Origins of Selectivity in Actinide Separations

Dr. Mark Jensen
Chemical Sciences and Engineering Division
Argonne National Laboratory

ABSTRACT
As a carbon-neutral energy source, nuclear energy accounts for about 20% of the electricity produced in the United States and around the world. Chemical separations of the radioactive actinide elements and their fission products have always played critical roles in the nuclear enterprise, but concepts under consideration for new generations of nuclear reactors that run on advanced nuclear fuels and produce less radioactive waste will require separations that far surpass the performance of the chromatographic and liquid-liquid extraction processes in use today. In this context, the most pressing separations needs are for efficient and effective separations of the fission product lanthanide elements from the actinide elements americium and curium; however the great chemical similarity of these groups of elements makes this a difficult and often inefficient separation. In order to rationally design a new generation of highly effective lanthanide-actinide separations, we need a systematic molecular-level understanding of the interactions that underlie the thermodynamic selectivity of the molecules used for such separations. I will describe my work studying the structural, electronic, and thermodynamic factors underlying the modest selectivity of nitrogen and sulfur-bearing molecules for the actinide elements. These studies also provide targets for improving the efficiency of the separations by illuminating the factors responsible for the large decrease in bond strength that accompanies the moderate increase in the selectivity of molecules that favor americium and curium over the lanthanides.

BIO
Mark P. Jensen is a chemist in the Chemical Sciences and Engineering Division at Argonne National Laboratory. After joining Argonne in 1994 as a postdoctoral research associate under the direction of E. Phillip Horwitz and Kenneth L. Nash, he moved to the Heavy Elements and Separation Science Group where he has performed research since 1995. Dr. Jensen’s research interests include actinide chemistry and biochemistry in separations and the environment, mechanisms of metal selectivity in separations, metal speciation in non-aqueous solutions, chemical thermodynamics, and general radiochemistry. Dr. Jensen received several awards throughout his career, and most recently was awarded the R. G. Haire Lectureship in Actinide Science from Auburn University. He has been the Associate Editor of Solvent Extraction and Ion Exchange since 2002, and has coauthored 75 open literature papers and 2 book chapters. Dr. Jensen received his Ph.D. in Chemistry from Florida State University in 1994 and his B.S. in Chemistry from Bethel College (Minnesota) in 1989.