Extraction of Cesium, Lanthanides, and Actinides from Acidic and Caustic Media: Applications to High-Level Waste Remediation.

Lætitia H. Delmau

Chemical Separations Group/Chemical Sciences Division

Oak Ridge National Laboratory

1 Bethel Valley Rd

Oak Ridge, TN 37831-6119

This talk will present an overview of the nuclear treatment options chosen by the US, Europe, and Japan. The focus will be on solvent extraction as a separation technique. Separation of certain radionuclides and radioelements from spent fuel reprocessing holding tanks can decrease the repository constraints for the raffinate, and subsequently allow major cost reductions. Due to its short half-life, cesium-137 is a major contributor to the radiation and heat generation in the nuclear waste. Also, because of their long half-lives and their alpha-radiotoxicity, the separation of actinides is also of high interest. To a definite advantage, cesium chemistry is similar enough in both acidic and caustic media that cesium separation can be accomplished with similar molecules regardless of the aqueous solution pH. This could not be further from the truth when studying actinides, particularly uranium, neptunium, plutonium, and americium. The challenges in their removal are two-fold: in acidic wastes, the presence of lanthanides makes the actinide extraction difficult and requires very selective extractants. In caustic wastes, the actinides tend to precipitate and form large anionic species with hydroxide and carbonate anions, requiring a different family of extractants. Current studies will be discussed.