scanning Tunneling Microscopy, Atomic Force Microscopy) and local scanning tunneling spectroscopy.
In the second year of the project, focus was placed on a detailed analysis and description of the Pd/SiC interface formation process. As an example, a series of X-ray photoelectron spectroscopy (XPS) survey spectra, that were taken for a SiC single crystal substrate after introduction into the system, after sputter-cleaning with Ar+ ions (2 keV), and after several Pd deposition steps are illustrated. In this particular case, the Pd deposition was performed at approx. 800 degrees C to simulate elevated temperatures in TRISO fuel. Furthermore, the SiC surface was very strongly sputtered, which induces a significant number of structural defects at the surface and is hence intended to simulate real SiC surfaces. An example of a detailed UV photoelectron spectroscopy (UPS) study of the corresponding samples is also provided, indicating how the electronic surface structure is converted from an adsorbate-induced character to a semiconductor (SiC) to a metallic thin film (for increasing Pd overlayer thickness). A detailed analysis of the valence band maxima and Fermi edges, together with a study of the work function (which can be derived from the secondary electron cutoff in the UPS spectra) gives detailed insight into the electronic structure of the Pd/SiC interface, which can be interpreted in view of pronounced intermixing effects, as well as the formation of an electronic Schottky barrier.
Chemical structure; Electronic structure; Metal-base fuel; Metal coating; Nuclear chemistry; Nuclear fuels; Palladium; Silicon carbide; X-ray spectroscopy
Chemistry | Materials Science and Engineering | Metallurgy | Nuclear Engineering | Oil, Gas, and Energy | Physical Chemistry
Interaction between Metal Fission Products and TRISO Coating Materials.
Available at: http://digitalscholarship.unlv.edu/hrc_trp_fuels/47