Migration Behavior of Alkali Earth Ions in Compacted Bentonite With Iron Corrosion Product Using Electrochemical Method

2010 ◽  
Vol 1265 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Daisuke Akiyama ◽  
Akira Eto ◽  
Yoshihiko Matsuki ◽  
Yaohiro Inagaki ◽  
...  
Keyword(s):  
Dispersion Coefficient ◽  
Electrical Potential ◽  
Reference Electrode ◽  
Electrochemical Analysis ◽  
Dry Density ◽  
Migration Behavior ◽  
Iron Corrosion ◽  
Compacted Bentonite ◽  
Tracer Solution ◽  
Corrosion Of Iron

AbstractCarbon steel overpack will corrode by consuming oxygen introduced during repository construction after closure of repository, that will keep the environment in the vicinity of repository reducing. The iron corrosion products can migrate in bentonite as ferrous cations (Fe2+) through the interlayer of montmorillonite replacing the exchangeable sodium ions in the interlayer. This replacement of sodium may affect the migration behavior in the altered bentonite not only for redox-sensitive elements but also the other ions. Therefore we have carried out electrochemical analysis, of calcium, strontium or barium with the ferrous ion supplied by anodic corrosion of iron coupons in compacted bentonite. Fifteen micro liters of tracer solution containing 8.6 M of CaCl2 or 3.0 M of SrCl2 or 1.5 M BaCl2 were sspiked on the interface between the iron coupon and bentonite, for which the dry density was in the range of 1.4 to 1.5 Mg/m3, before assembling. The iron coupons were connected as working electrodes to the potentiostat and held at a constant supplied potential between - 500 to +300 mV (vs. Ag/AgCl reference electrode) for up to 7 days. Calcium and strontium could migrate faster and deeper into the bentonite than iron in each condition, while barium could migrate slower than iron. A model using dispersion and electromigration can explain the measured profiles in the bentonite specimens. The fitted value of electromigration velocity was a function of applied electrical potential and 10 to 23 nm/s for calcium, 11 to 19 for strontium, around 4 nm/s for barium and 5 to 15 nm/s for iron, respectively. Alternatively, the fitted value of the dispersion coefficient was not a function of applied potential, and the values were 3 - 8 × 10-12 m2/s for calcium, 2 - 4 × 10-12 m2/s for strontium, 5 - 10 × 10-12m2/s for barium and 3 - 9 × 10-12 m2/s for iron, respectively.

Migration Behavior of Potassium and Rubidium in Compacted Bentonite Under Reducing Condition With Iron Corrosion Product

2009 ◽  
Vol 1193 ◽  
Author(s):  
Kazuya Idemitsu ◽  
Hirotomo Ikeuchi ◽  
Daisuke Akiyama ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Electrical Potential ◽  
Reference Electrode ◽  
The Other ◽  
Ferrous Ion ◽  
Dry Density ◽  
Migration Behavior ◽  
Iron Corrosion ◽  
Compacted Bentonite ◽  
Tracer Solution ◽  
Corrosion Of Iron

AbstractCarbon steel overpack will corrode by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The iron corrosion products can migrate in bentonite as ferrous ion through the interlayer of montmorillonite replacing exchangeable sodium ions in the interlayer. This replacement of sodium with ferrous ion may affect the migration behavior in the altered bentonite not only for redox-sensitive elements but also the other ions. Therefore the authors have carried out electromigration experiments of potassium or rubidium with source of iron ions supplied by anode corrosion of iron coupon in compacted bentonite. Five to fifteen micro liter of tracer solution containing 3.3 M of KCl or 2.2 M of RbCl was spiked on the interface between an iron coupon and bentonite, which dry density was around 1.4 Mg/m3, before assembling. The iron coupon was connected as the working electrode to the potentiostat and was held at a constant supplied potential between - 600 and 300 mV vs. Ag/AgCl reference electrode for up to 8 days. Potassium could migrate faster and deeper in bentonite specimen than iron in each condition. On the other hand rubidium could migrate slower than iron. Migration velocity was a function of applied electrical potential and 8 to 14 nm/s for potassium, 5 to 10 nm/s for iron and 3 to 5 for rubidium, respectively. Dispersion coefficient was also a function of applied potential and 10 to 14 × 10−12 m2/s for potassium, 4 to 8 overv 10−12 m2/s for rubidium and 2 to 4 overv 10−12 m2/s for iron, respectively. Diffusion experiments were also carried out for comparison. Potassium and rubidium might migrate slightly slower in the altered bentonite by iron corrosion than in ordinary compacted bentonite.

