Enhanced deuterium extraction efficiency from lithium-lead droplets in a vacuum

Abstract

The authors conducted tritium extraction from falling liquid lithium-lead (LiPb) droplets in a fusion blanket loop. We reported an extraction efficiency above 0.6 from LiPb droplets of diameter 1.89 mm at 15th International Symposium on Fusion Nuclear Technologies (ISFNT15_2023). Even though it is still below the European Demonstration Power Plant (EU-DEMO) design criteria of above 0.8 which is commonly recognized as requisite minimum. Furthermore, many droplet nozzles are required to attain LiPb flow rate design criteria. Therefore, the aim is to increase the efficiency and flow rate. Enlarging the droplet diameter is a simple way to boost the flow rate. However, this degrades the efficiency. To address this drawback, we considered the tandem extraction method, which consists of two extraction processes. In the first process, dissolved deuterium is extracted from the partially filled LiPb flow in an inlet pipe under a vacuum. The second process entails the conventional extraction from falling droplets. Experimental verifications and theoretical analyses were performed at the liquid metal experimental test loop installed at the National Institute for Fusion Science, at Toki Japan. A droplet size of 2.27 mm, 1.44 times the flow rate than the previous 1.89 mm, is applied to verify the process. The obtained overall efficiencies were between 0.75and 0.95, exceeding the estimated range of 0.65–0.85. The matured turbulent flow at the nozzle boosted the release of droplets, along with the tandem extraction. Other enhancement factors such as droplet break-up and surface oscillation were considered as scarce effects. Further verifications are inevitable even when the results suggest a high-efficiency extraction feasibility from larger droplets.