scholarly journals Swelling Pressure and Permeability of Compacted Bentonite from 10th Khutor Deposit (Russia)

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 742
Author(s):  
Artur Yu. Meleshyn ◽  
Sergey V. Zakusin ◽  
Victoria V. Krupskaya
Keyword(s):  
Swelling Pressure ◽  
Crystalline Rocks ◽  
Hydraulic Gradient ◽  
Deep Geological Repository ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Geological Repository ◽  
Hydraulic Conditions ◽  
Hydraulic Gradients

Bentonites from the 10th Khutor deposit (Republic of Khakassia, Russia) are considered a potential buffer material for isolation of radioactive waste in the crystalline rocks of Yeniseyskiy site (Krasnoyarskiy region). This study presents the results of a series of permeameter experiments with bentonite compacted to dry densities of 1.4, 1.6, and 1.8 g/cm3, saturated and permeated by the artificial groundwater from Yeniseyskiy Site. Permeation was conducted at hydraulic gradients of 180–80,000 m/m to simulate potential hydraulic conditions in the early post-closure phase of a deep geological repository (DGR). The respective swelling pressures of 0.8 ± 0.3, 2.2 ± 0.6, and 6.3 ± 0.3 MPa and permeabilities of (27 ± 15) × 10−20, (3.4 ± 0.8) × 10−20, and (0.96 ± 0.26) × 10−20 m2 were observed for the hydraulic gradient of 2000 m/m, which is recommended for the determination of undisturbed swelling pressures and permeabilities in permeameter experiments. Upon incremental increases in the hydraulic gradient, swelling pressures at all densities and permeability at the density of 1.8 g/cm3 remained unchanged, whereas permeabilities at 1.4 and 1.6 g/cm3 decreased overall by a factor of approximately 5 and 1.7, respectively. Seepage-induced consolidation and/or reorganisation of bentonite microstructure are considered possible reasons for these decreases.

Coupling Swelling and Water Retention Processes in Compacted Bentonite

2011 ◽  
Vol 6 (1) ◽  
Author(s):  
Antti Lempinen
Keyword(s):  
Water Retention ◽  
Spent Nuclear Fuel ◽  
Effective Strain ◽  
Swelling Pressure ◽  
Model Parameters ◽  
Confined Water ◽  
Swelling Properties ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Swelling Factor

Compacted bentonite is the main candidate for buffer material in several plans for spent nuclear fuel repositories. One of its important properties is high swelling capacity, which is caused by interaction between water molecules and exchangeable cations. This interaction makes bentonite behave differently from capillary materials. In this article, a model for thermo-hydro-mechanical state of partially water saturated bentonite is presented. It couples the water retention and swelling properties with introduction of the swelling factor in effective strain. The Helmholz energy density determines the state with a relatively small set of independent parameters: swelling pressure, swelling factor, maximum confined water content and the reference state. The model parameters are determined from experimental data for FEBEX bentonite, and as a simple consistency check, confined suction curves are calculated and compared to test results. Consistency of the model with observations on nano- and microscale of bentonite is also discussed.

A Study on Gas Migration Behavior in Buffer Material using X-ray CT Method

2006 ◽  
Vol 932 ◽  
Author(s):  
K. Tanai ◽  
M. Yui
Keyword(s):  
Water Saturation ◽  
Gas Injection ◽  
Swelling Pressure ◽  
Digital Data ◽  
Migration Behavior ◽  
Gas Migration ◽  
Migration Test ◽  
X Ray ◽  
Compacted Bentonite ◽  
Buffer Material

ABSTRACTThis paper presents a study on gas migration behavior in a bentonite specimen with the aid of X-ray computer tomography (CT) scan data. The laboratory experiment was carried out to clarify gas migration behavior through saturated, compacted bentonite. X-ray CT was used to estimate the spatial distribution of gas and water saturation during gas migration test in the bentonite. For the gas migration test, the controlled flow rate of gas injection was adopted for pre-compacted samples of Kunigel V1 bentonite using helium gas, which is safer than hydrogen gas.A specimen was isotropically consolidated and saturated by synthetic seawater, simultaneously, by applying a backpressure. This was followed by injecting the gas using a syringe pump. Inlet and outlet gas fluxes were monitored. This test exhibited a significant threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure.The procedure of the X-ray CT measurement is as follows; i) measurement of the initial condition (saturated condition) of the compacted bentonite, ii) measurement of the gas injection condition as a function of time. The digital data obtained from the X-ray CT usually includes some noise. The stacking method can reduce the noise in CT values and enables to identify the gas migration area. The results indicate that gas is transported through preferential pathways in compacted bentonite, and is not homogenous.

