Spectroscopic On-Line Monitoring for Control and Safeguarding of Radiochemical Streams at Spent Fuel Reprocessing Plant

There is a renewed interest worldwide to promote the use of nuclear power. The long term successful use of nuclear power is critically dependent upon adequate and safe processing and disposition of the spent nuclear fuel. Liquid-liquid extraction is a separation technique commonly employed for the processing of the dissolved spent nuclear fuel. Our approach is based on the prerequisite that real time monitoring of the solvent extraction flowsheets provides unique capability to quickly detect unwanted manipulations with fissile isotopes present in the radiochemical streams during reprocessing activities. Detection and quantification of a material diverted from a liquid-liquid solvent extraction contactor system has been previously successfully tested using on-line process monitoring. However, the diversion determination in real time relies on the ability to accurately quantify the mass balance of the material of interest at any given time. It could be challenging for the multi-stage extraction equipment such as centrifugal contactor system because of the lag time between the change in analyte concentration in the aqueous feed and in the corresponding organic product associated with the time required for the analyte to pass through the extraction stages and/or unequal aqueous and organic flow rates. To assess the effect of time lag on the material mass balance, the centrifugal contactor system operating with the simulant PUREX extraction system of Nd(NO3)3/nitric acid aqueous phase and TBP/n-dodecane organic phase was used. The aqueous and organic inlets and outlets of the contactor system are equipped with flow rate, temperature, density, and chemical spectroscopic monitoring tools. While the continuous extraction experiment was underway, a solution containing Nd(NO3)3 was introduced into the feed inlet for a 52 min duration, and then stopped, while the spectroscopic on-line process monitoring system was simultaneously measuring the feed, raffinate, organic solvent, and organic product streams. At the end of the flow experiment, the total mass balance of Nd3+ using information collected for all phases was confirmed. We conclude that real-time spectroscopic process monitoring would be a useful tool for the IAEA to detect the diversion of nuclear material in a timely manner. This report summarizes our methodology of on-line process monitoring and discusses recent results of specific examples.