Award Date

1-1-2008

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Committee Member

Clemens Heske

Number of Pages

58

Abstract

TRistructural-ISOtropic (TRISO) fuel particles are being developed for the use in next generation nuclear power plants. They consist of a UO2 kernel coated with layers of different materials to keep the fission products inside the particle. The kernel is surrounded by a porous carbon layer, followed by a dense inner pyrolytic carbon layer, a SiC layer, and a dense outer pyrolytic carbon layer. One central question of this technology is whether the fission products "corrode" this shell of the TRISO particle during operation. To answer this question, we have investigated the interface between cesium (Cs, which is one of the metal fission products) and silicon carbide (SiC, which is the main diffusion barrier in the TRISO particle) as well as highly oriented pyrolytic graphite (HOPG; which is structurally similar to the pyrolytic carbon layers found in the TRISO shell). Corresponding samples were characterized by X-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy as well as atomic force microscopy (AFM). Since XPS and UPS are very surface-sensitive techniques, the interface formation was monitored by step-wise deposition of Cs on HOPG and SiC using an alkali metal evaporator, which was designed and built within this thesis. The detailed analysis of the XPS line intensities of both Cs on HOPG as well as on SiC suggests an island-like growth of the Cs film. This model could be corroborated for HOPG by AFM measurements clearly showing the Cs islands on the HOPG surface. In addition to the structural information, the XPS spectra give insight into the chemistry occurring at the two interfaces. We can identify an additional carbon species that can be attributed to an interfacial species, suggesting a strong chemical interaction. Significant changes were found after heating a thick Cs film on HOPG in air. Most of the Cs atoms vanished from the HOPG surface, most likely due to diffusion into the HOPG. Furthermore, the AFM pictures taken of this sample show a strongly changed surface morphology with deep craters, suggesting a strong interaction between Cs and the HOPG surface; The findings of this thesis thus shed light on the detailed chemical and electronic interactions between a potential fission product and surrogate materials for TRISO coating layers. Based on these interactions, schemes can be designed and monitored to prevent the corrosion of TRISO coatings by metal fission products during reactor operation.

Keywords

Atomic; Carbide; Cesium; Force; Hopg; Interface; Microscopy; Photoelectron; Silicon; Spectroscopy; Study; Surface

Controlled Subject

Materials science; Nuclear chemistry

File Format

pdf

File Size

1157.12 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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