Diffusion Behavior for Se and Zr in Sodium-Bentonite

1994 ◽  
Vol 353 ◽  
Author(s):  
Haruo Sato ◽  
Mikazu Yui ◽  
Hideki Yoshikawa
Keyword(s):  
Diffusion Coefficients ◽  
Dominant Species ◽  
Atmospheric Condition ◽  
Aerobic Condition ◽  
Diffusion Method ◽  
Dry Density ◽  
Sodium Bentonite ◽  
Apparent Diffusion Coefficients ◽  
Anion Exclusion ◽  
Apparent Diffusion

AbstractApparent diffusion coefficients for Se and Zr in bentonite were measured by in-diffusion method at room temperature using water-saturated sodium-bentonite. KunigelVl® * containing 50wt% Na-smectite as a major mineral was used as the bentonite material. The experiments were carried out in the dry density range of 400–1800kg/m3. Bentonite samples were immersed with distilled water and saturated before the experiments. The experiments for Se were carried out under N2 atmospheric condition (O2: 2.5ppm). Those for Zr were carried out under aerobic condition. The apparent diffusion coefficients decrease with increasing density of the bentonite. Since dominant species of Se in the pore water is predicted SeO32-, Se may be retarded by anion-exclusion because of negative charge on the surface of the bentonite and little sorption. The dominant species of Zr in the porewater is predicted Zr(OH)5- or HZrO3-. Distribution coefficient measured for Zr on the bentonite was about 1.0m3/kg from batch experiment. Therefore, the retardation may be caused by combination of the sorption and the anion-exclusion. A modelling for the diffusion mechanisms in the bentonite were discussed based on an electric double layer theory. Comparison between the apparent diffusion coefficients predicted by the model and the measured ones shows a good agreement.

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.

Hydraulic and Diffusive Properties of Clay-Based Backfill Material for a Low-and Intermediate-Level Waste Repository

1994 ◽  
Vol 353 ◽  
Author(s):  
W.J. Cho ◽  
J.O. Lee ◽  
P.S. Hahn ◽  
H.H. Park
Keyword(s):  
Diffusion Coefficients ◽  
Experimental Studies ◽  
Clay Content ◽  
Dry Density ◽  
Compacted Clay ◽  
Southeastern Part ◽  
Apparent Diffusion Coefficients ◽  
Crushed Granite ◽  
Apparent Diffusion ◽  
Water Saturated

AbstractThe results of experimental studies performed to determine the radionuclide diffusion coefficients in a compacted clay and the hydraulic conductivities of clay/crushed granite mixtures with various clay contents are presented. Clay used in the experiments is a natural clay from the southeastern part of Korea, and it contains mainly calcium bentonite. The hydraulic conductivities of clay/crushed granite mixtures decreased with increasing clay content. In case of clay content of 50 wt.%, they maintain the considerably lower values even at the dry density of 1.5 Mg/m3. The diffusion coefficients for 90Sr, 137Cs, 60Co and 125I in water saturated clay at a dry density of 1.4 Mg/m3 were measured at room temperature. The average apparent diffusion coefficients obtained are 4.5 × 10−12 m2/s, 9.0 ×10−13 m2/s, 3.4 × 10−13 m2/s and 6.7 × 10−11 m2/s for 90Sr, 137Cs, 60Co, and 125I, respectively.

Distribution Coefficients and Apparent Diffusion Coefficients of Cesium in Compacted Bentonites

1999 ◽  
Vol 556 ◽  
Author(s):  
Akiko Okamoto ◽  
Kazuya Idemitsu ◽  
Hirotaka Furuya ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Diffusion Coefficients ◽  
Distribution Coefficients ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Apparent Diffusion ◽  
Tracer Solution ◽  
Cesium Concentration ◽  
Penetration Profile ◽  
Very High

