International Journal of Rock Mechanics and Mining Sciences, 136, p.104538_1 - 104538_8, 2020/12
It is necessary to apply reliable numerical simulation techniques to assess the mechanical behaviour of repositories for the geological disposal of radioactive waste over a long period of time. Having a constitutive model that can describe the mechanical behaviour of bentonite is key to such numerical simulations. In this study, the applicability of linear elastic constitutive model with swelling term is examined focusing on the density heterogeneity by applying to the in situ Full-scale Engineered Barrier Experiment (FEBEX) in Grimsel. It was confirmed that this constitutive model underestimates the density change. Instead, mechanical behaviour was re-simulated by unsaturated elasto-plastic constitutive model using the changes in degree of saturation as input data. Although no feedback effects of mechanical behaviour on hydraulic and thermal behaviour were taken into account, two-dimensional stress and density could be reproduced.
Takayama, Yusuke; Kikuchi, Hirohito*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(1), p.12 - 21, 2020/06
In this study, an applicability of the modified Cam clay model to the buffer material under saltwater conditions was examined. First, consolidated-undrained triaxial test was conducted using NaCl solution and artificial seawater. Based on the consolidated-undrained triaxial compression test results and the existing consolidation test results, the difference in the mechanical behavior of the buffer material under distilled water and saltwater condition was clarified. In particular, there was a difference in the unloading behavior in the consolidation test. Through reproducibility analysis of these experimental data, it was confirmed that the mechanical behavior of the buffer material can be roughly reproduced by setting the swelling index according to the salt concentration.
Takayasu, Kentaro; Onuki, Kenji*; Kawamoto, Koji*; Takayama, Yusuke; Mikake, Shinichiro; Sato, Toshinori; Onoe, Hironori; Takeuchi, Ryuji
JAEA-Technology 2017-011, 61 Pages, 2017/06
The Groundwater REcovery Experiment in Tunnel (GREET) was put into effect as development of drift backfilling technologies. This test was conducted by making the Closure Test Drift (CTD) recovered with water after carrying out a plug around 40m distance from northern edge face of horizontal tunnel of depth 500m, for the purpose of investigation of recovering process of rock mass and groundwater under the influence of excavation of tunnel. This report presents the efforts of backfilling investigation using bentonite composite soil and execution of backfilling into borehole pits excavated in the CTD which were carried out in fiscal 2014 as a part of GREET, and succeeding observation results inside pits from September 2014 to March 2016.
Mihara, Morihiro; Hirano, Fumio; Takayama, Yusuke; Kyokawa, Hiroyuki*; Ono, Shintaro*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 24(1), p.15 - 25, 2017/06
A computer program MACBECE has been developed to provide rigorous calculations of the long-term mechanical behavior of a TRU waste geological repository. Consideration is given to the expected chemical alteration of repository components, including cementitious materials and bentonite, and the mechanical interactions between repository and host rock. The long-term mechanical behavior of a TRU waste repository was evaluated in a deep soft rock site, where creep deformation is likely to occur from the initial construction phase to 10 years after repository closure. It was found that the stress didn't fall into a singularity of yield surface of the EC model applied to the mechanical behavior model of bentonite. The calculated displacement of the inner diameter of the repository, considering mechanical interaction between repository and host rock, was about half that of a result in 2nd progress report on R&D for TRU waste disposal in Japan.
Saito, Hiroshi; Sato, Yasushi*; Sakamoto, Atsushi*; Torikai, Kazuyoshi; Fukushima, Shigeru; Sakao, Ryota; Taki, Tomihiro
JAEA-Technology 2015-063, 119 Pages, 2016/03
Ningyo-toge Environmental Engineering Center has been conducting environmental remediation of the Ningyo-toge Uranium Mine, after decades of mine-related activities were terminated. Its purposes are to take measures to ensure safety and radiation protection from the exposure pathways to humans in future, and to prevent the occurrence of mining pollution. As part of the remediation, upstream part of the Yotsugi Mill Tailings Pond, the highest prioritized facility, has been remediated to fiscal year 2012. Multi-layered capping has been constructed using natural material, after specifications and whole procedure being examined in terms of long-term stability, radiation protection, economics, etc. Monitoring has been carried out to confirm the effectiveness of the capping, in terms of settlement, dose and radon exhalation rates, etc. Monitoring of drainage volume of penetrated rainwater is planned. Accumulated data will be examined and used for remediation of downstream part of the Pond.
