To investigate the influence of the drainage rate and the particle contact model on the main features of the pebble flow, a quasi-static pebble flow of full scale German HTR-MODUL pebble bed is performed with up to 360,000 frictional graphite spheres. The treatment of the sphere-wall boundary condition is analyzed to avoid underestimating the friction of pebble near the wall. The streamlines, diffusion of pebbles and velocity profiles of pebble flow are drawn and analyzed. It shows that the streamlines and diffusion of pebbles inside the pebble bed are barely affected by the drainage rate and the particle contact model used. However, it reveals that the drainage rate and the contact model obviously influence the pattern of velocity profiles. It demonstrates that the quasi-static pebble flow and the Hertzian model are optimal choices of the neutronic physical design of the pebble bed reactor when the residue time of pebbles is particularly concerned. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.