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Étude du ballonnement des gaines combustibles en Zircaloy-4 en situation d'Accident de Perte de Réfrigérant Primaire

Abstract : In a nuclear power plant, the nuclear fuel is contained within fuel clads made of cold-work stress relieved Zircaloy-4 alloy. During a LOCA (Loss Of Coolant Accident), claddings are subjected to severe thermo-mechanical loading, as a consequence of temperature and over pressure rise. As a consequence, the clads undergo major and unstable deformation leading to ballooning until rupture. LOCA is acomplex transient in which the clads are simultaneously subjected to a temperature ramp up to 100°C/s and an overpressure up to100bar. Furthermore, the temperature is not homogeneous over the clad surface. The aim of this work is a better comprehension of this phenomenon by carrying out a specific experimental campaign and the development of modelling, capable of reproduce the tests and improving the prediction of the ballooning and rupture for LOCA-representative conditions. A semi-integral LOCA test device was used to realize realistic transients. Constant-temperature creep tests were performed under three different temperatures (650°C, 700°C,750°C) and height overpressures (30bar, 40bar, 50bar, 60bar, 70bar, 80bar, 90bar, 100bar) in order to better understand the ballooning phenomenon under non-dynamic conditions. Ramp-tests were also performed for three different ramp rates (1°C/s, 5°C/s et 10°C/s) for similar overpressures than constant-temperature creep tests. Thermal field being a first order parameter, efforts have been made to characterize it. This characterization was made for constant-temperatures and for different ramp-rates by means of an equipped cladwith welded thermocouples and an infrared thermographic camera. Furthermore, high-resolution camera was used throughout the experiment to measure the strain during the experiments. The experiments showed a remarkable reproducibility of the results compared to the majority of similar tests conducted so far. The second part of this work is dedicated to the numerical modelling of ballooning. A temperature-dependent visco-plastic behavior law was identified from our experiments. A semi-analytical method based on a simplified shell analysis has been developed, allowing the ballooned geometry to be taken into account. The main advantages are a better comprehension of the influence of the model parameters upon the ballooning phenomenology and the computation time, infinitely lowerthan a finite elements simulation. The applicability has been proved for LOCA-representative conditions. The last part of the work is dedicated to the simulation of the tests using Code Aster®. A function has been found to describe the temperature field of our device and 3D computations were conducted that enabled to model the ballooning deformation with gradients values that did not allowed it until then.
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Submitted on : Friday, January 21, 2022 - 1:39:08 PM
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  • HAL Id : tel-03538946, version 1

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Julien Moryousef. Étude du ballonnement des gaines combustibles en Zircaloy-4 en situation d'Accident de Perte de Réfrigérant Primaire. Matériaux. Université Paris sciences et lettres, 2021. Français. ⟨NNT : 2021UPSLM019⟩. ⟨tel-03538946⟩

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