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Bentonite is utilized as a barrier material in high-level nuclear waste repositories due to its superior low permeability and swelling properties. However, its engineering properties are influenced by the chemical composition of the infiltrating pore water during operation. Understanding the effect of salt solution on the mechanical properties of bentonite is crucial for evaluating the performance of buffer and backfill barriers in deep geological repositories for nuclear waste. In this study, various concentrations and types of salt solutions were used to treat Na-bentonite samples, which were then subjected to free swell test, no loading swelling ratio test, Atterberg limits test, compaction test, and analysis of the content of exchangeable cations. The results showed that the content of counterbalance cations changed significantly after the addition of salt solution, and the decrease in free swelling rate increased gradually with the increase of solution concentration. The effect of different types of salt solutions on swelling was primarily determined by the type of cation that governs charge level and hydration capacity. The inhibition of the free swelling rate was stronger for high-concentration low-valence salt solution than that for low-concentration high-valence one. Bentonites undergoing cation exchange exhibited a decreased plasticity index, a decreased maximum dry density, and an increased optimum water content. This was mainly due to the cation exchange that occurred between bentonite layers under the action of the salt solution, which affected the crystal layer structure, double electric layer structure, and intergranular stress. Finally, the van’t Hoff equation was used to quantitatively characterize the differences in swelling in the test results. [ABSTRACT FROM AUTHOR]

Bentonite is an integral part of the engineered barrier system (EBS) in deep geological repositories (DGR) for nuclear waste, but its indigenous microorganisms may jeopardize long-term EBS integrity. To predict microbial activity in DGRs, it is essential to understand microbial reactions to the early hot phase of DGR evolution. Two bentonites (BCV and MX-80) with varied bentonite/water ratios and saturation levels (compacted to 1600 kg.m− 3 dry density/powder/suspension), were subjected to heat (90–150 °C) and irradiation (0.4 Gy.h− 1) in the long-term experiments (up to 18 months). Molecular-genetic, microscopic, and cultivation-based techniques assessed microbial survivability. Exposure to 90 °C and 150 °C notably diminished microbial viability, irrespective of bentonite form, with negligible impacts from irradiation or sample type compared to temperature. Bentonite powder samples exhibited microbial recovery after 90 °C heating for up to 6 months but not 12 months in most cases; exposure to 150 °C had an even stronger effect. Further long-term experiments at additional temperatures combined with the mathematical prediction of temperature evolution in DGR are recommended to validate the possible evolution and spatial distribution of microbially depleted zones in bentonite buffer around the waste canisters and refine predictions of microbial effects over time in the DGR. [ABSTRACT FROM AUTHOR]

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Evaluation of the stability of placement rooms and excavation damage in the surrounding geological formations of a deep geological repository (DGR) for high-level nuclear waste are essential components when assessing the overall repository performance. Assessment of the geomechanical performance of placement rooms for the duration of the regulatory period (typically 1 million years) usually involves simulations using numerical models capable of simulating coupled thermo-hydro-mechanical (THM) processes induced by different natural and repository-induced perturbations over different time and length scales. The numerical constitutive model used to represent the host medium should be capable of capturing highly nonlinear responses to stress changes, including development of damage and fracturing. In this paper, a novel approach for simulating the evolution of damage and fracturing around the repository rooms considering coupled THM processes is presented, including validation examples for the approach. The important and novel feature of this modeling approach is the use of the bonded-block model based on the distinct element method (DEM) to represent deformation, damage, and fracturing of the surrounding rock that could potentially result in rock fragmentation and collapse of the rock surrounding the placement rooms. As part of the study, the predictions of damage around placement rooms obtained using the new approach are compared with the conventional continuum mechanics model. Subsequently, the capability of the bonded-block model to simulate damage caused by in-situ and thermally induced stresses is validated by comparison with monitoring data and observations from field-scale experiments. Highlights: A novel numerical approach for modeling thermo-hydro-mechanical processes taking place around deep geological repositories is presented. The approach uses a coupling scheme that allows simulations of times relevant for performance assessment of the repositories. Formation of stress-induced microcracks and their effect on permeability changes and long-term stability of the rooms are explicitly simulated. The methodology is validated by comparison with field data and with a different numerical method. [ABSTRACT FROM AUTHOR]

