The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia

Cook, Megan and Etschmann, Barbara and Ram, Rahul and Ignatyev, Konstantin and Gervinskas, Gediminas and Conradson, Steven D. and Cumberland, Susan and Wong, Vanessa N. L. and Brugger, Joёl (2021) The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia. Scientific Reports, 11 (1). 10698. ISSN 2045-2322 (https://doi.org/10.1038/s41598-021-89757-5)

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Abstract

The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing 'hot' particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

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