Experimental study of the helium flow characteristics in pebble-bed under the condition of CFETR's blanket module

The concept of Chinese Fusion Engineering Testing Reactor (CFETR) was proposed to fill the gap between International Thermonuclear Experimental Reactor (ITER) and fusion demonstration plant. The tritium breeder blanket module, in which the purge gas flows through the pebble-bed formed by lithium silicate balls at low pressure and velocity, is designed to achieve the tritium self-sustaining feature in CFETR. The flow characteristics of purge gas are important for the normal operation of tritium extraction system. However, previous studies mainly focus on the flow and heat transfer characteristics of helium at high pressure and velocity in the first wall of CFETR. In this work, the low pressure purge gas flow characteristics in the pebble-bed filled up with stainless steel balls of 0.8 mm, 1.0 mm, 1.5 mm and 2.0 mm in diameter were experimentally researched. An experimental facility was built and the relationship of helium flow pressure drop and different helium mass flow rates, pebble-bed channel lengths, ball diameters and helium pressures were investigated. Results showed that the helium flow pressure drop increased with the helium velocity and it obeyed the flow characteristics in porous medium. The helium flow pressure drop was proportional to the channel length, while it decreased as the ball diameter increased in the pebble-bed. The theoretical analysis of helium flow in the porous medium was also performed. A fitted formula applicable to the experiment conditions was obtained based on the Ergun empirical correlation. The fitted formula could be used to predict the helium pressure drop in CFETR's tritium breeder blanket module.