Numerical investigation of liquid metal magneto-convection at high Grashof and Hartmann number in a prototypical water-cooled breeding blanket for fusion reactors

The breeding blanket is one of the critical components of a nuclear fusion reactor. It must fulfill the dual tasks of producing tritium through the breeding reaction and extracting the thermal power generated by the fusion reaction. The EUROfusion consortium is developing the Water-Cooled Lead Lithium (WCLL) breeding blanket concept for the European DEMOnstrator fusion reactor, utilizing a liquid metal as the tritium breeder and pressurized water for thermal power extraction. The interaction between the electrically conducting liquid metal in a thermal convection regime and the plasma-confining magnetic field leads to the so-called magneto-convection phenomena. These phenomena impact component performance and are crucial in fusion reactors due to the presence of a strong magnetic field, significant heat flux, and a volumetric heat source within the blanket. In this study, the WCLL elementary cell is analyzed under more realistic conditions compared to previous studies. In particular, the analysis considers a complete bi-directional magnetic field topology and more realistic boundary conditions to represent the cooling system of the blanket plasma-facing part (first wall) under operational conditions. It is found that the bi-directional magnetic field reorganizes the convective cells from a large-scale coherent structure into smaller-scale structures, reducing the average velocity and dampening heat exchange. This, combined with the effect of the more realistic boundary conditions, results in a temperature increase of approximately 70 K compared to previous studies.