Swelling Pressures of Compacted Bentonite/Sand Mixtures

1984 ◽  
Vol 44 ◽  
Author(s):  
M. N. Gray ◽  
S. C. H. Cheung ◽  
D. A. Dixon
Keyword(s):  
Threshold Value ◽  
Deionized Water ◽  
Silica Sand ◽  
Dry Density ◽  
Sodium Bentonite ◽  
Compacted Bentonite ◽  
Bentonitic Clay ◽  
Soil Fabric ◽  
Nuclear Fuel Waste ◽  
Limiting Value

AbstractCompacted bentonitic clay/sand mixtures are being considered for use as buffer materials in the Canadian concept for nuclear fuel waste disposal. This paper describes a laboratory study of the swelling pressures that develop in statically compacted, air-dry specimens of mixtures of sodium bentonite and silica sand as they are saturated with double-distilled, deionized water. The results are interpreted with the aid of scanning electron microscope observations of the soils' structures.It is shown that the sand acts as an inert filler material, and swelling pressures are controlled by a parameter termed the effective clay dry density, γC, defined as the ratio of the mass of clay to the combined volume of the claq plus voids in the mixture. A threshold value of γC exists below which swelling pressures can be expected to be isotropic. Above the threshold value of γC, pressures parallel to the axis of compaction can be expected to be greatgr than those perpendicular to it. This is related to a change in soil fabric as γC is increased above the threshold value. For the Canadian disposal concept, γC would probably be below the limiting value and swelling pressures of 2.5 MPS or less are expected. The swelling pressures are likely to be isotropic within a saturated buffer mass.

Diffusion of Uranium in Compacted Bentonite in the Presence of Carbon Steel

1993 ◽  
Vol 333 ◽  
Author(s):  
K. Idemitsu ◽  
H. Furuya ◽  
Y. Tachi ◽  
Y. Inagaki
Keyword(s):  
Carbon Steel ◽  
Pore Water ◽  
Silica Sand ◽  
High Level Waste ◽  
Dry Density ◽  
Compacted Bentonite ◽  
Reducing Conditions ◽  
Order Of Magnitude ◽  
The Difference ◽  
High Level

ABSTRACTIn a high-level waste repository, a carbon steel overpack will be corroded by consuming oxygen trapped in the repository after closure. This will create a reducing environment in the vicinity of repository. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as uranium.The apparent diffusivities of uranium were measured in compacted bentonite (Kunigel VI®, Japan) in contact with carbon steel under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusivities of uranium were 3.5 × 10-14 to 1.1 × 10-13 m2/s under reducing conditions and 9.0 × 10-13 to 1.4 × 10-12 m2/s under oxidizing conditions. There was no significant effect of dry density (1.6 to 1.8 g/cm3) and silica sand (0 or 40%) on the apparent diffusivities.Since the bentonite pore water would be buffered at a pH between 8 and 9, uranium in the bentonite pore water would probably exist as a neutral hydroxide complex under reducing conditions and as an anioníc carbonate or hydroxide complex under oxidizing conditions. The anion exclusion theory cannot explain the difference of diffusivities between the two conditions. The uranium concentrations in bentonite under oxidizing conditions were one order of magnitude higher than those under the reducing conditions. The uranium concentration in the bentonite pore water under the reducing condition is estimated to be two orders of magnitude lower than that under the oxidizing conditions under the assumption of diffusion in porous media.

scholarly journals Bentonite swelling characteristics with a hypersaline multi-component pore fluid

2021 ◽  
Vol 58 (3) ◽  
pp. 367-376
Author(s):  
R.W.I. Brachman ◽  
R.K. Rowe ◽  
A. Baral ◽  
M.S. Hosney ◽  
G. Su ◽  
...  
Keyword(s):  
Chemical Interaction ◽  
Total Dissolved Solids ◽  
Deionized Water ◽  
Pore Fluid ◽  
Dry Density ◽  
Michigan Basin ◽  
Volume Increase ◽  
Compacted Bentonite ◽  
Swelling Characteristics ◽  
Swell Pressure

Swelling characteristics of compacted bentonite when hydrated with a hypersaline pore fluid (332 g/L total dissolved solids; 6.6 mol/L ionic strength) are reported. The pore fluid mimics the multiple constituents and their concentrations found for the Cobourg limestone of the Michigan Basin and is dominated by sodium (25% mole fraction) with some potassium, calcium, and magnesium (10%, 5%, and 4% mole fractions). Measurements of swell pressure for two sodium bentonites when hydrated under conditions of zero volume increase are reported. Swell pressure reached a peak within 10–30 h from the onset of hydration, followed by a continual decrease over 1 year of testing from chemical interaction between the bentonite and pore fluid. After 1 year, the swell pressure of the MX-80 bentonite tested decreased by a factor of nine relative to the peak swell pressure with deionized water when the dry density was 1.6 Mg/m3. Swell pressures increased as dry density increased. However, chemical interactions appear to have more influence on swell pressure than density for the pore fluid examined as a swell pressure of just under 1200 kPa was measured for MX-80 after 1.8 years of hydration when compacted to the highest dry density of 1.8 Mg/m3 examined.

