MHD effect on tritium transport in WCLL at breeder unit level

The Water-Cooled Lithium-Lead (WCLL) is one of the four breeding blanket concepts proposed by Europe for the demonstrating fusion power reactor DEMO. In the WCLL, tritium, required for the D-T fusion reaction, is produced in the electrically conducting lead-lithium that flows inside the blanket. Its velocity field is strongly influenced by the external magnetic field used for plasma confinement due to a magnetohydrodynamic (MHD) effect, and by the temperature field. The non-isothermal condition is due to the presence of the heat flux incident on the first wall (FW), the plasma-facing area of the blanket, and the volumetric heat generation caused by the flux of energetic particles passing though the component. To avoid high temperatures, the WCLL is cooled with water, flowing in EUROFER tubes. The prediction of the velocity profile of Pb-Li and water is required to compute the transport of tritium inside the module, that allows to determine the T inventory and losses. In a first step, the reliability of the developed MHD codes has been checked solving benchmark cases, analytical and experimental, for which solutions are known. Then, the analysis of the WCLL module has been carried out, using the COMSOL multiphysics tool. Fluid dynamics with buoyancies has been solved for a quarter of module, the minimum relevant domain. MHD effects and tritium transport have been introduced in three simplified geometries with increasing complexity. In particular, a straight duct filled with lead-lithium with zero, one and two coolant tubes has been considered. Different tritium transport mechanisms (advection-diffusion of T into the lead-lithium eutectic alloy, transfer of tritium from the liquid interface towards the EUROFER, diffusion of tritium inside the steel, transfer of tritium from the EUROFER towards the coolant, and advection-diffusion of diatomic T into the water) have been included. With this study, it has been possible to evaluate the temperature field, velocity profiles of both lead-lithium and water and the concentration of tritium in the liquid metal, coolant and pipes.