Parametric investigation of mercury cell electrolysis for isotopic separation of Li using coupled numerical methods

Abstract

Fusion reactors will be one of the major resources of future energy. The fuel required for these reactors is deuterium–tritium (D-T). Tritium, which is not naturally available, is produced by the collision of neutrons with ⁶Li in the environment of these reactors. Various compounds, including lithium hydroxide (LiOH) solution, can be used to extract ⁶Li. The natural abundance of ⁶Li is approximately 7.5%, which is insufficient for producing tritium used in fusion reactors and necessitates further enrichment. Various methods, including electrolysis, can be employed to increase ⁶Li enrichment. In this research, the electrolysis exchange (ELEX) method has been used to extract ⁶Li from LiOH with a favorable separation factor. The simulation of this process using the design of a mercury cell has been conducted through Comsol 6.1 software. This geometry (mercury cell) is a sloping space for continuous movement of mercury. Mercury, which is actually the cathode in this system, absorbs lithium isotopes, especially ⁶Li, due to the mobility of this isotope compared to ⁷Li, and increases the percentage of ⁶Li abundance at the output of the system (LiHg). Electrochemical physics, involving the solution of Nernst-Planck equations, and turbulent flow physics, governed by the Navier-Stokes equations, have been employed to carry out the electrolysis process. It should be noted that, given the significance of diffusion coefficient values in the process of isotope separation by electrolysis, these values have also been determined through molecular dynamics simulations. Finally, and based on the parametric study that has been conducted on all the parameters affecting the electrolysis process, a separation coefficient of about 1.05 has been obtained. This separation coefficient, which has also been compared with experimental references, has been stabilized after approximately 3 h of operation.