Experimental study on the vibration behavior of the pebble bed in PB-FHR

Abstract Vibration induced by external excitations such as earthquake or mechanical operation is a threat to the safety of PB-FHR. A scaled model based on TMSR-SF is built to conduct vibration experiments under different conditions. Experiment results show that pebble bed keeps stable under weak vibration, while it becomes denser in few minutes when strong vibration occurs. The packing factor increases rapidly with about 5% variation in initial 5 min under strong vibration, which induces approximately 2500 pcm reactivity in reactor core. The vertical vibration which occurs first in earthquake has less impact on pebble bed than horizontal vibration. Increase of flow velocity may enhance support force between pebbles, which leads to more stable structure of pebble bed under vibration. The study analyzed the influence of vibration on the pebble bed in the reactor core. These experiment phenomena and results provide support to reactor design and safety analysis of PB-FHR.