Separation of Uranium and Zirconium in Alkali Chloride Melts Using Liquid Metal Cathodes

Alkali chloride melts are considered as prospective working media for non-aqueous pyrochemical reprocessing of spent nuclear fuels (SNFs). Separation of fissile materials from fission products in pyrochemical reprocessing can be achieved electrochemically and amongst all the fission products zirconium has the closest electrochemical properties to uranium. Uranium and plutonium fission produces several zirconium isotopes (from Zr-91 to Zr-97) and depending on the reactor neutron spectrum, nuclear fuel type, burnup and cooling time SNF arriving for reprocessing can contain ca . 5–13 kg of zirconium (as the fission product excluding cladding) per ton. Electrochemical separation of uranium and zirconium in fused salts is a challenging task. The present work was devoted to studying the electrochemical behavior of zirconium and uranium in 3LiCl–2KCl based melts using cyclic voltammetry and cathodic polarization. The experiments were performed in LiCl–KCl–ZrCl 4 , LiCl–KCl–UCl 4 , LiCl–KCl–UCl 3 and LiCl–KCl–ZrCl 4 –UCl 4 melts. On a solid tungsten electrode zirconium(IV) ions were reduced to Zr(0) in two stages and the metal deposition potentials were between –2.17 and –2.07 V (at 532–637 o C) vs . Cl – /Cl 2 couple. Changing the solid electrode to liquid zinc, gallium or gallium–zinc eutectic alloy (3.64 wt. % Zn) resulted in significant shift of zirconium deposition potential in the positive direction. Examples of the polarization curves are shown in the Fig. Polarization measurements performed in LiCl–KCl–ZrCl 4 –UCl 4 melt on the Ga–Zn electrode showed that reduction of U(IV) to U(III) and deposition of zirconium occurred at very similar potentials and deposition potential of uranium was significantly more negative. Separation factor for uranium/zirconium couple was also determined. Fig. Polarization of Ga–Zn eutectic alloy cathode in LiCl–KCl–UCl 4 (524 o C) and LiCl–KCl–ZrCl 4 (550 o C) melts. Figure 1