Pressurizing behavior on ingress of coolant into pebble bed of blanket of Fusion DEMO reactor

In the safety design and technology of blankets for the Fusion DEMO reactor developed in Japan, coolant ingress in the blanket box structure is one of the most important events. Especially, the thermal hydraulics in the pebble bed in the case of the high-pressure coolant ingress is very important to evaluate the pressure propagation and coolant flow behavior. This paper presents the preliminary results of the pressure loss characteristics by the coolant ingress in the pebble bed. Experiments have been performed to simulate the helium coolant ingress into breeder and multiplier pebble beds and to evaluate the pressure loss in the pebble beds. The measured pressure loss is compared with the predicted values by Ergun's equation, which is the correlation equation on pressure loss of the flow through porous medium. Parameter study is carried out and dependencies of pressure loss through pebble bed on pressure and packing factor is evaluated. Method to reduce the maximum pressure in solid breeder blanket after pipe rupture accident is discussed. Enhancement of pressure loss in upstream and reduction of pressure loss in downstream is effective.