Fundamental Properties of Monolithic Bentonite Buffer Material Formed by Cold Isostatic Pressing for High-Level Radioactive Waste Repository

1999 ◽  
Vol 556 ◽  
Author(s):  
S. Kawakami ◽  
Y Yamanaka ◽  
K. Kato ◽  
H. Asano ◽  
H. Ueda
Keyword(s):  
Hydraulic Conductivity ◽  
Radioactive Waste ◽  
Swelling Pressure ◽  
Cold Isostatic Pressing ◽  
Small Samples ◽  
Isostatic Pressing ◽  
High Level Radioactive Waste ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
High Level

AbstractThe methods of fabrication, handling, and emplacement of engineered barriers used in a deep geological repository for high level radioactive waste should be planned as simply as possible from the engineering and economic viewpoints. Therefore, a new concept of a monolithic buffer material around a waste package have been proposed instead of the conventional concept with the use of small blocks, which would decrease the cost for buffer material. The monolithic buffer material is composed of two parts of highly compacted bentonite, a cup type body and a cover. As the forming method of the monolithic buffer material, compaction by the cold isostatic pressing process (CIP) has been employed.In this study, monolithic bentonite bodies with the diameter of about 333 mm and the height of about 455 mm (corresponding to the approx. 1/5 scale for the Japanese reference concept) were made by the CIP of bentonite powder. The dry densities: pd of the bodies as a whole were measured and the small samples were cut from several locations to investigate the density distribution. The swelling pressure and hydraulic conductivity as function of the monolithic body density for CIP-formed specimens were also measured.High density ( ρd: 1.4–2.0 Mg/m3) and homogeneous monolithic bodies were formed by the CIP. The measured results of the swelling pressure (3–15 MPa) and hydraulic conductivity (0.5–1.4×10−3 m/s) of the specimens were almost the same as those for the uniaxial compacted bentonite in the literature. It is shown that the vacuum hoist system is an applicable the handling method for emplacement of the monolithic bentonite.

scholarly journals Distinguishing between more and less suitable bentonites for storage of high-level radioactive waste

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 289-302 ◽  
Author(s):  
S. Kaufhold ◽  
R. Dohrmann
Keyword(s):  
Hydraulic Conductivity ◽  
Radioactive Waste ◽  
Swelling Pressure ◽  
Point Of View ◽  
Dry Density ◽  
Swelling Clay ◽  
High Level Radioactive Waste ◽  
Key Issues ◽  
The Individual ◽  
High Level

AbstractOne of today's big challenges is to store safely the increasing amount of high-level radioactive waste (HLRW) in the world. In some of the concepts devised for this challenge, bentonite, a natural swelling clay, plays a key role in encasing the canisters containing the waste. The use of bentonite as a geotechnical barrier in HLRWrepositories is a new venture; specifications to ensure either optimum performance or that a minimum standard is reached at least do not exist yet. The present study summarizes relevant research and discusses possible HLRW-bentonite specifications. The importance of these specifications for any given repositories has to be assessed on a case by case basis, depending on the concept being employed and any special circumstances for the individual repositories.Ten key issues were identified which were used to discuss bentonite specifications. In some of these key issues the optimum bentonite performance depended more on processing and production (compaction) than on the bentonite type (e.g.swelling pressure and thermal conductivity). In contrast, in some of the other key issues, the type of bentonite was found to influence possible specifications: the bentonite should not alter its mineral composition or its geotechnical parameters such as the swellability. Therefore, the bentonite should contain neither soluble nor reactive phases (e.g.organic matter, pyrite, gypsum). The structural Fe content of the smectites should be small because of the lesser stability and greater reactivity of the Fe-rich bentonites. Also, a large layer-charge density of the swelling clay minerals leads to less corrosion at the iron–bentonite interface (relevant if iron canisters are used). The hydraulic conductivity and swelling pressure can be tailored by compaction of the bentonite resulting in different dry densities. From an engineering point of view, a bentonite with least dependence of the hydraulic conductivity/swelling pressure on the dry density would be best. Using a bentonite which has been investigated extensively over many years means less uncertainty compared to unknown materials.

