Date of Award

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Earth Science

Committee Member

Dr. Brian A. Powell, Committee Chair

Committee Member

Dr. Cindy Lee

Committee Member

Dr. Julianna Fessenden-Rahn

Committee Member

Dr. Lindsay Shuller-Nickles

Abstract

Tributyl phosphate (TBP) is used as an extractant in the Plutonium and Uranium Reduction Extraction (PUREX) process, as well as the Aqueous Chloride Process for Plutonium (Pu) recovery. These processes use nitric acid and hydrochloric acid, respectively. After nuclear reprocessing, TBP may be degraded in the Alkaline Hydrolysis Process using >12.5 M NaOH at 120-130 oC. TBP degrades to dibutyl phosphate (DBP), monobutyl phosphate (MBP), butanol, and phosphoric acid during hydrolysis. The goal of this dissertation is to use carbon stable isotopes to determine if there is a unique signature in TBP associated with nuclear reprocessing and solvent disposal. Acid hydrolysis experiments were performed for a three month period to determine if a fractionation in the carbon stable isotope of TBP exists over time. Alkaline hydrolysis experiments were also performed to simulate the solvent disposal process used to degrade TBP. Theoretical calculations predicting the carbon and oxygen stable isotope fractionations through use of ab initio methodology were performed and compared with experimental values. In addition, this work developed a semi-quantitative tool to determine the extent of TBP degradation as it is exposed to nitric acid and sodium hydroxide. The semi-quantitative tool involved the quantification of peak intensity ratios using FTIR-ATR spectroscopy. Another component of this work included solid phase extraction (SPE) to separate TBP and DBP from aqueous media. It was found that the extent of fractionation predicted by theory aligns well with the experimental results. The carbon stable isotope measurements in TBP revealed that a heavy shift occurs in reactions of TBP with nitric acid, hydrochloric acid, and sodium hydroxide. The largest shift of 8.3 per mil was seen when TBP was reacted with 9 M HCl at 75 oC. There was a 4 per mil difference between the carbon stable isotope value of TBP in 9 M HCl and 8 M HNO3 at 75 oC. It is suspected that this difference would merge over time. Hydrolysis experiments conducted in 4 M HCl and 4 M HNO3 at temperature ≤ 50 oC for three months showed no significant fractionation. However, only a small fraction of TBP was degraded within this short time-frame. The degradation of TBP in 12.5 M NaOH was near completion but less than a 2 per mil fractionation was measured. It is possible that this process does not give a significant fractionation due to its degradation mechanism. The FTIR-ATR peak intensity ratio for the alkaline hydrolysis system yields a close approximation of the extent of TBP degradation relative to the amount quantified by gas chromatography. This dissertation gives valuable insight on the characterization of carbon stable isotopes and the FTIR-ATR analysis of TBP that is helpful to the nuclear forensics community.

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