Deep geological disposal is currently the preferred method of treating high-level nuclear waste (HLW). A compacted bentonite buffer layer is established between the HLW canister and the surrounding rock to prevent nuclear leakage. However, the liquid in the cracks of surrounding rocks usually contains a variety of chemical substances, so it is necessary to evaluate the mechanical properties of bentonite in a chemical environment and the changes in its microstructure. Ensure the long-term stability of the repository in complex underground systems. To figure out the effect of groundwater pore solution on the mechanical properties and microstructure of bentonite, the compacted GMZ07 bentonite specimens were saturated and consolidated at different concentrations of Na2SO4 solutions, followed by a direct shear test. The laser particle analysis (LPA) and scanning electron microscope (SEM) were conducted to evaluate the microstructural changes. The results showed that the surface of bentonite particles was fine-grained in Na2SO4 solutions. As the concentration of the solution increases, the bentonite particle size decreases, which makes the connection of the bentonite particles tighter and easier to flocculate. Macroscopically, it shows the decrease in volume and the increase in strength of bentonite specimens. [ABSTRACT FROM AUTHOR]

Compacted bentonite is used as a buffer or backfill material in deep geological repositories. However, the seepage of pore water containing various salt and minerals can affect the hydro-mechanical performance of the bentonite. To investigate these effects, samples of compacted bentonite with initial dry densities of 1.50 Mg·m−3 and 1.70 Mg·m−3 were subject to saturation by distilled water, and solutions of NaCl and NaOH (0.1 M and 1.0 M), and the changes in swelling pressure and microstructure were monitored. The swelling pressure was seen to reduce with greater concentrations of the salt solution or when the initial dry density was decreased. At lower salt concentrations, the variation of the swelling pressure exhibited a double-peak, while further increases in the salt concentration caused the swelling pressure curve to exhibit only a single-peak. Compared to samples with a 1.7 Mg·m−3 dry density, the large swelling pressure decreased following the initial peak, and a smaller second peak was observed for samples with a 1.5 Mg·m−3dry density. The swelling pressure of samples saturated with NaOH solutions was notably lower, particularly after the second peak in the double-peaked curves. Applicable empirical kinetic equations were proposed to fit the relationship between the swelling pressure (p, MPa) and time (t, h) of the compacted sample saturated with DW and aqueous NaCl and NaOH. Microscopic analyses provide evidence that this reduction of swelling pressure could be attributed to the osmotic consolidation, ionic exchange, and mineral dissolution of bentonite. [ABSTRACT FROM AUTHOR]

Deep geological repositories (DGRs) are considered the most promising technology for the long-term management of nuclear wastes. One of the major functions of the buffer or barrier material used in DGRs for nuclear waste is to prevent the release of high-level radioactive chemicals into the environment in the event of failure. To accomplish this, the buffer is typically designed to have very low hydraulic conductivity. The effects of mix-composition, swelling condition, temperature and groundwater chemistry on the hydraulic conductivity of compacted bentonite–sand barrier material were investigated in this study. Permeability tests were carried out using flexible wall permeameter after flooding the compacted samples in simulated groundwater. The obtained results showed that the saline groundwater prevailing in the Guelph region of Canada as well as high temperature have a negative impact on the swelling potentials of the buffer material, consequently increasing the hydraulic conductivity. The saline water reduces the thickness of the diffuse double-layer which is accompanied by a weak repulsion between the clay minerals. Similarly, elevated temperature decreases the basal spacing between the bentonite clay minerals which also results in less swelling. The combination of high temperature and salt concentration have an increased negative influence on the hydraulic conductivity. Furthermore, it was observed that restricting the swelling of the bentonite–sand mixture produces a well-packed material with a very low hydraulic conductivity compared to the free swelling. High confining pressure generates higher swelling stress from the hydration of clay minerals, which expand to fill the voids between the sand particles. It was also observed that increasing the percentage of bentonite and the initial dry density of the mix reduced the hydraulic conductivity by eliminating interparticle voids in the material. The research findings presented in this manuscript provide valuable information that will contribute to gain a deeper insight into the impact of field conditions (temperature, groundwater chemistry, confinement) and material characteristics (composition, dry density) on the permeability of bentonite–sand barrier, which is essential for a safe long-term management of radioactive wastes. [ABSTRACT FROM AUTHOR]

