Production and Characterization of Monodisperse Uranium Particles for Nuclear Safeguards Applications

摘要

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]. Environmentalsampling is a very effective measure to detect undeclared nuclear activities. Generally, samples are takenas swipe samples on cotton. These swipes contain minute quantities of particulates which have aninherent signature of their production and release scenario. These inspection samples are assessed fortheir morphology, elemental composition and their isotopic vectors. Mass spectrometry plays a crucialrole in determining the isotopic ratios of uranium. Method validation and instrument calibration withwell-characterized quality control (QC)-materials, reference materials (RMs) and certified referencematerials (CRMs) ensures reliable data output. Currently, the availability of suitable well definedmicroparticles 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 WasteManagement 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 fundedby 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 IAEASafeguards between the Government of the Federal Republic of Germany and the IAEA” (in brief: GermanSupport Program, GER SP).In order to strengthen the IAEA’s analytical capabilities, a broad range of tailor-made uranium andplutonium containing particles with consistent characteristics are needed: (1) monodisperse particleswith a certified value on the number of atoms per particle (2) mixed particles sizes and (3) artificial QCsamples by embedding various monodisperse particle populations with different particle sizes ontoswipe samples (these swipes could additionally contain a “dirt” matrix to simulate real-life samples). Inthe long run, these particles are targeted to be used for quality assurance, method validation andinterlaboratory performance evaluations and finally as reference materials or even certified referencematerials. 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. Acomprehensive outlook will be given later on. The focus of the dissertation is (1) the implementation ofa working setup to produce monodisperse uranium oxide particles and (2) the characterization of theseparticles towards the application as QC-material.A successful working setup was implemented at IEK-6. Monodisperse uranium oxide particles wereproduced by spray pyrolysis. Spray pyrolysis is the production of aerosols and the subsequent thermalconversion to its corresponding oxides: A dilute hydro-alcoholic solution made from certified uranylnitrate solutions was used to produce monodisperse aerosol droplets. Monodisperse aerosol dropletswere generated using a vibrating orifice aerosol generator (VOAG). Particles were dried and thermallyconverted to uranium oxide within a preheating system and a four zone oven and after cooling they areremoved from the system by inertial collection. All in all, the entire setup was designed to be a closedsystem that can even be operated inside a glove box. All components were designed to be easilyreplaceable. As cost-effective connections and tubes, Swagelok and KF connectors and flanges wereused, which ensure a gas tight connection.