Current status of the continuous tritium recovery test campaign using PbLi droplets in vacuum

Highlights: • A practical plan for a continuous tritium recovery test campaign of PbLi is introduced. • Experimental setup is described. • Reliability of tritium extraction efficiency measurement is analyzed. • Current status of experimental is reported. -- Abstract: This report introduces a current status of the continuous tritium recovery test campaign of PbLi droplets in vacuum, using vacuum sieve tray (VST). The campaign aims to verify the viability of VST method at a prototype design level. The following verification are to be performed. 1) Verify the steady state extraction efficiency of tritium using a 0.6 mm nozzle. The target is greater than 80%. 2) Verify the mutual interference effects on efficiency degradation by multiple droplets by comparing 1, 4, 7, and 19 nozzles. 3) Verify the reliability of VST in continuous operation. At least 24 h of non-stop operation without efficiency degradation is the primary goal, which can be extended up to 48 h. A dedicated extraction setup is to be installed March 2019 into the Oroshhi-2 PbLi experimental loop at the National Institute for Fusion Science (NIFS) Toki-Japan, followed by a stand-alone test with a short flowing period at Kyoto University which is already finished. Deuterium (D₂), instead of tritium, is used for the experiment. Extraction efficiency is calculated by comparing the D₂ concentration before-drop and after-drop. The amount of released D₂ is also measured by a quadrupole mass spectrometer (QMS) and verified by the concentration difference. The PbLi temperature is between 375 ℃ and 450 ℃, and the flow velocity at the nozzle is between 1.5 m s⁻¹ and 4.5 m s⁻¹. The final report is scheduled to be completed by the end of 2019.