In the design of the fusion blanket, it is important to gather generated tritium as quick as possible and supply them to a fuel supply system for keeping fuel cycle and reducing tritium inventories in the fusion reactor at the same time.

In the advanced blanket concept which uses Lithium-Lead (LiPb) as the working fluid for heat removal, neutron shielding and tritium breeding, collection of generated tritium is thought not to be difficult as the solubility of hydrogen into the LiPb is small enough. But examination and design of these collecting systems was not fully studied.

In this paper, we made the conceptual design of the tritium collecting device using vacuum sieve tray, and studied formation process of LiPb droplets by making a simple experimental device. It was found that droplets of about 0.9-mm radius were formed at 8~12-cm distance from nozzle when LiPb discharges from the nozzle with 1-mm diameter hole at pressure of 2.5×104 Pa. Using this value, it is estimated that the tritium collecting efficiency of 45% can be achieved with 1-m height single stage sieve tray at temperature of 500 °C.