Preliminary Test on Gas Migration Through Bentonite-Sand Mixture

1994 ◽  
Vol 353 ◽  
Author(s):  
T. Hokari ◽  
T. Ishii ◽  
T. Nagasawa ◽  
R. Tomita ◽  
M. Nakajima
Keyword(s):  
Hydraulic Conductivity ◽  
Gas Permeability ◽  
Preliminary Test ◽  
Gas Migration ◽  
Overburden Pressure ◽  
Sand Mixture ◽  
Groundwater Flux ◽  
Disposal Facility ◽  
Gas Volume ◽  
Breakthrough Pressure

AbstractThe Low-Level Radioactive Disposal facility [1] is planned to cover the vaults with impermeable bentonite-sand mixture in order to minimize groundwater flux through the facility. In case that metal wastes are to be disposed of in the burial facility in the future, it is essential to confirm that bentonite mixture should have gas permeability enough for the gas volume which would be expected to be generated due to an aerobic corrosion of metals[2]. This report performed a preliminary test with a bentonite-sand mixture whose aggregate was Japanese Standard sand. Results are the followings;(l)Gas breakthrough pressure of the mixture was less than the overburden pressure. The gas permeability was estimated to be of order of 10-2 md. (2)The mixture did not deteriorate in hydraulic conductivity after gas breakthrough.

Gas Migration in Low- and Intermediate-Level Waste (LILW) Disposal Facility in Korea

2013 ◽  
Author(s):  
Jae-Chul Ha ◽  
Jeong-Hwan Lee ◽  
Haeryong Jung ◽  
Juyub Kim ◽  
Juyoul Kim
Keyword(s):  
Gas Permeability ◽  
Hydrogen Gas ◽  
Intermediate Level ◽  
Gas Migration ◽  
Gas Generation ◽  
Reference Case ◽  
Disposal Facility ◽  
Entry Pressure ◽  
Under Construction ◽  
Different Gases

The first low- and intermediate-level waste (LILW) disposal facility is under construction in saturated granite in Korea. The safety assessment report (SAR) identified that different gases, such as hydrogen, carbon dioxide, and methane are generated at the disposal facility due to the corrosion of metal wastes and steel drum, and microbial degradation of organic matters. Reinforced concrete plays a role as an engineered barrier at the disposal facility, so its properties with regard to gas migration were evaluated in laboratory-scale experiments. Then modeling of gas migration was carried out to evaluate gas pressure build-up in the disposal facility. The gas entry pressure and relative gas permeability of the concrete was determined to be 0.97±0.15 bar, and the relative gas permeability decreased exponentially with increasing water content. The results of the modeling showed that most of hydrogen gas was dissolved in groundwater and did not significantly influence pressure build-up inside the disposal facility based on the reference case of gas generation.

Experimental Study of Gas Permeabilities and Breakthrough Pressures in Clays

1996 ◽  
Vol 465 ◽  
Author(s):  
K. Tanai ◽  
T. Kanno ◽  
C. Gallé
Keyword(s):  
Two Phase Flow ◽  
Gas Permeability ◽  
Phase Flow ◽  
Gas Migration ◽  
Two Phase ◽  
Saturation State ◽  
Flow Models ◽  
Water Permeation ◽  
Compacted Bentonite ◽  
Breakthrough Pressure

ABSTRACTIn this study, gas migration experiments in unsaturated and saturated states were carried out to clarify the fundamental gas migration characteristics in compacted bentonite to be used for the geological disposal of high-level radioactive waste. In unsaturated experiments, the gas permeability for Japanese bentonite (Kunigel VI) as a function of degree of saturation was measured to examine the applicability of conventional two-phase flow models to compacted bentonite. The intrinsic permeability obtained in this study was about five orders of magnitude larger than that obtained in water permeation tests with the same density. The difference seems to originate from the change of pore structure due to the swelling phenomenon of the bentonite. Since these effects have not been evaluated quantitatively yet, various relative gas permeability functions of conventional two-phase flow models were applied as a first approximation.Saturated experiments designed to simulate the gas migration phenomenon in a repository for the waste were carried out to obtain relationship between breakthrough and swelling pressures using Kunigel VI and French Fo-Ca clay in saturation state. The reproducibility of the breakthrough pressure was also examined for Kunigel VI bentonite. The breakthrough pressure was almost the same as swelling pressure irrespective of the type of clay. As to the reproducibility of breakthrough pressure, it was observed that first and second breakthrough pressures were almost the same for Kunigel VI specimens with the dry densities of 1.7 and 1.8 g/cm3.

