Award Date

December 2023

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry and Biochemistry

First Committee Member

Frederic Poineau

Second Committee Member

Artem Gelis

Third Committee Member

Kenneth Czerwinski

Fourth Committee Member

Alexander Barzilov

Number of Pages

65

Abstract

During the reprocessing of nuclear fuel, the degradation of tributylphosphate (TBP) occurs as a result of radiolytic and thermal processes. These processes lead to the formation of minor amounts of dibutyl phosphate (HDBP). However, the presence of DBP poses a challenge in the partitioning of uranium (U), plutonium (Pu), and technetium (Tc) due to its chelating effects. The chelation of these elements by HDBP can interfere with their intended separation and purification, thereby impacting the efficiency and effectiveness of the reprocessing process. In this study, X-ray Absorption Fine Structure (XAFS) spectroscopy is employed to investigate the speciation of Tc following the extraction of Tc(IV) from both water (H2O) and 1M nitric acid (HNO3) using dibutyl phosphate (HDBP) in dodecane as the extracting system. The XAFS results revealed the formation of polymeric species containing Tc2O2 and Tc2O units. Specifically, the species extracted from H2O was proposed to have the formula [Tc2O2(DBP·HDBP)4] (1), while the species extracted from 1M HNO3 was proposed to have the formula [Tc2O(NO3)2(DBP)2(DBP·HDBP)2] (2). The interatomic Tc-Tc distances in the Tc2O2 and Tc2O units were found to be approximately 2.55(3) Å and 3.57(4) Å, respectively, resembling the distances observed in Tc(IV) dinuclear species. These findings suggest that the speciation of Tc(IV) in a HDBP/dodecane mixture involves the extraction of a species with a Tc2O unit in the case of (2), while the species observed in (1) may be attributed to the re-dissolution of a Tc(IV)-DBP solid. The reduction kinetics of Tc(VII) with hydrazine were monitored through UV-Vis spectroscopy. Respective concentrations in the aqueous and organic each phase was calculated using liquid scintillation counting.

Keywords

Dibutyl Phosphate; EXAFS; Nuclear Fuel Cycle; Technetium

Disciplines

Chemistry

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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