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Journal Articles

Effect of collapse behavior on changes in swelling pressure of bentonite during swelling pressure test

Takayama, Yusuke; Sato, Daisuke*; Kikuchi, Hirohito*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 29(2), p.101 - 111, 2022/12

Swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. It has been reported that the swelling pressure obtained by swelling pressure test increases monotonically or temporarily decreases after increasing with the passage of the time depending on the initial water content. In this study, swelling pressure tests were conducted under several different initial water content conditions, and the change in wet density distribution inside the specimen during the swelling pressure tests was observed by X-ray CT measurement. It was confirmed that the presence or absence of collapse behavior and its magnitude affect the shape of the change in swelling pressure. When the collapse deformation was large, the amount of temporary decrease in swelling pressure was large. On the other hand, swelling pressure increased monotonically when there was no deformation due to collapse.

Journal Articles

Observation of collapse behavior of bentonite during swelling pressure test using X-ray CT measurement

Takayama, Yusuke; Kikuchi, Hirohito*

Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 77(3), p.302 - 313, 2021/09

Numerous swelling pressure tests have been conducted to understand the swelling properties of bentonite which is planned to be used as a buffer material in repositories for the geological disposal of radioactive waste. In this study, in order to clarify the cause of the decrease in swelling pressure during the swell-in pressure test period, the change in wet density distribution inside the specimen during the swelling pressure test was observed by X-ray CT measurement. It was supposed that this phenomenon was caused by the collapse inside the specimen. Furthermore, in order to confirm that collapse is generated by water absorption, the swelling deformation test was carried out under various load conditions. As a result, it was confirmed that collapse occurs even under the load conditions that are equal to or slightly smaller than the swelling pressure. These test data are expected to be used for validation of coupled analysis codes for evaluating the mechanical behavior of disposal facilities during re-saturation period.

JAEA Reports

Backfill material characteristics using the bentonite/excavated rock mixture in the Horonobe Underground Research Laboratory Project (Contract research)

Sugita, Yutaka; Kikuchi, Hirohito*; Hoshino, Emiko*

JAEA-Data/Code 2020-017, 39 Pages, 2021/01


In Japan, high-level radioactive waste (HLW) will be buried in a purpose built repository in deep underground. In the vertical disposal concept of HLW, nuclear waste canisters will be emplaced in excavated vertical disposal holes, surrounded by bentonite/sand mixture. And the galleries will be backfilled with bentonite/excavated rock mixture, which will be isolated with a concrete plug. Japan Atomic Energy Agency has performed swelling test, permeability test, thermal property measurement, uniaxial compression test, water potential measurement and infiltration tests to identify coupled thermal-hydraulic-mechanical-chemical behavior that will operate in the backfill material using excavated rock in the Horonobe Underground Research Laboratory (URL). The obtained data will be used to support an ongoing full scale, in-situ experiment being conducted in the Horonobe URL.

Journal Articles

A Study on applicability of elasto-plastic constitutive model to mechanical behavior of buffer material in salt water conditions

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.

Journal Articles

Mineralogical, physical and chemical investigation of compacted Kunigel V1 bentonite in contact with a steel heater in the ABM test package 1 experiment, $"A$sp$"o$ Laboratory, Sweden

Sasamoto, Hiroshi; Isogai, Takeshi*; Kikuchi, Hirohito*; Sato, Hisao*; Svensson, D.*

Clay Minerals, 52(1), p.127 - 141, 2017/03

 Times Cited Count:3 Percentile:11.48(Chemistry, Physical)

