3D magneto-convective instabilities of liquid metal flow in a generic geometry related to WCLL blankets

The water-cooled lead lithium breeding blanket has been selected as one of the test blanket modules for the International Thermonuclear Experimental Reactor (ITER). In this blanket concept, heat generated by neutron collisions is extracted through water-cooled pipes immersed in the liquid eutectic lead-lithium alloy (PbLi), which serves as both a breeder material and a heat transfer medium. Temperature gradients in PbLi cause buoyancy-driven motion, while Lorentz forces, arising from flow-induced electrical currents in the presence of a magnetic field, act to suppress this motion. A comprehensive understanding of these complex 3D magnetohydrodynamic (MHD) phenomena is essential to assess the feasibility of liquid metal blankets. The present study investigates the convective MHD flow in a simplified model geometry featuring a long rectangular cavity with a coaxial circular cooling pipe maintained at a constant temperature, with imposed uniform volumetric heating in the fluid. Previous numerical simulations for an infinitely long cavity in axial direction reveal magneto-convective motion in transverse planes, where a cold plume “falls down” beneath the cooling pipe. The present 3D study extends previous analyses and identifies a bifurcation and transition from the 2D state to complex 3D flow structures at sufficiently high volumetric heating. The observed convection rolls preferentially align with the transverse horizontal magnetic field and affect significantly the convective heat transfer. • Investigating magneto-convective instabilities of liquid metal flow. • Buoyancy forces promote fluid motion whereas forces suppress convection. • Bifurcation from 2D to 3D fow patterns enhances convective heat transfer.