OXIDATION OF SILICON CARBIDE AND GRAPHITE FOR HIGH TEMPERATURE GAS-COOLED REACTOR APPLICATIONS

<p>"This research focuses on the oxidation behavior of silicon carbide and matrix grade graphite, specifically as it pertains to accident scenarios in Gen IV thermal spectrum high temperature gas cooled nuclear reactors. It is imperative to understand the oxidation behavior of such materials to predict their response to off-normal environments and certify their accident tolerance to implement Gen IV reactors. The onset of oxidation temperature of matrix graphite was found to have a strong dependence on the microstructure, and therefore processing parameters, of the materials. The A3-3 type grade contained regions of partially graphitized carbon that were more disordered and oxidized more readily than the A3-27 type that contained a more graphitic structure. The oxidation behavior of the SiC layer of tristructural isotropic (TRISO) fuel particles demonstrated different oxidation behavior than that of typical flat-plate chemical vapor deposited SiC and that of SiC fibers with regards to stress relief and devitrification in the SiO₂ scale. By comparing the oxide layer thickness of TRISO particles oxidized in atmospheres containing 0.2 and 20 kPa O₂, it was found that the mechanism responsible for oxide growth was different at each pO₂, with activation energies of 168 and 230 kJ/mol, respectively. The oxide growth mechanism was consistent from 6 – 20 kPa O₂, with a pO₂ dependence of 0.83. TRISO particles oxidized in 0.2 kPa O₂ exhibited raised nodules on the surface that were correlated with pockets of nanocrystalline SiC. The nodules were formed via the enhanced production of gaseous CO(g) and SiO(g) within grain boundaries. In regions of nanocrystalline SiC containing a high density of grain boundaries, SiO(g) within bubbles that formed along interfaces oxidized to redeposit SiO₂"--Abstract, p. iv</p>

Name thesis:degree_name

Ph. D. in Materials Science and Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Bratten, Adam Thomas

• Materials Science and Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3216

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4221