Magnetic field accelerated mass-transfer for the electrorefining of spent nuclear fuel: A multiphysics simulation study

Abstract

The mass-transfer in an electrorefiner for the pyroprocessing of spent fuel is investigated using multiphysics simulations, and a homogenous magnetic field is applied to accelerate the mass-transfer. The fields of current density, Lorentz force density, convective velocity, kinetic energy density, concentration and concentration gradient, and molar flux of uranium cations are calculated by numerical solution of the master equations using finite element method. It is concluded that a homogeneous magnetic field parallel to the electrode surface will induce Lorentz force, in perpendicular to both the magnetic field and the current density vector, normal to the electrode surface. The Lorentz force acts on the molten salt and enforces the molten salt to circulate around the electrodes. For comparison, the averaged kinetic energy induced solely by the magnetic field of 1 T (without stirring) at 0.754 J·m−3 is higher than that induced solely by stirring of 300 rpm (without magnetic field) at 0.595 J·m−3. The averaged kinetic energy induced by the combination of the magnetic field and the stirring at 1.118 J·m−3 is similar to the sum of that induced, respectively, by magnetic field and by stirring. If the circular electrodes are replaced with rectangular electrodes, the averaged kinetic energy reaches an even higher value of 1.278 J·m−3. Finally, it is concluded that the magnetically enhanced convective flow accelerates the mass-transfer of uranium cations by reduction of the thickness of boundary layer and thus of the concentration gradient around the electrodes.