During recent decades, argillaceous sedimentary formations have been studied as potential host formations for the geological disposal of long-living and heat-emitting radioactive waste—Boom Clay in Belgium and Opalinus Clay and Brown Dogger in Switzerland. A significant issue in the long-term performance of these potential host rocks concerns the generation and transport of gases. The pressure resulting from the generation of gas in an almost impermeable geological medium in the near field of a repository will increase. Under high gas pressures, the mechanical and hydraulic properties of the host rock are expected to change significantly. Preferential gas pathways may develop which exploit material heterogeneity, anisotropy (bedding planes), rock discontinuities, or interfaces between the different components of the repository, and may eventually lead to the release of the produced gases. Gas flow through these clayey rocks is investigated on the basis of laboratory work. Priority has been given to studying the volume change response of these initially water-saturated materials through relatively fast and controlled volume-rate gas injections. The effect of the gas injection rate, the confining pressure and the bedding orientation on the gas transport properties have been studied with particular attention paid to the coupling with strain behaviour. The results have shown features common to the three formations concerning the gas transfer process through preferential pathways, despite their initially differential properties. [ABSTRACT FROM AUTHOR]

Compacted bentonite–sand mixtures are commonly considered as the key materials for the construction of engineered barrier systems (EBSs) in deep geological repositories (DGRs) in Canada and other countries. These bentonite-based barriers can be simultaneously exposed to a wide range of chemical and thermal (nuclear waste heat decay) conditions of underground water. Thus, an understanding of the effects of groundwater chemistry and temperature and their interactions on the changes in the swelling properties as well as the microstructure of bentonite-based barriers is essential for assessing the durability and safety of an EBS in a DGR. This study experimentally investigates the impact of a Canadian deep underground water chemistry (C; total dissolved solids up to 300 g/L), temperature (T; 23 °C, 40 °C, and 80 °C), and the coupled effects of C and T on the swelling properties and microstructure of bentonite–sand barrier mixtures (30 to 70% by weight). The results show that the groundwater chemistry of southwestern Ontario (Canada) has a significant impact on the swelling characteristics of the examined bentonite–sand material. The swelling ability significantly decreases with respect to the groundwater chemistry. The mineralogical composition of the bentonite changes. Most of the Na-montmorillonite is mainly transformed to Ca-montmorillonite and traces of illite with a lower swelling capacity when the bentonite–sand barrier material is exposed mixed to saline water solutions. The temperature (alone) has a limited effect. However, the temperature–groundwater chemistry interactions significantly affect the swelling capacity of the studied bentonite–sand material. Future safety assessments and the final engineering design of engineered barriers for DGRs in Ontario should take into consideration the possibility of the long-term deterioration of bentonite–sand barriers from chemical attacks and/or thermochemical attacks induced by the high salinity of the groundwater and by simultaneous impact of the chemistry of the groundwater and the heat generated by the nuclear wastes, respectively. [ABSTRACT FROM AUTHOR]

Gaomiaozi (GMZ) bentonite has been considered as a potential material for construction of engineering barrier in Chinese deep geological repository for disposal of high-level nuclear wastes. In the present work, thermal conductivity tests were conducted on statically compacted GMZ bentonite specimens using the needle probe method. Cubic specimens with different initial saturation degrees and dry densities were prepared and the thermal conductivity tests were conducted along the directions both parallel and perpendicular to the bedding plane of the specimen. Results show that the thermal conductivity nonlinearly increases with increasing saturation degree with a transition point that proximately corresponding to the air entry value. Meanwhile, the thermal conductivity along the parallel direction is much higher than that along the perpendicular direction. The anisotropy coefficient decreases with increasing saturation. However, the anisotropy coefficient increases with increasing dry density and the influence depends on saturation degree. [ABSTRACT FROM AUTHOR]

