Magnetohydraulic flow in a rectangular channel filled with stream-wise obstacles

The Water-Cooled Lead Lithium (WCLL) Breeding Blanket (BB) is one of the two leading candidates for implementation as driver blanket in the European DEMO reactor, which is expected to start operation in the late 2050s and serve as a BB test facility. One of the main risks associated with the current WCLL concept is the large number of welds necessary to realize its horizontal (toroidal-radial) breeding zone cooling system and stiffening structure, which negatively affects its reliability. Hence, an alternative variant concept has been proposed which relies on vertical (radial-poloidal) “double-bundle” cooling tubes and stiffening plates: the WCLL double-bundle (WCLL-db). In this paper, we report the results of numerical analyses performed to characterize the Magnetohydrodynamics (MHD) regime in the WCLL-db where the liquid metal breeder flows vertically and it is obstructed by a large number of electrically conductive obstacles aligned with the stream-wise direction. Direct numerical simulations are performed with the aid of computational MHD tools to characterize the flow features and pressure losses in the WCLL-db breeding zone. The presence of many stream-wise obstacles affects the velocity distribution since the cooling tubes provide additional paths for the electric current closure. The most striking feature is the breaking down of the classic MHD slug core flow into many separate smaller regions, separated by internal layers. These occur tangential to the pipe walls, featuring velocity overshoots, and tend to propagate along the imposed magnetic field. A moderate (3.83–9.73%) pressure penalty is found compared with the analytical prediction for a channel devoid of obstacles.