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The extraction of hexavalent actinides An(VI) by tri-butyl phosphate (TBP) was investigated by electronic absorption and vibrational spectroscopies. Through a series of spectral subtractions, vibrational spectra associated with TBP, TBP–HNO3 adducts, and An(VI)–TBP complexes could be isolated. Investigation of U(VI) extracts indicated spectral features consistent with the formation of the expected [UO2(NO3)2(TBP)2] complex, but spectral features of other species were clearly evident. Likewise, multiple species were evident in the electronic absorption and vibrational spectra of TBP phases generated by extraction of Pu(VI). Although definitive characterization of the additional species formed could not be achieved in this work, it is hypothesized that they contain 3:1 TBP-to-An(VI) stoichiometry.

On-line monitoring based on optical spectroscopy provides unprecedented insight into the chemical composition of process streams or batches. Amplifying this approach through utilizing multiple forms of optical spectroscopy in sensor fusion can greatly expand the number and type of chemical species that can be identified and quantified. This is demonstrated herein, on the analysis of used nuclear fuel recycling streams: highly complex processes with multiple target and interfering analytes. The optical techniques of visible absorbance, near-infrared absorbance, and Raman spectroscopy were combined to quantify plutonium(III, IV, VI), uranium(IV, VI), neptunium(IV, V, VI), and nitric acid. Chemometric modeling was used to quantify analytes in process streams in real time, and results were successfully used to enable immediate process control and generation of a product stream at a set composition ratio. This represents a significant step forward in the ability to monitor and control complex chemical processes occurring in harsh chemical environments.

Understanding the fundamental rates of transfer and complex formation is crucial in maintaining optimal efficiency and effectivity in solvent extraction. Methodologies to analyze solvent ex...

Based on the current nuclear waste types, inventories, and production rates, the most viable option for closing the nuclear fuel cycle is solvent extraction. In solvent extraction, elements or groups of elements are separated to optimize reuse and disposition pathways. Initial efforts focused on isolation of plutonium and recovery of uranium for weapons production. In the 1980s, the research focus shifted to waste remediation, actinide recycling within the nuclear fuel cycle, and preparation of used nuclear fuel for final disposition. Processes for separating and isolating species and elements in used nuclear fuel are presented here, including standard (PUREX process), advanced (COEX process, etc.), and alternative (UREX+ process) processes. A brief background on language and parameters relevant to separations is presented before discussing extractant reagents, extraction processes, equipment utilized, and processing complications.

Microfluidic devices provide ideal environments to study solvent extraction. When droplets form and generate plug flow down the microfluidic channel, the device acts as a microreactor in which the kinetics of chemical reactions and interfacial transfer can be examined. Here, we present a methodology that combines chemometric analysis with online micro-Raman spectroscopy to monitor biphasic extractions within a microfluidic device. Among the many benefits of microreactors is the ability to maintain small sample volumes, which is especially important when studying solvent extraction in harsh environments, such as in separations related to the nuclear fuel cycle. In solvent extraction, the efficiency of the process depends on complex formation and rates of transfer in biphasic systems. Thus, it is important to understand the kinetic parameters in an extraction system to maintain a high efficiency and effectivity of the process. This monitoring provided concentration measurements in both organic and aqueous plugs as they were pumped through the microfluidic channel. The biphasic system studied was comprised of HNO