Diffusion Mecflanisms of Srrontium and Cesium in Compacrtd Sodium Bentonite

1986 ◽  
Vol 84 ◽  
Author(s):  
Armo Muurinen ◽  
Pirkkd Penitä-Hiltunen ◽  
Juba Rantanen
Keyword(s):  
Stationary State ◽  
Effective Diffusivity ◽  
Radioactive Tracer ◽  
Pore Diffusion ◽  
Batch Experiments ◽  
Diffusion Measurement ◽  
Sodium Bentonite ◽  
Compacted Bentonite ◽  
Effective Diffusivities

AbstractIn this research the diffusion of strontium and cesium through bento- nite slabs in stationary state has been measured. The measurement gives directly the transport through the sample and the corresponding effective diffusivity. The apparent diffusivity, diffusivity of the sorbed ions as well as the sorption factors can also be evaluated on the basis of the same diffusion measurement. The sorption on the coxmpacted bentonite has also been measured in a special sorption test where a radioactive tracer has been allowed to diffuse into compacted bentonite until equilibrium was reached.The measured effective diffusivities were clearly higher than they would be in the case of pure pore diffusion. The effective diffusivities also increase with K and the apparent diffusivities are almost independent on KD. This supports the theory that also the sorbed ions diffuse in their own phase. The sorption factors of the compacted bentonite correspond to the values of the batch experiments.

Diffusivities of Cesium and Strontium in Concretes and in Mixtures of Sodium Bentonite and Crushed Rock

1984 ◽  
Vol 44 ◽  
Author(s):  
Arto Muurinen ◽  
Juha Rantanen ◽  
Raisa Ovaskainen
Keyword(s):  
Surface Diffusion ◽  
Diffusion Model ◽  
Transport Phenomena ◽  
Pore Diffusion ◽  
Crushed Rock ◽  
Sorption Model ◽  
Sodium Bentonite ◽  
Sorption Data ◽  
Order Of Magnitude ◽  
Effective Diffusivities

AbstractDiffusivities of Cs and Sr in concretes and in mixtures of sodium bentonite and crushed rock were measured. The order of magnitude of the apparent diffusivities (Da) for Cs and Sr in concretes was −14−10−13 m2/s and in the mixtures of bentonite and crushed rock 10−13− 10−11 m2/s. The calculated effective diffusivities (De) in the mixtures of bentonite and crushed rock seemed in some cases to exceed the corresponding values in water, which suggests that the pore diffusion/sorption model cannot explain the transport phenomena in all cases.The experiments where the sorption factors were varied in the diffusion samples suggest that the nuclides diffuse also while being sorbed. A combined pore diffusion-surface diffusion model has been used to explain the transport and the corresponding diffusivities have been evaluated. This paper will give the measured diffusion and sorption data and discuss the models used to describe diffusion in porous sorbing agents.

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.

Grouted Waste Leach Tests: Pursuit of Mechanisms and Data for Long-Term Performance Assessment

1989 ◽  
Vol 176 ◽  
Author(s):  
R. Jeff Serne
Keyword(s):  
Diffusion Processes ◽  
Scale Up ◽  
Liquid Waste ◽  
Effective Diffusivity ◽  
Cementitious Materials ◽  
Solidified Waste ◽  
Effective Diffusivities ◽  
Long Term Performance ◽  
Term Performance

ABSTRACTAt Hanford, low-level liquid nuclear waste is being mixed with cementitious materials (grout) to form leach-resistant solid waste. Prior to grouting each liquid waste, an assessment must be performed to evaluate the long-term environmental impact. These predictions rely upon a diffusioncontrolled release model and short-term laboratory leach data on small grout samples. This paper describes size scale-up and inventory scale-up experiments that evaluate whether diffusion does in fact control the release of contaminants. The results of the volume scale-up test suggest that tests on grout cylinders between the sizes 3 cm dia. by 3 cm length and 30 cm dia. by 29 cm length yield comparable results. These data and other available literature suggest that extrapolation of leach results to large blocks of solidified waste is defensible.The inventory scale-up tests for 125I and selenium show a constant effective diffusivity regardless of the original inventory. This suggests that diffusion processes do in fact control the release of iodide and selenium from grout. The 99Tc effective diffusivities may not remain constant with changes in inventory.