Gaomiaozi (GMZ) bentonite has been recognized as the first choice for using as buffer/backfill material in deep geological repository for the disposal of high-level nuclear waste in China. High salinity and high pH of the pore solutions may cause changes in the mineralogical composition, and the swelling capacity of the bentonite results in affecting the long-term performance of the engineering barrier system. In the present work, a series of hydrothermal reactivity experiments were performed using batch reactors at 20, 35 and 80 °C for evaluating the chemical and mineralogical responses of GMZ bentonites. The results show that the dissolution of smectite releases Si and Al under the conditions of 1 M KOH at 35 and 80 °C and the released Si and Al may work as a cementing agent in GMZ bentonite. XRD pattern results show that alteration of the GMZ bentonite is expected to be insignificant for reaction with NaCl, KCl and NaOH solutions under low temperatures. However, it is obviously reacted with KOH solutions especially at 80 °C, during which cementitious material was produced leading to kaolinitization. When contacted with KOH solutions, the basal spacing (d001) of the main primary diffraction peaks (001) value of GMZ bentonite increases with increasing temperature. Salinity also can influence the smectite stability and accordingly loss of swelling capacity. This conclusion could be explained by the diffusing double-layer effects induced by salt solutions and ion exchange. [ABSTRACT FROM AUTHOR]

In this study, the effect of contact time, pH, competitive cations and equilibrium study of adsorption on Slovak illite/smectite Dolná Ves was investigated. The sorption processes was studied using batch techniques under aerobic conditions with radioisotope indication using Ni as a radiotracer. Studied material has proved to be as promising candidate for practically used as a barrier against the spread of undesirable substances in the environment landfill as insulating material of toxic and hazardous waste. [ABSTRACT FROM AUTHOR]

Radioisotope of nickel Ni is an important product of the neutron activation in engineering materials of nuclear power plants. Adsorption of nickel on Slovak rhyolitic bentonites Jelšový potok, Kopernica and Lastove was studied using batch method. Radionuclide Ni was used as a tracer. In this paper, we focused on effects of contact time, pH, competitive cations and equilibrium study. This study showed that Slovak rhyolitic bentonites are a promising candidate for removal of radionickel from aqueous solutions. [ABSTRACT FROM AUTHOR]

Adsorption of nickel on Slovak andesitic bentonite Lieskovec was studied using batch method. As a tracer was used radionuclide Ni. In this paper, we focused on effects of contact time, pH, competitive cations and equilibrium study using Langmuir model. Studied material has proved good adsorption ability and it can be used in the field of waste management for removal of radionickel from aqueous solutions. [ABSTRACT FROM AUTHOR]

The high potential of bentonites to volume changes depending on the water content is considered as their advantage for the engineered barriers in the deep geological repository of high-level radioactive waste and spent nuclear fuel because of swelling and self-healing of cracks in contact with water. On the other hand, drying may lead to opening of cracks and spaces between the bentonite blocks. This would increase the permeability and contamination risk around the hot container with high-level radioactive waste and spent nuclear fuel, especially if the host rock mass is dry. First shrinkage tests on four Slovak bentonites studied for engineered barriers were carried out. The water content at the shrinkage limit and the relative linear shrinkage are the first available shrinkage parameters received for the bentonite paste. The shrinkage hazard is higher in the best bentonites with high swelling potential-from Kopernica and Jelšový potok. The results indicated the necessity of further shrinkage tests to determine the relative linear and volume shrinkage of bentonite elements pressed of the loose bentonite powder of low water content. [ABSTRACT FROM AUTHOR]