Compacted bentonite has been considered as a candidate of engineering barrier material in many countries for the safe disposal of high-level radioactive waste. SKB set up an in situ experiment (named ABM project) to compare the stability of different bentonites under the conditions exposed to an iron source and elevated temperature (up to 130$$^{circ}$$C as maximum) at the $"A$sp$"o$ Hard Rock Laboratory, Sweden. Results for the Japanese bentonite (Kunigel V1) are summarized in the present paper. Mineralogical investigation using X-ray diffraction (XRD) and X-ray spectroscopy (SEM-EDX) suggested that no indication of smectite transformation or newly formed clay phases were observed. However, a distinct change of exchangeable cations of smectite was indicated (i.e., from Na type to Fe type) in the bentonite at the vicinity of the steel heater. Physical investigation by measurements of hydraulic conductivity and swelling property suggested that no significant change occur in the bentonite even at the vicinity of the steel heater. Such results might be considered due to the limited portion affected by the iron-bentonite interactions and partially occurred ion exchange reactions. Chemical investigation based on the measurements of methylane blue (MB), cation exchange capacity (CEC) and exchangeable cations showed that the lateral distribution for these parameters were basically constant without the significant gradient.

JAEA Reports

The Distinct element analysis for swelling pressure test of bentonite; Discussion on the effects of wall friction force and aspect ratio of specimen

Shimizu, Hiroyuki*; Kikuchi, Hirohito; Tanai, Kenji; Fujita, Tomoo

JAEA-Research 2011-024, 74 Pages, 2011/10


For geological isolation systems for HLW, due to the lack of standardization of swelling test method for bentonite as a buffer material, the accuracy and reproducibility of the results are not sufficiently proved. In this study, bentonite swelling pressure test were simulated by newly developed distinct element method, and the effects of wall friction force and aspect ratio of bentonite specimen were discussed.

JAEA Reports

Survey on current status of laboratory test method and experimental consideration for establishing standardized procedure of material containing bentonite; Report of Collaboration Research between JAEA and CRIEPI (Joint research)

Tanai, Kenji; Kikuchi, Hirohito; Nakamura, Kunihiko*; Tanaka, Yukihisa*; Hironaga, Michihiko*

JAEA-Research 2010-025, 186 Pages, 2010/08


Bentonite-based material is used as one of the components of the LLW, TRU and HLW disposal facilities. Required characteristics of bentonite-based material are low permeability, swelling property, etc. Those are evaluated in many cases by laboratory test results. However the uncertainty exists in the evaluation of those characteristics in construction. Because even if the index of the dry density etc is the same, laboratory test results have variability. In addition, the uncertainty in construction has the possibility to increase the uncertainty of long-term evaluation of characteristics. On the other hand, several of laboratory test methods of bentonite are not standardized. So, this is a possibility that is one of the uncertain causes of the evaluation of characteristics of the bentonite. Therefore, it is hoped that the laboratory tests of bentonite are standardized. Therefore, this study analysis the uncertainty on the physical properties by laboratory tests and put together the problem and ponts of concern in the tests.

Journal Articles

Analytical study of the long-term mechanical deformation of the buffer on HLW disposal

Tanai, Kenji; Kikuchi, Hirohito

Proceedings of European Nuclear Conference 2010 (ENC 2010) (Internet), 5 Pages, 2010/05

JAEA Reports

Assessment on mechanical effect of engineering barrier system to fault movement, 2

Saito, Yuya; Tanai, Kenji; Kikuchi, Hirohito*; Hirai, Takashi*; Nishimura, Mayuka*

JAEA-Research 2008-010, 35 Pages, 2008/03


Site with the potential to adversely affect the performance of the disposal system should be avoided by site selection in Japan. On the other hand, according to Atomic Energy Commission, the possibility to occur the natural and artificial events suddenly should be examined. So it is important to examine about the critical state of the engineering barrier system (EBS) when if the fault move across the EBS. And this study helps to be understood by the nation. In this paper, we examined the influence of the velocity of fault movement by the model test, and tried to improve the precision of the simulation analysis. Test results showed that the total pressure of the buffer inside was about 20% decreased when the velocity was a one-tenth. And it is important to set the permeability of the near-field rock appropriately when simulating the behavior of the buffer material affected by fault movement.

