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JAEA Reports

Impact assessment of density change on the buffer material on the coupled thermal-hydraulic and mechanical (THM) behavior in the near-field (Contract research)

Suzuki, Hideaki*; Takayama, Yusuke

JAEA-Research 2020-015, 52 Pages, 2020/12

JAEA-Research-2020-015.pdf:3.83MB

It is anticipated that the coupled thermal hydraulic and mechanical (THM) processes will occur, involving an interactive process with radioactive decay heat arising from the vitrified waste, infiltration of groundwater from the host rock into the buffer material, swelling pressure of buffer material due to its saturation in the near-field of a geological disposal system for high-level radioactive waste repository. In order to evaluate these phenomena in the near-field, the THM model has been developed. In this report, the density dependence of thermal, hydraulic and mechanical properties of the buffer material was investigated to evaluate the near-field environment. These density dependence schemes were added to the coupled THM model. The THM analysis of the in-situ experiment of engineered barrier system (EBS) experiment at the Horonobe Underground Research Laboratory was carried out. As a result, the effect of the density change of the buffer material on the temperature and infiltration behavior of buffer material was found. A case analysis on the long-term behavior of the near field was also carried out. Then, the behavior that the buffer material swelled out toward the backfill material and the density of the buffer material decreasing was shown.

Journal Articles

Commissioned research on geological disposal performed by JAEA Safety Research Center

Sawaguchi, Takuma

"Yugai Haikibutsu, Hoshasei Haikibutsu Eno Semento, Konkurito Gijutsu No Tekiyo Kenkyu Iinkai" Hokokusho (CD-ROM), p.165 - 173, 2020/12

no abstracts in English

Journal Articles

Long-term alteration of bentonite; For safety evaluation of deep geological disposal

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.

Journal Articles

Experimental and modeling study to predict long-term alteration of bentonite buffer materials with alkaline groundwater

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

Journal Articles

Modeling of variation in permeability of compacted bentonite with alkaline fluid for long-term safety assessment of geological disposal system

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

JAEA Reports

Activation energy of diffusivities for deuterated water in compacted sodium-bentonite; Through-diffusion experiment and molecular dynamics simulation

; Sato, Haruo; Ishidera, Takamitsu; Fujii, Naoki*; Kawamura, Katsuyuki*

JNC-TN8400 2001-031, 44 Pages, 2002/05

JNC-TN8400-2001-031.pdf:1.58MB

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$$^{3}$$. 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$$_{e}$$ 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$$_{e}$$ 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.

JAEA Reports

Passivation condition of carbon steel in bentonite/sand mixture

Taniguchi, Naoki; Kawakami, Susumu; *

JNC-TN8400 2001-025, 27 Pages, 2002/03

JNC-TN8400-2001-025.pdf:0.82MB

It is essential to understand the corrosion type of carbon steel under the repository conditions for the lifetime assessment of carbon steel overpack used for geological isolation of high-level radioactive waste. According to the previous study, carbon steel is hard to passivate in buffer material assuming a chemical condition range of groundwater in Japan. However, concrete support will be constructed around the overpack in the case of repository in the soft rock system and groundwater having a higher pH may infiltrate to buffer material. There is a possibility that the corrosion type of carbon steel will be influenced by the rise of the pH in groundwater. In this study, anodic polarization experiments were performed to understand the passivation condition of carbon steel in buffer material saturated with water contacted with concrete. An ordinary concrete and a low-alkalinity concrete were used in the experiment. The results of the experiments showed that the carbon steel can passivate under the condition that water having pH $$>$$ 13 infiltrate to the buffer material assuming present property of buffer material. If the low-alkalinity concrete is selected as the support material, passivation can not occur on carbon steel overpack. The effect of the factors of buffer material such as dry density and mixing ratio of sand on the passivation of carbon steel was also studied. The results of the study showed that the present property of buffer material is enough to prevent passivation of carbon steel.

JAEA Reports

A Research program for numerical experiments on coupled thermo-hydro-mechanical and chemical processes

Ito, Akira; Kawakami, Susumu; Yui, Mikazu

JNC-TN8400 2001-028, 38 Pages, 2002/01

JNC-TN8400-2001-028.pdf:2.35MB

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

JAEA Reports

Long-term effect of creep displacement of host-rock on stability of engineered barrier system for TRU waste; Two-dimensional analysis by the non-linear viscoelasticity model

Aoyagi, Takayoshi*; *; Mihara, Morihiro; Okutsu, Kazuo*; Maeda, Munehiro*

JNC-TN8400 2001-024, 103 Pages, 2001/06

JNC-TN8400-2001-024.pdf:11.6MB

In the disposal concept of TRU waste, concentrated disposal of wastes forms in large cross-section underground cavities is envisaged, because most of TRU waste is no-heat producing in spite of large generated volume as compared with HLW. In the design of engineered barrier system based on large cross-section cavities, it is necessary to consider the long-term mechanical process such as creep displacement of the host rock from the viewpoint of the stability of engineered barrier system. In this study, the long-term creep displacement of the host rock was calculated using the non-linear viscoelasticity model and the effects on the stability of engineered barrier system was evaluated. As a result, in the disposal concept of crystalline rock, no creep displacement occurred at the time after 1 milion year. On the other hand, in the disposal concept of sedimentary rock, creep displacement of 80$$sim$$90mm occurred at the time after 1 milion year. Also, in this calculation, a maximum reduction of 45mm concerned with the thickness of buffer material was estimated. But these values resulted within allowance of design values. Therefore, these results show that the effects of the creep displacement on the stability of engieered barrier system would not be significant.