The Effect of Pore Structural Factors on Diffusion in Compacted Sodium Bentonite

2000 ◽  
Vol 663 ◽  
Author(s):  
Haruo Sato
Keyword(s):  
Grain Size ◽  
Tritiated Water ◽  
Silica Sand ◽  
Single Fracture ◽  
Distilled Water ◽  
Structural Factors ◽  
Sodium Bentonite ◽  
Size Dependency ◽  
Through Diffusion ◽  
Effective Diffusivities

ABSTRACTFour kinds of diffusion experiments; (1) through-diffusion (T-D) experiments for diffusion direction dependency to compacted direction, (2) in-diffusion (I-D) experiments for composition dependency of silica sand in bentonite, (3) I-D experiments for initial bentonite grain size dependency, and (4) I-D experiments for the effect of a single fracture developed in bentonite, were carried out using tritiated water (HTO) to evaluate the effect of pore structural factors on diffusion. For (1), effective diffusivities (De) in Na-bentonites, Kunigel-V1Ŵ and Kunipia-FŴ, were measured for densities of 1.0 and 1.5 Mg.m-3 in the axial and perpendicular directions to compacted one. Although De values in Kunigel-V1Ŵ for both directions were similar over the density, De values for perpendicular direction to compacted one in Kunipia-FŴ were higher than those for the same direction as compacted one. For (2), apparent diffusivities (Da) in Kunigel-V1Ŵ with silica sand were measured for densities of 0.8 to 1.8 Mg.m-3. No significant effect of the mixture of silica sand was found. For (3), Da values for densities of 0.8 to 1.8 Mg.m-3 were measured for a granulated Na-bentonite, OT-9607Ŵ. However, no effect of initial bentonite grain size was found. For (4), Da values in Kunigel-V1Ŵ, in which a single fracture was artificially reproduced and immersed in distilled water, were measured. No effect of the fracture on Da was found. Based on this, it may be said that the composition of smectite in bentonite affects the orientation property of clay particle and also affects diffusion. Furthermore, a penetrated fracture formed in bentonite is restored for a short while and does not affect diffusion.

Effect of Polymerization on the Swelling Properties of a Sodium Bentonite and its Mechanism

2020 ◽  
Vol 1003 ◽  
pp. 228-232
Author(s):  
Ji Xiang Nie ◽  
Ryoga Tanaka ◽  
Jin Chun Chai
Keyword(s):  
Free Radical ◽  
Deionized Water ◽  
Polymer Chains ◽  
Nacl Solution ◽  
X Ray Diffraction ◽  
Swelling Properties ◽  
Sodium Bentonite ◽  
X Ray ◽  
Free Swelling ◽  
Polymerization Method

The effect of polymerization on the swelling properties of a sodium bentonite has been investigated experimentally using free swelling index (FSI). Using free radical polymerization method in cationic solution with acrylate acid as the monomer (M) and potassium persulfate as initiator (I), the optimum conditons for higher FSI value in 0.6 M NaCl solution were pH of 5.5 and I/M ratio of 0.005. The polymerized bentonite (PB) had much higher FSI values than that of untreated bentonite (UB) in deionized water and 0.6 M NaCl solution. However, in the 0.6 M CaCl2 solution, the FSI value of PB was slightly lower than that of UB and the reason is not clear yet. The X-ray diffraction (XRD) test shows that polymer chains did not enter the interlayer of sodium bentonite crystals and it is postulated that the polymers only wrapped around the particles of the bentonite.

Study on Retardation Mechanism of 3H, 99Tc, 137Cs, 237Np and 241AM in Compacted Sodium Bentonite

1992 ◽  
Vol 294 ◽  
Author(s):  
H. Sato ◽  
T. Ashida ◽  
Y. Kohara ◽  
M. Yui
Keyword(s):  
Diffusion Coefficient ◽  
Apparent Diffusion Coefficient ◽  
Atmospheric Condition ◽  
Diffusion Method ◽  
Dry Density ◽  
Sodium Bentonite ◽  
Apparent Diffusion Coefficients ◽  
Anion Exclusion ◽  
Apparent Diffusion ◽  
The One

ABSTRACTThe apparent diffusion coefficients were measured at room temperature (about 23°C) under atmospheric condition by the one-dimensional non-steady state diffusion method for 3H, 99Tc, 137Cs, 237Np and 241Am in compacted sodium-bentonite saturated with water. Sodium-bentonite, which is commercially available as KunigelVl®, was used in this study. Experiments were carried out in the density range of 0.4–2.0 (×103kg/m3). Bentonite in the cell was prepared to be saturated with distilled water. The measured apparent diffusion coefficient decreases with increasing dry density of bentonite. That the apparent diffusion coefficient of 3H decreased as a function of dry density of bentonite appears to be the effect of the change of porous structure with dry density of bentonite. 99Tc may be retarded by anion-exclusion because dominant diffusion specie of 99Tc is pertechnetate ion under atmospheric condition. Retardation for 137Cs may be caused by ion-exchange on bentonite. The sorption, anion-exclusion and molecular filtration are considered as a retardation mechanism for 237Np and 241Am because those dominant species are negatively charged and of large ionic size.

