Magnetohydrodynamic simulation of the WCLL breeding blanket with helical cooling pipes

The Water-Cooled Lead Lithium (WCLL) is a Breeding Blanket (BB) concept presently in the development phase for implementation in the DEMO fusion reactor demonstrator. The Lead lithium eutectic alloy (PbLi) breeder is moved at a slow velocity to diminish Magnetohydrodynamics (MHD) pressure losses. The task of power extraction is given to water that flows within double-walled pipes submerged in the breeder and square channels that are bored into the First Wall (FW). The combination of an intense magnetic field, a non-uniform volumetric heating, a low forced convection velocity (Re = 140) , and a complex geometry induces a MHD regime that is dominated by the interaction between buoyancy and electromagnetic forces (magnetoconvection). This study analyzes the magnetoconvective regime that is established in the latest design iteration of the WCLL, which involves the use of nested helical pipes in which water circulates to remove the fusion thermal power generated in PbLi. These electrically conductive pipes, being both aligned and transverse to the main flow direction, significantly impact the distribution of currents induced in PbLi by the skewed magnetic field. Moreover, the multiple heat sinks present and the interaction with the FW cooling system give rise to a complex magnetoconvective pattern. Thermal-hydraulic performances and flow pattern are analyzed taking as reference the equatorial central Breeding unit (BU) in the Central Outboard Blanket Segment (COBS)