Numerical Analysis of Bypass Flow in Ceramic Pebble Beds

摘要

Solid tritium breeding blanket applying pebble bed concept is promising for fusion reactors. Tritium bred in the pebble bed is purged out by inert gas. The purge gas flow distribution is nonuniform in pebble bed due to the oscillating porosity distribution. Using an anisotropic porous model with wall fraction modification, the purge gas flow distributions in pebble beds with different bed-pebble diameter ratios (BPDR) are computed by computational fluid dynamics method. The results show that the normalized velocities are fixed with specific BPDR under the velocity range. However, the normalized velocities have integral accelerating trends with increasing BPDR. The bypass flow in the wall region cannot be ignored and the bypass flow but can be alleviated with increasing BPDR. To avoid serious bypass flow in pebble bed, the BPDR is better considered larger than 25.