Investigation on Structural Incorporation of Dopants into Uranium Oxide
Structure Considering the Development of New Composite Reference
Microparticles

In the Safeguards laboratories of Forschungszentrum Juelich an aerosol-based process to produce uranium oxide reference microparticles has been implemented to support a sustainably robust quality control system of the International Atomic Energy Agency (IAEA) in particle analysis in nuclear safeguards. This quality control system includes analytical instrument calibration, method development and validation for analytical measurements of individual micrometer- and Submicrometer-sized particles as well as their application in interlaboratory exercises. The well-designed reference microparticles developed for this purpose must fulfil certain requirements, such as a defined elemental and isotopic composition, size, morphology, and shelf-life, to ensure the reliability of the mass spectrometric analytical measurements and to be as similar as possible to the U-containing microparticles collected by an IAEA safeguards inspector during in-field verification activities. These so-called environmental samples are analyzed for their isotopic composition by the IAEA’s Office of Safeguards Analytical Services and their dedicated Network of Analytical Laboratories. For the detection of even traces of fission products further development of analytical methods and the quality control of the analytical results from particle analysis itself as well as of the reference microparticles is required. But due to the yield limitations to microgram range of the aerosol-based process in Juelich, the characterization of these simulated fission products doped uranium-oxide microparticles is very challenging. Therefore, to unravel the incorporation mechanism of the dopants, such as lanthanides, Th, or Pu, into the uranium-oxide structure, a co-precipitation method was adjusted to produce doped bulk-scale materials as “internal refence materials” which can be investigated by standard analytical techniques. Using TG-DSC measurements, the temperature range of the phase transition from UO3 to U3O8 of the doped uraniumcontaining materials was determined. According to the previously identified temperature ranges, the doped materials were calcined and the obtained doped UO3 and U3O8 materials were characterized in more detail by additional systematic structural investigations of the long- and short-range order phenomena with XRD and Raman. This presentation will show results regarding the incorporation of dopants into the uranium oxide structures. These results will be transferred to the particle production process as an important input parameter to design reference microparticles.