Toward full simulations for a liquid metal blanket. Part 2: Computations of MHD flows with volumetric heating for a PbLi blanket prototype at Ha~104 and Gr~1012

On the pathway toward full simulations for a liquid metal blanket, this Part 2 extends a previous study of purely MHD flows in a DCLL blanket in Ref. 1 [Chen, L., Smolentsev, S., and Ni, M. J. (2020)] to more general conditions when the MHD flow is coupled with heat transfer. The simulated prototypic blanket module includes all components of a real liquid metal blanket system, such as supply ducts, inlet and outlet manifolds, multiple poloidal ducts and a U-turn zone. Volumetric heating generated by fusion neutrons is added to simulate thermal effects in the flowing PbLi breeder. The MHD flow equations and the energy equation are solved with a DNS-type finite-volume code “MHD-UCAS” on a very fine mesh of 470×10^6 cells. The applied magnetic field is 5 T (Hartmann number Ha~10^4), the PbLi velocity in the poloidal ducts is 10 cm/s (Reynolds number Re~10^5), whereas the maximum volumetric heating is 30 MW/m^3 (Grashof number Gr~10^12). Four cases have been simulated, including forced- and mixed-convection flows, and either an electrically conducting or insulating blanket structure. Various comparisons are made between the four computed cases and also against the purely MHD flows computed earlier in Ref. \cite{1} with regards to the (1) MHD pressure drop, (2) flow balancing, (3) temperature field, (4) flows in particular blanket components, and (5) 3D and turbulent flow effects. The strongest buoyancy effects were found in the poloidal ducts. In the electrically non- conducting blanket, the buoyancy forces lead to significant modifications of the flow structure, such as formation of reverse flows, whereas their effect on the MHD pressure drop is relatively small. In the electrically conducting blanket case, the buoyancy effects on the flow and MHD pressure drop are almost negligible.

Physical Background, Computations and Practical Issues of the Magnetohydrodynamic Pressure Drop in a Fusion Liquid Metal Blanket

In blankets of a fusion power reactor, liquid metal (LM) breeders, such as pure lithium or lead-lithium alloy, circulate in complex shape blanket conduits for power conversion and tritium breeding in the presence of a strong plasma-confining magnetic field. The interaction of the magnetic field with induced electric currents in the breeder results in various magnetohydrodynamic (MHD) effects on the flow. Of them, high MHD pressure losses in the LM breeder flows is one of the most important feasibility issues. To design new feasible LM breeding blankets or to improve the existing blanket concepts and designs, one needs to identify and characterize sources of high MHD pressure drop, to understand the underlying physics of MHD flows and to eventually define ways of mitigating high MHD pressure drop in the entire blanket and its sub-components. This article is a comprehensive review of earlier and recent studies of MHD pressure drop in LM blankets with a special focus on: (1) physics of LM MHD flows in typical blanket configurations, (2) development and testing of computational tools for LM MHD flows, (3) practical aspects associated with pumping of a conducting liquid breeder through a strong magnetic field, and (4) approaches to mitigation of the MHD pressure drop in a LM blanket.