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Corrosion sous contrainte de l'alliage 600 en milieu primaire des réacteurs à eau sous pression : apport à la compréhension des mécanismes

Abstract : Alloy 600, a nickel base alloy (containing 15 wt% Cr), is susceptible to intergranular stress corrosion cracking in hydrogenated PWR primary water. Despite the fact that many laboratory studies have been performed and that many models have been proposed in the literature, the SCC mechanisms involved are still not well understood. Among others models, the internal oxidation model and models based on hydrogen/material interactions appear likely to explain this phenomenon. Therefore, the aim of this study is to improve our knowledge of Alloy 600 SCC mechanisms in PWR primary water. Experimental tests and calculations were performed in order to select models. Imposed strain specimens (“U-bend”) and without imposed strain specimens (coupon) were tested in simulated PWR primary water containing tracers (18 oxygen and deuterium). After testing, crack tips and intergranular oxide penetrations were characterized by SEM, TEM, SIMS, Nano-SIMS, and hydrogen titration permit to discuss oxide thermodynamic stability, oxide geometry and nature in crack tip, hydrogen role, intergranular chromium carbide role and cracking mode. Thus, a new model of cracking has been proposed. This model is based upon chromium oxide formation in the grain boundary. Material parameters (defect rate, strain, grain boundary type) and environmental parameters (hydrogen content, temperature) would affect oxygen diffusion kinetic across the oxide formed in the grain boundary and chromium diffusion kinetic in the grain boundary of the alloy.
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Submitted on : Monday, July 27, 2009 - 5:53:32 PM
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  • HAL Id : tel-00407846, version 1

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Pierre Laghoutaris. Corrosion sous contrainte de l'alliage 600 en milieu primaire des réacteurs à eau sous pression : apport à la compréhension des mécanismes. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2009. Français. ⟨NNT : 2009ENMP1617⟩. ⟨tel-00407846⟩

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