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Okumura, Masahiko; Kerisit, S.*; Bourg, I. C.*; Lammers, L. N.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K. M.*; Machida, Masahiko
Journal of Environmental Radioactivity, 189, p.135 - 145, 2018/09
Times Cited Count：68 Percentile：87.30(Environmental Sciences)no abstracts in English
Lammers, L.*; Bourg, I. C.*; Okumura, Masahiko; Kolluri, K.*; Sposito, G.*; Machida, Masahiko
Journal of Colloid and Interface Science, 490, p.608 - 620, 2017/03
Times Cited Count：142 Percentile：94.13(Chemistry, Physical)no abstracts in English
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. We can investigate diffusion/adsorption behavior of cesium ion and sodium ion in clay minerals and water systems at molecular scale using molecular dynamics simulation on a supercomputing system. In this study, we evaluated the free energy profiles of cesium and sodium ions adsorption to the interlayer of Na-montmorillonite from bulk water in mesopore. As a result, we found that the minimum of free energy profiles of these cations locates in the interlayer of Na-montmorillonite, and the minimum of free energy profile of cesium is lower than that of sodium. This result shows that the affinity of cesium ion to Na-montmorillonite is stronger than that of sodium ion. Moreover, we confirmed that the affinities of both cations to Na-montmorillonite decrease with salinity increase, and these cations maintain their adsorption mechanism. In the presentation, we discuss layer charge and layer size dependence on the free energy profiles of these cations.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. We can investigate diffusion/adsorption behavior of cesium ion and sodium ion in clay minerals and water systems at molecular scale using molecular dynamics simulation on a supercomputing system. In this study, we evaluate the free energy profiles of the cesium and sodium ions adsorption to the montmorillonite interlayer from bulk water in mesopore. We found that the free energies in the interlayer of Na-montmorillonite are smaller than those in the bulk water for the cesium and sodium ions, and the averaged free energy value for cesium in the interlayer is lower than that for sodium. This result shows that cesium ion is more strongly adsorbed to the interlayer of Na-montmorillonite than sodium ion. Moreover, we found differences in the shape of these free energy profiles in the interlayer. The free energy profile for the cesium ion has a spiky structure with many local minimums, although that for the sodium ion is almost uniform. These results suggest that the cesium ion forms the inner-sphere complex at these local minimums and the sodium ion forms the outer-sphere complex. Furthermore, we investigated salinity dependence on the free energy profiles. We confirmed that the affinities of both cations to Na-montmorillonite decrease with increasing salinity, and the adsorption mechanism of these cations does not depend on salinity. In the presentation, we discuss the free energy profiles with different layer charges, interlayer distances, etc.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K.*; Bourg, I.*; Okumura, Masahiko
no journal, ,
In the geological disposal of high-level radioactive waste, bentonite plays an important role in retarding radionuclide migration by adsorbing cationic species. Cesium ions (Cs
), in particular, are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We employed classical molecular dynamics simulations to investigate the adsorption behavior of Cs and sodium ions (Na) from bulk water into the interlayer of Na-montmorillonite, by evaluating their free energy profiles. Moreover, we evaluated the dependence of the layer charge on the free energy profiles. As a result, our simulations reproduced the experimental trend showing that Cs is more strongly adsorbed on Na-montmorillonite than Na, as the layer charge increases. In the presentation, we will also discuss the detailed adsorption mechanisms, and comparisons with experimental data.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K.*; Bourg, I.*; Okumura, Masahiko
no journal, ,
In the geological disposal of high-level radioactive waste, bentonite plays a crucial role in retarding radionuclide migration by adsorbing cationic species. Cesium ions (Cs), in particular, are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We employed classical molecular dynamics simulations to investigate the adsorption behavior of Cs and sodium ions (Na) from bulk water into the interlayer of Na-montmorillonite, by evaluating free energy profiles. Our results revealed that Cs adsorbs more strongly into the interlayer than Na due to the formation of the inner- and outer-sphere complexes of Cs and Na, respectively. In the presentation, we will also discuss the fundamentals of classical molecular dynamics, the physical origin of the free energy profiles, detailed adsorption mechanisms, and comparisons with experimental data.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to clarify and model the migration behavior of radionuclides in clay minerals used as buffer material on a molecular scale. In this study, we perform classical molecular dynamics simulations in clay minerals-water systems and evaluate free-energy profiles of clay minerals to clarify and model the diffusion behavior of cesium on a molecular scale.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. The recent development of supercomputers enables us to perform large-scale classical molecular dynamics (MD) simulations to evaluate the adsorption properties of cation to clay minerals. We evaluated the free-energy profiles of cesium adsorption from mesopore to the interlayer of Na-montmorillonite by classical MD on a supercomputer. We found that the free-energy profiles of cesium adsorption depend on the interlayer distance of the Na-montmorillonite and mesopore salinity in the water system. In the presentation, we also discuss the distribution and diffusion coefficients of cesium ions.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
Understanding the radionuclide diffusion phenomena is crucial for the safe geological disposal of high-level radioactive waste. The diffusion in clay-water systems is particularly important for the performance of the artificial barrier made of bentonite. Numerical simulation is one of the best research methods for understanding the phenomenon at the microscopic level. Recently, large-scale molecular dynamics (MD) simulations of the systems with clay particles and water molecules were realized. In this presentation, we will show numerical simulation results of diffusion of cesium in the large system with MD. Our recent results suggest that cesium is less diffuse than sodium.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to understand the migration behavior of radionuclides in clay minerals used as buffer materials. In this study, the difference in the diffusion behavior of cesium and sodium ions in Na-montmorillonite is analyzed by evaluating the free energy using classical molecular dynamics simulations.
Okumura, Masahiko; Kerisit, S.*; Bourg, I.*; Lammers, L.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K.*; Machida, Masahiko
no journal, ,
no abstracts in English
