Migration Behaviour of Ferrous Ion in Compacted Bentonite Under Reducing Conditions Controlled With Potentiostat

2008 ◽  
Vol 1107 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Syeda Afsarun Nessa ◽  
Shigeru Yamazaki ◽  
Hirotomo Ikeuchi ◽  
Yaohiro Inagaki ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Dispersion Coefficient ◽  
Corrosion Products ◽  
Ferrous Ion ◽  
Iron Ions ◽  
Ferrous Ions ◽  
Iron Corrosion ◽  
Compacted Bentonite ◽  
Migration Behaviour ◽  
Buffer Material

AbstractCarbon steel overpack is corroded by consuming oxygen introduced by repository construction after closure of the repository and then maintains the reducing environment in the vicinity of the repository. The migration of iron corrosion products through the buffer material will affect the migration of redox-sensitive radionuclides. 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, and migration of redox-sensitive radionuclides. Electromigration experiments have been conducted with the source of iron ions supplied by anode corrosion of the iron coupon in compacted bentonite. The carbon steel coupon was connected as the working electrode to the potentiostat and was held at a constant supplied potential between - 650 to +300 mV vs. Ag/AgCl electrode for up to 168 hours. The amount of iron penetrated into a bentonite specimen was in good agreement with the calculated value from the corrosion current under the assumption that iron is dissolved as ferrous ions. A model using dispersion and electromigration could explain the measured iron profiles in the bentonite specimens. The fitted value of electromigration velocity depended on the potential supplied. On the other hand the fitted value of the dispersion coefficient did not depend on the potential supplied but a constant. This constant dispersion coefficient could be due to the much larger diffusion coefficient of ferrous ion in bentonite compared with the effect of mechanical dispersion. The experimental configurations used in this study are applicable to the examination of the migration behaviour of cations with the source of iron ions under a reducing condition controlled with a potentiostat.

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

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.

Diffusion of Corrosion Products of Iron in Compacted Bentonite.

1992 ◽  
Vol 294 ◽  
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.

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.

Migration Behavior of Plutonium in Compacted Bentonite Under Reducing Condition Using Electromigration

2006 ◽  
Vol 985 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Yosuke Yamasaki ◽  
Syeda Afsarun Nessa ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Electric Potential ◽  
Initial Period ◽  
High Level Waste ◽  
Diffusion Field ◽  
Migration Behavior ◽  
Ferrous Ions ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Reducing Condition

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. Carbon steel overpack 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. The migration of iron corrosion products through the buffer material will affect migration of redox-sensitive radionuclides. Therefore the authors have carried out electromigration experiments with source of iron ions supplied by anode corrosion of iron coupons attached to compacted bentonite. Authors tried to use plutonium in this experimental configuration to obtain the knowledge of migration behavior of actinides. Authors also used cesium as reference. The concentrations of iron and sodium showed nearly complementary distributions. It is expected that iron ion could migrate as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. Concentration profiles of plutonium in bentonite grew as time supplying electric potential as long as 168 h. Plutonium migrated from the iron anode toward cathode as deeper than 1 mm of the interior of bentonite even in 48 h, though plutonium could not diffuse 1 mm for 2 years. On the other hand, profiles of cesium seemed to be controlled by ordinary diffusion because of large diffusion coefficient of cesium in bentonite as large as 10$^{-12}$ m$^{2}$/s. Drift of the cesium profile by electric potential gradient could be observed clearly after 240 h at individual experiment for cesium. Apparent dispersion coefficients of plutonium were calculated from the profiles and were as large as 10$^{-13}$ m$^{2}$/s. Since plutonium migration was accelerated by electric potential, plutonium chemical species would have positive charge and were estimated as PuOH$^{2+}$ or PuCl$^{2+}$ by the thermodynamic calculation. Thus this experiment can provide a diffusion field for cations under a reducing condition with ferrous ions in water-saturated bentonite.

Migration Behavior of Cesium in Compacted Bentonite Under Reducing Conditions Using Electromigration

2006 ◽  
Vol 932 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Masaru Yamamoto ◽  
Yosuke Yamasaki ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Diffusion Field ◽  
Hydraulic Pressure ◽  
Migration Behavior ◽  
Ferrous Ions ◽  
Iron Corrosion ◽  
Osmotic Flow ◽  
Apparent Diffusion Coefficients ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Electro Osmotic Flow

ABSTRACTCarbon steel overpack 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. The migration of iron corrosion products through the buffer material will affect migration of redox-sensitive radionuclides. Therefore the authors have carried out electromigration experiments with source ofiron ions supplied by anode corrosion of iron coupons in compacted bentonite. However, their migration behavior was complex and difficult to explain. Thus, authors tried to use cesium, whose migration behavior is well known, inthis experimental configuration to obtain knowledge of the migration behavior of cations. The concentrationsof iron and sodium showed nearly complementary distributions. It is expected that iron ion could migrate as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. On the other hand, cesium profiles seemed to be controlled by ordinary diffusion. Drift of the cesium profile by electric potential gradient could be observed clearly only after 240 h. Apparent dispersion coefficients of cesium were calculated from the profiles and were in reasonable agreement with literature values of apparent diffusion coefficients. Thus this experiment can provide a diffusion field for cations under a reducing condition with ferrous ions in water-saturated bentonite. The effect of electro-osmotic flow on ion migration was negligibly small in this experiment because electro-osmotic flow was compensated by hydraulic pressure caused by the water content gradient developed in the specimen within 24h.

