Uranium-235 and plutonium-239 fission to produce zirconium – including stable, long-lived, and short-lived Zr isotopes –, with Zr concentrations similar to those of Pu for several reactor designs. The co-extraction of Zr(IV) with U(IV) and Pu(IV) during the reprocessing of used nuclear fuel presents a challenge for the nuclear industry and a selective separation of Zr from Pu(IV) is needed. A ligand-driven Pu precipitation presents a concern from a proliferation standpoint, but polyaminopolycarboxylate ligands are promising contenders as Zr holdback reagents. Our work on the determination of thermodynamic data for complexes of Hf(IV) (Zr analog), Zr(IV), and Pu(IV) with oxalate and various polyaminopolycarboxylate ligands indicates that trans-1,2-diaminocyclohexane-N,N,N’,N’-tetraacetic acid (CDTA) is a favorable candidate. We determined the 1:0:1 CDTA complex stability constants for Zr(IV) and Pu(IV) to be 29.6 and 24.2 (log units), respectively Additionally, a new 1:4:2 Zr complex was identified with a stability constant of 58.5 (log units) and the 1:2:1 Pu complex stability constant is 25.8 (log units). Calculations based on our thermodynamic data show efficient Pu(IV)/Zr(IV) separations with 0.1 M CDTA, with a Pu/Zr separation factor varying between 125 and 7, in a solvent extraction systems using 0.1 M of the extractant thenoyltrifluoroacetone (TTA) and with an aqueous phase with a 0.1 - 1.0 M acid concentration range.

Selective separation of Zr(IV) from Pu(IV) for used nuclear fuel reprocessing applications

2019 Spring National Meeting

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