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Comportement anisotherme et rupture des gaines combustibles en alliages de zirconium : Application à la situation d'accident d'insertion de réactivité (RIA)

Abstract : Fuel clads made of zirconium alloys are the first safety barrier in the nuclear power plants. This work aims to enhance the understanding of the thermomechanical behavior of Zirlcaoy-4 during RIA accidental scenario. Indeed, the current experimental databases are mainly constituted of uniaxial tensile tests carried out under isothermal conditions. The anisothermal character of the loading, coupled or not with the biaxiality of the mechanical loading, has been poorly studied. The aim of the thesis is to develop new experimental setups to highlight the effect of anisothermal loading. A first experimental test device was developed to study the effects of temperature transient on the cladding material during uniaxial tensile test. The experimental setup allows to reproduce loading conditions close to the ones occuring during a RIA accident. It allows clad testing up to 600 °C.s-1 heating rates coupled to rapid mechanical loading reaching 5 s-1 in terms of strain rate. First experiments showed first effects of anisothermal loading and allowed us to establish as a second step a comparison between isothermal and anisothermal states. A marked effect of anisothermal loading was observed at low strain rates and high heating rates : the flow stress is much higher than that expected from the isothermal tests. A study of the recrystallization of the material under dynamic conditions has shown that a delay in triggering the recrystallization process would be the cause of the anisothermal e ects observed during the tensile tests. A second experimental device was developed to couple effects of biaxial and anisothermal loading. A sheet of Zircaloy-4 was tested along its two main directions (rolling and transverse) with an induction heating system. Several heating rates and biaxiality ratios were explored and failure strains were determined for each experimental condition. The analysis of the tests showed that the multiaxiality of the loading is the dominant parameter with regard to the ductility of the material, no significant influence of the anisothermal loading was observed during these tests. In support of the analysis of uniaxial and biaxial anisothermal tensile tests, numerical FEM calculations were undertaken using a macroscopic mechanical behavior model developed in this study. These simulations made it possible to determine the stress fields of the biaxial tests and showed that the tests carried out were in the field of interest of the RIA studies.
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Submitted on : Tuesday, March 3, 2020 - 2:07:32 PM
Last modification on : Wednesday, October 14, 2020 - 3:52:48 AM
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  • HAL Id : tel-02497015, version 1

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Ahmed Chaieb. Comportement anisotherme et rupture des gaines combustibles en alliages de zirconium : Application à la situation d'accident d'insertion de réactivité (RIA). Mécanique [physics.med-ph]. Université Paris sciences et lettres, 2019. Français. ⟨NNT : 2019PSLEM005⟩. ⟨tel-02497015⟩

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