Segregated and block-coupled approaches for electric potential coupling in multi-region magnetohydrodynamic flows within fusion liquid metal breeding blankets

Liquid metal breeding blankets in fusion reactors operate under strong magnetic fields, which results in the occurrence of complex magnetohydrodynamic (MHD) effects driven by electric currents that couple fluid and solid regions. Accurate modeling of this electromagnetic coupling is essential for reliable prediction of MHD flows in fusion blankets. This work compares two numerical strategies for electric potential coupling in multi-region MHD flows: a block-coupled and a segregated approach. The block-coupled method solves the governing equations in all regions simultaneously, providing strong interface coupling and rapid convergence, but requires strict mesh conformity at fluid–solid interfaces, which is difficult to achieve in complex geometries using automatic meshing tools. A segregated multi-region solver that solves the governing equations sequentially, tolerates nonconforming meshes through iterative interface coupling. The segregated approach is validated and applied to simulations of liquid metal flow in a mock-up of a water-cooled lithium lead test blanket module for ITER. Numerical results show good agreement with experimental observations and confirm a strongly non-uniform liquid metal flow distribution among the breeder units. The study highlights the respective strengths and limitations of both approaches and provides guidance for selecting appropriate electric potential coupling strategies in high fidelity simulations of blanket systems for ITER and DEMO.