Micro-Analytical Characterization of Uranium Particles in Support of Environmental Sampling for Safeguards

The International Atomic Energy Agency uses Environmental Sampling for Safeguards (ESS) to give additional assurance of the absence of undeclared nuclear materials and activities in States covered by comprehensive safeguards agreements. The analysis of individual micrometer-sized particles (so-called “particle analysis”) has been used since the beginning of the ESS programme because of its high inherent sensitivity (pg levels) and the wide range of isotopic information which can be obtained with methods such as secondary ion mass spectrometry (SIMS) and fission-track thermal ionization mass spectrometry (FT-TIMS). This paper will describe our investigations of several other micro-analysis methods, thus demonstrating their ability to provide additional diagnostic information about particles which would complement the isotopic information coming from SIMS or FT-TIMS. These methods include scanning electron microscopy (SEM) with X-ray fluorescence (XRF) spectrometry, micro-Raman spectroscopy, transmission electron microscopy with electron diffraction and SIMS used in a multi-element analysis mode. A set of typical uranium compounds was first studied to catalogue the diagnostic information coming from each of the various methods. Morphological and compositional differences were seen, even for materials that were thought to be quite similar. For example, one sample of UF4 showed a strong Raman spectral band while another sample of the same nominal compound did not. SEM measurements also showed interesting morphological differences between batches of different uranium oxides. Following this study, a set of 6 UO2 test samples was submitted blind to the QinetiQ laboratory in an attempt to group them into classes reflecting the production processes which formed them. The conclusions were fully consistent with the known origin of the samples. This study demonstrated the power of these combined methods to distinguish between materials of different origin, thus increasing the ability of the IAEA to detect undeclared materials in the presence of nominally very similar declared materials. These investigations point the way to future work to improve and extend this type of analysis.