New equations for swelling characteristics of bentonite-based buffer materials

2003 ◽  
Vol 40 (2) ◽  
pp. 460-475 ◽  
Author(s):  
Hideo Komine ◽  
Nobuhide Ogata
Keyword(s):  
Double Layer ◽  
Nuclear Waste ◽  
Van Der Waals ◽  
Swelling Pressure ◽  
Van Der Waals Force ◽  
Diffuse Double Layer ◽  
Mass Ratio ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Swelling Characteristics

Compacted bentonite and sand–bentonite mixtures are attracting greater attention as buffer material for repositories of high-level nuclear waste. This buffer material is expected to fill up the space between the canisters containing the waste and the surrounding ground by swelling. To produce the specifications, such as dry density, sand–bentonite mass ratio, and dimensions, of the buffer material, the swelling characteristics of compacted bentonite and sand–bentonite mixtures must be evaluated quantitatively. New equations for evaluating the swelling behavior of compacted bentonite and sand–bentonite mixtures are presented that can accommodate the influences of the sand–bentonite mass ratio and the exchangeable-cation composition of bentonite. The new method for predicting swelling characteristics is presented by combining the new equations with the theoretical equations of the Gouy–Chapman diffuse double layer theory and of the van der Waals force, which can evaluate the repulsive and attractive forces of montmorillonite mineral (i.e., the swelling clay mineral in bentonite). Furthermore, the applicability of the new prediction method has been confirmed by comparing the predicted results with laboratory test results on the swelling deformation and swelling pressure of compacted bentonites and sand–bentonite mixtures.Key words: bentonite, diffuse double layer theory, van der Waals force, nuclear waste disposal, swelling deformation, swelling pressure.

Flaw Acceptance Evaluation for the Final Disposal Canister Under Earthquake Induced Rock Shear

2019 ◽  
Author(s):  
Hsoung-Wei Chou ◽  
Szu-Ying Wu
Keyword(s):  
Crack Detection ◽  
Spent Nuclear Fuel ◽  
Global Model ◽  
Deep Geological Repository ◽  
Element Analysis ◽  
Final Disposal ◽  
Shear Loads ◽  
Buffer Material ◽  
Geological Repository ◽  
Loading Case

Abstract When a canister used for final disposal of spent nuclear fuel is in the deposition hole of deep geological repository, the loading case which would most impact the structure integrity of the canister is to postulate an earthquake induced rock shear through a deposition hole. This paper evaluates the acceptable sizes of defects in the cast iron insert of canister using fracture mechanics analysis. The submodelling technique of finite element analysis was employed to calculate the fracture behavior of the canister with postulated defects subjected to shear loads due to earthquake. At first, the stresses of the global model and the uncracked submodel were compared to check the correctness of the transferred displacements from the global model to the submodel. Then, surface and internal flaws with various shapes and depths were modeled individually in the submodel. A 5 cm shear displacement was applied on buffer and then transmitted to the canister. The calculations of J-integral of each flaw indicate that the surface semi-elliptical defect is more critical and the density of buffer material significantly affects the acceptable size of postulated defects. Present results can provide acceptance criteria of crack detection for canisters during manufacture and examination processes.

