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Machida, Masahiko; Okumura, Masahiko; Nakamura, Hiroki; Sakuramoto, Kazuhiro*
Proceedings of Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015) (CD-ROM), 12 Pages, 2015/04
In order to clarify physicochemical behaviors of radioactive Cs released into environment from the Fukushima Daiichi Nuclear Power Plants, we study on two issues, i.e., hydration structures of Cs
and its adsorption on a specific edge in a clay particle (mica) by employing first principles calculations. In this paper, firstly, we report on hydration structures of Cs by using Born-Oppenheimer first-principles molecular dynamics. Our striking finding in the hydration structures is that Cs has no clear second hydration shell in contrast to any other alkali cations. Secondly, we construct a model of the Frayed Edge Site and confirm that the model actually becomes selective for Cs when expanding the interlayer distance from that of the original crystal structure through the calculation of the ion-exchange energy.
Machida, Masahiko; Sakuramoto, Kazuhiro*; Okumura, Masahiko; Nakamura, Hiroki; Sato, Yuya*; Akutsu, Keiko*; Shiga, Motoyuki
no journal, ,
We report the results of ab initio molecular dynamics simulation on the hydration structure of monovalent Cs cation, which is one of the most fundamental issues in terms of chemical forms of Cs. The ion hydration of heavy alkali species, Rb and Cs, have been not studied thoroughly as Na and K. Using the VASP code, ab initio molecular dynamics are performed to examine and compare the hydrated structures of monovalent Li, Na, K, Rb, and Cs ions. It is found that hydrated Rb and Cs ions constitute very flexible solvation shells. Moreover, we also investigate the dynamical properties, such as the residence time of water molecules in the first shell. Consequently, we find that the exchange rate of water molecules of the first shell in Cs is significantly fast compared to other ion cases.