JAEA Reports

Status of assessment tools on the performance guarantee contents of buffer material

Tanai, Kenji; Jintoku, Takashi*; Kikuchi, Hirohito*; Nishimura, Mayuka; Matsumoto, Kazuhiro*; Aoyanagi, Shigeo; Yui, Mikazu

JAEA-Research 2006-035, 32 Pages, 2006/06


In order to contribute to the safety standards and guidelines which a regulator decides, state-of the art assessment method is investigated and summarized in the table about performance guarantee contents of buffer material related to the mechanical support and protection of the overpack and rock matrix, and the retardation of radionuclide. In addition, examples of the assessment tool are described. In this report, summary of (1) basic properties of bentonite, including swelling properties, mechanical properties and hydraulic properties, (2) long-term behavior of bentonite, including creep deformation, penetration into host rock, erosion and alteration, (3) gas permeability, (4) colloid filtration and (5) mechanical stability of the near-field is described. Check points, assessment methods (based on the data obtained from the experimental results, the estimation value obtained from empirical equations and database, and the modeling calculations) and latest results of these R&D programs were also summarized.

JAEA Reports

The Study plan on applicability to actual geological environment conditions of the engineering technology for geological disposal of high level nuclear-waste through the second phases in Horonobe Underground Research Project

Aoyanagi, Shigeo; Yui, Mikazu; Tanai, Kenji; Kawakami, Susumu; Fujita, Tomoo; Taniguchi, Naoki; Shibata, Masahiro; Konishi, Kazuhiro; Nishimura, Mayuka; Kikuchi, Hirohito*; et al.

JAEA-Review 2006-014, 61 Pages, 2006/03


no abstracts in English

Journal Articles

Study of long-term behavior of engineered and geological barrier system

Aoyanagi, Shigeo; Oda, Yoshihiro; Sasamoto, Hiroshi; Shibata, Masahiro; Tanai, Kenji; Taniguchi, Naoki; Nishimura, Mayuka; Fujisaki, Kiyoshi; Kikuchi, Hirohito*; Matsumoto, Kazuhiro*

Hoshasei Haikibutsu Anzen Kenkyu Nenji Keikaku (Heisei-13-Nendo$$sim$$Heisei-17-Nendo) Kenkyu Seika Hokokushu, p.179 - 203, 2006/03

no abstracts in English

JAEA Reports

Permeation Behavior of Organic Matter in the Compacted Bentonite under Saline Condition

Tobitsuka, Sachiko; Kikuchi, Hirohito*; Matsumoto, Kazuhiro*; Iijima, Kazuki; Sato, Haruo

JNC TN8400 2005-019, 65 Pages, 2005/08


The permeation behavior of organic matter through a compacted bentonite was evaluated in low and high ionic strength condition. The concentration of organic matters eluting from bentonite was analyzed. Polyacrylic acid solutions (average molecular weight:15,000 or 450,000) were permeated during maximum 140 days to the compacted bentonite (Kunigel V1, 100%) at dry density 1.2 g/cm$$^{3}$$. In low ionc strength condition, polyacrylic acid sodium (MWave: 15,000) was detected after 70 days in the permeated solution. In high ionic strength condition, it was found after 52 days. Polyacrylic acid (MWave: 450,000) didn't permeate in the both of system. It indicates that organic matters less than MWave: 450,000 aren't filtrated by bentonite. It is supposed that the organic compound which can change its conformation to a chain-like structure, are not likely to be filtrated, even if its molecular weight is more than 15,000. In low ionic strength condition, the concentration of eluting organic carbon from bentonite is 7.4-12.5 mg /l. In high ionic strength condition it is 4.2-6.5 mg /l.

