• Title, Summary, Keyword: Bentonite

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Conceptual Modeling Coupled Thermal-Hydrological-Chemical Processes in Bentonite Buffer for High-Level Nuclear Waste Repository (고준위 방사성폐기물 처분장에서 벤토나이트 완충제에 대한 열-수리-화학 작용 개념 모델링)

  • Choi, Byoung-Young;Ryu, Ji-Hun;Park, Jinyoung
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.14 no.1
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    • pp.1-9
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    • 2016
  • In this study, thermal-hydrological-chemical modeling for the alteration of a bentonite buffer is carried out using a simulation code TOUGHREACT. The modeling results show that the water saturation of bentonite steadily increases and finally the bentonite is fully saturated after 10 years. In addition, the temperature rapidly increases and stabilizes after 0.5 year, exhibiting a constant thermal gradient as a function of distance from the copper tube. The change of thermal-hydrological conditions mainly results in the alteration of anhydrite and calcite. Anhydrite and calcite are dissolved along with the inflow of groundwater. They then tend to precipitate in the vicinity of the copper tube due to its high temperature. This behavior induces a slight decrease in porosity and permeability of bentonite near the copper tube. Furthermore, this study finds that the diffusion coefficient can significantly affect the alteration of anhydrite and calcite, which causes changes in the hydrological properties of bentonite such as porosity and permeability. This study may facilitate the safety assessment of high-level radioactive waste repositories.

The Compatibility of Slurry Wall Materials with Leachate for Cut -off of Contaminated Sites (오염지역 차폐용 슬러리월 재료와 침출수의 반응 특성)

  • 이용수;정하익
    • Geotechnical Engineering
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    • v.13 no.2
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    • pp.9-16
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    • 1997
  • Cut-off methods of controlling leachate migration from waste landfills and contaminated sites are studied. Permeability and chemical compatibility tests are prrforlned on slurry wall materials including soil-bentonite, cement-bentonite, cement / fly ash-bentonite, plastic concrete. Hydraulic conductivity of soil-bentonite mixture is the lowest of these four bacuill materials. The leachate from municipal solid waste has little influence on the permeability of the backfill materials. The bentonite slurry becomes flocculated and aggregated when exposed to the leachate. The results of the permeability test showed that the hydraulic conductivities of the backfill materials are in the order soil-beiltonite, Plastic concrete, cement-bentonite. And the result c: the compatibility test showed increase in permeability due to the effects of leachate. Thus, in designing the slurry wall it is essential to check the behaviour of the bentonite slurry and backfill materials on the compatibility with the contaminants.

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A Study on the Nonlinear Structural Analysis for Spent Nuclear Fuel Disposal Container and Bentonite Buffer (고준위폐기물 처분장치와 이를 감싸고 있는 벤토나이트 버퍼에 대한 비선형 구조해석)

  • 권영주;최석호
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.19-26
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    • 2002
  • In this paper, the nonlinear structural analysis for the composite structure of the spent nuclear fuel disposal container and the 50cm thick bentonite buffer is carried out to predict the collapse of the container while the sudden rock movement of 10cm is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Horizontal symmetric rock movement is assumed in this structural analysis. Elastoplastic material model is adopted. Drucker-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the container(cast iron insert, copper outer shell and lid and bottom). Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffer, the container structure still endures elastic small strains and stresses below the yield strength. Hence, the 50cm thick bentonite buffer can protect the container safely against the 10cm sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the container structure due to the shear deformation of the bentonite buffer. The elastoplastic nonlinear structural analysis for the composite structure of the container and the bentonite buffer is performed using the finite element analysis code, NISA.

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An Elastoplastic Analysis for Spent Nuclear Fuel Disposal Container and Its Bentonite Buffer: Asymmetric Rock Movement (고준위폐기물 처분장치 및 완충장치에 대한 탄소성해석 : 비대칭 암반력)

  • 권영주;최석호
    • Transactions of Materials Processing
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    • v.12 no.5
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    • pp.479-486
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    • 2003
  • This paper presents an elastoplastic analysis for spent nuclear fuel disposal container and its 50 cm thick bentonite buffer to predict the collapse of the container while the horizontal asymmetric sudden rock movement of 10 cm is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucker-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the container. Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffer, the container structure still endures elastic small strains and stresses below the yield strength. Hence, the asymmetric 50 cm thick bentonite buffer can protect the container safely against the 10 cm sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the container structure due to the shear deformation of the bentonite buffer. The finite element analysis code, NISA, is used for the analysis.

