MHD Flow in Curved Pipes Under a Nonuniform Magnetic Field

In fusion reactors, a very hot deuterium–tritium plasma is confined in a toroidal volume by means of a strong magnetic field. In the blanket structure that surrounds the fusion plasma, high-energy neutrons, produced in the D-T fusion reaction, are absorbed by the lithium-containing liquid metal releasing their kinetic energy in the form of volumetric thermal load and breeding the fuel component tritium. The liquid metal flows from the blanket toward external ancillary systems for purification and tritium extraction. When the electrically conducting fluid moves in the strong plasma-confining magnetic field, induced electric currents generate electromagnetic Lorentz forces, which modify velocity distribution and increase pressure losses compared with hydrodynamic flows. These magnetohydrodynamic (MHD) effects have to be investigated to determine their impact on blanket performance. A number of studies on pressure -driven and buoyant MHD flows in geometries related to blanket modules are available, while only few works consider MHD flows in pipelines connecting blanket and ancillary systems. In the present study, we investigate numerically liquid metal MHD flows in the pipes, which cross the shield that protects the superconducting magnets from neutron radiation-induced damages. The geometry features two bends in series that turn the flow from the radial direction perpendicular to the magnetic field into a direction parallel to it and then back to a perpendicular orientation. The correct radial distribution of the magnetic field, as expected along the pipe axis, is taken into account. The flow experiences strong 3-D effects caused by Lorentz forces due to large-scale current loops driven by axial potential differences along the bend axis. In spite of very strong local MHD effects on velocity and pressure distribution, the overall pressure drop does not increase significantly compared with the one in a fully developed flow in a straight pipe of same length.