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 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.

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.

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 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 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.

Migration Behavior of Selenium in the Presence of Iron in Bentonite

2014 ◽  
Vol 1665 ◽  
pp. 157-163
Author(s):  
Kazuya Idemitsu ◽  
Hikaru Kozaki ◽  
Daisuke Akiyama ◽  
Masanao Kishimoto ◽  
Masaru Yuhara ◽  
...  
Keyword(s):  
Oxidation State ◽  
High Level Waste ◽  
Dry Density ◽  
Precipitation Reaction ◽  
Migration Behavior ◽  
Ferrous Ions ◽  
Edge Structure ◽  
Tracer Solution ◽  
High Level ◽  
X Ray Absorption

ABSTRACTSelenium (Se) is an important element for assessing the safety of high-level waste disposal. Se is redox-sensitive, and its oxidation state varies from -2 to 6 depending on the redox conditions and pH of the solution. Large quantities of ferrous ions formed in bentonite due to corrosion of carbon steel overpack after the closure of a repository are expected to maintain a reducing environment near the repository. Therefore, the migration behavior of Se in the presence of Fe in bentonite was investigated by electrochemical experiments. Na2SeO3 solution was used as tracer solution. Dry density range of bentonite was from 0.8 to 1.4 ×103 kg/m3.Results indicated that Se was strongly retained by the processes such as precipitation reaction with ferrous ions in bentonite. Se K-edge X-ray absorption near-edge structure (XANES) measurements were performed at the BL-11 beamline at SAGA Light Source, and the results revealed that the oxidation state of Se in the bentonite remained Se(IV).

Migration Behavior of Copper in Compacted Bentonite Using Electromigration Techniques

MRS Advances ◽  
2020 ◽  
Vol 5 (3-4) ◽  
pp. 141-147
Author(s):  
Kazuya Idemitsu ◽  
Keisuke Yoshida ◽  
Yaohiro Inagaki ◽  
Tatsumi Arima
Keyword(s):  
Current Flow ◽  
Dispersion Coefficient ◽  
Corrosion Current ◽  
Migration Behavior ◽  
Compacted Bentonite ◽  
Buffer Material ◽  
Constant Potential ◽  
Deep Underground ◽  
And Migration ◽  
Good Agreement

ABSTRACTCopper is a candidate for use as an overpack material in deep underground nuclear waste disposal. Copper, however, is susceptible to corrosion following closure of the repository and migration of the corrosion products through the buffer material may affect the migration of redox-sensitive radionuclides. Electromigration experiments were performed whereby a copper coupon, which was in contact with compacted bentonite, served as the working electrode and was held at a constant potential of between +100 to +400 mV vs. Ag/AgCl electrode for up to 48 h. The amounts of copper that migrated into the bentonite specimens were found to be in good agreement with the calculated values based on the corrosion current flow for the assumption that copper underwent anodic dissolution as Cu(II). A model based on dispersion and electromigration was able to explain the measured copper profiles in the bentonite specimens. The fitted values of the dispersion coefficient did not depend on the applied potential and were about 10-12 m2/s.

Diffusion Behavior of Humic Acid in Compacted Bentonite: Effect of Ionic Strength, Dry Density and Molecular Weight of Humic Acid

2008 ◽  
Author(s):  
Kazuki Iijima ◽  
Seiichi Kurosawa ◽  
Minoru Tobita ◽  
Satoshi Kibe ◽  
Yuji Ohuchi
Keyword(s):  
Molecular Weight ◽  
Humic Acid ◽  
Ionic Strength ◽  
Dry Density ◽  
Diffusion Behavior ◽  
Compacted Bentonite
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