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

摘要

There is a renewed interest worldwide to promote the use of nuclear power. The long term successful use ofnuclear power is critically dependent upon adequate and safe processing and disposition of the spent nuclearfuel. Liquid-liquid extraction is a separation technique commonly employed for the processing of thedissolved spent nuclear fuel. Our approach is based on the prerequisite that real time monitoring of thesolvent extraction flowsheets provides unique capability to quickly detect unwanted manipulations withfissile isotopes present in the radiochemical streams during reprocessing activities.Detection and quantification of a material diverted from a liquid-liquid solvent extraction contactor systemhas been previously successfully tested using on-line process monitoring. However, the diversiondetermination in real time relies on the ability to accurately quantify the mass balance of the material ofinterest at any given time. It could be challenging for the multi-stage extraction equipment such ascentrifugal contactor system because of the lag time between the change in analyte concentration in theaqueous feed and in the corresponding organic product associated with the time required for the analyte topass through the extraction stages and/or unequal aqueous and organic flow rates. To assess the effect of timelag on the material mass balance, the centrifugal contactor system operating with the simulant PUREXextraction system of Nd(NO_3)_3/itric acid aqueous phase and TBP-dodecane organic phase was used. Theaqueous 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 wasunderway, a solution containing Nd(NO_3)_3 was introduced into the feed inlet for a 52 min duration, and thenstopped, 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 massbalance of Nd~(3+)using information collected for all phases was confirmed. We conclude that real-timespectroscopic process monitoring would be a useful tool for the IAEA to detect the diversion of nuclearmaterial in a timely manner. This report summarizes our methodology of on-line process monitoring anddiscusses recent results of specific examples.