Abstract
This work compared the 3D Random Pore Model (3D-RPM) with experimental and characterization data to systematically study the effect of nuclear graphite microstructure and air oxidation temperature. It is well known that oxidation-induced weight loss at elevated temperatures degrades graphite structure and properties; however, a fundamental understanding of the role of graphite microstructure is still unclear. In this work, three diverse grades of nuclear graphite—IG-110, NBG-18, and PCEA—were examined and tested at air oxidation temperatures of 600, 650, 700, and 750 °C following ASTM D7542. The 3D-RPM reproduced the microstructure and temperature dependence of mass loss curves for these grades. For the first time, measurements and modeling were combined to show how bulk density and the amount and spatial distribution of open and closed porosity affects oxidation. IG-110 was less dense and had an open pore network that is finer and more uniformly spread, and showed fastest oxidation. PCEA porosity was less uniform and showed less oxidation, while NBG-18 was more dense, had the least fine and uniform porosity, and showed the slowest oxidation. In general, oxidation proceeds faster if open porosity is more uniformly distributed and can incrementally access closed pore surface area with more ease.
| Original language | English |
|---|---|
| Pages (from-to) | 132-145 |
| Number of pages | 14 |
| Journal | Carbon |
| Volume | 191 |
| DOIs | |
| State | Published - May 2022 |
Funding
This work was supported by the US Department of Energy's Office of Nuclear Energy under the Advanced Reactor Technologies—Gas Cooled Reactor program. Oak Ridge National Laboratory is managed by UT-Battelle LLC under contract DE-AC05-00R22725. Finally, although predicting overall and local mass loss due to oxidation is important, the greatest need is to understand the effect on mechanical and thermal properties. Properties such as strength, modulus, thermal conductivity, and thermal expansion are used to compute the integrity of graphite components, and mechanical-thermal integrity could be reduced if oxidation occurs. Future work could extend the 3D-RPM to be used in combination with structure-property models. Both reactor designers and operators will need data on the structure-property relationships for oxidized graphite grades being considered for high-temperature gas cooled reactors. Research into oxidation and other degradation mechanisms for graphite are key parts of the USA Advanced Reactor Technologies R&D Program for Graphite funded by the Department of Energy to provide data to enable the realization of an operational reactor [ 3 ].
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Office of Nuclear Energy | |
| Oak Ridge National Laboratory | |
| UT-Battelle | DE-AC05-00R22725 |
Keywords
- Microstructure
- Nuclear graphite
- Oxidation
- Porosity
- Reactivity