Yamaguchi, Tetsuji; Minase, Naofumi; Iida, Yoshihisa; Tanaka, Tadao; Nakayama, Shinichi
JAERI-Conf 2005-007, p.150 - 155, 2005/08
no abstracts in English
Tanaka, Tadao; Sakamoto, Yoshifumi; Yamaguchi, Tetsuji; Takazawa, Mayumi; Akai, Masanobu; Negishi, Kumi; Iida, Yoshihisa; Nakayama, Shinichi
JAERI-Conf 2005-007, p.105 - 110, 2005/08
Highly alkaline environments induced by cementitious materials in radioactive waste repositories are likely to dissolve and to alter montmorillonite, the main constituent of bentonite buffer materials. For the prediction of the long-term variations in permeability of compacted sand-bentonite mixtures, long-term alteration of bentonite should be quantified based on information accumulated by using the compacted or powdered bentonite materials, with batch experiments or column experiments. In this study, we summarize distinctive information obtained from various experimental systems, and propose functional and effective integration of experimental approaches to prediction of bentonite alteration.
Takazawa, Mayumi; Negishi, Kumi; Sakamoto, Yoshifumi; Akai, Masanobu; Yamaguchi, Tetsuji; Iida, Yoshihisa; Tanaka, Tadao; Nakayama, Shinichi
JAERI-Conf 2005-007, p.236 - 241, 2005/08
no abstracts in English
Takazawa, Mayumi; Yamaguchi, Tetsuji; Sakamoto, Yoshifumi; Akai, Masanobu; Tanaka, Tadao; Nakayama, Shinichi
NUMO-TR-04-05, p.A3_59 - A3_62, 2004/10
no abstracts in English
Maeda, Toshikatsu; Tanaka, Tadao; Mukai, Masayuki; Ogawa, Hiromichi; Yamaguchi, Tetsuji; Munakata, Masahiro; Matsumoto, Junko; Kozai, Naofumi; Bamba, Tsunetaka; Fan, Z.*; et al.
Nippon Genshiryoku Gakkai Wabun Rombunshi, 2(3), p.336 - 341, 2003/09
no abstracts in English
; Sato, Haruo; Ishidera, Takamitsu; Fujii, Naoki*; Kawamura, Katsuyuki*
JNC-TN8400 2001-031, 44 Pages, 2002/05
In order to quantify effect of temperature on diffusivity of deuterated water (HDO) in compacted sodium-bentonite, through-diffusion experiments were conducted at elevated tempemture from 298 to 333 K. Kunipia F (Na-montmorillonite content 98 wt. %; Kunimine Industly Co.) was compacted to a dry density of 0.9 and l.35 Mg/m. Since smectite flakes were perpendicularly oriented to a direction of compaction, anisotropy of diffusivity was investigated parallel and normal to the preferred orientation of smectite. Effective diffusion coeficient D of HDO was larger for a diffusional direction parallel to the preferred orientation than normal to that for both dry densities. These results well agreed to the previously reported ones for tritiated water. Activation energies of D in compacted bentonite increased with increasing dry density in the range of 19 - 25 kJ/mol which was slightly larger than that in bulk water (18 kJ/mol). This relationship can be considered to be due to both the pore structure development and high activation energy of water (18-23 kJ/mol) in the vicinity of smectite surface (within 2 nm) on the basis of molecular dynamics simulations.