Influence of alkalinity on the hydraulic conductivity of bentonite-sand liners

1998 ◽  
Vol 38 (2) ◽  
pp. 151-157 ◽  
Author(s):  
David G. Wareham ◽  
Arman Farajollahi ◽  
Mark W. Milke
Keyword(s):  
Hydraulic Conductivity ◽  
Charge Density ◽  
Liquid Limit ◽  
Permeability Test ◽  
Clay Particles ◽  
Sand Mixture ◽  
Compacted Bentonite ◽  
Limit Test ◽  
The Impact

The aim of this research is to record the impact of specific changes in the molding water alkalinity on the hydraulic conductivity of a compacted bentonite-sand mixture. Adding alkalinity to the molding water influences the charge density existing on the clay particles. This can increase the amount of separation of the bentonite particles which causes a decrease in the hydraulic conductivity of the compacted mixture. At the optimum alkalinity the mixture possesses the smallest hydraulic conductivity. In this research an optimum alkalinity (pH=10.1) for a compacted bentonite-sand mixture (7.5% bentonite) was derived from the liquid limit test and the falling-head permeability test.

Multi-scale integrated characterization of heterogeneous hydraulic and thermal properties of a deltaic aquifer

2020 ◽  
Author(s):  
Jean-Marc Ballard ◽  
Cynthia Lee ◽  
Nataline Simon ◽  
Jerome de la Bernardie ◽  
Daniel Paradis ◽  
...  
Keyword(s):  
Thermal Properties ◽  
Hydraulic Conductivity ◽  
Fiber Optics ◽  
Tracer Test ◽  
Future Application ◽  
Quebec City ◽  
Aquifer Characterization ◽  
Characterization Methods ◽  
Direct Push ◽  
Groundwater Flux

<div>Historically, heat and temperature observations have been occasionally used to help understand aquifer systems or constrain numerical flow models. However, the development of fiber optics (FO) as part of the Distributed Temperature Sensing (DTS) technology has spun a renewed interest in the use of heat as a groundwater tracer. Recent studies have shown the possibility to carry out an active heat tracer test using fiber optics and heating cables installed by direct push and to invert the resulting thermal responses to estimate a vertical profile of groundwater fluxes. However, a better understanding of how FO-DTS results compare to other aquifer characterization methods is needed to guide its future application and integration into a practical workflow. The objective of this study was thus to compare the information provided by FO-DTS with other direct and indirect measurements used to characterize the heterogeneity of granular aquifers at multiple scales. </div><div>The multiscale integrated characterization was carried out at a heterogeneous deltaic aquifer located north of Quebec City, Canada. This aquifer has been the object of a complete hydrogeological characterization and thus provides a wide range of existing data against which the acquired data can be compared. This communication will focus on the multiscale methodology for the granular aquifer characterization including FO-DTS measurements. Based on an existing numerical hydrogeological model, three sites with a range of horizontal groundwater fluxes were selected for active FO-DTS heat tracer experiments. At one of the sites, direct push monitoring wells were also installed downstream to measure the hydraulic conductivity of the hydrofacies and the arrival of the thermal front from the heat tracer test. A previous study established a relationship between the hydrofacies of the deltaic aquifer to cone penetration test (CPT) response. As such, each FO cable and monitoring well direct-push installation was preceded by a co-located CPT. Soil cores were also taken for laboratory measurements of hydraulic and thermal properties. </div><div>The vertical profiles of groundwater fluxes from FO-DTS were found to correlate well with the relative magnitude of permeability of the hydrofacies identified with CPT profiles. FO-DTS could thus provide a qualitative or quantitative proxy for hydraulic conductivity and allow the recognition of hydrofacies at a fine scale. At the aquifer scale, the total flux measured by FO-DTS can also be compared to fluxes obtained from numerical models and thus provide a constraint to validate models. Overall, this study shows that not only does FO-DTS provide coherent results with other characterization methods, but it also adds the key measurement of groundwater flux that cannot be easily obtained by other means. FO-DTS thus has the potential to become a significant addition to existing characterization methods for granular aquifers.</div>