Swelling characteristics of bentonites in artificial seawater

2009 ◽  
Vol 46 (2) ◽  
pp. 177-189 ◽  
Author(s):  
Hideo Komine ◽  
Kazuya Yasuhara ◽  
Satoshi Murakami
Keyword(s):  
Radioactive Waste ◽  
Swelling Pressure ◽  
Radioactive Waste Disposal ◽  
Exchangeable Cation ◽  
Deformation Characteristics ◽  
High Level Radioactive Waste ◽  
Disposal Facility ◽  
Buffer Material ◽  
Swelling Characteristics ◽  
High Level

Bentonite is currently designated for use as a buffer material for the repository of high-level radioactive waste because such a material requires swelling characteristics to seal the waste. A high-level radioactive waste disposal facility may be built in a coastal area of Japan because transportation of this waste by ships is feasible. Therefore, it is important to investigate the effects of seawater on a bentonite-based buffer. This study is intended to investigate the influence of seawater on the swelling pressure and swelling deformation characteristics of five common types of bentonite. The experiments described herein clarify the relations between the influence of seawater grade and compaction density, type of exchangeable cation, montmorillonite content of the bentonite, and vertical pressure condition. Based on experimental results, suitable specifications have been defined for a bentonite-based buffer that can withstand the effects of seawater.

scholarly journals Alteration of compacted GMZ bentonite by infiltration of alkaline solution

Clay Minerals ◽  
2016 ◽  
Vol 51 (2) ◽  
pp. 237-247 ◽  
Author(s):  
Chen Bao ◽  
Guo Jiaxing ◽  
Zhang Huixin
Keyword(s):  
Radioactive Waste ◽  
Alkaline Solution ◽  
Chemical Properties ◽  
Swelling Pressure ◽  
Cementitious Materials ◽  
Gmz Bentonite ◽  
High Level Radioactive Waste ◽  
Buffer Material ◽  
Porosity And Permeability ◽  
High Level

AbstractConcepts for geological disposal of high-level radioactive waste usually include bentonite buffer materials. Numerous studies have been performed with most usingWyoming bentonite. Gaomiaozi (GMZ) bentonite has been selected as a potential buffer/backfill material for the deep geological repository of high-level radioactive waste in China. In this context, the highly alkaline environment induced by cementitious materials in the repository is likely to alter montmorillonite, the main clay mineral in GMZ bentonite. This alteration may result in deterioration of the physical and/or chemical properties of the buffer material. To acquire quantitative data which would allow us to assess the dissolution of montmorillonite and changes in the diffusivity of hydroxide ions as well as their effects on the swelling pressure and permeability of the compacted GMZ bentonite, an experimental study was conducted under highly alkaline (NaOH solutions with various pH values were used), simulated groundwater conditions. The GMZ bentonite also contains cristobalite which may also have been dissolved. The microstructure of the compacted bentonite samples after the experiments was determined by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDX) was carried out to identify mineralogical changes. At pH >13, the permeability of specimens increased significantly; the swelling potential decreased with increasing pH. Furthermore, the pore volume and pore size of GMZ bentonite changed when exposed to alkaline solution, resulting in an increase in porosity and permeability. The main alteration mechanisms of compacted GMZ bentonite undergoing infiltration by highly alkaline solution are likely to be dissolution and modifications in terms of the microstructure and mineralogy.

scholarly journals Thermal Conductivity of Compacted GO-GMZ Bentonite Used as Buffer Material for a High-Level Radioactive Waste Repository

