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

MRS Proceedings ◽

10.1557/proc-333-939 ◽

1993 ◽

Vol 333 ◽

Cited By ~ 3

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.

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

MRS Proceedings ◽

10.1557/proc-412-683 ◽

1995 ◽

Vol 412 ◽

Cited By ~ 5

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.

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

MRS Proceedings ◽

10.1557/proc-465-909 ◽

1996 ◽

Vol 465 ◽

Cited By ~ 7

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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Diffusion of Corrosion Products of Iron in Compacted Bentonite.

MRS Proceedings ◽

10.1557/proc-294-467 ◽

1992 ◽

Vol 294 ◽

Cited By ~ 2

Author(s):

K. Idemitsu ◽

H. Furuya ◽

Y. Inagaki

Keyword(s):

Carbon Steel ◽

Corrosion Product ◽

Hydrogen Generation ◽

Ferric Hydroxide ◽

Corrosion Products ◽

Ferrous Ion ◽

Silica Sand ◽

High Level Waste ◽

Buffer Material ◽

The Difference

ABSTRACTCarbon steel is one of the candidate overpack materials for high-level waste disposal. The corrosion rate of carbon steel is reduced by the presence of buffer materials such as bentonite and seems to be affected by the diffusion of corrosive materials and corrosion products through the buffer material.The apparent diffusivities of corrosion product of iron were measured in some bentonite specimens in contact with carbon steel. The apparent diffusivities of iron were also measured without carbon steel for comparison. The apparent diffusivities of corrosion product were on the order of 10−12 m2/s and showed a tendency to decrease with increasing density of the bentonite specimen. There was no significant effect of silica sand on the apparent diffusivities. The apparent diffusivities of iron in the system without carbon steel were in the range of 10−14 m2/s and showed a tendency to increase with increasing silica sand content. The difference of the diffusivities between corrosion product and iron without carbon steel seems to be due to the difference of diffusing species. The color of the corrosion product was dark-green during contact with bentonite specimens and became red on exposure to air in a few minutes. Gas bubbles were also observed in the corrosion product. This suggests hydrogen generation during corrosion of the carbon steel. Thus the diffusing species seems to be in a reduced state, probably ferrous ion. On the other hand, the diffusing species of iron without carbon steel was probably a ferric hydroxide complex that was negatively charged. This suggests that ferrous ion could diffuse in the surface water adsorbed on bentonite, while ferric complex was excluded.

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

MRS Proceedings ◽

10.1557/opl.2012.641 ◽

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.

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

MRS Proceedings ◽

10.1557/proc-506-351 ◽

1997 ◽

Vol 506 ◽

Cited By ~ 6

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.

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Migration Behavior of Ferrous Ions in Compacted Bentonite Under Reducing Conditions Using Electromigration

MRS Proceedings ◽

10.1557/proc-824-cc8.47 ◽

2004 ◽

Vol 824 ◽

Author(s):

Kazuya Idemitsu ◽

Xiaobin Xia ◽

Yoshiro Kikuchi ◽

Yaohiro Inagaki ◽

Tatsumi Arima

Keyword(s):

Carbon Steel ◽

Corrosion Rate ◽

Electrical Potential ◽

Infiltration Rate ◽

Corrosion Products ◽

Ferrous Ion ◽

High Level Waste ◽

Dry Density ◽

Compacted Bentonite ◽

Buffer Material

AbstractCarbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. The lifetime of the carbon steel overpack will depend on its corrosion rate. The corrosion rate of carbon steel is reduced by the presence of buffer material such as bentonite. Buffer material will delay the supply of corrosive materials and discharge of corrosion products through it. Carbon steeloverpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. Therefore, it is important to study the migration of iron corrosion products through the buffer material because it may affect the corrosion rate of overpack, migration of redox-sensitive radionuclides, and the properties of the buffer material. Electromigration experiments have been carried out with source of iron ions supplied byanode corrosion of iron coupon in compacted bentonite. The carbon steel coupon was connected as the working electrode to the potentiostat and was held at a constant applied potential between - 200 to 1000 mV vs. Ag/AgCl electrode for 48 hours. Corrosion currents were 0.5 to 2mA initially and depended on the supplied electrical potential, then decreased to approximately 0.1 mA in a few hours. The final corrosion current was independent of supplied electrical potential. It is expected that iron ion could migrate as ferrous ion through interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. The rate-determining process of this experimental configuration could be infiltration rate of ferrousioninto bentonite. Infiltration rate of ferrous ion into bentonite was increasing with dry density of bentonite.

