Understanding pebble flow characteristics and residence time distribution is essential for reactor design, fuel burnup estimations, and safety analysis of High-Temperature Gas-Cooled Pebble Bed Reactors. However, due to the complex nature of the dense granular flow, pebble flow remains inadequately understood and challenging to study through experiments. In this work, a three-dimensional experimental pebble-bed setup was developed to investigate pebble flow behavior in pebble-bed reactors. For the first time, 6.0 cm graphite pebbles were utilized, and features such as one pebble at a time discharge mode and continuous pebble recirculation were incorporated. The overall and zonal residence time distributions and the zonal-averaged axial velocity were investigated using a radioisotope-based residence time distribution (RTD) technique. The results showed that the overall residence time increases as the radius of the initial seeding position increases, but with a higher increase rate at the wall compared to the center region. The zonal residence time findings indicated a uniform profile in the upper section of the bed, except near the wall. However, non-uniformity in the radial profile increased in the lower sections, with the greatest variation occurring in the conical section. The axial velocity of the pebbles was found to be small and nearly uniform in the upper section of the bed. In the lower section, however, the velocity increased significantly for the center-region pebbles compared to those at the wall, resulting in a pronounced non-uniform radial profile. Moreover, a consistent hexagonal arrangement of pebbles was observed across the entire container wall after recirculating several bed inventories, which is worth further investigation.