NUMERICAL SIMULATION OF GRAPHITE DUST DEPOSITION IN PEBBLE BED REACTOR CORE OF HTGR

The deposition of graphite dust produced by the collision between graphite components would cause the security issue in HTGR and need to be analyzed. In this paper, a numerical calculation about the graphite dust's deposition in the pebble bed reactor core of high-temperature gas cooled reactor was conducted. The three-dimensional steady-state solver was employed for the calculation of flow field and temperature field during simulation. The discrete phase model (DPM) and Lagrange method were applied for the simulation of graphite dust. Effects of parameters such as particle diameter, pebble bed layer numbers, inlet velocity and surface temperature of fuel elements on deposition of graphite dust are analyzed. The results indicated that a majority of particles deposit on the first layer pebble because of first layer's shielding effect on nether layers. Moreover, deposition efficiency of graphite dust increases with increasing particles diameter and increasing inlet velocity due to greater motion inertia of particles. Compared with fewer layers, more layers structure would lead to larger deposition efficiency because of more opportunities for collision between graphite dust and pebbles, but the difference is not obvious. In addition, the higher surface temperature of fuel elements would cause lower deposition efficiency due to larger thermophoretic force which would drive particles to deviate from pebbles.