Influence of non-insulated gaps between flow channel inserts in ducts of DCLL blankets

Dual coolant liquid metal blankets with helium cooled structure and self-cooled breeding zone have been proposed for a DEMO reactor. The feasibility of this concept is strictly related to the possibility of reducing the pressure drop caused by the intense magnetohydrodynamic (MHD) interactions, namely related to electromagnetic forces induced in the fast flowing liquid metal. In order to minimize the MHD pressure losses electrically insulating channels should be used. The interruption of the current path through conducting walls could be reached by fitting low conducting flow channel inserts into the ducts. Due to fabrication issues or maintenance requirements the insulating liners could present axial gaps, which determine a local discontinuity of the electric insulation at the wall. Magnetohydrodynamic flows close to gaps of insulating inserts in electrically conducting channels are investigated by asymptotic methods and by 3D numerical simulations for different magnetic fields and various values of the electrical conductivity of the walls. The additional pressure drop resulting from three dimensional current loops that close through pipe walls and in the fluid is quantified.