JAEA Reports

Basic Characteristic Test of Buffer / Backfill Material under Horonobe Groundwater Condition

Kikuchi, Hirohito*; Tanai, Kenji

JNC TN8430 2004-005, 96 Pages, 2005/02


By the second progress report (H12) on research and development for the geological disposal of HLW in Japan, Japan Nuclear Cycle Development Institute (JNC) extended the database on basic properties of compacted bentonite, and this was mainly obtained by using distilled water as test fluid. This report presents influence of Buffer and Backfill material on the Basic properties under Horonobe groundwater, which was simulated by use of synthetic seawater. In the Horonobe groundwater targeted in this report, the groundwater of GL-300m or less was used bore hole HDB-6 of the underground laboratory of Horonobe construction site neighborhood. In addition, it examined it by using distilled water, synthetic seawater, and NaCl solution. Experimental results are as follows ; 1)Swelling characteristics, Hydraulic characteristics, and Mechanical characteristics of the buffer material and backfill material specification decrease by the influence of saline water. The relationship between effective clay density and swelling stress is obtained by the following equation. The relationship between effective clay density and intrinsic permeability is obtained by the following equation. The relationship between effective clay density and unconfined compressive strength is obtained by the following equation. 2)Saline water doesn't influence the heat characteristic of the buffer material specification. The thermal conductivity and specific heat are appreciable by the relational expression that uses include water content that has been obtained so far.

JAEA Reports

Basic Characteristics Data Base of Buffer Material

Kikuchi, Hirohito*; Tanai, Kenji

JNC TN8450 2003-010, 18 Pages, 2004/02


For the buffer material of geological disposal of High-Level radioactive Waste (HLW) in Japan, it is expected to maintain its low water permeability, thermal conductivity, self-sealing, radionuclide sorption and retardation, chemical buffering, overpack support and stress buffering properties over a long period of time. Natural clay is mentioned as a material that can relatively satisfy above functions. Among the kinds of natural clay, bentonite when compacted is superior because (i) it has exceptionally low water permeability and properties to control the movement of water in buffer, (ii) it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (iii) it has the ability to exchange cations and to adsorb cationic radioelements. Japan Nuclear Cycle Development Institute has extended the basic characteristics data of buffer material as one of the base information required for safe regulation of a country and HLW disposal project. This report presents the basic characteristics data of the buffur material which JNC acquired by December, 2003 was collected as a collection of data.

JAEA Reports

Study on Proper Constitutive Model for Evaluation of Long Term Mechanical Behavior of Buffer Material

Hirai, Takashi; Tanai, Kenji; Kikuchi, Hirohito*; Shigeno, Yoshimasa*; Namikawa, Tsutomu*; Takaji, Kazuhiko*; Onuma, Satoshi*

JNC TN8400 2003-034, 158 Pages, 2004/02


The objective of this report is to make a proposal of the proper constitutive models and parameters for the evaluation of the long term mechanical behavior of the buffer material in the engineered barrier system. In the second progress report by JNC, it was reported that the well designed engineered barrier system is stable and safety on mechanical support of the overpack to ensure stability and stress which acts on the overpack by using analysis which based on the popular constitutive models for the general caly soils. However, the buffer material which has swelling characteristics is considered not to be ordinary clay soils. So it is necessary to select the reliable constitutive models again. Therefor the proper models were selected again systematically in the several models which have been used for the assessment of the behavior of clay soils and the simulation analysis on the laboratory tests were carried out by using these models. From the result of the simulation analysis it appeared that the selected two models were alike to assess the behavior of the buffer material and the parameters which need to simulate the consolidation tests are different from those for the triaxial compression tests. Finally the analysis was conducted to evaluate the effect of the swelling of the overpack by the collosion and the self weight which causes the sedimentation of the overpack. From the analytical result, it was clarified that two kinds of parameter sets are necessary to evaluate the deformation and the stress of the buffer material in the engineered barrier system.

