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

Published online by Cambridge University Press:  28 March 2012

Kazuya Idemitsu ,
Daisuke Akiyama ,
Yoshihiko Matsuki ,
Yusuke Irie ,
Yaohiro Inagaki  and
Tatsumi Arima
Kazuya Idemitsu
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
Daisuke Akiyama
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
Yoshihiko Matsuki
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
Yusuke Irie
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
Yaohiro Inagaki
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
Tatsumi Arima
Affiliation:
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University, Fukuoka, Japan
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Abstract

After 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.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1475: Symposium NW – Scientific Basis for Nuclear Waste Management XXXV , 2012 , imrc11-1475-nw35-p54
Copyright
Copyright © Materials Research Society 2012

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References

REFERENCES

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