; Sato, Haruo
JNC-TN8410 2001-028, 36 Pages, 2002/03
For a safety assessment of the high-level radioactive waste disposal, effective diffusion coefficients (D) of radionuclides in bentonite have been accumulated by the through-diffusion method. It has been found recently that experimental results on Ds for several cations (cesium and strontium) by the fairly standard experimental method in JNC differ from those previously reported in several papers. Discrepancy can be considered to be due to different design of diffusion cell and system. In order to confirm influences of the experimental design on cation diffusivities in bentonite, a flow-through diffusion system was developed and several diffusion experiments were conducted.As a result, magnitude of D and its salinity dependence were relatively different between the standard and flow-through diffusion system. Since the latter system can control boundary conditions of the experiment more strictly than the standard method, we can conclude that the flow-through diffusion system provide correct results. In addition, we apply this flow-through diffusion system to a modification of controlling boundary condition during the experiment and to the diffusion experiment under controlled temperature.
JNC-TN8430 2001-007, 56 Pages, 2002/01
In the geological disposal concept of radioactive wastes, a kind of clay with sorption ability and low permeability, called bentonite, is envisaged as an engineered barrier system in the geological repository. Also, the cemetitious material is envisaged as the backfill material in the vaults and the structure material of the vaults. The groundwater in contact with the cementitious material will promote hyperalkaline conditions in the repository environment and these conditions will affect the performance of the bentonite. Therefore, it is necessary to investigate the interaction between the cementitious material and the bentonite for the evaluation of long term stability of the disposal system. In this study, for the identification and the investigation of the secondary minerals, the batch immersion experiments of the powder bentonite were carried out using synthetic cement leachates (pH=7, 12.5, 14) at 200C. As the results, it was confirmed that Na as exchangeable cations in the bentonite can exchange relatively easily with Ca in the solution from the experiment results. And the ratio of cation exchange was estimated to be about 25% based on the amount of exchangeable cations Ca between layers. Furthermore, it was concretely shown that the generation of analcime might be affected by the Na concentration from results of the solution analyses and a stability analysis of analcime using the chemical equilibrium model, in addition to the pH in the solution.
Ito, Akira; Kawakami, Susumu; Yui, Mikazu
JNC-TN8400 2001-028, 38 Pages, 2002/01
In a repository for high-level radioactive waste, coupled thermo -hydro -mechanical and chemical (THMC) processes will ocurr, involving the interactive processes between radioactive decay heat from the vitrified waste, infiltration of groundwater, swelling pressure generation and chemical evolution of the buffer material and porewater chemistry. In this program, numerical experiment system for the coupled THMC processes will be developed in order to predict the long-term performance of the near-field (engineered barrier and host rock) for various geological environments. The simulation code development has been started in FY 2001 and three development steps are planned, because (1)development will be continued for some years, (2)feasibility of numerical experiment have to be confirmed by using existing tools. This report presents the following items of the simulation code development for the coupled THMC processes. (1)First step of the simulation code development (2)Mass transport passways in compacted bentonite (3)Parallelization of the simulation code
JNC-TN1400 2001-011, 129 Pages, 2001/07
no abstracts in English
Futakuchi, Katsuhito*; Hashimoto, Shuji*; Sakuramoto, Yuji*; ;
JNC-TN8400 2001-007, 52 Pages, 2001/04
As a natural analogue, the authors investigted a Tertiary argillaceous bed and a Quarternary hypabyssal rock (porphyrite) which intruded into the argillaceous rock, distributed in the Nishikubiki district of Niigata prefecture in Japan. We examined the variation of clay mineral species in the argillaceous rock surrounding the intrusive rock and carried out thermal analyses for the argillaceous rock based on the coolig history of the intrusive rock. The predominant clay mineral varied from montmorillonite to illite through illite/montmorillonite interlayers with approaching to the intrusive rock. The thermal analyses indicated that the temperature descended from 270 to 15 C during the 7.5 10 years at alocalty of argillaceous rock containing 75% illite in the interlayers. On the assumption that the alteration from montmorillonite to illite was regarded as a first-order reaction, we evaluated the apparent activation energy based on the thermal condition mentioned above; about 103 kJ/mol was obtained for this illitization. This was within the range of values reported previously by laboratory experiments and/or examinations of natural illitizations.
