• Tunnel and Underground Space
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• v.20 no.4
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• pp.284-291
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• 2010

In the present design concept of a high-level waste repository, the bentonite and bentonite-sand mixture are considered as the buffer and backfill material. For the Kyungju bentonite which is a candidate material, the thermal conductivities of compacted bentonite and bentonite-sand mixture were measured. A correlation has been proposed to predict the thermal conductivity of the Kyungju bentonite and the bentonite-sand mixture as a function of the dry density, the water content and the sand fraction. The proposed correlation can predict the thermal conductivity with a difference less than 10% under the experimental conditions.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.2
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• pp.101-109
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• 2008

For the Kyungju bentonite which is considered as a candidate material for the buffer and backfill in the high-level waste repository, the thermal conductivities of compacted bentonite and a bentonite-sand mixture were measured. The thermal conductivities of the compacted bentonites with a dry density of 1.2 to $1.8\;Mg/m^3$ and the bentonite-sand mixture with a dry density of 1.6 and $1.8\;Mg/m^3$ were measured within the gravimetric water content range of 10wt% to 20wt% and the sand fraction range of 10 to 30wt%. The thermal conductivity of compacted bentonite and a bentonite-sand mixture increases with increasing dry density and sand weight fraction in the case of constant water weight fraction, and increases with increasing water weight fraction and sand weight fraction in the case of constant dry density. The empirical correlations to describe the thermal conductivity of compacted bentonite and a bentonite-sand mixture as a function of water fraction at each dry density were suggested. These correlations can predict the thermal conductivities of bentonite and a bentonite-sand mixture with a difference below 10%.

• Journal of the Korean Geosynthetics Society
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• v.18 no.2
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• pp.1-10
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• 2019

This study was intended to evaluate the water permeability and structure for calcium bentonite-sand mixtures to utilize calcium bentonite as a liner. This study conducted physico-chemical properties tests, compaction tests, permeability test and Scanning Electron Microscopy analysis (SEM) analysis. It was found the higher the ratio of calcium bentonite, the lower the dry density with coefficient of permeability, and the higher the optimum moisture content. In particular, SEM analysis was found the higher the ratio of calcium bentonite, the higher the area of the montmorillonite particles. In conclusion, the optimum coefficient of permeability that finds the landfill liner condition (must be less than $1{\times}10^{-7}cm/sec$) was obtained when the ratio of calcium bentonite was 40% or higher. These findings may improve the understanding of the calcium bentonite as a liner. Calcium bentonite shows a similar permeability to sodium bentonite 7% when mixed at 40% or more. Therefore, it is considered that calcium bentonite can be utilized as a liner.

• KCID journal
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• v.5 no.1
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• pp.63-74
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• 1998

This study was performed to evaluate the hydraulic conductivity of sand-bentonite mixtures according to 8 kinds of the bentonite content using the reassembled air-entry permeameter. Results obtained are as follows: 1. The maximum dry density and optimum m

• KCID journal
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• v.5 no.2
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• pp.9-19
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• 1998

A series of model tank and rigid wall permeameter tests was performed in order to determine the long-term hydraulic conductivity of the sand-bentonite liners reinforced by geotextile. Main conclusions are as follows 1. The maximum dry density and optimum

• Geotechnical Engineering
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• v.13 no.2
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• pp.17-28
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• 1997

In this study sodium chloride solution is employed for chemicals, and several cylindrical triaxial tests are performed on the sand-bentonite mixtures saturated with sodium chloride solution. Deformation(elastic modulus, E) and strength(cohesion, c', and angle of friction, f') parameters are obtained from the triaxial tests as functions of confining pressure and sodium chloride solution concentrations. The results here indicate an increase in the value of effective cohesion with increase in the concentration of NaCl solution, which can be explained by using the Gouy-Chapman model. The value of the effective angle of shearing resistance does not show significant change with the increase in concentration of NaCl solution. The Young's modulus also increases with the increase in concentration of NaCl solution.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.113-123
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• 2022

The required density relationship according to the press pressure of the floating die method and the homogeneity of the density distribution in the buffer block was evaluated to analyze the manufacturing characteristics of engineering scale bentonite-sand buffer blocks. In addition, the thermal conductivity was measured and compared with that of the pure bentonite buffer block to evaluate the level of thermal conductivity performance improvement of the bentonite-sand buffer material. As a result, it was confirmed that the standard deviation of dry density decreased to 0.011 and showed a homogeneous density distribution under the condition of press pressure greater than 400 kg/cm². Furthermore, as a result of the thermal conductivity test, the thermal conductivity of the buffer with optimum moisture content conditions was 1.345 and 1.261 W/(m·K) under the press pressure of 400 and 600 kg/cm², respectively. It increased by 16.1% and 11.0% compared to the pure bentonite buffer material. Based on the results of this study, it is judged that it can be used as fundamental data for manufacturing a homogeneous bentonite-sand buffer block on an engineering scale.

• Journal of the Mineralogical Society of Korea
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• v.19 no.2 s.48
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• pp.89-98
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• 2006

The thermal conductivities of bentonite blocks with various dry densities (1.6 and $1.8g/cm^3$), water contents (5, 9.4, 15, 20 wt%) and sand contents (0, 10, 20, 30 wt%) were measured in order to investigate the improvement in physical performance of buffer as an engineered barrier. The raw material was domestic bentonite from Oksan mine located in Gyeongju city. The increase in water content was most effective for improving the thermal conductivity. Especiallly, the bentonite blocks with more than 15 wt% of water content showed more than 1.0 W/mK values of thermal conductivity regardless of their dry densities and sand contents. Therefore, if the domestic Oksan bentonite is used as a buffer material, we can suggest that the manufacture of bentonite block having dry density of $1.6g/cm^3$, sand content of $10{\sim}30$ wt% and water content of 15 wt% will be most effective considering the easiness of a manufacturing of bentonite block and the efficiency of an increase in the thermal conductivity.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.10a
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• pp.275-275
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• 1998

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.507-515
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• 1994

Fly ash and betonite samples were selected and characteristics of them were investigated. Fly ash was found to be similar to bentonite in particle size distribution but quite different in microstructure. The most special aspect of fly ash was high alkalinity of its solution. Distribution coefficients of Cs and Co on the samples were measured to survey the effects of mixing. Fly ash showed higher distribution coefficient of Co than that of Cs. Through various experiments, factors affecting the distribution coefficients of Co and Cs on mixture of bentonite and fly ash were identified. Comparison of the distribution coefficients of Cs on fly ash and bentonite mixture with those on sand and bentonite mixture suggests that fly ash would be useful as an efficient additive of backfill material if pertinent mixing ratio was chosen.