Performance Evaluation of Batchwise Multistage Countercurrent Extraction in a LiCl–KCl/Cd System to Separate Actinides from Rare Earth Fission Products

Abstract

The electrorefining of spent metallic fuels is conducted in LiCl–KCl eutectic–based salt to recycle U, Pu, and minor actinides when chemically active fission products of rare earth, alkali, and alkaline-earth metals accumulate in the salt. For removing the fission products from the salt, a batchwise multistage countercurrent extraction technique using a liquid Cd solvent and a Li reductant was investigated and found to achieve both a high recovery ratio of actinides and a sufficient degree of separation from rare earths. Vessels containing salt were prepared in accordance with the number of stages, and a smaller vessel containing liquid Cd was immersed in them sequentially to extract actinides from the salt. This operation is simple and reliable. The results calculated using the equilibrium separation factors reported in the literature suggested that four-stage extraction offers satisfactory performance for the separation of actinides from rare earths: more than 80% of Nd remained in the salt when 99.9% of Pu was recovered. Moreover, demonstration tests were conducted using Nd and Dy as surrogates of actinides and rare earths, respectively. The separation factor between Dy and Nd was determined to be 21, which was approximately equal to that between Nd and Pu reported in the literature. It was shown that the experimental results of extracting Nd while leaving Dy in the salt were in good agreement with the calculated results. In conclusion, batchwise multistage countercurrent extraction was proved to be a promising actinide separation method.