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JAEA Reports

Raman spectroscopic measurements of porewater in bentonite

Suzuki, Satoru; ; *

JNC TN8400 2000-020, 25 Pages, 2000/04

JNC-TN8400-2000-020.pdf:0.94MB

Nature of porewater in bentonite plays important roles on the mass transport in the compacted bentonite used as a physical and chemical buffer material of the multi-barrier system in the high level radioactive waste manegement Higher activation energies of diffusion in the compacted bentonite than those in the aqueous solution is due probably to change in molecular structure of water in the porewater. The Raman spectroscopy was applied to studying the structure of porewater in bentonite at room temperature. Bentonite (Kunipia F, 98-99wt% of Na-smectite) was mixed with ion-exchanged water by water content of 75, 80, 90, 95 and 98wt% of water or with 0.5M NaCl aqueous solution by 75 and 80wt% of NaCl solution. Intensity maxima of the spectra of ion exchanged water, NaCl solution and their porewater were observed near 3200 to 3250, 3400, 3630cm$$^{-1}$$. These bands can be attributed to water molecules forming stronger hydrogen bond in this manner. Ratio of intensity, 3250cm$$^{-1}$$/3400cm$$^{-1}$$, increased from 0.97 to 1.1 with a decrease in water content of 100wt% (water) to 75wt%. On the other hand, intensity ratio of 3400cm$$^{-1}$$/3250cm$$^{-1}$$ of NaCl aqueous solution, 80wt%and 75wt% were 0.92, 1.2 and 1.3, respectively. Since the Raman scattering near 3250cm$$^{-1}$$ was attributed to water molecule forming the strongest hydrogen bonding in the three bands, those changes in intensity ratio suggests an increase in number of water molecule forming strong hydrogen bond in porewater of the bentonite. The constrained porewater possibly results in the high activation energy of diffusion in the compacted bentonite.

JAEA Reports

Experimental study of pyrite oxidation in compacted sodium bentonite

JNC TN8400 2000-012, 33 Pages, 2000/04

JNC-TN8400-2000-012.pdf:1.04MB

The redox condition of near-field is expected to affect the performance of engineered barrier system. Especially, the oxygen initially existing in the pore space of compacted bentonites strongly affects the redox condition of the near-field. For assessing the influence of the oxygen, the transport parameters of it in the compacted bentonite and consumption process should be known. Therefore, following researches were conducted. In order to understand the diffusion of dissolved oxygen (DO) in compacted bentonite and to predict the effect of DO, the effective diffusion coefficients of DO in compacted sodium bentonite were measured by electrochemistry. As the results, the following relationship between the dry density of compacted sodium bentonite and the effective diffusion coefficient of DO in compacted sodium bentonite was derived: De=1.53$$pm$$0.13$$times$$10$$^{-9}$$exp(-2.15$$pm$$0.24$$times$$10$$^{-3}$$p) where De is the effective diffusion coefficient (m$$^{2}$$s$$^{-1}$$) of DO in compacted sodium bentonite and $$rho$$ is the dry density (kg m$$^{-3}$$) of compacted sodium bentonite. The oxygen concentration in the bentonite is expected to be controlled by oxidation of pyrite as impurity in the bentonite. In order to investigate the above idea, the rates of pyrite oxidation by DO in compacted sodium bentonite were estimated from the experimental data on pyrite-bentonite systems usig the obtained effective diffusion coefficient of DO. The results show that the averages of the rate constants of pyrite oxidation by DO in the bentonite for dry densities of 0.8, 0.9, 1.0, 1.1 and 1.2$$times$$10$$^{3}$$kgm$$^{3}$$ were 1.38$$pm$$0.32$$times$$10$$^{-8}$$, 1.10$$pm$$0.24$$times$$10$$^{-8}$$, 1.16$$pm$$0.35$$times$$10$$^{-8}$$, 9.36$$pm$$2.23$$times$$10$$^{-9}$$ and 7.48$$pm$$1.92$$times$$10$$^{-9}$$ms$$^{-1}$$, respectively. The relationship between the dry density ($$rho$$) and the rate constant (k') was expressed as follows: k'=3.94$$pm$$1.06$$times$$10$$^{-8}$$exp(-1.33$$pm$$0.28$$times$$10$$^{-3}$$$$rho$$) ...

