Electrowinning of U-Pu onto inert solid cathode in LiCl-KCl eutectic melts containing UCl3 and PuCl3

Electrowinning process was investigated for extracting actinides from molten salts used for the pyrochemical reprocessing of spent nuclear fuels. The separation of actinides from lanthanides is expected to be enhanced by employing inert solid cathodes due to larger potential differences on these cathodes. In this study, the co-deposition behavior of Pu and U metals onto an inert solid cathode made of tungsten was examined in LiCl-KCl eutectic melts containing UCl3 and PuCl3 at 773 K. The standard potential of U3+/U is 0.31 V more positive than that of Pu3+/Pu. The U3+ concentration was varied in the range of 0.11-0.66 wt%, while the Pu3+ concentration was maintained at approximately 2.9 wt%. When the U3+ concentration was not sufficiently low, the deposited U metal readily grew outward from the electrode surface and the electrode surface area rapidly increased, which facilitated only the deposition of U metal. It was estimated that metallic Pu can be efficiently collected along with U at U3+ concentrations lower than ∼0.2 wt%.