Pebble flow experiments for pebble bed reactors

A series of one-to-ten-scale experiments were conducted at the Massachusetts Institute of Technology (MIT) to explore several key aspects of pebble flow in pebble-bed reactors. These experiments were done to assess not only the flow lines but also the relative velocities of the pebbles of various radii from the center line of the core. Half-model and full 3-D experiments were performed to verify that there were no surface effects that would affect the flow lines. In addition, an experiment was conducted to determine whether, for dynamic annular cores, the mixing zone could be eliminated greatly improving the capability of the core to produce power. An analysis was performed to establish the size of a ring to be inserted in the top of the core that would preclude the central graphite pebbles from bouncing out of the center region and fuel pebbles in the outer periphery from bouncing in. These experiments showed conclusively that the mixing zone could be effectively eliminated while maintaining the annular column during the recirculation process. The flow tests were performed under fast and slow flow conditions replicating the actual performance in a reactor