Development of plutonium recovery process by molten salt electrorefining. Behavior of plutonium at liquid cadmium cathode

Fundamental experiments were carried out with small liquid cadmium cathodes in order to investigate the effect of the electrochemical parameters and to determine adequate conditions for plutonium recovery. Major results are as follows. (1) At cathodic current density lower than about 40 mA/cm2, plutonium was smoothly recovered into the liquid cadmium cathode up to about 8 wt% with collection efficiency of approximately 100%, even without cathode stirring. At higher cathodic current densities, lithium or plutonium metal was produced at the cathode, and these metals reacted with the ceramic materials to decrease the collection efficiency. (2) After cooling, plutonium deposits were found to accumulate at the bottom of the cathode in the chemical form of PuCd6. (3) It was supposed that americium deposition was restrained so that local equilibrium was maintained at the surface of the cathode when plutonium was recovered into the liquid cadmium cathode beyond its solubility limit. (4) Extrapolation of the plutonium recovery rate observed in these tests to practical conditions gives a processing rate of about 280 grams of plutonium per hour for each cathode, which is considered to be satisfactorily high performance. (author)