Resuspension of graphite dust from a wall under shear flow in HTGRs based on DEM simulations and AFM measurements

Pebble-bed high-temperature gas-cooled reactors (HTGRs) generate micron-sized graphite dust particles during their operation. These dust particles are deposited on the inner surface of the reactor’s primary loop and could become resuspended by the gas flow in the event of a breach, increasing the risk of radioactive dispersion. Therefore, studying the resuspension behavior of graphite dust particles is important for the safety of HTGRs. During the process of graphite dust resuspension, the particle–particle, particle–wall, and particle–gas flow interactions play decisive roles that are closely related to the particle shape and the structure of particle deposition. In this study, atomic force microscopy is used to investigate the interaction forces between particles and the particle–wall interface. Based on adhesion force data, numerical simulations of particle resuspension are carried out using the discrete element method, and the resuspension process is studied for the case of multilayer deposition structures. The results indicate that the particle–wall adhesion force is greater than the particle–particle adhesion force. The deposition structures formed by nonspherical rod-like particles are significantly larger than those formed by spherical particles. During particle resuspension, the particles move in a rolling regime, and particle clusters deform, stretch, break, and become suspended under the influence of near-wall shear flows, leaving a wake region at the trailing end of the particle cluster. With an increase in the particle deposition height, the resuspension rate rises, and rod-like particles generally exhibit higher resuspension rates than spherical and ellipsoidal particles.