Thermo-hydraulic optimization study for a high heat flux unit of the K-DEMO divertor target

Exhaust the very demanding incident heat flux of about 10 ∼ 20 MW/m2 concentrated on the narrow area of the divertor target is one of the most challenging requirements in the fusion DEMO reactor. The divertor has to remove the plasma power within allowable temperature ranges of the comprising materials such as armor, heat sink, and coolant. To satisfy the requirement, the optimized design of the divertor is significant as well as the selection of the comprising materials. In the K-DEMO (Korean fusion demonstration reactor), the target peak heat flux of 10 MW/m2 was set in the steady-state operation and a water-cooled divertor concept employing the tungsten monoblock has been primarily considered. RAFM (reduced activation ferritic martensitic) steel has been considered the primary candidate as heat sink material and CuCrZr has been the second best plan in the K-DEMO divertor. The purpose of this study is to derive optimum design for two design options: RAFM and CuCrZr. To carry out the design optimization based on thermo-hydraulic and statistical analyses, input parameters such as top thickness and lateral thickness of monoblock and thickness of coolant tube and output parameters such as maximum temperatures of monoblock and coolant tube are defined. In the parameter correlation analysis, regression equations defining the relation between the input and output parameters were derived with statistical values. Finally, the optimized designs for CuCrZr and RAFM models satisfying objectives and constraints were derived by the response surfaces optimization. The optimized designs applying the derived design parameters showed the designs satisfy the thermal requirement.