Flow of individual pebbles in cylindrical vessels

The movement of individual pebbles in a simulated recirculating pebble bed nuclear reactor has been investigated. Experimental and statistical results are presented concerning the transit number spectra of groups of pebbles and the transit of individual pebbles in recirculated random packings of identical pebbles. A cylindrical vessel with a variable base angle and a single axial outlet contained the pebbles which varied in diameter, shape, and specific gravity. The pebbles flowed downward under the influence of gravity and through a rotating extractor in the base. Transit number spectra were found by seeding many coloured pebbles at a particular radius and noting the amount of recirculation required before they emerged. While the packing descended, a radioactively tagged pebble inserted at the top of the bed was tracked as it moved through the vessel. Tracks and velocities of pebbles for various combinations of seeding radius, bed and pebble parameters were determined. Using these tracks, patterns and effects of flow zones were deduced. (Auth.)