Method of Designing Bentonite/Sand Mixture to Achieve the Target Permeability

1994 ◽  
Vol 353 ◽  
Author(s):  
Hitoshi Nakashima ◽  
Takashi Ishii ◽  
Tatsuro Nagasawa ◽  
Nobuhide Ogata ◽  
Hideo Komine
Keyword(s):  
Radioactive Waste ◽  
Waste Disposal ◽  
Void Ratio ◽  
Radioactive Waste Disposal ◽  
Permeability Test ◽  
Sand Mixture ◽  
Compaction Test ◽  
Disposal Facility ◽  
Effective Component ◽  
Effective Void Ratio

AbstractBentonite/sand mixture is expected to be an effective component of barriers for radioactive waste disposal facility. Impermeable mixture can be obtained through enrichment of the bentonite content,but it is difficult to estimate a permeability of bentonite/sand mixture before permeability test. At designing of bentonite/sand mixture, we have to decide which sand to be used, and what bentonite content is. But.this means that designing will be a time-consuming task. In this report, we made many kinds of bentonite/sand mixtures using some kinds of sand with different bentonite content, and permeability tests were conducted for these mixtures. After examination of the permeability tests results, the effective void ratio of bentonite/sand mixture which was obtained by compaction test, is an efficient parameter for estimation of the permeability. Last of all, we propose the method of designing bentonite/sand mixture using the effective void ratio.

scholarly journals Gas Migration in Low- and Intermediate-Level Waste (LILW) Disposal Facility in Korea

2014 ◽  
Vol 12 (4) ◽  
pp. 267-274
Author(s):  
Jaechul Ha ◽  
Jeong-Hwan Lee ◽  
Haeryong Jung ◽  
Juyub Kim ◽  
Juyoul Kim
Keyword(s):  
Intermediate Level ◽  
Gas Migration ◽  
Disposal Facility

scholarly journals Capillary pressure–saturation curves of thin hydrophilic fibrous layers: effects of overburden pressure, number of layers, and multiple imbibition–drainage cycles

2019 ◽  
Vol 89 (23-24) ◽  
pp. 4906-4915 ◽  
Author(s):  
Amir Hossein Tavangarrad ◽  
S. Majid Hassanizadeh ◽  
Rodrigo Rosati ◽  
Luigi Digirolamo ◽  
Martinus Th van Genuchten
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Capillary Pressure ◽  
Unsaturated Soils ◽  
Measured Data ◽  
Text Data ◽  
Overburden Pressure ◽  
Number Of Layers ◽  
Thin Porous Media ◽  
Data Points

Unsaturated fluid flow in thin porous media depends on hydraulic properties, such as the capillary pressure, P c, as a function of saturation, S. We measured this relationship for two different types of compressible thin hydrophilic fibrous layers under varying conditions. Among other factors, we changed the number of layers and the overburden pressure (i.e. the confined solid pressure applied on top of the sample) imposed on one layer or a stack of layers. Applying an overburden pressure drastically affected the [Formula: see text] curves. However, increasing the number of fibrous layers had little impact on the capillary pressure–saturation curves. We also investigated the effect of multiple imbibition–drainage cycles on the [Formula: see text] data. Measured data points were used to find general expressions for the [Formula: see text] relationships of compressible thin porous media. Existing quasi-empirical correlations used in vadose zone hydrology, notably expressions by van Genuchten (Van Genuchten MTh. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci Soc Am J 1980; 44: 892-898) and Durner (Durner W. Hydraulic conductivity estimation for soils with heterogeneous pore structure. Water Resour Res 1994; 32: 211–223) for single- and dual-porosity media, respectively, were employed to fit the measured data points.

Performance of polymer-enhanced bentonite–sand mixture for covering arsenic-rich gold mine tailings for up to 4 years

2017 ◽  
Vol 54 (4) ◽  
pp. 588-599 ◽  
Author(s):  
M.S. Hosney ◽  
R. Kerry Rowe
Keyword(s):  
Ionic Strength ◽  
Hydraulic Conductivity ◽  
Water Content ◽  
Mole Fraction ◽  
Mine Tailings ◽  
Direct Contact ◽  
Gold Mine ◽  
Confining Stress ◽  
Sand Mixture ◽  
Gold Mine Tailings

Experiments conducted over a 4 year period, on a polymer-enhanced bentonite–sand mixture (PEBSM) used as cover for gold mine tailings are reported. The effect on PEBSM hydraulic conductivity (k) of subgrade porewater chemistry, subgrade water content, and confining stress are investigated. Results show that the reduction in the mole fraction of bound Na+ (ESP) and corresponding increase in k of PEBSM with time was highly dependent on the ionic strength of the subgrade porewater. When the PEBSM was in direct contact with gold mine tailings with porewater having an ionic strength of 145 mmol/L, ESP decreased from 59% to 2% and k increased from 4 × 10−11 to 6.9 × 10−9 m/s. The ESP and k values of PEBSM over tailings with 11 mmol/L porewater were 21% and 6.9 × 10−11 m/s, respectively. A 0.15 m thick foundation layer between tailings and PEBSM layer significantly lowered the reduction in ESP and increase in k with time as did a reduction in the subgrade water content. There was no effect of changing confining stress from 15 to 7.5 kPa on k values of PEBSM. The PEBSM layer acted as a good barrier to the migration of arsenic from tailings upward towards cover soil above the PEBSM layer.

