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Yotsuji, Kenji*; Tachi, Yukio; Kawamura, Katsuyuki*; Arima, Tatsumi*; Sakuma, Hiroshi*
Nendo Kagaku, 58(1), p.8 - 25, 2019/00
Molecular dynamics (MD) simulations were conducted to investigate physical properties of water and cations in montmorillonite interlayer nanopores. The swelling behaviors and hydration states were firstly evaluated as functions of interlayer cations and layer charge. The diffusion coefficients of water and cations in interlayer nanopores were decreased in comparison with those in bulk water and came closer to those in bulk water when basal spacing increased. The viscosity coefficients of interlayer water estimated indicated a significant effect of viscoelectricity at 1- and 2-layer hydration states and higher layer charge of montmorillonite. These trends from MD calculations were confirmed to be consistent with existing measured data and previous MD simulation. In addition, model and parameter related to viscoelectric effect used in the diffusion model was refined based on comparative discussion between MD simulations and measurements. The series of MD calculations could provide atomic level understanding for the developments and improvements of the diffusion model for compacted montmorillonite.
Anraku, Sohtaro; Matsubara, Isamu*; Morimoto, Kazuya*; Sato, Tsutomu*
Nendo Kagaku, 55(2), p.17 - 30, 2017/00
Anionic radionuclides are important for the long-term safety assessment of Japanese transuranic (TRU) waste disposal facilities. Degradation of cementitious materials used to construct the TRU waste disposal facilities, however, can produce a hyperalkaline leachate and so it is necessary to understand the reaction mechanisms that will control the behavior and fate of anionic radionuclides under these hyperalkaline conditions. An excellent natural analogue site to study relevant reaction mechanisms is provided in Oman where hyperalkaline spring waters (pH 
11) from serpentinized peridotites discharge into moderately alkaline rivers. Aragonite was found in all secondary mineral samples, with accessory minerals of calcite, layered double hydroxide (LDH) and brucite. LDH was observed at the high Al concentration springs and brucite at the low Al concentration springs. Calcite was only found close to the springs. Distal calcite formation was inhibited due to high Mg concentrations in the river water. The spatial distribution of minerals therefore implicates the importance of the mixing ratio of spring to river water and the relative chemical compositions of the spring and river waters. Supporting mixing model calculations could successfully reproduce the precipitation of aragonite and LDH. The observed decrease in Ca concentration could be explained by aragonite precipitation. pH exerted a strong control on the precipitation of LDH and so too, therefore, on Al concentration. In the mixing water experiments containing up to 40% river water, LDH and brucite were both oversaturated, but brucite was not always identified by XRD. The possible inhibition of brucite by LDH precipitation was an unexpected result.
Kameda, Jun*; Shimizu, Mayuko
Nendo Kagaku, 54(3), p.105 - 113, 2016/00
Yokoyama, Shingo*; Nakata, Kotaro*; Suzuki, Shinichi
Nendo Kagaku, 54(1), p.28 - 35, 2015/08
no abstracts in English
Matsue, Naoto*; Abidin, Z.*; Fujii, Naoki*; Oda, Chie; Honda, Akira
Nendo Kagaku, 52(2), p.62 - 70, 2014/00
Bentonite is expected to be used along with cement as engineered barrier components of TRU waste geological disposal system. There is a concern that the bentonite dissolved or altered owing to the contact with strong alkaline and high Ca concentration water derived from the reaction of the cement and groundwater. The first-principles quantum chemical calculations using the cluster model of montmorillonite, the main component of bentonite, were performed, and it was indicated that octahedral Al has higher solubility than octahedral Mg under strong alkaline condition and unsaturated Si-O-Al bond connecting tetrahedral and octahedral sheets at the edge of 110 and 010 planes cleaves easily. The adsorption of OH
on tetrahedral Si atom caused dissolution of adjacent Si and Al atoms in addition to the Si atom. While, the dissociation of Si-OH and Al-OH
groups and the difference in exchangeable cation species were shown to be less likely to affect the dissolution behavior of montmorillonite.
Oda, Chie; Honda, Akira; Takase, Hiroyasu*; Ozone, Kenji*; Sasaki, Ryoichi*; Yamaguchi, Kohei*; Sato, Tsutomu*
Nendo Kagaku, 51(2), p.34 - 49, 2013/02
Proposed TRU repository designs for geological disposal envisage the use of a bentonite buffer to limit the migration of radionuclides by impeding groundwater flow. Under highly alkaline conditions due to cementitious materials could cause a complex series of coupled changes in the porewater chemistry, mineralogy and, ultimately, the mass transport properties of the bentonite buffer. To elucidate the consequences of these coupled changes, reactive-transport model analyses have been conducted for eight bentonite alteration test cases using different combinations of secondary minerals that could form in the bentonite buffer. It was found that after 100,000 years the amount of dissolved bentonite was at a maximum when metastable secondary minerals precipitated. It was also found that the diffusion and hydraulic coefficients after 100,000 years in all test cases were on the same order of magnitude as the initial values.
Naganawa, Hirochika
Nendo Kagaku, 50(2), p.52 - 57, 2012/01
no abstracts in English
Saeki, Kazutoshi*; Nakagawa, Kei*; Wada, Shinichiro*; Shibata, Masahiro; Horoshiro, Yoshinari*; Jinno, Kenji*
Nendo Kagaku, 42(1), p.1 - 5, 2002/08
None
Suzuki, Satoru; Fujishima, Atsushi; Ueno, Kenichi; Ichikawa, Yasuaki*; Kawamura, Katsuyuki*; Fujii, Naoki*; Shibata, Masahiro; Sato, Haruo; Kitayama, Kazumi*
Nendo Kagaku, 41(2), p.43 - 57, 2001/12
None
