Axial Concentration of Dissolved Deuterium by Dispersion in a LiPb Experimental Loop

The axial concentration of deuterium by dispersion in a circulating liquid lithium-lead (LiPb) loop was analyzed and experimentally verified. In previous fusion blanket studies, the tritium transport rate in flowing LiPb was treated by convection a priori; i.e., the dispersion effect was negligible. In contrast, Taylor dispersion theory shows conflicting results, exhibiting axial transport enhancement via convective flow. In the current paper, the experimental setup consists of a deuterium dissolving tube that substitutes for tritium breeding and a deuterium concentration monitor by LiPb droplets in a vacuum with four nozzles of ϕ = 1.0 mm. The released deuterium mass flux from the droplets was measured using a quadrupole mass spectrometer. An electromagnetic pump circulated 49 L of LiPb at 350°C at a rate between 0.15 and 0.3 L∙min^–1 with the corresponding Re number between 600 and 1000, i.e., in the laminar flow range. The dispersion coefficient was analyzed by measuring the temporal distortion of the deuterium concentration profile. The obtained axial dispersion coefficients of dissolved deuterium in LiPb were between 4.6 × 10^–2 and 1.2 × 10^–1 (m²∙s^–1) and approximately seven orders of magnitude greater than those under static conditions. The results agreed with the Taylor dispersion theory, which studied the mass transport enhancement by convection. The applicability of Taylor’s theory to the deuterium flow in liquid LiPb is suggested, whereas the Prandtl number was three orders of magnitude lower and the Schmidt number was one order of magnitude higher than that of the water.