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Yong-Gui Chen ◽  
Xue-Min Liu ◽  
Xiang Mu ◽  
Wei-Min Ye ◽  
Yu-Jun Cui ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Radioactive Waste ◽  
Water Content ◽  
Radioactive Waste Disposal ◽  
Dry Density ◽  
Gmz Bentonite ◽  
High Level Radioactive Waste ◽  
Buffer Material ◽  
High Level ◽  
Crucial Parameter

In China, Gaomiaozi (GMZ) bentonite serves as a feasible buffer material in the high-level radioactive waste (HLW) repository, while its thermal conductivity is seen as a crucial parameter for the safety running of the HLW disposal. Due to the tremendous amount of heat released by such waste, the thermal conductivity of the buffer material is a crucial parameter for the safety running of the high-level radioactive waste disposal. For the purpose of improving its thermal conductivity, this research used the graphene oxide (GO) to modify the pure bentonite and then the nanocarbon-based bentonite (GO-GMZ) was obtained chemically. The thermal conductivity of this modified soil has been measured and investigated under various conditions in this study: the GO content, dry density, and water content. Researches confirm that the thermal conductivity of the modified bentonite is codetermined by the three conditions mentioned above, namely, the value of GO content, dry density, and water content. Besides, the study proposes an improved geometric mean model based on the special condition to predict the thermal conductivity of the compacted specimen; moreover, the calculated values are also compared with the experimental data.

Manufacturing and Handling Techniques of the Monolithic Buffer Material for HLW Disposal

2001 ◽  
Author(s):  
Toshihiko Awano ◽  
Takeshi Kanno ◽  
Susumu Kawakami ◽  
Hiroyoshi Ueda ◽  
Takahiro Kimoto
Keyword(s):  
Radioactive Waste ◽  
Large Scale ◽  
Cold Isostatic Pressing ◽  
Large Block ◽  
Technical Feasibility ◽  
Geological Disposal ◽  
Buffer Material ◽  
Manufacturing Tests ◽  
High Level ◽  
Large Scale Tests

Abstract Small and large scale tests were performed to evaluate technical feasibility of the monolithic buffer material, defined as a large block of bentonite formed by the cold isostatic pressing, for geological disposal of high-level radioactive waste. Trial manufacturing tests up to approximately 70 [%]-scale of a Japanese disposal concept were carried out and emplacement tests were carried out by vacuum lifting and forklift-type methods for vertical and horizontal emplacement concepts, respectively. Based on the large engineering-scale tests, technical feasibility of the monolithic buffer was demonstrated.

Modeling Hydraulic Conductivity and Swelling Pressure of Several Kinds of Bentonites Affected by Salinity of Water

2010 ◽  
Author(s):  
Yukihisa Tanaka ◽  
Takuma Hasegawa ◽  
Kunihiko Nakamura
Keyword(s):  
Hydraulic Conductivity ◽  
Radioactive Waste ◽  
Ground Water ◽  
Quantitative Evaluation ◽  
Coastal Area ◽  
Evaluation Method ◽  
Saline Water ◽  
Swelling Pressure ◽  
Compacted Bentonite ◽  
Swelling Characteristics

In case of construction of repository for radioactive waste near the coastal area, the effect of salinity of water on hydraulic conductivity as well as swelling pressure of bentonite as an engineered barrier should be considered because it is known that the hydraulic conductivity of bentonite increases and swelling pressure decreases with increasing salinity of water. Though the effect of salinity of water on hydraulic conductivity and swelling pressure of bentonite has been investigated experimentally, it is necessary to elucidate and to model the mechanism of the phenomenon because various kinds of bentonites may possibly be placed in various salinities of ground water. Thus, in this study, a model for evaluating hydraulic conductivity as well as swelling pressure of compacted bentonite is proposed considering the effect of salinity of water as follows: a) Change in number of flakes of a stack of montmorillonite because of cohesion. b) Change in viscosity of water in interlayer between flakes of montmorillonite. Quantitative evaluation method for hydraulic conductivity and swelling characteristics of several kinds of bentonites under saline water is proposed based on the model mentioned above.

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