Effect of freeze–thaw on the hydraulic conductivity and morphology of compacted clay

1993 ◽  
Vol 30 (2) ◽  
pp. 236-246 ◽  
Author(s):  
Majdi A. Othman ◽  
Craig H. Benson
Keyword(s):  
Hydraulic Conductivity ◽  
Three Dimensional ◽  
Compacted Clay ◽  
Clay Liners ◽  
Overburden Pressure ◽  
Thin Sections ◽  
Freeze Thaw ◽  
State Of Stress ◽  
Soil Liners ◽  
Compacted Clays

Several studies have shown that freeze–thaw causes changes in the hydraulic conductivity of compacted clays. Cracks formed by ice lensing and shrinkage cause the hydraulic conductivity to increase. In this paper, changes in hydraulic conductivity are related to changes in morphology. Photographs of thin sections of frozen specimens show that ice lenses form in compacted clay during freezing in a closed system. Photographs also show that similar ice structures are obtained for one- and three-dimensional freezing, which explains why similar hydraulic conductivities are obtained for both conditions. The photographs also show that a significant network of cracks forms in a single cycle of freeze–thaw. With additional cycles, new ice lenses are created and thus the hydraulic conductivity continues to increase. However, after about three cycles the number of new ice lenses becomes negligible and hence further changes in hydraulic conductivity cease. The temperature gradient and state of stress affect morphology and hydraulic conductivity of compacted clays subjected to freeze–thaw. At larger temperature gradients, more ice lenses form and hence the hydraulic conductivity increases. In contrast, application of overburden pressure inhibits the formation of ice lenses and reduces the size of the cracks remaining when lenses thaw. As a result, the hydraulic conductivity is reduced. Key words : compacted clay, hydraulic conductivity, clay liners, soil liners, freeze-thaw, ice lenses, structure.

Centrifuge Modeling of Radioactive Waste Migration Through Backfill in a Near Surface Disposal Facility

2007 ◽  
Author(s):  
C. Gurumoorthy ◽  
O. Kusakabe
Keyword(s):  
Hydraulic Conductivity ◽  
Diffusion Mechanism ◽  
Real Life ◽  
Centrifuge Modeling ◽  
Modeling Technique ◽  
Near Surface ◽  
Disposal Facility ◽  
Disposal Option ◽  
Real Life Situation ◽  
Time Required

Investigations on the performance of backfill barrier in Near Surface Disposal Facility (NSDF) for radioactive wastes are important to ensure the long term safety of such disposal option. Favorable condition to delay migration of radionuclides from disposed waste to far fields is diffusion process. However, advective dispersion/diffusion mechanism plays an important role due to changes in backfill over a period of time. In order to understand these mechanisms, detailed laboratory experiments are usually conducted for developing mathematical models to assess the behaviour of backfill. However, these experiments are time consuming and suffer with the limitations due to material complexity. Also, there are constraints associated with validation of theoretical predictions due to intricacy of boundary conditions as well as the time scale is quite different as compared to the time required for completion of the processes in the field. Keeping in view these aspects, centrifuge modeling technique has been adopted by various researchers to model and understand various geoenvironment problems in order to provide a link between the real life situation termed as the ‘Prototype’ and its model, which is exposed to a higher gravitational field. An attempt has been made in this paper to investigate the feasibility of this technique to model advective dispersion/diffusion mechanism of radionuclides through saturated Bentonite-Sand (B:S) backfill. Various stages of centrifuge modeling are highlighted. Column tests were conducted in the centrifuge to evaluate the hydraulic conductivity of B:S mixture under prototype NSDF stress conditions. Results showed that steady state hydraulic conductivity under saturated conditions was 2.86 × 10−11m/sec. Studies indicate the feasibility of centrifuge modeling technique and usefulness to model advective diffusion of radionuclides through B:S backfill.

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