Influence of modifications of HCLL blanket design on MHD pressure losses

Abstract In 2008–2009 experiments have been performed to investigate liquid metal magnetohydrodynamic (MHD) flows in a scaled mock-up of a helium cooled lead lithium (HCLL) blanket. In order to improve the mechanical stiffness of HCLL blanket modules the design of the stiffening plate between two hydraulically connected breeder units (BUs) has been later modified. In the former design the liquid metal passed from one BU into the adjacent one by flowing through a narrow gap that extended along the entire width of the BU. In the most recent design this opening has been replaced by a series of smaller gaps. Therefore the velocity increases locally owing to the reduced cross-section along the flow path and the liquid metal contracts and expands along magnetic field lines to enter the neighboring BU. These flow conditions are known to create additional MHD pressure losses. In order to estimate the influence of design changes on MHD flow and pressure drop the previous test section has been adapted to the new design. Experimental results show that the modifications of the design at the first wall lead to an increase of pressure drop near the first wall by a factor 3–3.5. As a consequence the total pressure drop becomes larger. The 3D MHD phenomena that occur at the first wall seem to be mainly related to inertia effects that are confined in layers parallel to the magnetic field.