Investigation of Optical Spectroscopy Techniques for On-Line Materials Accountability in the Solvent Extraction Process

The goal of this project is to examine the potential for using optical spectroscopy techniques, such as UV-Visible Spectroscopy and Laser Fluorescence Spectroscopy, for special nuclear materials accountability applications for the UREX+ and other solvent extraction processes. To increase the inherent proliferation resistance of the solvent extraction process, it is necessary to develop on-line techniques to directly measure the concentrations of special nuclear materials in-process. By providing on-line materials accountability for the processes, the potential for covert diversion of the materials streams becomes much more difficult to implement. On-line monitoring of material streams will also allow for improved plant operation, as well as serving as an additional safety measure for plant operations. Laser fluorescence and UV-Visible spectroscopy have been demonstrated for use in determining the concentration of the actinides at the laboratory scale. These processes are adaptable to flow-thru applications, and should be highly radiation-tolerant, which suggests that they should be applicable to the spent fuel treatment environment. Work Proposed for Academic Year 2005-2006, Goals, and Expected Results: Year 1: Impact of process parameters Year 2: Adaptation to flowing systems Year 3: Impact of radiation on detection systems and optics Funding Profile: Academic Year: 2005-2006 2006-2007 2007-2008 Total (K$) $147.5 $157.7 $163.4 UNLV TRP: Optical Spectroscopy Proposal Background and Rationale: One of the primary challenges facing any advanced fuel cycle is the proliferation resistance of that fuel cycle, especially the potential for illicitly diverting nuclear material from the fuel cycle for other purposes. The key step in almost all of the fuel cycles currently under evaluation in the Advanced Fuel Cycle Initiative is the chemical separation and partitioning of used nuclear fuel, either as the starting point for treating existing used fuel, or as a key step in the recycling and destruction of the higher actinides. Any partitioning of the actinides has the potential for increasing the proliferability of the fuel cycle unless the process or plant can be designed to prevent, or at least detect, the diversion of nuclear material from the process. To address this concern, the AFCI has proposed that any new separations plant include in its design an integral system capable of providing materials accountability for the actinide elements with less than 0.1% uncertainty. It is proposed that optical spectroscopic techniques, such as Ultraviolet-Visible Spectroscopy (UV-Vis) and Laser Fluorescence Spectroscopy (LFS), would allow for the on-line, real-time analysis of the actinide elements for a solvent extraction process. UV-Vis and LFS are quantitative analytical techniques that have been used for measuring the concentration of the actinides under laboratory conditions, and are easily adaptable to multiple sampling geometries, such as dip probes, fiber-optic sample cells, and flow-through cell geometries. This research project will evaluate the application of these analytical techniques to the on-line, real-time measurement of the actinide elements in the process streams of a solvent extraction process, with particular attention to the UREX+ and PUREX processes. Researchers will evaluate the impact of process conditions on the sensitivity of these techniques, providing plant engineers with the information they will be able to use to evaluate these techniques for inclusion as part of the materials accountability system for future plant designs. In UV-Vis spectroscopy, the sample is illuminated by a continuous spectrum (from the UV through the Visible wavelengths). The transmitted light is measured, allowing the determination of the absorbance of the light as a function of wavelength. The wavelength of the absorbance is dependant on the electronic structure of the absorbing atom, and is proportional to the concentration of the absorbing element in the sample. For LSF, the sample is illuminated at a single wavelength, which is absorbed by the target atoms in the sample. The energy absorbed is reemitted through fluorescence. The wavelength of the absorbance, and the fluorescence-response, is again dependant on the electronic structure of the absorbing atom, and is proportional to the concentration of the absorbing element in the sample. In addition to the potential materials accountability applications, UV-Vis Spectroscopy and LFS can provide information regarding the speciation of the actinides in the process stream (oxidation state, complex formation, etc.). This information will help elucidate the behavior of the actinides under process conditions, improving our understanding of the chemical interactions underlying these separations processes. Research Objectives and Goals: The research objectives are: • To evaluate the potential for utilizing UV-Visible and laser fluorescence spectroscopy to determine actinide concentrations under process conditions • To examine the impact of process environment on the sensitivity of UV-Visible and laser fluorescence spectroscopy to the actinides, including the impact of o Acid concentration o Solvent concentration o Ligand concentration (TBP, AHA) o Iron o Fission Products o Competing Actinide elements • To examine the impact of process conditions on the sensitivity of UV-Visible and laser fluorescence spectroscopy for the determination of actinide elements, including o Flow rate o Process temperature o Plant Geometry (pipe diameter, shape, etc.) • To examine the potential impact of radiation fields on the spectroscopy systems