The performance and safety assessment and technology demonstration are the main objectives of research programs for feasibility studies for deep geological repository of radioactive waste. In this context, the French national radioactive waste management agency (ANDRA) started to develop the Meuse/Haute-Marne underground research laboratory (URL) at Bure, nearly 300 km East of Paris. The host formation consists of a Callovo-Oxfordian claystone found between 420 and 550 m below ground, overlain and underlain by poorly permeable carbonate formations. One of the major concerns related to performance assessment is the excavation-induced fractures which may provide groundwater preferential pathway for radionuclide migration. The extent of the fractures possibly acting significantly in the radionuclide migration is known as the excavation damaged zone (EDZ). A scientific study on the EDZ characterization is performed at the main level of the URL (−490 m). Observations such as structural analysis on core, overcored resin-filled samples, geological survey of the drift face and sidewalls, were made to better understand the fracture network characteristics, extent and its generation. Pulse and constant head test hydraulic conductivity measurements were performed with multi packer system to estimate the extension of the EDZ hydraulic conductivity. Fractures exhibited high transmissivity near the excavation walls, but farther from the exaction walls, shear fractures showed hydraulic conductivity values reflecting values of undisturbed or slightly disturbed rock mass condition. The major findings in terms of geometry and properties of excavation-induced fractures are discussed in detail in this paper. For example, it is observed that the shape of the fracture network depends on the orientation of the drift in relation to the orientation of the in situ stress field. [ABSTRACT FROM AUTHOR]

Radionuclide adsorption on clay rocks has in recent years been studied mainly in connection with their use as sealing barriers in nuclear waste and spent nuclear fuel repositories. In Slovakia we find deposits of bentonites which should be used for the above mentioned purpose. The usability of adsorbents in practical applications depends on the speed of the adsorption process of the adsorbate on the adsorbent surface and distribution ratio. The work objective was the study of the kinetics of Sr adsorption on clay adsorbents with different geological origin. The geological origin of bentonite significantly influences its mineralogical and chemical composition and therein its adsorption properties. The adsorption process of strontium was fast. Adsorption equilibrium was reached for all three samples studied within 1 min from the beginning of the contact between solid and liquid phases. After the adsorption equilibrium was reached there were no more changes in the values of distribution coefficients and the adsorption percentage, and comparable values were reached in the contact-phase time span studied within 10 days. The values of adsorbed strontium were decreasing in the following order: J250 > L250 > DV45. The pseudo second-order kinetic models was used to describe model the kinetic data and provided excellent kinetic data fitting ( R > 0.999). [ABSTRACT FROM AUTHOR]

Bentonites which are characterized by good rheological, mineralogical and chemical stability is considered used as sealing barriers in multibarrier Slovak system of deep geological repository for high-level radioactive waste and spent nuclear fuel. In Slovak Republic there are several significant deposits of bentonite, which are characterized by appropriate adsorption properties and meet the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites and other smectites is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, radioisotopes Cs and Cs. The present paper investigates and compares the cesium adsorption properties of Slovak and North America bentonites composed mainly of dioctahedral smectite montmorillonite (J, L, SAz-1 and STx-1) and trioctahedral smectites saponite (SapCa-2) and hectorite (SHCa-1). [ABSTRACT FROM AUTHOR]

Slovak bentonites characterized by good rheological, mineralogical and chemical stability are considered as suitable sealing barriers for construction of Slovak deep geological repository for high-level radioactive waste and spent nuclear fuel. There is several Slovak bentonite deposits, bentonites of which have appropriate adsorption properties meeting the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites (mainly smectites) is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, β-emitter Sr with long half-life, biological half-life and high mobility. The present paper investigates and compares the strontium adsorption properties of bentonites of different mineral composition consisted mainly of dioctahedral and trioctahedral smectites. [ABSTRACT FROM AUTHOR]

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (Cs and Sr), prior to and after irradiation of bentonites with a Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelšový potok, Kopernica, Lastovce, Lieskovec and Dolná Ves. The EPR spectra of bentonites from deposits Jelšový potok and Lieskovec with absorbed doses of 10 and 10 Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe-bentonite from deposit Lieskovec and Ca-Mg-bentonite from deposit Jelšový potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude. [ABSTRACT FROM AUTHOR]

