The law of the "sorting phenomenon" to the solid blanket with the mixed pebble bed in fusion reactor

Both the China Fusion Engineering Test Reactor (CFETR) and Japan's DEMO solid water-cooled blanket have proposed a mixed pebble bed for neutron multiplier and tritium breeder, which has higher initial packing factor with the special size ratio of the mixed pebble and therefore improves the effective thermal conductivity and tritium breeding comparing with the single particle pebble. However, the study of the behavior of the mixed pebble bed under various disturbances is still lacking. It is found that the mixed pebble bed under the disturbance will produce the phenomenon of "sorting" in the experiment. The effect of sorting on the mixed pebble bed has not been considered for the evaluation of TBR (tritium breeder rate). The pebble bed will inevitably suffer from various forms of disturbance during service of the blanket in the fusion reactor. Therefore, it is significant to consider the influence of the sorting phenomenon caused by the disturbance on the design of the mixed pebble bed structure of the fusion reactor. This paper presents the sorting phenomenon with mixed pebble bed under disturbance, the results indicate that: 1). The sorting degree is sensitive to the structure of the pebble bed. 2). The sorting behavior of the pebble bed is mostly influenced by the disturbance intensity, and also influenced somehow by the density ratio and size ratio in different way and magnitude. As a result, it is necessary to pay attention to this phenomenon with the design of the blanket using the mixed pebble bed.