Thermohydraulic Assessment for the Modified Concept of the K-DEMO Divertor Target

A pressurized water cooling divertor target applying the tungsten monoblock type has been primarily considered in the Korean fusion demonstration reactor (K-DEMO). The target peak heat flux locally concentrated around the striking point was set to 10 MW/m² in K-DEMO divertor system. In a previous study [Im et al., IEEE Trans. Plasma Sci., Vol. 44, p. 2493 (2016)] the thermomechanical analyses for a high heat flux unit of K-DEMO divertor target applying reduced activation ferritic martensitic (RAFM) steel as heat sink material were carried out to verify the thermal and mechanical stabilities. The results of the thermomechanical analyses showed that the stabilities of the divertor target design applying the derived design parameters were close to the allowable limits, since the thickness of RAFM coolant tube was too thin due to the low thermal conductivity of RAFM steel. The aim of this study is to propose the structurally modified divertor concept switching the flowing path of coolant from poloidal direction to toroidal direction. By changing the flow direction, the design and material could be independently selected by the local intensity of the heat flux. The CuCrZr and RAFM steel were employed to the peak heat flux region and the non-peak heat flux region as a heat sink material, respectively. The effects of the modified concept were assessed by performing thermohydraulic analyses. The result showed that the modified concept more efficiently dissipated the heat flux compared to the conventional concept.