Matrix Diffusion of Some Alkali- and Alkaline Earth-Metals in Granitic Rock

1996 ◽  
Vol 465 ◽  
Author(s):  
H. Johansson ◽  
J. Byegård ◽  
G. Skarnemark ◽  
M. Skålberg
Keyword(s):  
Alkaline Earth ◽  
Tritiated Water ◽  
Size Fraction ◽  
Effective Diffusivity ◽  
Alkaline Earth Metals ◽  
Capacity Factor ◽  
Dimensional Solution ◽  
Crushed Material ◽  
Fine Grained ◽  
Effective Diffusivities

ABSTRACTStatic through-diffusion experiments were performed to study the diffusion of alkali- and alkaline earth-metals in fine-grained granite and medium-grained Äspö-diorite. Tritiated water was used as an inert reference tracer. Radionuclides of the alkali- and alkaline earth-metals (mono- and divalent elements which are not influenced by hydrolysis in the pH-range studied) were used as tracers, i.e. 22Na+, 45Ca2+ and Sr The effective diffusivity and the rock capacity factor were calculated by fitting the breakthrough curve to the one-dimensional solution of the diffusion equation. Sorption coefficients, Kd, that were derived from the rock capacity factor (diffusion experiments) were compared with Kd determined in batch experiments using crushed material of different size fractions.The results show that the tracers were retarded in the same order as was expected from the measured batch Kd. Furthermore, the largest size fraction was the most representative when comparing batch Kd with Kd evaluated from the diffusion experiments. The observed effective diffusivities tended to decrease with increasing cell lengths, indicating that the “transport” porosity decreases with increasing sample lengths used in the diffusion experiments.

scholarly journals Sorption and Diffusion Properties of H- and Modified Forms of ZSM-5 Zeolites

1996 ◽  
Vol 13 (6) ◽  
pp. 495-508 ◽  
Author(s):  
P. Hudek ◽  
D. Bobok ◽  
A. Smiešková ◽  
Z. Židek
Keyword(s):  
Physical Adsorption ◽  
Gravimetric Method ◽  
Equilibrium Concentration ◽  
Sorption Isotherms ◽  
Effective Diffusivity ◽  
Micropore Volume ◽  
Unit Cell ◽  
Adsorption Of Nitrogen ◽  
Effective Diffusivities ◽  
Modified Forms

The sorption properties of samples of H-ZSM-5 zeolite and their forms modified with P, B and Mg were determined by the physical adsorption of nitrogen and evaluated by BET isotherm and t-plot methods. The diffusivities of the samples were measured using a new flow gravimetric method involving the sorption of p- and o-xylenes. The BET specific surface area decreased from 358 m2/g to 35–90 m2/g mainly because of a decrease in micropore volume as determined by the t-plot method. The rate of sorption of p-xylene on all the samples investigated followed Fick's second law of diffusion, leading to an effective diffusivity of ca. 1.7 × 10−11 m2/s, irrespective of whether the H-form or the modified forms were investigated. The sorption isotherms for o-xylene showed some unusual steps. Values for the effective diffusivities decreased from 2.6 × 10−12 m2/s for the H-form to 2.0–2.3 × 10−12 m2/s for the modified forms. The equilibrium concentration of o-xylene at P/P0 = 0.1 was only 0.38–0.68 mol/unit cell, while that of p-xylene was 4.40–5.98 mol/unit cell.

Effects of Processing Factors on Microstructure and Diffusivity of Diethylbenzene Dehydrogenation Catalyst

2010 ◽  
Vol 297-301 ◽  
pp. 233-238
Author(s):  
Mohammad Ebrahim Zeynali ◽  
I. Soltani
Keyword(s):  
Grain Size ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Bulk Diffusion ◽  
Effective Diffusivity ◽  
Catalyst Pellet ◽  
Different Types ◽  
Effective Diffusivities ◽  
Processing Factors

In this study, different mechanisms of diffusion such as Knudsen and bulk were investigated for diethylbenzene diffusion into a catalyst and it was concluded that the pore sizes should be in the range that permit transitional diffusion (both Knudsen and bulk diffusion). The catalyst grain size can be controlled and varied by different parameters such as speed and time of mixing, type of alkali, temperature and pH. Particle size distribution experiments were conducted for different types of alkali and speed of mixing to characterize the catalyst. The effects of grain size formed during coprecipitation on pore size distribution of the catalyst pellet which affect the effective diffusivity were discussed. Pore size distribution of the model catalyst was obtained and the effective diffusivities were calculated by numerical integration of Johanson-Stewart equation.

