Thermal-hydraulic design of water cooled first wall of the fusion reactor under DEMO conditions

The heat loads on the First Wall (FW) of the European DEMO are not yet defined, but when extrapolated from ITER, the loads are expected to exceed the capabilities of current designs. Since DEMO will use Eurofer 97 as the structural material and Pressurized Water Reactor (PWR) conditions at the coolant inlet, the design of the heat sink will be challenging. Indeed, the thermal conductivity of the heat sink material is quite low and the temperature limits are also quite restrictive (between 285 °C and 550 °C). As in ITER, there are two different kinds of heat sinks that were designed for the FW: the first is the normal heat flux channel and the second is the enhanced heat flux channel. For handling normal heat fluxes (NHF), round tubes with counter-current flow are chosen while for handling enhanced heat fluxes (EHF), the Hypervapotron (HV) channel is chosen. Simulations were carried out to find the limits from the thermal hydraulic point of view using commercial Computational fluid dynamics code STAR-CCM+. For NHF channels after optimization the limit from the thermal hydraulics point of view, was found to be ∼1.7 MW/m2, for EHF channels it is ∼3 MW/m2.