Effect of Applied Voltage on Isotope Separation Factor By Electrodialysis Using Lithium Ion Conductive Electrolyte La0.57Li0.29TiO3

Tritium, which is used as a fuel in a thermonuclear fusion reactor, is produced in the fusion reactor blanket by the reaction of neutrons with lithium whose 6 Li-isotope-ratio is 90%. Other than the mercury amalgam method, which has a large environmental impact, no practical lithium isotope enrichment technology has been established. Electrodialysis using the lithium ion conductive electrolyte La 0.57 Li 0.29 TiO 3 (LLTO) is promising, as reported to achieve high isotope enrichment [1]. In this study, we investigate the effect of applied voltage in electrodialysis on the isotope separation factor. An anode (primary solution side) and a cathode (secondary solution side) were formed on both front and back surfaces of LLTO. One reference electrode was also formed on each surface of the LLTO. DC voltage of various magnitudes was applied between the anode and the cathode. The electrochemical impedance between the reference electrode on the primary solution side and the anode during the application of this voltage was measured by AC impedance spectroscopy. At the same time, the electrochemical impedance between each of the secondary solution side reference electrode and the cathode was also measured. The amount of transferred lithium and the isotope ratio of lithium were measured by an inductively coupled plasma mass spectrometer (ICP-MS). The lithium isotope separation factor increased linearly with decreasing applied voltage. Here we assume the following: ① The existence probability of such atoms with respect to the minimum value of the energy required for lithium in the crystal lattice to move to the adjacent site has a normal distribution, ② In 6 Li and 7 Li, the standard deviation of the normal distribution is the same and the energy average the values are different. Then, in a narrow energy region near the activation energy of 6 Li or 7 Li transfer, it is expected that the ratio of 6 Li in the energy transfer lithium decreases linearly with the increase in energy. Our experimental results seem to follow this prediction. [1] S. Honda, K. Shin-mura and K. Sasaki, J. Ceram. Soc. Japan , 126 , [5], 331-335 (2018).