Hydraulic behaviour of dune sand-bentonite mixtures under confining stress

  • Gueddouda, M.K.;Lamara, M.;Abou-bekr, N.;Taibi, S.
    • Geomechanics and Engineering
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    • v.2 no.3
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    • pp.213-227
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    • 2010
  • Compacted layers of sand-bentonite mixtures have been proposed and used in a variety of geotechnical projects as engineered barriers for the enhancement of impervious landfill liners, cores of zoned earth dams and radioactive waste repository systems. This paper presents a study on the valorization of local materiel such as dune sand from Laghouat region and mine bentonite intended for the realization of liner base layers in the conception of insulation barriers for hazardous waste centers. In the practice we try to get an economical mixture that satisfies the hydraulic and mechanical properties specified by regulation rules. The effect of the bentonite additions on the mixture is reflected by its capability of clogging the matrix pores upon swelling. In order to get an adequate dune sand-bentonite mixture, an investigation on hydraulic and mechanical behaviours is carried out in this study for different mixtures. Using oedometer test, the adequate bentonite addition to the mixture, which satisfies the conditions on permeability, is found to be around 12% to 15%. These results are also confirmed by direct measurement using triaxial cell.

A new method to predict swelling pressure of compacted bentonites based on diffuse double layer theory

  • Sun, Haiquan
    • Geomechanics and Engineering
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    • v.16 no.1
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    • pp.71-83
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    • 2018
  • Compacted bentonites were chosen as the backfill material and buffer in high level nuclear waste disposal due to its high swelling pressure, high ion adsorption capacity and low permeability. It is essential to estimate the swelling pressure in design and considering the safety of the nuclear repositories. The swelling pressure model of expansive clay colloids was developed based on Gouy-Chapman diffuse double layer theory. However, the diffuse double layer model is effective in predicting low compaction dry density (low swelling pressure) for certain bentonites, and invalidation in simulating high compaction dry density (high swelling pressure). In this paper, the new relationship between nondimensional midplane potential function, u, and nondimensional distance function, Kd, were established based on the Gouy-Chapman theory by considering the variation of void ratio. The new developed model was constructed based on the published literature data of compacted Na-bentonite (MX80) and Ca-bentonite (FoCa) for sodium and calcium bentonite respectively. The proposed models were applied to re-compute swelling pressure of other compacted Na-bentonites (Kunigel-V1, Voclay, Neokunibond and GMZ) and Ca-bentonites (FEBEX, Bavaria bentonite, Bentonite S-2, Montigel bentonite) based on the reported experimental data. Results show that the predicted swelling pressure has a good agreement with the experimental swelling pressure in all cases.

An Investigation of Diffusion of Iodide Ion in Compacted Bentonite Containing Ag2O (Ag2O를 첨가한 압축 벤토나이트에 대한 요오드 이온의 확산 특성 관찰)

  • Yim, Sung-Paal;Lee, Ji-Hyun;Choi, Heui-Joo;Choi, Jong-Won;Lee, Cheo-Kyung
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.9 no.1
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    • pp.33-40
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    • 2011
  • In the compacted bentonite containing $Ag_2O$, the transport of iodide ion was investigated by Through-diffusion method. It is confirmed that Iodide ion is transported by diffusion process in the compacted bentonite containing $Ag_2O$ as well as in the compacted bentonite without $Ag_2O$. However, the lag-time of iodide ion in the compacted bentonite containing $Ag_2O$ is larger than that in the compacted bentonite without $Ag_2O$. The increase of the lag-time was observed in pure iodide ion solution and also in 0.1M NaCl-iodide ion solution. The apparent diffusion coefficient of iodide ion in the compacted bentonite containing $Ag_2O$ has lower value than that in the compacted bentonite without $Ag_2O$. The effect of $Ag_2O$ on the effective diffusion coefficient was not clearly investigated in the compacted bentonite containing $Ag_2O$ while the values of effective diffusion coefficient of iodide ion in the compacted bentonite without $Ag_2O$ obtained in this study were similar to those in the compacted bentonite reported in the literature.