The basic strategic aims in the field of managing high-level radioactive waste and liquidation of nuclear power plants are all contained in the Energy policy of the Slovak Republic. Its aim is to resolve the concept of the backside of the nuclear energetics fuel cycle-long-term deposition of high-level radioactive waste and spent nuclear fuel (SNF). The most important form of high-level radioactive waste and SNF long-term deposition is their deposition in deep geological formations created by natural as well as engineering barriers used to isolate the long-lived radionuclides from the biosphere. The basic components of these barriers are clays, of which bentonite is generally referred to as the most suitable clay material. There are a few significant bentonite deposits in the Slovak Republic: Jelšový potok, Kopernica, Lastovce, Lieskovec, Dolná Ves. The review article summarizes the information on geotechnical properties of Slovak bentonites published up-to-date, which is inevitable to know for the intention of their use. It highlights the advantages and shows drawbacks of five Slovak deposits. It suggests further research direction, to draw a thorough hydraulical, microbial and radiation profile of Slovak bentonites. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of illitic clay minerals from Slovak deposit suitable for application in engineering barriers for high level radioactive waste repositories and spent nuclear fuels were studied. The isolation of spent nuclear fuels and high level radioactive wastes from the outer environment in a deep repository is gained by means of a system of multiple engineering and natural sealing barriers. Vital segments in a multiple barrier system are clay rocks, of which bentonites represent the most suitable clay material. Cs-adsorption on fine fractions of adsorbents (bentonites from three Slovak deposits: Jelšový potok J15, Kopernica K15, Lieskovec L15 and montmorillonite K10) has been studied with using batch of radiometric techniques. Adsorption parameters have been determined for adsorbent-cesium solution system as a function of contact time and adsorbate concentration. The influences of pH change, the effect of competitive cations, complex-forming organic chelating agents on the adsorption of Cs have also been studied. [ABSTRACT FROM AUTHOR]

The influence of chemical activation–natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space. [ABSTRACT FROM AUTHOR]

Bentonite is a natural clay and one of the most promising candidates for use as a buffer material in the geological disposal systems for spent nuclear fuel and high-level nuclear waste. It is intended to isolate metal canisters with highly radioactive waste products from the surrounding rocks because of its ability to retard the movement of radionuclides by adsorption. Slovak Republic avails of many significant deposits of bentonites. Adsorption of Cs on five Slovak bentonites of deposits (Jelšový potok, Kopernica, Lieskovec, Lastovce and Dolná Ves) has been studied with the use of batch technique. In the case of Dolná Ves deposit, the mixed-layer illite–smectite has been identified as the main clay component. Natural and irradiated samples, in two different kinds of grain size: 45 and 250 μm have been used in the experiments. The adsorptions of Cs on bentonite under various experimental conditions, such as contact time, adsorbent and adsorbate concentrations have been studied. The Cation Exchange Capacity values for particular deposits drop in the following order: Jelšový potok > Kopernica > Lieskovec > Lastovce > Dolná Ves. Bentonites irradiated samples with 390 kGy have shown higher specific surface and higher values of the adsorption capacity. Distribution coefficients have been determined for bentonite-cesium solution system as a function of contact time and adsorbate and adsorbent concentration. The data have been interpreted in terms of Langmuir isotherm. The uptake of Cs has been rapid and the adsorption of cesium has increased with increasing metal concentrations. The adsorption percentage has decreased with increasing of metal concentrations. Adsorption of Cs has been suppressed by presence of Ca2+ more than Na+ cation. Sorption experiments carried out show that the most suitable materials intended for use as barriers surrounding a canister of spent nuclear fuel are bentonites of the Jelšový potok and Kopernica deposits. [ABSTRACT FROM AUTHOR]

In this study the cesium sorption on two different bentonites (Ca-Mg bentonite Rokle and Na bentonite Volclay KWK 20-80) has been compared using two different experimental approaches — batch and diffusion methods. The distribution coefficients (Kds) calculated for variable liquid-to-solid ratio (batch) and dry density (diffusion) were evaluated with respect to the main uncertainties affecting both approaches. It has been concluded that there are significant differences between selected bentonites in mineral composition, cation exchange capacity (CEC) and sorption characteristics. The Kd values calculated from batch sorption and diffusion data were found comparable only for Na bentonite Volclay KWK 20-80. The considerably higher sorption of Cs on Ca-Mg bentonite Rokle was explained by its higher content of cesium-selective sorbents (illite, vermiculite). [ABSTRACT FROM AUTHOR]