AbstractDistribution coefficients and apparent diffusion coefficients of cesium in some compacted bentonites were determined by the penetration profile method. Cylindrical compacted bentonites with the dry density of 0.8 to 1.6 Mg/m3 were contacted with tracer solutions containing 1000, 100 or 10 ppm of cesium. The apparent diffusion coefficients were obtained from the concentration profiles of cesium in compacted bentonites. The distribution coefficients were obtained concurrently by dividing the intercepts of the profiles by the concentration of the tracer solution. The apparent diffusion coefficients of cesium in compacted bentonite were obtained in the range of 0.42 to 9.6· 10−12 m2/s. The apparent diffusion coefficients in the compacted bentonite contacted with three different concentrations of cesium tended to decrease with increasing dry density of the specimen; but, they had no dependence on cesium concentration within a factor of 3 at the same dry density. The distribution coefficient of cesium for the specimens contacted with three different concentrations of cesium were obtained in the range of 0.3 to 90 L/kg and had little dependence on dry density. The distribution coefficients obtained in the compacted bentonites were dependent on pH of the solution rather than concentration of cesium. These distribution coefficients obtained in the compacted bentonites were 10 to 1000 times smaller than those obtained by batch experiments. The data suggest that not all sorption sites for cesium are available in highly compacted bentonite. It is necessary to consider surface diffusion as a significant migration mechanism of cesium through the compacted bentonites at very high pH condition such as 12.

The Dependence of the Diffusion Coefficients of 3H and Cs on Grain Size in Compacted Montmorillonite

1997 ◽  
Vol 506 ◽  
Author(s):  
Mamoru Nakajima ◽  
Tamotsu Kozaki ◽  
Hiroyasu Kato ◽  
Seichi Sato ◽  
Hiroshi Ohashi
Keyword(s):  
Grain Size ◽  
Diffusion Coefficients ◽  
Dry Density ◽  
Formation Factor ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Apparent Diffusion ◽  
Different Grain Size ◽  
High Level

ABSTRACTCompacted bentonite is a candidate buffer material in geological disposal of high-level radioactive waste. The transport of radionuclides in compacted bentonite is dominated by diffusion, because of its very low permeability. In this study, we focused on the grain size of clay mineral, which is considered to be closely related to the formation factor in the pore water diffusion model[1,2]. The apparent diffusion coefficients (Da) of HTO and cesium ions in compacted clays were determined using montmorillonite samples with different grain size and dry density, and the effect of the grain size on diffusion behavior was discussed.

Effect of Carbonate on the Migration Behavior of Lanthanides in Compacted Bentonite

MRS Advances ◽  
2018 ◽  
Vol 3 (21) ◽  
pp. 1155-1160 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Kazuyuki Fujii ◽  
Noriyuki Maeda ◽  
Yuki Kakoi ◽  
Noriya Okubo ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Atomic Number ◽  
Diffusion Coefficients ◽  
Chemical Species ◽  
Dry Density ◽  
Migration Behavior ◽  
Bicarbonate Concentration ◽  
Apparent Diffusion Coefficients ◽  
Carbonate Ion ◽  
Apparent Diffusion

ABSTRACTThe apparent diffusion coefficients of La, Nd, Eu, Dy, Er, and Lu in compacted bentonites were investigated at various bicarbonate concentrations. The apparent diffusion coefficients of these lanthanides tended to decrease with increasing dry density. At bicarbonate concentrations below 0.25 M, lanthanum had the largest diffusion coefficient (ca. 10-13 m2/s) at 1.0 Mg/m3, and the diffusion coefficient decreased with increasing atomic number. On the other hand, at bicarbonate concentrations above 0.25 M, lutetium had the largest diffusion coefficient, and the diffusion coefficient decreased with decreasing atomic number. In particular, lanthanum and neodymium had diffusion coefficients below 10-14 m2/s, even at 1.0 Mg/m3. The diffusion coefficient of europium was around 10-13 m2/s at 1.0 Mg/m3 and was influenced less by the bicarbonate concentration. The diffusion coefficient of lutetium increased from 2 × 10-14 to 10-12 m2/s as the bicarbonate concentration was increased to 1.0 M. The concentration of carbonate ion in the pore water of bentonite is estimated to be much lower than that in solutions in contact with bentonite from the viewpoints of solubility and chemical species of lanthanides.

