In 2020, the safeguards laboratories at Forschungszentrum Jülich GmbH (FZJ) were officially qualified as the first member for the provision of microparticulate reference materials to the IAEA’s (International Atomic Energy Agency’s) worldwide NWAL (Network of qualified Analytical Laboratories). These reference particles are applied to strengthen the IAEA’s quality control system for particle analyses including, e.g. the application in interlaboratory exercises as well as to support the pressing demand to build-up new NWAL capabilities. Very recently the first available batches of highly enriched uranium (HEU) particles with 50% and 90% 235U enrichment were produced in the NWAL laboratories at FZJ using an aerosol-based particle production process and thoroughly analysed using advanced mass spectrometric methods. This paper will discuss – exemplarily for the 90% 235U enriched material - several steps towards the provision of these HEU reference microparticles. They include (1) the preparation and certification of starting solutions conducted at Joint Research Centre (JRC) in Geel (Belgium), (2) the production of the particles at FZJ and particularly (3) the required analyses of process control measurements as well as the verification measurements via MC-ICP-MS (Multicollector - Inductively Coupled Plasma Mass Spectrometry) and LG-SIMS (Large Geometry - Secondary Ion Mass Spectrometry) conducted at FZJ, Oak Ridge National Laboratory and Heidelberg University, respectively. The results of these measurements demonstrate the high quality of the HEU reference particles, and the reliability of the particle production process established at FZJ. Additionally, a preview on recent activities related to the development of microparticulate reference materials for age-dating applications will be addressed. Therefore, a co-precipitation method was adopted to produce Th-doped bulk-scale materials as a kind of “internal reference materials”. These materials allow for investigations with state-of-the-art analytical techniques to unravel the structural incorporation mechanism of Th into uranium oxide crystal structures (UO3 and U3O8) in dependence of the amount of Thdoping. Regarding the transferability of the results to the particle production process, the phase transformation from UO3 to U3O8 is of particular interest. Thus, the pristine materials (Thdoped ammonium diuranate) were investigated with TG-DSC (Thermogravimetry - Differential Scanning Calorimetry) to identify the temperature at which the phase transformation of UO3 to U3O8 for the doped materials occurs. Subsequently, the materials were calcined at the identified temperatures and structurally characterised with XRD (X-ray Diffractometry). The results indicate to an incorporation of Th-dopant into the UO3 and U3O8 crystal structure which is an important material property of reference particles for reliable age_dating measurements. They help to identify relevant process parameter such as the aerosol heating temperature to produce high quality microparticulate reference materials to the IAEA’s NWAL.
Year
2024
Abstract