JAEA Reports

The Activity of sulfate reducing bacteria in bentonite and the effect of hydrogen sulfide on the corrosion of candidate materials for overpacks

Taniguchi, Naoki; Kawasaki, Manabu*; Fujiwara, Kazuo*

JNC-TN8400 2001-011, 62 Pages, 2001/03

JNC-TN8400-2001-011.pdf:6.42MB

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 H$$_{2}$$S gas and the corrosion behavior was compared with the results in N$$_{2}$$ 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 H$$_{2}$$S gas. The absorption of hydrogen into titanium specimens was not affected by purging H$$_{2}$$S gas, but the difference of hydrogen absorption between pure titanium and titanium alloy containing 0.06%-Pd was observed.

JAEA Reports

Experimental investigations of the effect of alkali fluids on montmorillonite, albite and quartz

JNC-TN8400 2001-008, 36 Pages, 2001/03

JNC-TN8400-2001-008.pdf:2.26MB

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 - 150$$^{circ}$$C 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$$_{a}$$) 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

JAEA Reports

Direct pH measurement of porewater in compacted bentonite (III); Influence of low alkalinity cement on bentonite porewater

Isogai, Takeshi*; Oda, Chie

JNC-TN8400 2000-025, 48 Pages, 2000/09

JNC-TN8400-2000-025.pdf:2.1MB

Porewater chemistly in compacted bentonite would affect a performance of engineered barrier system in a high-level radioactive waste repository, whereas there are little information of the porewater based on experimental data. The previous study provided a new method of direct pH measurement for highly compacted bentonite system and demonstrated some tests for compacted bentonite samples (the dry densities: 1.6 [g/cm$$^{3}$$] and 1.8 [g/cm$$^{3}$$]) both with the de-ionized water and with the NaCl solution. In this study, the solution equilibrated with low alkalinity cement were used in the direct pH measurement to see the effect of the composition of the external solutions, in which the bentonite column immersed. The result showed that the pH value of porewater in the cementitious condition was around 9 during the immersed time 1 to 3 months, while after 6 months became the porewater pH 10.6, which was equal to pH of the external solution.

JAEA Reports

Experimental study of gas generation by microorganism

Mine, Tatsuya*; Mihara, Morihiro;

JNC-TN8430 2000-010, 27 Pages, 2000/07

JNC-TN8430-2000-010.pdf:0.72MB

In the geological disposal system of the radioactive wastes, gas generation by microorganism could be significant for the assessment of this system, because organic material included in groundwater, buffer material and wastes might serve as carbon sources for microorganisms. In this study, gas generation tests using microorganisms were carried out under anaerobic condition. The amount of methane and carbon dioxide that were generated by activity of Methane Producing Bacteria (MPB) were measured with humic acid, acetic acid and cellulose as carbon sources. The results showed that methane was not generated from humic acid by activity of MPB. However, in the case of using acetic acid and cellulose, methane was generated, but at high pH condition (pH=10), the amount of generated methane was lower than at low pH (pH=7). It was not clear whether the pH would affect the amount of generated carbon dioxide.

JAEA Reports

None

*

JNC-TN1400 2000-006, 68 Pages, 2000/07

JNC-TN1400-2000-006.pdf:2.18MB

no abstracts in English

JAEA Reports

None

*

JNC-TN1400 2000-004, 0 Pages, 2000/07

JNC-TN1400-2000-004.pdf:4.27MB

None

JAEA Reports

Reliability evaluation of simulation models for nearfield groundwater flow and radionuclide transport computation

*; *; *; *

JNC-TJ8400 2000-006, 232 Pages, 2000/05

JNC-TJ8400-2000-006.pdf:7.75MB

In this research, simulations with some parameters which characterize ground water flow and the reliability evaluation for the expansion of the calculation method of groundwater flow were carried out by using the radionuclide transport computations in nearfield heterogeneous porous media. Concretely contents are follows: (1)With the series of calculation method for three-dimensional saturated/unsaturated groundwater flow and one-dimensional radionuclide transport. the computational analyses with the parameters used in JNC report in 2000 was carried out and the influence of the different input flux was evaluated. (2)The examination of the application for the different ways of inverse laplace transformation which is used in one-dimensional radionuclide tansport analysis code "MATRICS" was carried out. (3)The examination of the application of multi-element "MATRICS" (m-MATRICS) for radionuclide transport computations in nearfield heterogeneous porous media was carried out. (4)The series of calculation methods from three-dimensional saturated/unsaturated ground water flow simulation code to one-dimensional radionuclide transport simulation code was integrated.