Diffusion of Cs and Sr in Compacted Bentonites Under Reducing Conditions and in the Presence of Corrosion Products of Iron

1997 ◽  
Vol 506 ◽  
Author(s):  
K. Idemitsu ◽  
Y Tachi ◽  
H. Furuya ◽  
Y. Inagaki ◽  
T. Arima
Keyword(s):  
Carbon Steel ◽  
Corrosion Product ◽  
Diffusion Coefficients ◽  
Corrosion Products ◽  
High Level Waste ◽  
Dry Density ◽  
Iron Corrosion ◽  
Apparent Diffusion Coefficients ◽  
Reducing Conditions ◽  
Apparent Diffusion

ABSTRACTIn high-level waste repositories, a carbon steel overpack will be corroded by consuming oxygen trapped in the repository after closure. Iron corrosion products are expected to interfere with migration of radionuclides by filling the pore in bentonite and sorbing radionuclides. In this study the apparent diffusion coefficients of cesium and strontium were measured in compacted Na-bentonites (Kunigel VI® and Kunipia F®, JAPAN) contacted with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients of cesium with and without corrosion product were 2.2 to 13 × 10−12 m2/s. The apparent diffusion coefficients of strontium with and without corrosion product were 3.1 to 25 × 10−12 m2/s. There were significant effects of dry density (0.8 to 2.0 g/cm3) and montmorillonite contents (50% for Kunigel V1 or 100% for Kunipia F). The presence of corrosion product decreased the apparent diffusion coefficients of Cs in both bentonites and that of Sr in Kunigel V1, especially at low dry density. This may be due to corrosion product filling the pore in the bentonite, decreasing the free pore size and density for diffusion.

Effect of Carbonate on the Migration Behavior of Strontium in Compacted Bentonite

MRS Advances ◽  
2019 ◽  
Vol 4 (17-18) ◽  
pp. 1021-1027
Author(s):  
Kazuya Idemitsu ◽  
Ryota Yamada ◽  
Masayuki Hirakawa ◽  
Yuki Kakoi ◽  
Hajime Arimitsu ◽  
...  
Keyword(s):  
Diffusion Coefficients ◽  
Inductively Coupled Plasma ◽  
Acrylic Resin ◽  
Diffusion Profile ◽  
Dry Density ◽  
Migration Behavior ◽  
Inductively Coupled ◽  
Apparent Diffusion Coefficients ◽  
Apparent Diffusion ◽  
The Face

ABSTRACTThe apparent diffusion coefficients of strontium in compacted bentonites were investigated at various concentrations of NaHCO3. Purified sodium bentonite Kunipia-F® was compacted with a jig into cylindrical pellets 10 mm in diameter and 10 mm high with dry densities of 1.0 to 1.6 Mg/m3. Each bentonite pellet was inserted into an acrylic resin column and saturated with carbonated water containing 0.1 to 1.0 M NaHCO3 for more than 1 month. The face of the bentonite specimen was spiked with 5 μL of 1.0 M SrCl2 tracer solution. After a few weeks, the strontium diffusion profiles were measured by inductively coupled plasma-mass spectrometry. The apparent diffusion coefficients of strontium decreased slightly with increasing dry density. NaHCO3 concentrations of 0.5 M decreased the apparent diffusion coefficients of strontium by half at a dry density of 1.0 Mg/m3 and quarter at 1.6 Mg/m3. At a higher NaHCO3 concentration of 1.0 M, no strontium diffusion profile was observed, whereas white precipitate was observed on the face of the bentonite specimen where it was spiked with strontium. This white precipitate could be strontianite, which is strontium carbonate. Diffusion experiments using cesium were carried out for comparison, and the presence of carbonate had no effect on the apparent diffusion coefficient.

DIFFUSION THROUGH SODIUM AND POLYMER ENHANCED BENTONITES EXPOSED TO DILUTE AND AGGRESSIVE SOLUTIONS

2020 ◽  
Author(s):  
Shan Tong ◽  
Kristin Sample-Lord ◽  
Gretchen Bohnhoff
Keyword(s):  
Diffusion Coefficients ◽  
Transport Mechanism ◽  
Sodium Bentonite ◽  
Apparent Diffusion Coefficients ◽  
Steady State Flux ◽  
Expected Performance ◽  
Apparent Diffusion ◽  
Order Of Magnitude ◽  
Cacl2 Concentration ◽  
Diffusion Properties