JAEA Reports

Static mechanical properties of buffer material

Takachi, Kazuhiko; Suzuki, Hideaki*

JNC TN8400 99-041, 76 Pages, 1999/11

JNC-TN8400-99-041.pdf:4.49MB

The buffer material is expected to maintain its low water permeability, self-sealing properties, radionuclides adsorption and retardation properties, thermal conductivity, chemical buffering properties, overpack supporting properties, stress buffering properties, etc. over a long period of time. Natural clay is mentioned as a material that can relatively satisfy above. Among the kinds of natural clay, bentonite when compacted is superior because (1)it has exceptionally low water permeability and properties to control the movement of water in buffer, (2)it fills void spaces in the buffer and fractures in the host rock as it swells upon water uptake, (3)it has the ability to exchange cations and to adsorb cationic radioelements. In order to confirm these functions for the purpose of safety assessment, it is necessary to evaluate buffer properties through laboratory tests and engineering-scale tests, and to make assessments based on the ranges in the data obtained. This report describes the procedures, test conditions, results and examinations on the buffer material of unconfined compression tests, one-dimensional consolidation tests, consolidated-undrained triaxial compression tests and consolidated-undrained triaxial creep tests that aim at getting hold of static mechanical properties. We can get hold of the relationship between the dry density and tensile stress etc. by Brazillian tests, between the dry density and unconfined compressive strength etc. by unconfined compression tests, between the consolidation stress and void ratio etc. by one-dimensional consolidation tests, the stress pass of each effective confining pressure etc. by consolidated-undrained triaxial compression tests and the axial strain rate with time of each axial stress etc. by consolidated-undrained triaxial creep tests.

JAEA Reports

A Study on Pore Structure of Compacted Bentonite (Kunigel-V1)

Sato, Haruo

JNC TN8400 99-064, 22 Pages, 1999/10

JNC-TN8400-99-064.pdf:1.45MB

Four kinds of diffusion experiments; (1)through-diffusion(T-D) experiments for compaction direction dependency, (2)in-diffusion(I-D) experiments for composition dependency of silica sand in bentonite, (3)I-D experiments for initial bentonite gain size dependency, and (4)I-D experiments for the restoration property of an artificial single fracture in compacted bentonite, were carried out using tritiated water which is a non-sorbing nuclide to evaluate the effect of pore structural factors for eompacted bentonite on diffudion. For(1), effective diffusivities (De) in Na-bentonites, Kunigel-V1 and Kunipia-F were measured for 1.0 and 1.5 Mg$$cdot$$m$$^{-3}$$. For(2), apparent diffusivities (Da) in Kunigel-V1 were measured for 0.8, 1.4 and 1.8 Mg$$cdot$$m$$^{-3}$$ with silica sand of 30 and 50 wt%. For(3), Da values for 0.8, 1.4 and 1.8 Mg$$cdot$$m$$^{-3}$$ were measured for a granulated Na-bentonite, OT-9607 which grain-size distribution is in a rang between 0.1 and 5 mm. For (4), Da values in Kunigel-V1 which a single fracture was artificially reproduced and was immersed in distilled water for 7 or 28 days for the restoration of the fracture, were measured for 1.8 Mg$$cdot$$m$$^{-3}$$. Although De values in Kunigel-V1 were approximately the same for both compacted directions over the density, De values for perpendicular direction to compacted direction were higher than those for the same direction as compacted direction in Kunipia-F. For composition dependency of silica sand in bentonite, no significant effect of the mixure of silica sand in bentonite on Da was found. For initial bentonite grain size dependency, Da values obtained for OT-960 were approximately the same as those for Kunigel-V1 and no effect of initial grain size of bentonite on diffusion was found. For the restoration property of a single fracture in compacted bentonite, no restoration period dependency on Da was found. Based on this, it may be said that diffusion of nuclides in compacted bentonite, ...

