Abstract
Graphite dust is generated in the reactor core during normal operation of very high temperature reactors (VHTRs). This dust is transported throughout the reactor circuit and plates-out at different locations. The resuspension of graphite dust is believed to be a major contributor to the nuclear source term. The adhesion force is an important parameter governing the resuspension of the dust. The present study employed an atomic force microscope to measure the adhesive force between a reactor-grade graphite cluster “particle” and VHTR structural materials including Inconel 617 and Hastelloy X in an air glove box. Results for a reactor-grade graphite (MLRF-1 from SGL Carbon Ltd.) cluster particle interacting with Inconel 617 and Hastelloy X samples are reported under four different surface conditions including as received, and after 5, 10, and 15 min of oxidation. These forces were also predicted using the Johnson-Kendall-Roberts theoretical model with the estimate of the work of adhesion. The measured values depend on oxidation times but are in general a factor of about 20 lower than the predicted values. With surface roughness taken into account, the predicted values differ from the measured values by factors of 2 and 4 at the maximum for Hastelloy X and Inconel 617, respectively.
Acknowledgments
This research has been carried out within the facilities and with the support of the Nuclear Science and Engineering Institute (NSEI) at the University of Missouri. We acknowledge the Life Science Center and Scanning Electron Microscope Core at the University of Missouri for use of their facilities and equipment. We also thank Shawn Campbell (NSEI) for his help with calculations.
Nomenclature
| = | pull-off force (µN) | |
| R = | = | radius of a spherical particle (µm) |
| = | particle radius | |
| = | reduced radius taking roughness into account (µm) | |
| = | radius due to hemispherical features on material surfaces | |
| = | work of adhesion (mJ/m2) | |
| = | Greek | |
| = | surface energy (mJ/m2) |