PNNL

Abstract

Advanced techniques that enhance safeguarding of spent fuel reprocessing plants are urgently needed. Our approach is based on the prerequisite that real-time monitoring of solvent extraction flowsheets at a spent fuel reprocessing plant provides the unique capability to quickly detect unwanted manipulations with fissile isotopes present in the radiochemical streams during reprocessing activities. The methods used to monitor these processes must be robust and capable of withstanding harsh radiation and chemical environments. A new on-line monitoring system satisfying these requirements and featuring Raman spectroscopy combined with a Coriolis and conductivity probes recently has been developed by our research team for tank waste retrieval. It provides immediate chemical data and flow parameters of high-level radioactive waste streams with high brine content generated during retrieval activities from nuclear waste storage tanks at the Hanford Site. The nature of the radiochemical streams at the spent fuel reprocessing plant calls for additional spectroscopic information that can be gained by using Vis-NIR capabilities augmenting Raman spectroscopy. A fiber optic Raman probe allows monitoring of high concentration species encountered in both aqueous and organic phases within the UREX suite of flowsheets, including metal oxide ions, such as uranyl, components of the organic solvent, inorganic oxo-anions, and water. Actinides and lanthanides are monitored remotely by Vis-NIR spectroscopy in aqueous and organic phases. In this report, we present our results on spectroscopic measurements of simulant flowsheet solutions and commercial fuels designed to demonstrate the applicability of Raman and Vis-NIR spectroscopic analysis for actual dissolver feed solutions.