Department of Chemistry Seminar – Dr. Nathan P. Bessen

About the event

Speaker: Dr. Nathan P. Bessen

Host: Dr. Ivan Popov

Title: Actinide Separations in the Nuclear Fuel Cycle

Abstract:

Used nuclear fuel contains a significant amount of uranium along with some amount of the heavier actinide elements (Np, Pu, Am, Cm, etc.) and a wide variety of lighter elements produced from nuclear fission. The actinides complicate handling and disposal of the used nuclear fuel as they present nuclear non-proliferation challenges and contribute to its radioactivity at longer time scales, yet they also have the potential to be recycled for further beneficial use. The ability to separate the actinides both from other actinide and non-actinide elements in the used fuel can be usefully exploited to recycle the used fuel and reduce concerns with its disposal, yet the isolation of certain actinides presents additional non-proliferation risk. Processes for the chemical separation of different actinide elements have been in use for decades, but further improvements continue to be made. Here, two different projects related to actinide separations are presented.

In the first project, the lipophilic ligand bis-(2-ethylhexyl)-iso-butyramide (DEHiBA), which selectively binds hexavalent actinides is examined for its ability to selectively dissolve only the U from used fuel simulants containing Np, Pu, or Tc directly into an organic phase. Further purification and recovery of the U from the organic phase by solvent extraction was also examined. It was found that U fully dissolves, but a small portion of the Np and Pu dissolves too and further purification would be necessary.

The second work examines the Actinide Lanthanide SEParation (ALSEP) process which is a solvent extraction system designed to extract and separate Am, Cm, and the trivalent lanthanides from used nuclear fuel solutions after the U, Np, and Pu have already been removed. In an industrial scale process, it is likely that the U, Np, and Pu may not be completely removed, so the fate of these elements in their different oxidation states when introduced to the ALSEP process was examined. The tetravalent metals were found to partition with the lanthanides, while the hexavalent metals are strongly retained by the organic phase.