Scale-up And Production Of Uranium-bearing QC Reference Particulates By An Aerosol Synthesis Method

The International Atomic Energy Agency (IAEA) requires actinide-containing reference particulates for use in quality control (QC) proficiency swipe testing applications to support the international network of analytical laboratories. The QC particle products must be uniform in physical characteristics and produced at milligram-scale to ensure enough material quantities for repeated periodic use. To meet these needs, an aerosol-based method to manufacture monodisperse QC particulate actinide materials for IAEA safeguards analysis applications in the requisite milligram-scale quantities was developed. This capability was realized through the development of the Monodisperse Particle Production and Collection System (MPPaCS), which utilizes a liquid-to-particle aerosol-based technique to fabricate particles with controllable size, material phase, and isotopic composition. The MPPaCS combines a commercial aerosol generator, in-line process monitoring instrumentation, and electrostatic collection to aggregate particulates in the form of flowable powders. Scale-up engineering involved examination of production efficiency, tuning of production parameters, and characterization of products using microanalytical methods. Sustained milligram-scale particle production required multi-day continuous operations to produce monodisperse uranium particulates with an average diameter near 1‑µm and a geometric standard deviation (GSD) less than 1.15. Production rates were approximately 0.33 mg per hour and batches of 5-10 milligrams each were generated. Among several uranium solution feedstocks tested, uranyl oxalate demonstrated the most useful drying dynamics to facilitate monodispersed particle size populations and spherical morphologies. The resultant products are a primarily an oxalate phase as characterized by Raman spectroscopy and have a calculated density of approximately 3.1 g/cm3 via in­‑situ aerodynamic particle size spectrometer measurements. Particles generated with two deplete uranium feedstock isotopic compositions were analyzed by secondary ion mass spectrometry to characterize and confirm interparticle isotopic homogeneity. Future efforts will be focused on the inclusion and development of in-line heating components to allow thermal conversion of oxalate feedstocks into oxide particulates.