Pebble flow in the core of a pebble bed high-temperature reactor (HTR) is a typical granular flow with a huge number of monosized spherical pebbles, where the kinematics of the pebbles needs to be predicted more accurately. In this study the discharge of monosized glass beads from a semi-cylindrical silo has been investigated using the Discrete Element Method (DEM), in which the particle-particle interaction model is based on contact mechanics with measured friction coefficients for precisely predicting the flow behaviour. Particle flow experiments were carried out with a transparent semi-cylindrical silo. Two cases were considered: one is for tracking the trajectories of identified particles with 11,500 glass beads, and the other is for the 'double-zone' flow for estimating the mixing evolution with 10,460 glass beads. Comparisons between the experimental and DEM results show good agreement, which indicates the applicability of DEM for predicting the pebble flow in a HTR. (C) 2009 Elsevier B.V. All rights reserved.