Development of Bentonite Composite Liners for Landfill Sites (폐기물매립지 침출수 누출방지용 벤토나이트 복합라이너 개발)

  • 최우진;이원영;진성기;하헌중;김두영
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • pp.73-76
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    • 1999
  • Soil-bentonite mixtures are frequently used as impervious for waste disposal sites. In the present work, bentonite composite liner systems(BCL) have been developed by utilizing Korean zeolitic bentonites. The geomechanical properties of the liner systems, such as strength, hydraulic conductivity, etc. have been studied. The laboratory and field test results are also be presented.

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Characteristics of Bentonite Filter Cake on Vertical Cutoff Walls Evaluated by Modified Fluid Loss Test (수정 fluid loss 시험을 이용한 연직 차수벽에 생성된 벤토나이트 필터케익 특성 평가)

  • Nguyen, The-Bao;Park, Moon-Seo;Lim, Jee-Hee;Choi, Hang-Seok;Han, Shin-In
    • Journal of the Korean Geotechnical Society
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    • v.27 no.2
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    • pp.53-62
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    • 2011
  • During the construction of vertical cutoff walls, filtration of bentonite slurry into the adjacent soil formation fabricates a layer of bentonite filter cake on the wall surface. The bentonite filter cake possesses much lower hydraulic conductivity compared to that of backfill materials in the cutoff wall. Hydraulic conductivity of bentonite filter cakes formed with three different types of bentonites has been measured by performing the modified fluid loss test under various pressure levels. Three different mixture ratios, 4, 6, and 8%, were selected for fabricating bentonite filter cakes to represent common field conditions. Two analysis methods for interpreting the experimental data from the modified fluid loss tests were employed to estimate hydraulic conductivity of the bentonite cakes. The range of hydraulic conductivities of the three bentonite cakes is between $2.15{\times}10^{-11}\;m/s$ and $2.88{\times}10^{-10}\;m/s$ which is 1 to 2.7 orders of magnitude lower than that of the design cutoff wall backfill. The stress distribution and thickness of the bentonite cakes were also evaluated in this paper.

Mineralogical Characteristics and Genetic Environment of Zeolitic Bentonite in Yeongil Area (영일 지역 제올라이트질 벤토나이트의 광물특성 및 생성환경)

  • 노진환;고상모
    • Journal of the Mineralogical Society of Korea
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    • v.17 no.2
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    • pp.135-145
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    • 2004
  • A zeolitic bentonite, which exhibits whitish appearance and contains considerable amounts (nearly 〉 5%) of zeolites, frequently occurs as thin beds less than 1 m in Yeongil area. The bentonites are mostly found in closely association with zeolite beds in the Nuldaeri Tuff and Coal-bearing formations of the Janggi Croup. A discordant occurrence of the bentonite against the bedding plane is also locally found. Montmorillonite, the major mineral constituent of the bentonite, is mostly associated with clinoptilolite as a zeolite. However, instead of clinoptilolite, mordenite is sometimes included in the case of more silicic bentonite, and heulandite in the less silicic one. It is characteristic that the mordenite is accompanied by lots of opal-CT in the silicic bentonite. SEM observations characteristically indicate that these authigenic phases, especially the montmorillonite and zeolite, nearly coexist as mixtures not forming a fine-scale zoning. The zeolitic bentonite seems to be formed in the comparatively silicic pore fluid at the alkaline condition accompanying pH fluctuation Compared to the zeolite-free normal bentonite, the zeolitic types exhibit somewhat higher REE abundance. These chemical characteristics, together with modes of occurrences and authigenic mineral associations, may suggest that the zeolitic bentonite is not merely diagenetic products and a possible hydrothermal alteration could not be excluded in the bentonite genesis.