Multiphysics Simulation of an Electrorefiner with Continuous Circulation of Molten Salt for Separation of Uranium and Neptunium

Abstract A 3-D continuous electrorefiner is designed and investigated using multiphysics simulation for the separation of uranium and neptunium from spent nuclear fuel in molten salt. The concentration distribution field, the electric field, the ionic flux density field, and the flow field are evaluated under galvanostatic and pulse electrorefining.
During the electrorefining without molten salt recirculation, the transport of the electroactive cations is controlled by diffusion and electromigration and high concentration gradient is built near electrodes. In a galvanostatic electrorefining with a current density of 200 A·m –2 , the concentration of U 3+ decreases to 1.3 mol·m –3 near cathode and increases to 62.6 mol·m –3 near anode within 6.7 s, and the co-deposition of uranium and neptunium occurs after 0.28 mg of pure uranium is collected. With moderate molten salt recirculation, the transport of the electroactive cations is controlled by convection. The concentration of U3+ decreases to 21.1 mol·m –3 near cathode and increases to 62.6 mol·m –3 near anode within 6.7 s, there is no co-deposition of uranium and neptunium occurred. In addition, it is proved that the pulse electrorefining does not improve the recovery of uranium compared with galvanostatic electrorefining with a corresponding average current.