Conceptual Design of High Temperature Water-Cooled Divertor Plasma-Facing Unit for Fusion Reactor

Abstract

Tokamak, a type of fusion experimental device, is considered as the most promising device on which net fusion power could be outputted for electricity production, i.e., the fusion reactor. Divertor, as one of the core components in Tokamak, has to sustain very high heat flux from high temperature plasma, up to tens of MWs, so that the design of divertor plasma-facing unit (PFU) is quite important. Up to now, the most advanced mature PFU technology is the ITER W/Cu PFU, which is a monoblock structure with tungsten, Cu and CuCrZr as the plasma-facing material, interlayer and heat sink, respectively. However, due to high activation of Cu element by neutron irradiation, CuCrZr is not appropriate for the material of heat sink anymore for future fusion reactor. In the paper, a design of PFU with a low activation material (named CLAM, China Low Activation Martensitic steel) as the heat sink was proposed based on ITER monoblock structure, i.e., W/CLAM PFU. With the temperature operation window as the design limit, thermal analysis of W/CLAM PFU was done initially with the same structural dimensions as ITER monoblock. Then the structural dimensions were optimized for the purpose of improving the heat loads removing capability, more than 10 MW/m2. As a consequence, thermal stresses were calculated for the W/CLAM PFU, where stress in CLAM heat sink was found beyond the material limit. The issue was discussed and the solution was preliminary proposed. This can provide the necessary theoretical basis for improvement of heat flux handling capacity to divertor PFU in future application.