Preliminary study on the development of the fluidic system for the fabrication of pebble with core–shell structure

• Core-shell droplet fabrication system was developed to form a protective coating layer for breeder materials with high lithium density and low strength, such as Li 4 SiO 4 . • Core-shell droplet fabrication system was developed from the T–shape based fluidic system used in many previous studies. • Li 4 SiO 4 –Li 2 TiO 3 pebbles manufactured using the core–shell droplet fabrication system were found to have a diameter of approximately 2.3 mm and a Li 2 TiO 3 coating layer of 200–300 μm. • Li 4 SiO 4 –Li 2 TiO 3 pebble had a crush load that is 2.03 times higher than of a single Li 4 SiO 4 pebbles. Li 4 SiO 4 , used as a tritium breeder material in fusion reactors, has high lithium density but suffers from lower mechanical strength compared to another promising material, Li 2 TiO 3 . In this study, a fluidic system was designed to fabricate core-shell structured pebbles (Li 4 SiO 4 –Li 2 TiO 3 ) consisting of a Li 4 SiO 4 core and a Li 2 TiO 3 shell. The system was constructed using a T–shaped fluid flow channel with a double–tube design, enabling the controlled formation of core-shell droplets by adjusting the flow rates of the continuous and dispersed phases. The resulting Li 4 SiO 4 –Li 2 TiO 3 pebbles exhibited a crush load approximately 2.03 times higher than that of single-phase Li 4 SiO 4 pebbles, and the stable formation of the core–shell structure was confirmed. This study presents a novel fabrication process with the potential to enhance the mechanical performance of Li 4 SiO 4 as a tritium breeder material.