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.

Fluid Dispersion and Distribution in Porous Media Using the Frequency Response Method With a Radioactive Tracer

1966 ◽  
Vol 6 (02) ◽  
pp. 143-152 ◽  
Author(s):  
R.R. Goddard
Keyword(s):  
Porous Medium ◽  
Phase Velocity ◽  
Frequency Response ◽  
Fluid Velocity ◽  
Effective Diffusivity ◽  
Radioactive Tracer ◽  
Dead End ◽  
Frequency Response Method ◽  
Response Method ◽  
The Waves

Abstract By use of the frequency response method with a radioactive tracer, it was possible to determine fluid dispersion and distribution in a natural consolidated and an unconsolidated medium. Measurements were made in a linear flow system at oleic saturations of 69 per cent in the consolidated medium, and 100 per cent in both media. Dispersion and distribution were obtained by measuring the amplitude attenuation and the phase velocity of sinusoidal waves with a dual monitor apparatus. The gamma ray emissions permitted in situ measurements at any distance along the porous samples. One result of importance was that the effective diffusivity increased as the wave length increased. As a consequence, a dispersion coefficient appropriate for the injection of large slugs might exceed the value measured by use of small slugs. Since flow models based solely on fluid velocity and an effective diffusivity coefficient imply that the diffusivity should be independent of frequency, such representations were not adequate for the data of this study. A comparison was made with a capacitance model of porous media with dead-end PV's, but even this model was not completely adequate. By using attenuation and phase velocity data, fluid dispersion can be predicted without postulating a differential equation satisfied by the tracer concentration, thereby eliminating the need of a complicated model to represent dispersion. Introduction The flow of similar miscible fluids through a porous medium can be fairly adequately described by two parameters: the average fluid velocity and the effective diffusivity.1-3 It has been pointed out recently, however, that significant discrepancies exist between this representation and the experimental data.4-7 An improved agreement can be obtained by introducing additional parameters based on the concept of dead-end pores. The purpose of the present investigation was to find out whether the frequency response method could be used to measure the relevant parameters. The method was used in the following form. A stream of fluid was flowed at a constant rate through a sample of porous material and the concentration of a radioactive tracer in the fluid was varied sinusoidally at a fixed frequency. The effects of flow through a porous medium are a decrease in the amplitude of the concentration wave and an increase in the velocity of the peaks of the waves above the average velocity. Attenuation and phase velocity of the waves were measured as a function of frequency and fluid velocity. The simple two-parameter model implies that the diffusivity should be independent of frequency. Data reported in this paper show that the diffusivity decreases as the frequency increases. Hence, as shown also by many others, the two-parameter model is not completely adequate. Coats and Smith5 used two additional parameters in their model: the volume of the dead-end pores and the rate of mass transfer between dead-end pores and the flowing stream. Their capacitance model of a porous medium containing some stagnant fluid, to which transfer occurs by molecular diffusion, did not explain the dispersion results of either the present study or of theirs. Instead, the capacitance effect can be better described as the result of extreme velocity variations within the pores of the medium, with transfer between the velocity zones by convection.

Effective diffusivity of neptunium and plutonium in granite from Inada, Ibaraki, Japan under anaerobic conditions

2002 ◽  
Vol 90 (12) ◽  
Author(s):  
Tetsuji Yamaguchi ◽  
S. Nakayama ◽  
H. Okamoto
Keyword(s):  
Effective Diffusivity ◽  
Diffusion Method ◽  
Anaerobic Conditions ◽  
Through Diffusion ◽  
Effective Diffusivities

SummaryThe effective diffusivities of neptunium and plutonium in Inada granite have been determined using the through–diffusion method. Experiments were performed under anaerobic conditions in the presence of carbonate. The actinides are expected to be present as carbonato or carbonatohydroxo complexes. Effective diffusivity (D

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