Identification des conditions de rupture fragile des gainages combustibles en alliage de zirconium oxydés sous vapeur d’eau à haute température et trempés sous charge axiale

Abstract : During hypothetical Loss-Of-Coolant-Accident (LOCA) scenarios, zirconium alloy fuel cladding tubes are subjected to severe thermo- mechanical loading conditions in highly oxidising chemical environments. Pressure and temperature evolution together with cooling water can lead to ballooning and burst followed by steam oxidation and hydrogen uptake at high temperature, and then axial loading during the final reflooding stage.This study focuses on the identification of mechanisms and key parameters which drive cladding fracture during the reflooding stage under axial tensile load.Laboratory-scale semi-integral tests simulating LOCA transients on Zircaloy−4 test rods have been realised. A fracture/no-fracture threshold of oxidation duration at high temperature has been determined. Two fracture locations have been identified: i) the burst zone with maximal oxidation and no hydrogen uptake, and ii) the “secondary hydriding” zone below the burst zone, with substantial hydrogen absorption and lower oxidation levels. Moreover, a scenario of fracture as a function of the reflooding chronology has been identified. Nevertheless, the macroscopic treatment of these tests has not permitted to discriminate these two fracture locations because fracture independently occurs in and out of the burst zone, whatever the applied transient and the balloon and burst morphologies.From systematic microstructural and fractographic characterisation of test specimens, a local approach aiming at identifying a fracture threshold as a function of the microstructural state of the material has been applied. The complex distribution of chemical elements and phases across the cladding thickness has been determined. Phase transformations in the highly-oxidised balloon, leading to a globally brittle microstructure have been explicated. In the secondary hydriding zone, a fracture threshold criterion has been identified by means of layer thickness measurements and hydrogen uptake profile.
Document type :
Theses
Complete list of metadatas

https://pastel.archives-ouvertes.fr/tel-02191672
Contributor : Abes Star <>
Submitted on : Tuesday, July 23, 2019 - 3:34:04 PM
Last modification on : Wednesday, July 24, 2019 - 1:32:56 AM

File

2018PSLEM022_archivage.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02191672, version 1

Citation

Ronan Thieurmel. Identification des conditions de rupture fragile des gainages combustibles en alliage de zirconium oxydés sous vapeur d’eau à haute température et trempés sous charge axiale. Matériaux. PSL Research University, 2018. Français. ⟨NNT : 2018PSLEM022⟩. ⟨tel-02191672⟩

Share

Metrics

Record views

114

Files downloads

62