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

Published online by Cambridge University Press:  01 February 2011

Kazuya Idemitsu ,
Syeda Afsarun Nessa ,
Shigeru Yamazaki ,
Hirotomo Ikeuchi ,
Yaohiro Inagaki  and
Tatsumi Arima
Kazuya Idemitsu
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
Syeda Afsarun Nessa
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
Shigeru Yamazaki
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
Hirotomo Ikeuchi
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
Yaohiro Inagaki
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
Tatsumi Arima
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., Fukuoka, JAPAN
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Abstract

Carbon 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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1107: Scientific Basis for Nuclear Waste Management XXXI , 2008 , 501
Copyright
Copyright © Materials Research Society 2008

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