JAEA Reports

Acquisitions of effective diffusion coefficients (De) for Ni(II), Am(III), Sm(III) and Se(IV) in bentonite by through-diffusion method

Sato, Haruo

JNC TN8400 99-062, 16 Pages, 1999/10

JNC-TN8400-99-062.pdf:0.81MB

Effective diffusion coefficients (De) for Ni$$^{2+}$$, Sm$$^{3+}$$, Am$$^{3+}$$ and SeO$$_{3}^{2-}$$ were measured as a function of the ionic charge of diffusion species to quantitatively evaluate the effect of ionic charge in compacted bentonite. The De measurements for Ni$$^{2+}$$ and Sm$$^{3+}$$ were carried out for a bentonite dry density of 1.8 Mg$$cdot$$m$$^{-3}$$ with a simulated porewater condition of pH5$$sim$$6 by through-diffusion method. The De values for SeO$$_{3}^{2-}$$ were measured for a bentonite dry density of 1.8 Mg$$cdot$$m$$^{-3}$$ with a simulated porewater condition of pH11. The De measurements for Am$$^{3+}$$ were carried out for the dry densities of 0.8, 1.4 and l.8 Mg$$cdot$$m$$^{-3}$$ with a porewater condition of pH2 in order to check cation exclusion. Sodium bentonite, Kunigel-V1 was used for those measurements. For the measurements of Am, H-typed Kunigel-V1 which interlayer ion (Na$$^{+}$$) was exchanged with H$$^{+}$$ was used, because the experiments are carried out for a low pH range. The order of obtained De values was Sm$$^{3+}$$ $$>$$ Ni$$^{2+}$$ $$>$$ Am$$^{3+}$$ $$>$$ SeO$$_{3}^{2-}$$. These De values were compared to those reported to date. Consequently, the order of De values was Cs$$^{+}$$ $$>$$ Sm$$^{3+}$$ $$>$$ HTO $$>$$ Ni$$^{2+}$$ $$>$$ anions (I$$^{-}$$, Cl$$^{-}$$, CO$$_{3}^{2-}$$, SeO$$_{3}^{2-}$$ TcO$$_{4}^{-}$$, NpO$$_{2}$$CO$$_{3}^{-}$$, UO$$_{2}$$(CO$$_{3}$$)$$_{3}^{4-}$$), showing a tendency of cations $$>$$ HTO $$>$$ anions. Only the De values of Am$$^{3+}$$ were approximately the same degree as those of anions. The reason that the De of Ni$$^{2+}$$ was lower than that of HTO may be because the free water diffusion coefficient (Do) of Ni$$^{2+}$$ is about 1/3 of that of HTO. The cause that the De of Am$$^{3+}$$ was approximately the same degee as those of anions may be because the Do of Am$$^{3+}$$ is about 1/3 of that of HTO and that Am$$^{3+}$$ was electrostatically repulsed from the surface of bentonite by cation exclusion. The formation factors (FF), calculated normalizing Do, were in the ...

JAEA Reports

None

Suzuki, Hideaki*; Fujita, Tomoo

JNC TN8400 99-016, 34 Pages, 1999/03

JNC-TN8400-99-016.pdf:14.8MB

no abstracts in English

JAEA Reports

None

PNC TN8420 93-016, 63 Pages, 1993/10

PNC-TN8420-93-016.pdf:1.41MB

None

JAEA Reports

None

Sonobe, Hitoshi; Ishiguro, Katsuhiko

PNC TN8410 92-114, 85 Pages, 1992/03

PNC-TN8410-92-114.pdf:4.03MB

None

Oral presentation

Evaluation of colloid filtering function by compacted bentonite; Application of dendrimer

Endo, Takashi*; Ishidera, Takamitsu; Terashima, Motoki; Tachi, Yukio

no journal, , 

To evaluate the colloid filtering function by compacted bentonite, colloidal stability tests and through-diffusion tests of dendrimer, a dendritic macromolecule, were carried out under high saline conditions. As a result, dendrimer can allow to evaluate the colloid filtering function of compacted bentonite under the high saline condition which has been difficult by conventional method.

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