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Evidence for Neptunium Incorporation into Uranium (VI) Phases

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Abstract

This paper examines the ability of electron energy-loss spectroscopy (EELS) combined with transmission electron microscopy (TEM) to detect both low concentrations of Np in a U matrix and to provide evidence for incorporation of Np in U(VI) phases. The case for U(VI) secondary minerals acting as solubility-controlling phases for Np in repository performance assessment models has not been fully established. Direct evidence for incorporation, rather than sorption, continues to be difficult to obtain. Detection of Np with TEM-EELS is hampered by the occurrence of a plural (multiple) scattering event from the more abundant U atoms (U-M5 + U-(O4,5), that results in severe overlap on the Np-M5 edge at ~3665 eV. By examining the energy 'gap' between the Np-M5 and Np-M4 edges (184 eV), a method for observing Np independently of the plural scattering event has been established. Clear evidence of Np incorporation into synthetic studtite {(UO2)(O2)(H2O)2](H2O)2} and uranophane {Ca(UO2)2(SiO3OH)2(H2O)5} has been found with TEM-EELS. The EELS technique continues to remain an important tool for examining the potential for transuranic behavior in nuclear waste materials.

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Acknowledgments

The transmission electron microscopy work was performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by DOE's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory, operated for DOE by Battelle under Contract DE-AC06-76RL01830. We thank Drs. Jonathan Icenhower (PNNL and Jeffrey Fortner (ANL) for their insightful reviews.

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Authors and Affiliations

  1. Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA, 99352, USA

    Edgar C. Buck, Brady D. Hanson, Judah I. Friese, Matt Douglas & Bruce K. McNamara

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  1. Edgar C. Buck
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  2. Brady D. Hanson
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  3. Judah I. Friese
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  4. Matt Douglas
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  5. Bruce K. McNamara
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Correspondence to Edgar C. Buck.

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Buck, E.C., Hanson, B.D., Friese, J.I. et al. Evidence for Neptunium Incorporation into Uranium (VI) Phases. MRS Online Proceedings Library 824, 538–543 (2004). https://doi.org/10.1557/PROC-824-CC9.3

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  • DOI: https://doi.org/10.1557/PROC-824-CC9.3

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