Chemical incompatibility between sodium bentonite (NaB) and aggressive waste solutions has led to the development of enhanced bentonites for geoenvironmental applications. Enhanced bentonites, such as bentonite-polyacrylic-acid composite (BPC), have been shown to maintain low enough values of hydraulic conductivity (e.g. < 10-10 m/s) for diffusion to be the dominant transport mechanism, even upon exposure to aggressive solutions. However, quantification of diffusion properties of enhanced bentonites has been limited. In this study, apparent diffusion coefficients (Da) for chloride were measured for NaB and polymer enhanced NaBs. Diffusion tests were performed using dilute (5 mM) to aggressive (100 mM) calcium chloride (CaCl2) solutions. In addition, scanning electron microscopy was performed to support interpretation of diffusion results. For CaCl2 solutions < 100 mM, Da values for BPC were lower (by approximately half an order of magnitude) than Da values for NaB. However, differences in Da due to polymer enhancement diminished as CaCl2 concentration increased. Predicted steady-state flux through a BPC geosynthetic clay liner (GCL) was dominated by diffusion and up to two orders of magnitude lower than flux through an NaB GCL. These results provide insight regarding diffusion in polymer enhanced bentonites and expected performance of containment barriers with enhanced-bentonite GCLs.

Diffusion of Uranium in Compacted Bentonites in the Reducing Condition with Corrosion Products of Iron

1995 ◽  
Vol 412 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Y. Tachi ◽  
H. Furuya ◽  
Y. Inagaki ◽  
T. Arima
Keyword(s):  
Carbon Steel ◽  
Pore Water ◽  
Diffusion Coefficients ◽  
Corrosion Products ◽  
Redox Conditions ◽  
High Level Waste ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Reducing Conditions ◽  
Apparent Diffusion

AbstractIn high-level waste repository, a carbon steel overpack will be corroded after closure. This will create a reducing environment in the vicinity of the repository. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as uranium.The apparent diffusion coefficients of uranium were measured in compacted bentonites (Kunigel VI® and Kunipia F®, JAPAN) in contact with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients measured were 10-12 to 10-14 m2/s under oxidizing conditions and 10-13 to 10-14 m2/s under reducing conditions. There were significant effects of redox conditions, dry density (0.8 to 2.0 g/cm3) and montmorillonite contents (60% for Kunigel VI or 100% for Kunipia F) on the apparent diffusion coefficients. The sorption of uranium on corrosion products of iron was smaller than that on montmorillonite. Montmorillonite density could be a good index to explain density dependence of the diffusion coefficients under the reducing conditions. Uranium would diffuse in free pore water with diffusion coefficients greater than 10-13 m2/s in low density bentonites under both redox conditions because the diffusion coefficients depended on sorption coefficients. Since diffusion coefficients were independent of sorption coefficients in high density bentonites where free pore water is scarce, surface diffusion might occur with coefficients were of about 10-13 m2/s.

Diffusion of Technetium in Compacted Bentonites in the Reducing Condition with Corrosion Products of Iron

1996 ◽  
Vol 465 ◽  
Author(s):  
Yuji Kuroda ◽  
K. Idemitsu ◽  
H. Furuya ◽  
Y. Inagaki ◽  
T. Arima
Keyword(s):  
Carbon Steel ◽  
Diffusion Coefficients ◽  
Corrosion Products ◽  
High Level Waste ◽  
Dry Density ◽  
Apparent Diffusion Coefficients ◽  
Reducing Conditions ◽  
Apparent Diffusion ◽  
Reducing Environment ◽  
High Level

ABSTRACTIn the vicinity of a high-level waste repository, corrosion of carbon steel overpacks will create a reducing environment. Reducing conditions are expected to retard the migration of redox-sensitive radionuclides such as technetium.The apparent diffusion coefficients of technetium were measured in compacted bentonites (Kunigel VI® and Kunipia F®, JAPAN) in contact with carbon steel and its corrosion products under reducing conditions or without carbon steel under oxidizing conditions for comparison. The apparent diffusion coefficients measured were 10-12 to 10-13 m2/s under oxidizing conditions and 10-12 to 10-13 m2/s under reducing conditions. There were significant effects of redox condition, dry density (0.2 to 2.3 g / cm3) and montmorillonite content (50% for Kunigel VI or 100% for Kunipia F) on the apparent diffusion coefficients. Montmorillonite density could be a good index to explain density dependence of the diffusion coefficients under both reducing and oxidizing conditions.

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