JAEA Reports

Assessment on Bearing Capacity of Buffer Material to Overpack

Hirai, Takashi; Tanai, Kenji; Kikuchi, Hirohito*; Takaji, Kazuhiko*; Onuma, Satoshi*

JNC TN8400 2003-031, 48 Pages, 2004/02


The objective of this report is to clarify the characteristics of the bearing capacity of the buffer material against the deformation of the overpack in the engineered barrier system. In the second progress report by JNC, it was reported that the well designed engineered barrier system is stable and safety on mechanical support of the overpack to ensure stability and stress which acts on the overpack by some analysis. However, the degree of the capacity to the ultimate state and the background datas of the design are not necessary clarified in the report. Therefore it is considered to be mportant to assess the ultimate state and make the relationship clear between deformation and bearing capacity of the overpack in the engineered barrier system. So the scale test and the simulation analysis were carried out for the longitudinal deformation of the overpack in the saturated buffer material constrained by the host rock. From the result of the scale test and the analysis it appears that the bearing capacity is increasing with the deformation of the overpack even if the bearing capacity is over the yielding force and the relationship between deformation and bearing capacity can be approximately expressed by the simple fanction.

JAEA Reports

Heat Physical Properties Examination of Buffer Material (III)

Kikuchi, Hirohito*; Tanai, Kenji

JNC TN8430 2003-009, 27 Pages, 2003/12


Usualy, the specific heat of buffer material for the thermal analysis was calculated from the thermal conductivity and the thermal diffusivity measured by using a different measurement technique and different specimen. However, these point become factors of dispersion of data. It is necessary to measure such a thermal characteristics at the same time to a chiue the quality assurance of data and the staudardization of the selational equation.Therefore, the specific heat of bentonite and bentonite/sand mixtures material was calculated by the surface-source method which was able to measure the thermal conductivity and thermal diffusivity at the same time.Experimental results are as follows ;The thermal conductivity and the specific heat of buffer material increase as water content increase.The specific heat is corresponding the theoretical predict value obtained from the composition component of buffer material such as solid, liquid and gas phase.The thermal conductivity and the specific heat of buffer material is shown as a function of water content of buffer material.

JAEA Reports

Basic Examination of the Backfilling Material under Synthetic Seawater Condition

Kikuchi, Hirohito*; Tanai, Kenji; Sugita, Yutaka

JNC TN8430 2003-008, 31 Pages, 2003/11


In geological disposal of high-level radioactive waste, closure of repository is the technique of filling clearance using the backfilling material to preserve barrier performance of the engineered barrier system. One of the expecting behaviors of the tunnel backfilled with backfilling material is appearance of a clearance between backfilling material and concrete lining due to alteration of the concrete lining. Therefore, filling (swelling) performance is one of the required performances of the backfilling material. Then, basic examination of the backfilling material is performed. This examination focused on the feasibility of the backfilling material described in H12 report and the adequate bentonite/sand mixture to obtain conservative filling clearance performance.Results of the examination showed, under test conditions that 30% of the volume of concrete lining decreases due to alteration and such volume become clearance between the backfilling material and concrete lining, in distilled water condition, the specification (bentonite/sand mixture) of the backfilling material described in H12 report almost filled the clearance. However, in synthetic seawater, 50% and more bentonite was required to fill the clearance.Since this examination fixed the clearance, water stopping performance will be examined in next phase. Through the synthetic seawater examination, the basic clearance filling curve was obtained.

JAEA Reports

Preliminary Test on Filling Gap Behavior of the Swollen Buffer in the Engineered Barrier System (II)

Sugita, Yutaka; Kikuchi, Hirohito*; Tanai, Kenji

JNC TN8430 2003-007, 33 Pages, 2003/11


Laboratory tests considering the gap between the buffer and rock mass, in case of the installation of the block type buffer, that is one of the candidate option technique, in geological disposal of the high-level radioactive waste were performed.In case of swelling of the buffer with the gap, initial condition, swelling behavior and change of density after filled the gap of the buffer should be observed.

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