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Production and characterization of monodisperse uranium particles for nuclear safeguards applications

The International Atomic Energy Agency (IAEA) is the official body to apply nuclear safeguards toverify compliance with existing legal bilateral or multilateral safeguards agreements [a]. Environmental sampling is a very effective measure to detect undeclared nuclear activities. Generally, samples are taken as swipe samples on cotton. These swipes contain minute quantities of particulates which have an inherent signature of their production and release scenario. These inspection samples are assessed for their morphology, elemental composition and their isotopic vectors. Mass spectrometry plays a crucial role in determining the isotopic ratios of uranium. Method validation and instrument calibration with well-characterized quality control (QC)-materials, reference materials (RMs) and certified reference materials (CRMs) ensures reliable data output. Currently, the availability of suitable well defined microparticles containing uranium and plutonium reference materials is very limited. Primarily, metals,oxides and various uranium and plutonium containing solutions are commercially available. Therefore, the IAEA’s Safeguards Analytical Services (SGAS) cooperates with the Institute of Nuclear Waste Management and Reactor Safety (IEK-6) at the Forschungszentrum Jülich GmbH in a joint task entitled “Production of Particle Reference Materials”. The work presented in this thesis has been partially funded by the IAEA, Forschungszentrum Jülich GmbH and the Federal Ministry of Economic Affairs and Energy(BMWi) through the “Joint Program on the Technical Development and Further Improvement of IAEA Safeguards between the Government of the Federal Republic of Germany and the IAEA” (in brief: German Support Program, GER SP). In order to strengthen the IAEA’s analytical capabilities, a broad range of tailor-made uranium and plutonium containing particles with consistent characteristics are needed: (1) mono disperse particles with a certified value on the number of atoms per particle (2) mixed particles sizes and (3) artificial QC samples by embedding various monodisperse particle populations with different particle sizes onto swipe samples (these swipes could additionally contain a “dirt” matrix to simulate real-life samples). In the long run, these particles are targeted to be used for quality assurance, method validation and interlaboratory performance evaluations and finally as reference materials or even certified reference materials. The first step towards monodisperse microparticles was the development of pure uraniumoxide particles made from certified reference materials. This work in this thesis represents the efforts and results made during the last three years. A comprehensive outlook will be given later on. The focus of the dissertation is (1) the implementation of a working setup to produce monodisperse uranium oxide particles and (2) the characterization of these particles towards the application as QC-material. A successful working setup was implemented at IEK-6. Monodisperse uranium oxide particles were produced by spray pyrolysis. Spray pyrolysis is the production of aerosols and the subsequent thermal conversion to its corresponding oxides: A dilute hydro-alcoholic solution made from certified uranyl nitrate solutions was used to produce monodisperse aerosol droplets. Monodisperse aerosol droplets were generated using a vibrating orifice aerosol generator (VOAG). Particles were dried and thermally converted to uranium oxide within a preheating system and a four zone oven and after cooling they are removed from the system by inertial collection. All in all, the entire setup was designed to be a closed system that can even be operated inside a glove box. All components were designed to be easily replaceable. As cost-effective connections and tubes, Swagelok and KF connectors and flanges were used, which ensure a gas tight connection.