JAEA Reports

Development of the evaluation methodology for earthquake resistance of the engineered barrier system (III)

Mori, Koji*; Neyama, Atsushi*; Nakagawa, Koichi*

JNC-TJ8400 2000-064, 175 Pages, 2000/03

JNC-TJ8400-2000-064.pdf:5.23MB

In this study, the following tasks have been performed in order to evaluate the stability of earthquake resistance for the engineered barrier system(EBS) of High Level Waste (HLW) geological isolation system. (1)validation studies for the liquefaction model. The function of single-phase analysis without interaction between soil and pore water in three-dimensional effective stress analysis code, which had been developed in this study, have been verified using by actual vibration test data. This fiscal year, some validation studies for the function of liquefaction analysis was conducted usig by actual measured data through the laboratory liquefaction test. (2)Supplemental Studies for JNC Second Progress Report. Through the JNC second progress report, it was considered that the stability of earthquake resistance of the engineered barrier system would be maintained under the major seismic event. At the same time we have recognized that several model parameters for joint-crack element, which takes into account for the response behavior of material discontinuous surface such as between overpack and buffer material, will become important in the response behavior of the whole EBS. This year, we have studied about several topics, which arise from technical discussion on JNC second progress report and we have discussed about total seismic stability of EBS. (3)Supplemental Studies for joint study with NRIDP. At this fiscal year, the joint study with National Research Institute for Disaster Prevention (NRIDP) will be final stage. UP to this day, incremental validation studies had been continued using by mesuared data obtained from vibration test. In this final stage, validation analysis has been conducted again using by current version new analysis code and maintained the validation data which will be contribute to the joint study mentioned above.

JAEA Reports

Natural analogue of alteration of bentonite contacting with concrete

Imai, Jun*

JNC-TJ8400 2000-008, 113 Pages, 2000/03

JNC-TJ8400-2000-008.pdf:20.79MB

The objective of this research is to make clear long-term alteration processes of bentonite contacting with concrete under a repository condition for radioactive waste. The Uzu tunnel in yamagata prefecture in Japan, constructed during the term of December of 1963 to July 1967, was selected as an appropriate natural analogue: the tunnel wall was made of portland cement and which has been contacting with a bentonite bed during $$geq$$ 32 years. Sample analyses indicated that the original bentonite was Na$$^{+}$$-type and it changed to Ca$$^{2+}$$-type in the range of a few millimeters from the contact. Although a Ca$$^{2+}$$ leaching was also observed from the concrete near the contact, neither transformation to zeolite nor to illite was recognized. On the other hand, sulfur increased and ettringite (3CaO $$cdot$$ Al$$_{2}$$O$$_{3}$$ $$cdot$$ 3CaSO$$_{4}$$4 $$cdot$$ 32H$$_{2}$$O) was recognized in the concrete within the depth about 30 mm from the contact.

JAEA Reports

Research on engineering procedure and models on buffer materials

Amemiya, Kiyoshi*; TRAN DUC PHI OAN*; Yamashita, Ryo*

JNC-TJ8400 2000-056, 487 Pages, 2000/02

JNC-TJ8400-2000-056.pdf:16.24MB

JNC presented the 2$$^{nd}$$ progressive reports on HLW disposal system. The documents impressed the importance of developing the engineering procedures and the model evaluating the thermo-hydro-mechanical phenomena in waste disposal system. In this research, the methods filling the gap between buffer and rock or buffer and overpack were examined. Bentonite pellets were tested as the filling materials. In order to assess the full-scale system performance, the Japanese experiences of buffer mass experiments were compared with the Prototype Repository Project of SKB in Sweden. Father more, the thermo-hydro-mechanical (THM) code named TRAMES was validated at the international co-research programs of DECOVALEX II.

JAEA Reports

Research on engineering procedure and models on buffer materials

Amemiya, Kiyoshi*; TRAN DUC PHI OAN*; Yamashita, Ryo*

JNC-TJ8400 2000-055, 49 Pages, 2000/02

JNC-TJ8400-2000-055.pdf:4.15MB

JNC presented the 2$$^{nd}$$ progressive reports on HLW disposal system. The documents impressed the importance of developing the engineering procedures and the model evaluating the thermo-hydro-mechanical phenomena in waste disposal system. In this research, the methods filling the gap between buffer and rock or buffer and overpack were examined. Bentonite pellets were tested as the filling materials. In order to assess the full-scale system performance, the Japanese experiences of buffer mass experiments were compared with the Prototype Repository Project of SKB in Sweden. Father more, the thermo-hydro-mechanical (THM) code named THAMES was validated at the international co-research programs of DECOVALEX II.

132 (Records 1-20 displayed on this page)