Numerical investigation of purge gas flow through binary-sized pebble beds using discrete element method and computational fluid dynamics

摘要

The main function of the breeder materials, such as Li2TiO3, Li4SiO4, and Li2ZrO3, in a solid type breeding blanket is to produce tritium, which is transferred to the fuel cycle system by helium purge gas and is used as a fuel for nuclear fusion reactions. Since the configuration of the breeder should be designed considering the purge gas flow, the form of pebble beds is mainly adopted, thereby leading to the smooth flow inside a blanket. The flow characteristics can be important design drivers because they also affect the design of the fuel cycle system. In order to increase a tritium production rate, a large number of breeders should be placed in the same space and various sizes of pebbles instead of one size of pebbles can be thus applied to increase the packing fraction of pebble beds. In this case, however, the flow resistance may increase and hence the relationship between the pebble bed configuration and the purge gas flow should be carefully investigated. In this study, a computational framework for one-way coupling analysis of the discrete element method and computational fluid dynamics is established to simulate the purge gas flow through binary-sized pebble beds. The configurations of pebble beds are obtained using the discrete element method and their geometries are modified by smoothing the sharp circular edges at the contact points of pebbles to construct proper meshes for computational fluid dynamics simulations. The flow resistance of binary-sized pebble beds is then investigated in terms of the pressure drop in the breeding zone.