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Long-Term Extrapolation of Passive Behavior of Alloy 22

Published online by Cambridge University Press:  11 February 2011

Osvaldo Pensado
Affiliation:
Center for Nuclear Waste Regulatory Analyses (CNWRA), 6220 Culebra Road, San Antonio TX, U.S.A.
Darrell S. Dunn
Affiliation:
Center for Nuclear Waste Regulatory Analyses (CNWRA), 6220 Culebra Road, San Antonio TX, U.S.A.
Gustavo A. Cragnolino
Affiliation:
Center for Nuclear Waste Regulatory Analyses (CNWRA), 6220 Culebra Road, San Antonio TX, U.S.A.
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Abstract

Common assumptions to extrapolate the lifetime of proposed high-level waste disposal containers made of Ni-Cr-Mo alloys, in the absence of environmental and electrochemical conditions leading to localized corrosion and stress corrosion cracking, are evaluated based on a mechanistic model for passive dissolution. The predominant charge conduction mechanism through the oxide film formed on Ni-Cr-Mo alloys is hypothesized to be interstitial transport of metal cations. Dissolution of the alloy and conduction of interstitial species through the film create vacancies in the alloy. The anodic current density under potentiostatic control decreases as a function of time, and potentiostatic decays in the current density are rationalized on the basis of vacancy accumulation at the metal-oxide interface. It is concluded that the dissolution process is regulated by vacancy-enhanced diffusion of the elements in the alloy. Long-term stoichiometric dissolution arises if the diffusion coefficients of the alloying elements are similar. No credible scenario is envisioned by which catastrophic failure may occur as a result of longterm passive dissolution.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

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