Water Vapor Oxidation Of A3-type Graphitic Matrix Material
Abstract
High-temperature gas-cooled reactors (HTGRs) rely heavily on graphitic materials. While nuclear-grade graphite is used for core structural materials, graphitic matrix is used to hold thousands of TRISO particles together in the form of fuel compacts or fuel pebbles. This study investigates the water vapor oxidation of A3- based graphitic matrix—namely, A3–3 and A3–27—under conditions resembling a steam ingress accident scenario in an HTGR. The graphitic matrix was subjected to temperatures of 800 °C–1100 °C, with a water vapor partial pressure of 20 kPa. In a 20 kPa water vapor atmosphere, while the oxidation mechanism for A3–3 type graphitic matrix stayed in the 'mixed regime' or regime II of graphite oxidation, A3–27 type showed a clear shift in oxidation mechanisms from 'kinetic regime' (regime I) to 'mixed regime' (regime II) around 900 °C and then to 'diffusion-controlled regime' (regime III) between 1000 and 1050 °C. Kinetic analysis revealed the apparent activation energy for water vapor oxidation at 20 kPa to be 36.9 kJ/mol for the A3–3 type. For the A3–27 type, the apparent activation energy was 143.5, 46.3, and 9.7 kJ/mol in the kinetic, mixed, and diffusion-controlled regimes, respectively. With a low apparent activation energy in the mixed regime, the A3–3 type graphitic matrix appeared to oxidize more readily in steam. Transmission electron microscopy (TEM) and Raman spectroscopy showed that, despite A3–27's higher content of partially graphitized carbon (PGC) as compared to A3–3, the PGC in A3–27 exhibited a greater degree of order and crystallinity, making it more graphite-like. Raman spectroscopy also revealed that the less-ordered PGC in A3–3 oxidized more quickly than that in A3–27.
Recommended Citation
V. Jalan et al., "Water Vapor Oxidation Of A3-type Graphitic Matrix Material," Journal of Nuclear Materials, vol. 633, article no. 157061, Elsevier, Nov 2026.
The definitive version is available at https://doi.org/10.1016/j.jnucmat.2026.157061
Department(s)
Materials Science and Engineering
Publication Status
Full Text Access
Keywords and Phrases
Graphitic matrix; Microstructure; Oxidation; Raman; TEM; TGA
International Standard Serial Number (ISSN)
0022-3115
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2026 Elsevier, All rights reserved.
Publication Date
01 Nov 2026
Comments
Office of Nuclear Energy, Grant DE-NE0008753