Abstract
The flow-through method and the profile method are used for determining diffusion coefficients. If the diffusion coefficient is small, only the profile method is suitable. In the profile method, the apparent diffusion coefficient can be obtained by setting an appropriate diffusion period. However, if an experiment is conducted with a longer diffusion period, the apparent diffusion coefficient may appear small. This phenomenon is observed in the diffusion of neptunium in compacted bentonite in an atmosphere with high carbonate ion concentrations. One interpretation is that the neptunyl carbonate complex can only pass through a limited size of pores in the compacted bentonite because the complex is so large and negatively charged. In this work, a long-term diffusion experiment was conducted over 3 years, and the diffusion profile of neptunium in compacted bentonite was exponential owing to filtration and did not change over time. Exponential profiles were also observed for large oxoanions, such as molybdate ions, and for plutonium in a 20-year iron corrosion environment.
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The datasets generated during and/or analyzed during the current study are available from corresponding author on reasonable request.
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Acknowledgments
ICP-MS/MS measurements of Np were performed at the International Research Center for Nuclear Materials Science, Institute of Materials Research, Tohoku University and the authors thank Makoto Watanabe and Chikage Abe of the Institute for assistance. The authors also wish to thank Midori Watanabe of Center of Advanced Instrumental Analysis, Kyushu University, for her support in ICP-MS measurements of Se, Mo, and I. The authors would like to thank the many laboratory graduates who assisted in this study.
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All authors contributed to the study conception and design. Data collection and analysis were performed by KI. The first draft of manuscript was written by KI, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
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Idemitsu, K., Inagaki, Y. & Arima, T. Long-term diffusion of neptunium and other elements in compacted bentonite reveals filtration. MRS Advances 8, 214–223 (2023). https://doi.org/10.1557/s43580-023-00501-9
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DOI: https://doi.org/10.1557/s43580-023-00501-9