Permeability, Swelling and Radionuclide Retardation Properties of Candidate Backfill Materials

1981 ◽  
Vol 6 ◽  
Author(s):  
J. H. Westsik ◽  
L. A. Bray ◽  
F. N. Hodges ◽  
E. J. Wheelwright
Keyword(s):  
Nuclear Waste ◽  
Initial Permeability ◽  
Nuclear Waste Repository ◽  
Dry Density ◽  
Sodium Bentonite ◽  
Backfill Materials ◽  
Waste Repository ◽  
Temperature Radiation ◽  
Bentonite Clays ◽  
Calcium Bentonite

ABSTRACTA backfill placed between a nuclear waste canister and the host geology of a nuclear waste repository can impede the migration of water through the waste package and retard the movement of radionuclides into the geologic formation. Hydraulic conductivities and swelling pressures are being determined as functions of the density of the compacted backfill, temperature, radiation dose, hydraulic head and the chemical composition of the permeating fluid. Bentonite clays and bentonite/sand mixtures have received initial emphasis. Sodium bentonite and calcium bentonite samples compacted to a dry density of 2.1 g/cm3 had hydraulic conductivities in the range of 10−12 to 10−13 cm/s. In addition, batch distribution ratios (Rd) for Sr, Cs, Am, Np, I, U and Tc have been measured for a number of candidatebackfill materials. Both initial permeability and sorption studies have used a synthetic basaltic ground water.

Migration Behaviour of Lanthanides in Compacted Bentonite with Iron Corrosion Product Using Electrochemical Method

2012 ◽  
Vol 1475 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Daisuke Akiyama ◽  
Yoshihiko Matsuki ◽  
Yusuke Irie ◽  
Yaohiro Inagaki ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Dispersion Coefficient ◽  
Reference Electrode ◽  
High Level Waste ◽  
Dry Density ◽  
Migration Behavior ◽  
Iron Corrosion ◽  
Compacted Bentonite ◽  
Steel Coupon ◽  
Best Fit

ABSTRACTAfter the closure of a high-level waste repository, corrosion of the carbon steel overpack will occur. The corrosion products can then migrate into bentonite and affect the migration behavior of radionuclides in bentonite. Therefore, electrochemical experiments, with Fe2+ supplied by anodic corrosion of carbon steel, were carried out to study trivalent lanthanides in compacted bentonite. The interface between a carbon steel coupon and bentonite (dry density, 1.5 Mg/m3) was spiked with a tracer solution containing Nd(NO3)3, Eu(NO3)3, Dy(NO3)3, and Er(NO3)3. The carbon steel coupon was connected as the working electrode to a potentiostat and held at a constant potential between -550 and 0 mV (vs. Ag/AgCl reference electrode) for 7 days. A model using dispersion and electromigration could explain the measured profiles in the bentonite specimens. The best-fit electromigration velocity was related to the applied electric potential and was 1.0–3.8 nm/s for Nd, Eu, Dy, and Er ions. For these lanthanides, the best-fit dispersion coefficient was also related to the applied potential and was 0.8–1.6 μm2/s, and the dispersion length was calculated as 0.2 mm from the linear relationship between the dispersion coefficient and electromigration velocity. Finally, the apparent diffusion coefficient for these lanthanides was estimated as 0.6–0.9 μm2/s.

Diffusion Measurements in Concrete and Compacted Bentonite

1982 ◽  
Vol 15 ◽  
Author(s):  
A. Muurinen ◽  
J. Rantanen ◽  
R. Ovaskainen ◽  
O.J. Heinonen
Keyword(s):  
Cylindrical Sample ◽  
Laboratory Method ◽  
Theoretical Curve ◽  
Concentration Profiles ◽  
Sodium Bentonite ◽  
Diffusion Data ◽  
Compacted Bentonite ◽  
Measured Profile

ABSTRACTA laboratory method for measurement of diffusion of radionuclides inconcretes and compacted bentonite has been developed. In this method a tracer is introduced through one end into the cylindrical sample closed in a tube and preequilibrated with water. After the introduction period of the tracer the tube is sealed hermetically and the concentration profiles of the radionuclides are measured periodically from the outside of the sample using a collimated detector. Diffusivities are calculated from the activity profiles by fitting the theoretical curve with the measured profile. The paper will give diffusion data for Co, Sr and Cs in some concrete products and for Co and Cs in compacted sodium bentonite.

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