Experimental MHD – flow analyses in a mock-up of a test blanket module for ITER

Magnetohydrodynamic experiments in a scaled mock-up of a helium-cooled lead lithium test blanket module designed for being tested in ITER have been performed in the MEKKA liquid metal laboratory at the Forschungszentrum Karlsruhe. The mock-up consists of four breeder units connected by feeding and draining manifolds. Each breeder unit contains five internal walls simulating the helium-cooled plates which remove in the original design the heat from the breeding zone. Due to the electric conductance of all walls the whole structure represents a complex coupled system, since currents induced by the motion of the fluid under the influence of the strong plasma-confining magnetic field can cross the walls and couple electrically neighboring fluid domains. The present work is focussed on the experimental study of flow partitioning in subchannels of breeder units, depending on flow rate and strength of the applied magnetic field. For strong magnetic fields one can observe that the flow distribution is similar as assumed in the design. In accordance with theoretical predictions the outer subchannels of breeder units show higher velocities than those in central ducts. This is a consequence of the established strong coupling of flow domains inside breeder units and by the fact of a weak coupling of neighboring breeder units. With increasing flow rate or decreasing magnetic field uneven flow distributions and even flow reversal are observed. Such unfavorable flow regimes, however, occur only at parameters that are out of scope of normal ITER operation.