'Environmental Sampling' is routinely used for the application of nuclear safeguards to verify the completeness and correctness of a State's nuclear activities. The swipe samples collected by safeguards inspectors in a nuclear facility contain sub-micrometer to micrometer-sized uranium-bearing particles, which are analyzed by the International Atomic Energy Agency's (IAEA's) Network of Analytical Laboratories (NWAL). One of the ongoing research projects at IRMM is the development of new certified test samples of uranium reference particles for NUSIMEP (Nuclear Signatures Inter-laboratory Measurement Evaluation Programme). Uranium particles are formed via hydrolysis of well characterized IRMM uranium hexafluoride, certified for major and minor uranium isotope ratios. The solid product, particulate uranyl fluoride, is deposited on graphite planchets. They are used as quality control samples representative of real-life particles collected on swipes.The first IRMM pilot campaign devoted to particle analysis (NUSIMEP-6) revealed good performance of participating laboratories. Graphite disks prepared for this purpose were prepared according to the aerosol deposition technique available at IRMM at that time, which was not yet fully optimized. The NUSIMEP-6 test samples therefore contained only particles with a single isotopic enrichment. Based on the participants' feedback, the production of uranium oxyfluoride particles was modified to improve the quality of our control samples and to better simulate real-life uranium particles found on swipes. Our effort to optimize the sample preparation was verified by Scanning Electron Microscopy (SEM) and by Secondary Ion Mass Spectrometry (SIMS), both mainstay techniques for particle analysis. Graphite disks coated with particles obtained via the modified procedure were verified by ITU and IAEA laboratories. This optimized method was used to prepare new control samples with a double isotopic enrichment, used in the NUSIMEP-7 inter-laboratory comparison. NUSIMEP-7 is organized in support to European Safeguards (DG ENERGY), the IAEA's NWAL and laboratories in the field of particle analysis.

Development of uranium oxyfluoride particulate material used for Nuclear Signature Interlaboratory Measurement Evaluation Program NUSIMEP-7

242nd National Meeting (2011)

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