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Effect of pH on Plutonium Migration Behavior in Compacted Bentonite

MRS Advances ◽

10.1557/adv.2017.183 ◽

2016 ◽

Vol 1 (61) ◽

pp. 4011-4017

Author(s):

Ryo Hamada ◽

Noriyuki Maeda ◽

Kazuya Idemitsu ◽

Yaohiro Inagaki ◽

Tatsumi Arima ◽

...

Keyword(s):

Pore Water ◽

Diffusion Coefficients ◽

High Level Waste ◽

Migration Behavior ◽

Effect Of Ph ◽

Apparent Diffusion Coefficients ◽

Compacted Bentonite ◽

Ph Values ◽

Apparent Diffusion ◽

High Level

ABSTRACTIn disposing of high-level radioactive waste, the drop in pH in the repository as the iron overpack corrodes must be considered. Plutonium migration behavior may be affected by the pH of pore water in compacted bentonite barriers in high-level waste repositories. To examine the effect of pH on migration behavior, H-bentonite was prepared by treating Japanese Na-bentonite, Kunipia-F, with hydrochloric acid. Diffusion experiments were performed with mixtures of Na- and H-bentonites. The pH value in the pore water of the water-saturated bentonite mixtures decreased from 8 to 3 as the mixing ratio of H-bentonite increased. Diffusion experiments were carried out by using238Pu then apparent diffusion coefficients were determined from the plutonium distribution in the specimens. The apparent diffusion coefficients were on the order of 10-13to 10-12m2/s at pH values lower than 4, whereas they were less than 10-14m2/s at pH values higher than 6.5. These results indicate that plutonium diffused faster as Pu3+or PuO22+due to disproportionation at lower pH while plutonium could be retarded as Pu(OH)40by sorption on bentonite at higher pH.

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Effect of Compacted Bentonite on the Corrosion behavior of Carbon Steel as Geological Isolation Overpack Material

MRS Proceedings ◽

10.1557/proc-212-287 ◽

1990 ◽

Vol 212 ◽

Cited By ~ 6

Author(s):

A. Honda ◽

T. Teshima ◽

K. Tsurudome ◽

H. Ishikawa ◽

Y. Yusa ◽

...

Keyword(s):

Aqueous Solution ◽

Carbon Steel ◽

Corrosion Rate ◽

Sea Water ◽

Test Period ◽

Dry Density ◽

Compacted Bentonite ◽

Influence Of Temperature On ◽

Order Of Magnitude ◽

Average Corrosion Rate

ABSTRACTThe corrosion rate of carbon steel in compacted bentonite was evaluated with regard to the test period length, temperature, chemicals of solution and bulk density of compacted bentonite.The average corrosion rate decreased gradually with increasing test period up to 180 days in immersion tests. The corrosion rate of carbon steel in compacted bentonite at a dry density of 1.32g/cm3 was estimated to be about 0.01 mm/y which was one order of magnitude lower than that in bentonite slurry. No significant influence of temperature on corrosion rates was observed in compacted bentonite in the range of 50∼180 °C. Variation of kinds and concentration of anion(chloride, floride, sulfate, and carbonate)in aqueous solution did not have much influence on the corrosion rate of carbon steel.Immersion tests of carbon steel in compacted bentonite at a dry density of 0.69 ∼ 1.32 g/cm3, which was mixed with an aqueous solution(synthetic sea water and distilled water), were carried out. The corrosion rate in compacted bentonite decreased from 0.04 to 0.005mm/y as the density of bentonite increased.This result suggests that the corrosion rate of carbon steel in compacted bentonite is governed by the diffusivity of corrosive materials. In general, oxygen is the dominate factor affecting corrosion rate, therefore prediction of the average corrosion rate of carbon steel was carried out on the basis of the diffusion behavior of dissolved oxygen in compacted bentonite. The prediction agreed with experimental results.

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Performance Assessment of a High-Level-Waste Repository in Clay

MRS Proceedings ◽

10.1557/proc-127-563 ◽

1988 ◽

Vol 127 ◽

Author(s):

Jan L. Marivoet ◽

Geert Volckaert ◽

Arnold A. Bonne

Keyword(s):

Performance Assessment ◽

Maximum Dose ◽

High Level Waste ◽

Clay Layer ◽

Geological Disposal ◽

Dose Rates ◽

Consequence Analysis ◽

Calculated Dose ◽

Order Of Magnitude ◽

High Level

ABSTRACTPerformance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.

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