Migration behavior of plutonium affected by ferrous ion in compacted bentonite by using electrochemical technique

2014 ◽  
Vol 1665 ◽  
pp. 79-84
Author(s):  
Daisuke Akiyama ◽  
Kazuya Idemitsu ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima ◽  
Kenji Konashi ◽  
...  
Keyword(s):  
Dispersion Coefficient ◽  
Migration Velocity ◽  
Corrosion Products ◽  
High Level Waste ◽  
Dry Density ◽  
Migration Behavior ◽  
Ferrous Ions ◽  
Compacted Bentonite ◽  
Reducing Environment ◽  
Experiment Duration

ABSTRACTThe migration behavior of plutonium is expected to be affected by the corrosion products of carbon steel in compacted bentonite at high-level waste repositories. Electrochemical experiments were carried out to simulate the reducing environment created by ferrous iron ions in equilibrium with anoxic corrosion products of iron. The concentration profiles of plutonium could be described by the convection -dispersion equation to obtain two migration parameters: apparent migration velocity Va and apparent dispersion coefficient Da. The apparent migration velocity was evaluated within 1 nm/s and was found to be independent of the experiment duration and the dry density of bentonite in the interval 0.8-1.4 Mg/m3. The apparent dispersion coefficient increased with the experiment duration at a dry density of 1.4 Mg/m3. The results for other dry densities also showed the same trend. These findings indicate that plutonium migration likely starts after ferrous ions reach the plutonium, in other words, the reducing environment due to ferrous ions could change the chemical form of plutonium and/or the characteristics of compacted bentonite. The apparent diffusion coefficient was estimated to be around 0.5 to 2.2 µm2/s and increased with decreasing the dry density of bentonite.

Migration Behavior of Iron Ion in Compacted Bentonite Under Reducing Condition by using Electromigration.

2002 ◽  
Vol 757 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Seiji Yano ◽  
Xiaobin Xia ◽  
Yoshiro Kikuchi ◽  
Yaohiro Inagaki ◽  
...  
Keyword(s):  
Carbon Steel ◽  
Corrosion Rate ◽  
Initial Period ◽  
Corrosion Products ◽  
High Level Waste ◽  
Migration Behavior ◽  
Iron Ions ◽  
Iron Ion ◽  
Buffer Material ◽  
Reducing Condition

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 steel overpack 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. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the diffusion of corrosion products of iron in buffer material is important to discuss the corrosion rate of overpack, properties of buffer material and migration of redox-sensitive radionuclides. Electromigration experiments have been carried out with source of iron ions supplied by anode corrosion of iron coupon. Iron ions migrated as fast as 2mm in 2 or 3 hours under electrical field of 100V/m to the direction of cathode. Because the iron ions displaced exchangeable sodium ions in bentonite at a ratio of 1 to 2 during the electromigration, migrating iron ion could be ferrous ion.

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.

Hydrogen gas bubble nucleation from corrosion of steel in compacted bentonite

2021 ◽  
Author(s):  
Alexandros Papafotiou ◽  
Chao Li ◽  
Nikitas Diomidis ◽  
Olivier Leupin
Keyword(s):  
Carbon Steel ◽  
Gas Phase ◽  
Steel Surface ◽  
Bubble Nucleation ◽  
Hydrogen Gas ◽  
Flow And Transport ◽  
Compacted Bentonite ◽  
Shrinkage Cracks ◽  
Buffer Material ◽  
Steel Coupon

<p>The reference concept for the deep geological disposal of spent fuel and high-level radioactive waste in Switzerland foresees carbon steel disposal canisters surrounded by compacted bentonite buffer material. In support of performance assessments, long-term in-situ corrosion experiments were conducted in Opalinus Clay at the Mont Terri Underground Research Laboratory (URL) in Switzerland, wherein carbon steel coupons were embedded in MX-80 bentonite. The preparation of the steel specimens and bentonite, the exposure in a sealed borehole in the URL, and the retrieval, dismantling and imaging of specimens were conducted under strictly anoxic conditions. Samples were removed for analysis after exposure durations of 372, 628, 1024, and 2008 days. A key finding was the development of visible reddish-brown corrosion fronts around the metal surfaces and along shrinkage cracks that extend up to approximately 0.5 cm into the bentonite. Iron that originated from the corroded surface was transported along the cracks and precipitated as Fe-hydroxides due to oxygen sorbed on bentonite.</p><p>The formation of shrinkage cracks is thought to result from a local desaturation of the bentonite near the steel surface. To test this hypothesis i.e., to test the likelihood of a separate gas phase forming in addition to hydrogen mass dissolved in liquid water, it is necessary to evaluate the fate of hydrogen in the bentonite adjacent to the steel surface. For this, a flow and transport numerical model of the steel coupon surface and surrounding bentonite was implemented for the simulation of hydrogen release with the simultaneous consumption of water at the steel surface. The effect of single- and (potentially) two-phase flow with the diffusive and advective transport of the hydrogen and water components in the gas and liquid phases were modelled in a fully coupled manner. The numerical simulations were performed probabilistically in a Monte Carlo framework to account for parametric uncertainty, comprising 1’000 perturbations of all flow and transport parameters used in the model for the bentonite.</p><p>Overall, the simulation results are consistent with the hypothesis of a link between cracks observed in the bentonite and a temporary formation of a gas phase that results in preferential pathways for the transport of iron corrosion products.  The probability of gas formation in the model lies between 89% and 94% at the steel-bentonite interface and decreases significantly at distance of 1 cm from the steel coupon. Peak gas saturation at the steel-bentonite interface ranges up to approximately 1% with a mean value of approximately 0.18%. In all simulations, any gas phase forming in the bentonite dissolves back into the liquid phase within 300 days.</p>

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