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Theses

Comportement des gaines en alliages de zirconium en conditions thermo-mécaniques représentatives d’un accident RIA

Abstract : The aim of this work is to enhance the understanding of the thermomechanical behavior at rupture of the fuel rod cladding during an accidental transient of the RIA type. A new mechanical test has been developed in order to apply a strain biaxiality ratio ɛzz/ɛ00 between -0,2 et 1. It allows reproducing loading conditions close to the ones occurring during a RIA accident. An experimental campaign at room temperature carried out with this device made it possible to study the effects of strain biaxiality ratios and strain rate on the fracture of the cladding. The tests carried out show a significant effect of the biaxiality on the hoop strain at failure which has a minimum of a plane strain state where the strain biaxiality is close to 0. A slight decrease in ductility was also recorded during the increase in the strain rate for all biaxiality levels. The damage mechanisms and failure modes of specimens are identified from the surfaces and failure profiles depending on the stress conditions. Numerical finite element simulations were performed with the CAST3M code to model the test and simulate the failure of cladding with biaxial loading. A second experimental device has been developed to couple the effects of biaxial mechanical loading and rapid thermal loading. The objective is to heat the cladding with temperature rise rates greater than 100 °C.s-1 in order to avoid the restoration of the defects linked to the hydriding and to the irradiation during the test. The method was used to perform thermomechanical tests at high heating rates, high strain rates, and high biaxiality levels to reproduce full loadings in a reactivity accident. The first results show, for a virgin cladding, that the strain at the break was not affected by temperature or by the rate of heating. Finite element simulations were undertaken to model the different heating methods tested and to optimise the chosen method. These simulations made it possible in particular to model the passage of electric current and heat flow through solid-solid interfaces.
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  • HAL Id : tel-03201656, version 1

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Ahmed Zouari. Comportement des gaines en alliages de zirconium en conditions thermo-mécaniques représentatives d’un accident RIA. Matériaux. Université Paris sciences et lettres, 2020. Français. ⟨NNT : 2020UPSLM058⟩. ⟨tel-03201656⟩

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