The Stability of Uranium Microspheres for Future Application as Reference Standard in Analytical Measurements

The monitoring of fuel-cycle facilities provides a tool to confirm the compliant operation, for example with respect to emissions into the environment or to supervise non-proliferation commitments. Hereby, anomalous situations can be detected in a timely manner and responsive action can be initiated to prevent an escalation into an event of severe consequence to society. In order to verify non-nuclear weapon states' compliance with the non-proliferation treaty (NPT), international authorities such as the International Atomic Energy Agency (IAEA) conduct inspections at facilities dealing with fissile or fertile nuclear materials. One measure consists of collection of swipe samples through inspectors for later analysis of collected nuclear material traces in the laboratory. Highly sensitive mass spectrometric methods provide a means to detect traces from nuclear material handling activities that provide indication of undeclared use of the facility. There are, however, no relevant (certified) reference materials available that can be used as calibration or quality control standards. Therefore, an aerosol-generation based process was established at Forschungszentrum Jülich for the production of spherical, mono-disperse uranium oxide micro-particles with accurately characterized isotopic compositions and amounts of uranium in the picogram range. The synthesized particles are studied with respect to their suitability as (certified) reference material in ultra-trace analysis. Several options for preparation and stabilization of the particles are available, where preparation of particles in suspension offers the possibility to produces specific particle mixtures. In order to assess the stability of particles, dissolution behavior and isotope exchange effects of particles in liquid suspension is studied on the bulk of suspended particles and also via micro-analytical methods applied for single particle characterization. The insights gained within these studies will form the basis on the choice of the further route towards preparation of uranium particle reference standard and certification as a reference material.