Multi-criteria site assessment process for candidate deep geological repository sites: Case study from the Czech Republic 

2021 ◽  
Author(s):  
Lukas Vondrovic ◽  
Jaromir Augusta ◽  
Antonin Vokal ◽  
Katerina Konopacova ◽  
Eva Popelova ◽  
...  
Keyword(s):  
Czech Republic ◽  
Assessment Process ◽  
Deep Geological Repository ◽  
Data Set ◽  
Site Assessment ◽  
The Czech Republic ◽  
Second Stage ◽  
Geological Repository

<p>The future deep geological repository for radioactive waste in the Czech Republic will be constructed in a suitable crystalline rock mass around 500 metres below the earth’s surface. The commencement of operation is planned for 2065. The current DGR development phase is devoted principally to the determination of the optimum disposal concept and the selection of the most suitable site. A total of nine potential sites have been assessed with the aim of reducing their number to four.</p><p>The data set subjected to assessment included site descriptions from the geological point of view (3D geological and hydrogeological model), and long-term site stability (seismotectonic, climate and erosion) and geomechanical data. A further assessed dataset included information on construction issues and on the evaluation of both environmental characteristics and the presence of groundwater resources. All the assessed characteristics were derived from surface-based exploration without the need for borehole drilling.</p><p>The key criteria reflected the three main areas of concern i.e. long-term and operational safety (including geological and hydrogeological indicators), technical feasibility and environmental impacts. The assessment of the sites was performed in two stages. The first stage involved the assessment of the probability of fulfilling the exclusion criteria (total 26), while the second stage involved the mutual comparison of the sites in terms of the defined key criteria (total of 13, divided into 38 indicators). The second stage involved the determination of weightings for the various criteria and indicators via the application of the SAATY method for the expert comparison of the significance of criteria. This method distinguished between relatively strongly weighted and less weighted criteria. The sites were graded with respect to the value estimation of the criteria; moreover, the grading of the sites considered various types of data.</p><p>A total of eight calculations were performed for five scenarios using various procedures for the estimation of the weightings and for data normalisation purposes. The first assessment stage indicated that all the sites fulfilled the DGR site assessment methodology requirements. The second stage, which comprised the assessment of the comparison of the site calculations (assessment grades) for each of the sites, was based on the levels of significance of the indicators and criteria and the resulting representative values for each site. The results of the subsequent comparison calculations indicated that the same four sites always occupied the first four positions with only minor variations in the order. The differences in the gradings of the four most suitable sites and the four relatively less suitable five sites ranged between 11% and 17.8% (between the fourth and fifth sites), which convincingly differentiated between the two groups of sites. One site was always in last position according to the calculations. In compliance with the assessment results, the four  sites were subsequently recommended to the Government of the Czech Republic for further follow-up research and analysis. Those sites that were not recommended for the next stage of research will continue to be considered as reserve (i.e. backup) sites.</p>

Pressure conditions in the hole erosion test

2015 ◽  
Vol 52 (1) ◽  
pp. 114-119 ◽  
Author(s):  
Jaromír Říha ◽  
Jan Jandora
Keyword(s):  
Shear Stress ◽  
Soil Erosion ◽  
Numerical Study ◽  
Critical Shear Stress ◽  
Technical Note ◽  
Hydraulic Gradient ◽  
Hydraulic Gradients ◽  
Erosion Test ◽  
The Difference

The hole erosion test (HET) is used in the study of soil erosion in the case of what is known as “piping” when concentrated leaks occur. The HET enables the determination of soil erosion characteristics such as the critical shear stress along the pre-formed hole (pipe) and the coefficient of soil erosion. Normally, in the HET, the hydraulic gradient is determined from the difference between the piezometric heads measured at the inflow and outflow chambers (upstream and downstream of the soil specimen). Hydraulic analysis shows that such measurements ignore losses at the entrance and exit of the hole, causing the overestimation of the hydraulic gradient along the length of the hole, and thus the calculated shear stress. In this technical note, the results of preliminary analysis using the Bernoulli principle and of numerical study of the pressure conditions in the HET apparatus are shown. The turbulent flow in the HET apparatus was calculated using ANSYS commercial CFD (computational fluid dynamics) software. The analysis was performed for various hole entrance shapes. The conclusion of this note details the differences between traditionally determined hydraulic gradients and those numerically derived along the length of a hole.

scholarly journals Low-suction water retention capacity of bentonite at high temperature

2020 ◽  
Vol 195 ◽  
pp. 04010
Author(s):  
María Victoria Villar ◽  
Carlos Gutiérrez-Álvarez ◽  
Pedro Luis Martín
Keyword(s):  
High Temperatures ◽  
Water Retention ◽  
Water Retention Capacity ◽  
Dry Density ◽  
Retention Capacity ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Hydraulic Gradients ◽  
Radioactive Waste Repositories ◽  
Waste Repositories

