ÉTUDE EXPÉRIMENTALE ET MODÉLISATION MÉCANIQUE DE LA CORROSION SOUS CONTRAINTE DES GAINES EN ZIRCALOY-4

Olivier Fandeur 1
1 LM2S - Laboratoire de Mécanique Systèmes et Simulation
DM2S - Département de Modélisation des Systèmes et Structures : DEN/DM2S/SEMT
Abstract : In Pressurised Water Reactor fuel assemblies, cladding tubes constitute the first safety barriers against the fission product dissemination. It is therefore essential to ensure their integrity under all the reactor operating conditions. During an important loading, resulting from severe reactor power transients, clad failures can be induced by a Stress Corrosion Cracking phenomenon (SCC) due to the combined action of mechanical loading and gaseous fission products generated by the fuel pellets.The aim of our work is to study the role played by different parameters on the SCC phenomenon of Zircaloy-4 claddings. It is made up of three complementary parts:-the modelling of local mechanical fields applied during laboratory tests;-the design of specific SCC experiments to investigate the influence of several mechanical parameters;-the observation of the damage mechanisms occurring during these different experiments.Coupling mechanical modelling and laboratory tests allowed to obtain some local information which cannot be obtained experimentally. A hierarchical approach was then used to develop accurate constitutive laws of the stress-relieved Zircaloy-4 alloy. The constitutive equations derived from this approach were fitted to the mechanical loading applied during the experiments.The specific SCC tests results and SEM observations proved the existence of a time incubation period, which lasts for an important part of the lifetime measured in the SCC pressurisation tests. This incubation period is closely related to the experimental conditions of the laboratory tests. However the incubation period must be distinguished from the actual SCC mechanisms and corresponds to the time required for the metal surface to strip of its oxide layer by mechanical cracking and/or attack of zircon. First results obtained on pre-cracked samples showed that this stage, which introduces an artefact in the experimental test analysis, can be suppressed. Moreover, we have borne out that initiation and propagation of SCC cracks can be very fast when metal is laid bare and when iodine is present.
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Olivier Fandeur. ÉTUDE EXPÉRIMENTALE ET MODÉLISATION MÉCANIQUE DE LA CORROSION SOUS CONTRAINTE DES GAINES EN ZIRCALOY-4. Mécanique des matériaux [physics.class-ph]. ÉCOLE CENTRALE DES ARTS ET MANUFACTURES « ÉCOLE CENTRALE PARIS », 2001. Français. ⟨NNT : 2001ECAP0734⟩. ⟨tel-01094621⟩

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