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Long-term Corrosion of Zircaloy-4 and Zircaloy-2 by Continuous Hydrogen Measurement under Repository Condition

Published online by Cambridge University Press:  23 January 2013

Tomofumi Sakuragi ,
Hideaki Miyakawa ,
Tsutomu Nishimura  and
Tsuyoshi Tateishi
Tsutomu Nishimura
Affiliation:
Kobe Steel, Ltd., 4-7-2 Iwaya-Nakamachi, Nada-ku, Kobe 657-0845, Japan
Tsuyoshi Tateishi
Affiliation:
Kobelco Research Institute, Inc., 1-5-5 Takatsukadai, Nishi-ku, Kobe 657-2271, Japan
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Abstract

Corrosion behavior is a key issue for the waste disposal of irradiated metals, such as hulls and endpieces, and is considered to be a leaching source of radionuclides including C-14. However, little information about Zircaloy corrosion in anticorrosive conditions has been provided.

In the present study, long-term corrosion tests of Zircaloy-4 and Zircaloy-2 were performed in assumed disposal conditions (dilute NaOH solution, pH 12.5, 303 K) by using the gas flow system for 1500 days. The corrosion rate, which was determined by measuring gaseous hydrogen and the hydrogen absorbed in Zircaloy, decreased with immersion time and was lower than the value of 2×10−2 μm/y used in performance assessment (1500-day values: 5.84×10−3 and 5.66×10−3 μm/y for Zircaloy-4, 1000-day values: 8.81×10−3 μm/y for Zircaloy-2). The difference in corrosion behavior between Zircaloy 4 and Zircaloy-2 was negligible. The average values of the hydrogen absorption ratios for Zircaloy-4 and Zircaloy-2 during corrosion were 91% and 94%, respectively.

The hydrogen generation kinetics of both gas evolution and absorption into metal can be shown by a parabolic curve. This result indicates that the diffusion process controls the Zircaloy corrosion in the early corrosion stage of the present study, and that the thickness of the oxide film in this stage is limited to approximately 25 nm and may therefore be in the form of dense tetragonal zirconia.

Keywords

corrosionZrwaste management
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1518: Symposium LL – Scientific Basis for Nuclear Waste Management XXXVI , 2012 , pp. 173 - 178
Copyright
Copyright © Materials Research Society 2013 

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References

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