The study of the hydro-mechanical properties of compacted bentonite is relevant in the context of deep geological radioactive waste repositories, where bentonite will be used as buffer material between the waste canisters and the host rock and will be subjected to high temperatures and hydraulic gradients. This research aimed at determining the water retention curves of bentonite compacted at a repository-significant dry density (1.6 g/cm3) and at high temperatures (up to 100°C). This had been previously undertaken, but below suctions around 10 MPa the accurateness of the curves obtained was very low because of the methods and instruments used to determine them. To overcome this uncertainty, thermocouple psychrometers, which work properly in the low-suction range (below ~6 MPa), were tested. However, calibration showed that their performance was compromised when temperature rose above 60°C. Nevertheless, the results obtained were consistent with previous ones and allowed to confirm the decrease of water retention capacity with temperature. Additionally, it was checked that this decrease was more important for the low suctions.

Geochemical Processes at the Carbon steel/bentonite Interface in Repository Conditions

2006 ◽  
Vol 985 ◽  
Author(s):  
Elena Torres ◽  
María Jesús Turrero ◽  
Pedro Luis Martin
Keyword(s):  
Carbon Steel ◽  
Exchange Capacity ◽  
Spent Fuel ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Geological Repository ◽  
Geological Formation ◽  
Gaseous Corrosion ◽  
High Level

AbstractThe Deep Geological Repository (DGR) is currently the most accepted management option for the isolation of high level radioactive wastes. The DGR is based on a multibarrier system, which will limit releases of mobile radionuclides to the biosphere. In the design of the repository the spent fuel is encapsulated in canisters of carbon-steel. The space between the canister and the host geological formation will be filled with bentonite buffer clay. Under the prevailing conditions in a DGR, both localized and generalized corrosion phenomena are possible.Corrosion of the canister will result in formation of solid and gaseous corrosion products, which can influence the behaviour of both the canister and the bentonite. Many studies have been carried out in order to improve the knowledge on the reactivity of these barriers. Most of them have focused on the mineralogical alteration of the bentonite as a function of temperature, time, iron/clay and liquid/rock ratio in batch conditions. The aim of this study is to provide experimental evidences, at repository conditions, on chemical and mineralogical changes during the canister-compacted bentonite interaction: determination of secondary minerals and their alteration reactions, the advance of the corrosion front in the compacted bentonite, and changes in porosity, permeability and cation exchange capacity.

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.

Application of Elasto-Plastic Model to Mechanical and Hydraulic Behavior of Buffer Material Under Water Uptake in a Repository

1990 ◽  
Vol 212 ◽  
Author(s):  
T. Fujita ◽  
K. Hara ◽  
Y. Yusa ◽  
N. Sasaki
Keyword(s):  
Water Uptake ◽  
Mechanical Stability ◽  
Near Field ◽  
Swelling Pressure ◽  
Plastic Model ◽  
Hydraulic Behavior ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Swelling Coefficient ◽  
Engineered Barrier

ABSTRACTMechanical and hydraulic behavior of buffer material during water uptake in a repository is a major issue from the viewpoint of mechanical stability of engineered barriers and near-field conditions for performance assessment. This paper presents the results of hydraulic-mechanical modeling of buffer material and the simulations carried out on an engineered barrier system under water uptake.Hydraulic behavior of compacted bentonite of buffer material was modeled as moisture diffusion. An elasto-plastic model was applied to the deformation behavior of compacted bentonite, of which swelling pressure was described by swelling coefficient under restraint condition. The hydraulic diffusivity and swelling coefficient were given based on the result of swelling tests of KUNIGEL-V1 bentonite which contains about 50 % montmorillonite. Being used this model, simulations on re-saturation behavior of an engineered barrier system were carried out for the cases of water uptake from the whole surface of both crystalline and sedimentary rock and from partial surface of opening. The results are : (1) The hydraulic and mechanical behavior of compacted bentonite can be described by a swelling-elasto-plastic model. (2) The distribution of the water content depends on the water uptake conditions. (3) The deformation of compacted bentonite and the displacement of the overpack under water uptake are negligibly small.

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