Year
2015
Abstract
The Hybrid K-Edge/XRF Densitometry (HKED) system is a powerful tool, which is widely used to determine uranium and plutonium concentrations in dissolver and product solutions during fuel reprocessing. Safeguards authorities rely on HKED as the \"workhorse\" measurement system in reprocessing facilities because of its relatively fast analysis time, and high throughput, accuracy and precision. This paper describes two approaches that have been utilized for calibrating a commercial Hybrid K-Edge/XRF Densitometry system, which is being used in the On-Site Laboratory (OSL) at the Rokkasho Reprocessing Plant (RRP) for the analysis of mixed U/Pu product solution samples (before co-denitration process) with U:Pu ratio of the order 1:1 and Fission Products free. The first calibration approach assumes the use of several single element calibration standards, which can be only used to determine the diagonal elements of the ?µ matrix. The off-diagonal ?µ values in this case are taken according to the default theoretical values. This is the traditional calibration approach, which is currently utilized at OSL. This approach is labour intensive and time consuming. It requires additional preparation and characterization of separated pure uranium and plutonium solutions. The second calibration approach assumes the use of two or more multi-elemental calibration standards of various concentrations and U:Pu ratios. This calibration method allows more precise derivation of all elements of the ?µ matrix without the need for using theoretical values. The off-diagonal elements of the ?µ matrix can be determined and refined from the set of calibration measurements. Another advantage of using the second approach is that it only requires preparation of mixed U/Pu solutions, and this type of samples is readily available from sample taking during safeguards DA verification activities at RRP. Both approaches were used to calibrate the HKED system installed at OSL, and, using a number of measurements of mixed U-Pu solutions, the results were compared and discussed. Our further validation of Multi-Elemental KED algorithms and both calibration approaches will potentially involve close collaboration through Member States Support Programmes between the IAEA and various international research organizations, such as Oak Ridge National Laboratory (USA) and Commissariat à l'énergie atomique (CEA) et aux énergies alternatives (France).