Taniguchi, Naoki; Kawasaki, Manabu*; *
JNC-TN8400 2001-011, 62 Pages, 2001/03
The corrosion of metallic materials used in natural environment are sometimes affected by microbial action. It is apprehended that microorganism living in deep underground or brought from ground surface during excavation makes an impact on overpack material for geological disposal of high-level radioactive waste. Sulfate reducing bacteria (SRB) is known to be one of the most representative microorganism which affects the corrosion of metals. In this study, the behavior of growth of SRB was investigated at first under the presence of bentonite as a main component of buffer material which encloses the overpack. The results of the tests showed that the population of SRB after the culture in synthetic sea water mixed with bentonite decreased with increasing the ratio of bentonite/solution. SRB was hardly grown in medium whose bentonite/solution ratio exceeded 1000g/l. As a conservative case, the effects of sulfide on the corrosion of overpack materials were also studied assuming high activity of SRB. Carbon steel, copper and titanium specimens were immersed in synthetic sea water purging 0.1MPa HS gas and the corrosion behavior was compared with the results in N gas purging environment. Obvious effect of sulfide on the corrosion of carbon steel was not observed, but the corrosion rates of copper specimens were accelerated several hundred times by purging HS gas. The absorption of hydrogen into titanium specimens was not affected by purging HS gas, but the difference of hydrogen absorption between pure titanium and titanium alloy containing 0.06%-Pd was observed.
JNC-TN8400 2001-008, 36 Pages, 2001/03
Research on geologic disposal of high-level radioactive waste(HLW) has been underway in many countries. Bentonite exhibiting a low permeability, high swelling property and high sorption capacity for many radioelements is proposed as a buffer material in many countlies. Recently, cementitious materials are considered as candidate matelials for the geologic disposal of high-level radioactive waste. As the pH and the Ca, Na, K contents of hyperalkaline pore water from the cementitious materials are high, this hyperalkaline pore water would alter the buffer material. The main aim of this study is to investigate the effect of alkaline pore water into the bentonite. Used materials are montmorillonite, albite and quartz composing bentonite. These minerals mixed in a constant ratio (1:1wt%) made to react to distilled water and the alkali solutions (pH11-13). These studies have been conducted at temperatures of 50 - 150C and run times of 10 - 200 day. XRD(X-ray powder diffraction) and SEM (Scanning Electron Microscopy) analyses were applied to studying the structure and quantitative data of each sample. From the result of this study, the main formed mineral of this experiment was analcime, which showed the tendency with a large amount of generation at a higher pH and temperature. Quantitative data of this study was conducted by X-ray powder diffraction method. THe order of the amount of the second analcime in each experiment is shown in the following. Montmorillonite and albite mixing test Montmorillonite test Montmorillonite and quartz mixing test Activation energies (E) using the quantitative data of each test are shown in the following. (1)Montmorillonite test : 54.9kJ/mol (2)Montmorillonite and albite mixing test : 51.9kJ/mol (3)Montmorillonite and quartz mixing test : 59.6kJ/mol
JNC-TN8410 2001-003, 40 Pages, 2001/01
A program (TDROCK1.FOR) for simulation and analysis of through-diffusion experiments for a single layer of diffusion media was developed. This program was made by Pro-Fortran language, which was suitable for scientific and technical calculations, and relatively easy explicit difference method was adopted for an analysis. In the analysis, solute concentration in the tracer cell as a function of time that we could not treat to date can be input and the decrease in the solute concentration as a function of time by diffusion from the tracer cell to the measurement cell, the solute concentration distribution in the porewater of diffusion media and the solute concentration in the measurement cell as a function of time can be calculated. In addition, solution volume in both cells and diameter and thickness of the diffusion media are also variable as an input condition. This simulation program could well explain measured result by simulating solute concentration in the measurement cell as a function of time for case which apparent and effective diffusion coefficients were already known. Based on this, the availability and applicability of this program to actual analysis and simulation were confirmed. This report describes the theoretical treatment for the through-diffusion experiments for a single layer of diffusion media, analytical model, an example of source program and the manual.
Sato, Tsutomu*; *; Iida, Yoshihisa; Yamaguchi, Tetsuji; Nakayama, Shinichi
Clay Science for Engineering, p.593 - 598, 2001/01
no abstracts in English