Thermal-hydraulic characteristics of IFMIF liquid lithium target

International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-based deuteron–lithium neutron source for testing fusion materials. High-speed flow up to 20 m/s is required for the liquid lithium target to remove high heat load 1 GW/m2 of deuteron beams. Thermal-hydraulic stability of the target system is required during long-term operation of IFMIF. Thermal-hydraulic analyses and simulation experiments with water jets were carried out to verify the stability of the IFMIF target flow. Appropriateness of concept of the high-speed flow on concave back-wall was verified by the analyses. There were enough temperature margins to avoid boiling and a thickness margin of 3 mm in the target. Acceptable range of the back-wall radius was 100–1000 mm. By the experiments with different nozzle wall roughness, main cause of surface waves was found to be boundary layer at the nozzle exit depending on the wall roughness. Cause of increased surface waves in case of the coarse-wall nozzle was a transition from laminar to turbulent boundary layer. Based on the experimental results, a wall roughness less than 6.3 μm was recommended for IFMIF target. These results give stable conditions of the IFMIF target, verify the appropriateness of its design and give guidelines on its fabrication.