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Theses

Étude expérimentale et modélisation cinétique de l'oxydation à haute température sous air et vapeur d'eau du Zircaloy-4 pré-oxydé.

Abstract : The vulnerability of the spent nuclear fuel pools (SFPs) was highlighted since the Fukushima accident. It is a nuclear safety issue because SFPs are generally placed outside the reactor building so that the zirconium fuel clad is the only barrier against fission product release in case of dewatering. To gain knowledge in this field and to better evaluate the safety margins, the French Institut (IRSN) has launched the DENOPI project.This research focuses on the oxidation phenomena of low tin Zircaloy-4 (Zy-4) alloy with a pre-oxide layer at high temperature in an oxygen, nitrogen and steam atmosphere. The objective is to determine the oxidation mechanisms of the Zy-4 and a kinetic model for a better assessment of the available safety margins before runaway conditions are reached. The initial material used in this work shows an oxide layer thickness of 30 μm to simulate the corroded layer formed due to the action of the liquid water in the industrial reactor. The sample mass gain is measured with a symmetric thermobalance. The tests confirm the detrimental effect of nitrogen when it is associated to oxygen and/or steam in a range on 750 - 950°C. A kinetic acceleration is observed, related to the loss of protectiveness of the oxide scale. Moreover, in mixed air and steam atmospheres, the contribution of both oxidant species (water and oxygen) was demonstrated by 18O/Raman spectroscopy and measurement of hydrogen content. A complete kinetic study is conducted by temperature jumps and gas partial pressure jumps performed during the tests in order to evaluate the kinetic response of the Zy-4 sample to an abrupt change of one of the thermodynamic variables. At the end, a kinetic model is proposed taking into account the thermodynamic variables (temperature and gas partial pressure) and the sample’s geometry.
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https://tel.archives-ouvertes.fr/tel-03534233
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Submitted on : Wednesday, January 19, 2022 - 12:13:03 PM
Last modification on : Friday, January 21, 2022 - 3:05:36 AM
Long-term archiving on: : Wednesday, April 20, 2022 - 6:32:24 PM

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Mathilde Gestin. Étude expérimentale et modélisation cinétique de l'oxydation à haute température sous air et vapeur d'eau du Zircaloy-4 pré-oxydé.. Autre. Université de Lyon, 2019. Français. ⟨NNT : 2019LYSEM002⟩. ⟨tel-03534233⟩

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