Buoyant convection in the HCLL blanket in a strong, uniform magnetic field

Abstract

Modelling of steady-state magneto-convective flows has been performed for typical geometries of currently investigated Helium-Cooled Lithium Lead (HCLL) blankets. For fusion relevant magnetic fields the flow has been studied for a purely diffusive heat transfer regime and for a convective regime with finite Peclet number. The effect of the direction of the gravity has been investigated by studying the two limiting cases, i.e. horizontal liquid-metal layers and vertical layers, related to blanket modules in the equatorial plane and near the top poloidal position, respectively. Depending on the cavity's orientation, the flow is organised in a single convective circulation or in double recirculation cells located at the hot part of the cavity, where the volumetric power density has its maximum. The main component of vorticity of these recirculation cells is aligned with the magnetic field. For superimposed forced flows with Pe = 1.2, the buoyant convection is sufficiently strong to impose its flow pattern on the cross flow in parts of the cavity. A remarkable result of the present analysis is that the buoyancy induced flow may reach, or even overcome the magnitude of the imposed forced flow that is required for tritium removal. For that reason buoyant MHD flows in HCLL blanket modules is a phenomenon that has to be considered for reliable designs.