Alexander Knott Production and Characterization of Monodisperse Uranium Particles for Nuclear Safeguards Applications


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Inhaltsangabe zu „Production and Characterization of Monodisperse Uranium Particles for Nuclear Safeguards Applications“ von Alexander Knott

The International Atomic Energy Agency (IAEA) is the official body to apply nuclear safeguards to
verify 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) monodisperse 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 uranium
oxide 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

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