Critical review of forced-flow cooling technologies for fusion breeding blankets and primary heat transfer systems

This review critically assesses forced-flow cooling strategies in breeding blankets (BBs) and primary heat transfer systems (PHTS) in tokamaks, particularly in terms of their role in ensuring efficient cooling and tritium breeding in demonstration (DEMO) reactors. Existing studies have emphasized that coolant selection, blanket configuration, and system integration affects thermo-hydraulic performance, structural integrity, and operation reliability under high heat flux operation. Helium coolant has been widely discussed due to its inertness and high temperature capabilities, though it has poor heat capacity and high pumping power issues for heat removal efficiency. Liquid metals, such as lithium-lead (LiPb), have superior thermal performance, though there are issues of magnetohydrodynamic (MHD) effects and material compatibility. Molten salts have moderate thermo-hydraulic performance with potential benefits in thermal stability, but there are still concerns about corrosion and long-term behavior. The thermo-hydraulic performance of BB is complicated by complex geometry, non-uniform heat flux distribution, and combined modes of heat transfer in PHTS, which require careful design integration to ensure reactor safety and performance. For the development of improved BB cooling technologies for DEMO reactors, there are challenges to be addressed in coolant behavior, MHD effects, pressure drop, structural limitations, and system integration. Future work should focus on building up a comprehensive framework for comparison, enhancing predictive models of thermo-hydraulic performance, and optimizing coolant selection and design to improve performance and feasibility of fusion power systems.