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Yamaguchi, Tetsuji; Yamada, Fumika; Negishi, Kumi*; Hoshino, Seiichi; Mukai, Masayuki; Tanaka, Tadao; Nakayama, Shinichi
Physics and Chemistry of the Earth, 33(Suppl.1), p.S285 - S294, 2008/00
It is important to assess long-term alteration of engineered barrier composed of bentonite and cement for the safety assessment of radioactive waste disposal. In order to promote our development of the assessment methodologies, we developed a secondary mineral formation model for cement based materials and a hydraulic conductivity model for bentonite buffer materials. These models were verified by comparing with experimental observations. We also calculated changes in mineralogy of bentonite buffer materials and accompanying changes in the hydraulic conductivity over 10,000 y. We identified the temperature as an important factor dominating the alteration of the buffer. We also identified that the alteration is limited by slow kinetics of the dissolution of montmorillonite and by the diffusive mass transfer. Our calculation showed that the mineralogical change proceeds rather fast during the initial 1,000 y and slows down afterwards, and that salinity of the groundwater has both positive and negative effects on the hydraulic conductivity.
Sato, Haruo
Physics and Chemistry of the Earth, 33(Suppl.1), p.S538 - S543, 2008/00
Swelling pressure of bentonite was estimated based on the thermodynamic data of water on the surface of smectite which is a major clay mineral constituent of the bentonite composing engineered barriers and backfill materials. The activity and the relative partial molar Gibbs free energy (dEa) of water on the surface of smectite as a function of water content in a density range of 0.6-0.9 Mg/m
. The activity and dG of water decreased with decreasing water content and showed similar trend to data of Kunipia-F bentonite (almost 100wt.% smectite) reported in the past. Swelling presure was estimated from the difference in the chemical potential balance of water in equilibrium state between free water and misturized smectite, and compared to data measured for various kinds of bentonites. The calculated swelling pressures were in good agreement with the measured data. This indicates that swelling pressure of bentonite can be calculated based on the thermodynamic data of water.
O and applying electric potential gradientTanaka, Shingo*; Noda, Natsuko*; Higashihara, Tomohiro*; Sato, Seichi*; Kozaki, Tamotsu*; Sato, Haruo; Hatanaka, Koichiro
Physics and Chemistry of the Earth, 33(Suppl.1), p.S163 - S168, 2008/00
In order to identify mass transport pathway in compacted bentonite, water transport behavior in compacted montmorillonite which is the major clay mineral constituent of the bentonite was studied. Back-to-back diffusion and electro-osmosis experiments for HO were carried out at montmorillonite densities of 1.0, 1.2 and 1.4 Mg/m using HO as a tracer. Apparent diffusivities from the diffusion experiments and advection velosities and hydraulic dispersities from the electro-osmosis experiments were determined. The mass transport pathways were discussed by comparing with concentration profiles and peak positions of He, Na and Cl which were reported in the past. The hydraulic dispersities decreased in the order of He, HO, Cl and Na, and these differences were considered to be due to that transport pathway depended on species and hydraulic dispersity for each species also depended on transport pathway.
Tanai, Kenji; Matsumoto, Kazuhiro*
Proceedings of 3rd International Meeting on Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, p.57 - 64, 2008/00
As a candidate buffer material for geological disposal of high level radioactive waste, densely compacted bentonite has a number of favourable properties, such as its low permeability and high capacity for radionuclide sorption. Furthermore, as the bentonite will be resaturated and swelled gradually after repository closure, not only will any gaps within the bentonite be sealed, but the bentonite may also be excluded into fractures in the surrounding rock, diverting a part of the water flow away from the repository. This situation is potentially advantageous to repository safety. However, if loss of bentonite into fractures due to extrusion and subsequent erosion of the extruding front by flowing groundwater is too pronounced, then the decrease in density of the bentonite within the repository may lead to reduce its favourable properties. Therefore, the extrusion and erosion of bentonite buffer from the disposal pit or tunnel should be quantitatively understood to ensure long-term performance of the engineered barriers for the geological disposal system. In this study, an attempt was made to use X-ray CT technique to measure, non-destructively, the density distribution of bentonite buffer extruded into the artificial fractures.
Kunimaru, Takanori; Yamamoto, Hajime*
no journal, ,
The Japan Atomic Energy Agency (JAEA) has undertaken the underground research laboratory (Horonobe URL) project at Horonobe-cho, in northwest Hokkaido, Japan since fiscal year 2000. The project has now completed the first stage of surface based investigation, including environmental survey, airborne survey, geophysical survey, geological survey, and borehole drilling investigations, in the town. The conceptual model was carried out developing based on field investigations. The numerical simulations were performed based on conceptual model. This paper discusses to develop the conceptual and numerical hydrochemical models based on field investigations.
Kurikami, Hiroshi; Takeuchi, Ryuji; Yabuuchi, Satoshi
no journal, ,
Representative elementary volume is an important factor on hydraulic investigations regarding geological disposal of high-level radioactive waste because it is strongly relevant to the scale of the environmental model and groundwater flow simulation for the use of safety assessment. For example, a large-scale groundwater flow simulation can provide the direction and the amount of groundwater flow but it is not suitable to show migration of radionuclide based on real velocity instead of Darcy's velocity, which is a smaller-scale behavior. This paper discusses the scale effect, the heterogeneity and porosity-dependence of hydraulic conductivities of sedimentary rocks obtained by the various hydraulic investigations using deep boreholes drilled in the Horonobe Underground Research Project in Japan.
Sahara, Fumihiro*; Murakami, Takeshi*; Kobayashi, Ichizo*; Mihara, Morihiro; Oi, Takao
no journal, ,
In this paper, the model for the long-term behavior of bentonite-based materials adopted in MACBECE is mainly described.