Papers by Keyword: Stress-Diffusion Coupling

Abstract: Hydrogen diffusion in metals is still an ongoing topic of research due to its technical relevance (hydrogen embrittlement, hydrogen storage...). In the last decades, significant progress in understanding the time evolution of the hydrogen concentration in solids was completed. This paper presents a modeling of hydrogen diffusion with a general and thermodynamically based diffusion concept coupled with mechanical and chemical aspects. This model was previously used to simulate the oxidation of a metal [1][2]. This concept has been upgraded to offer a thoroughly macroscopic behavior law used to simulate hydrogen diffusion in metal parts under mechanical loadings. The thermodynamic approach of the stress-diffusion coupling was implemented in a finite element code in order to study the hydrogen diffusion mode into a strained metal. Simulations were performed on a cylindrical austenitic steel tank under important internal pressure. The results of this study allow us to understand how hydrogen diffusion and mechanical stresses are mutually induced and modified.

Abstract: In PWR, the Zircaloy based clad is the first safety barrier of the fuel rod, it must prevent the dispersion of the radioactive elements, which are formed by fission inside the UO₂ pellets filling the clad. We focus here on internal corrosion that occurs when the clad is in tight contact with the UO₂ pellet. In this situation, with temperature of 400 °C on the internal surface of the clad, a layer of oxidised Zircaloy is formed with a thickness ranging from 5 to 15 µm. In this paper, we will underline the specific behaviour of this internal corrosion layer compared to wet corrosion of Zircaloy. Simulations will underline the differences of stress field and their influences on corresponding dissolved oxygen profiles. The reasons for these differences will be discussed as function of the mechanical state at inner surface of the clad which is highly compressed. Differences between mechanical conditions generated by an inner or outer corrosion of the clad are studied and their influences on the diffusion phenomena are highlighted.

Abstract: Our recent modelling works and corresponding numerical simulations realized to describe the UO₂ oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The results of our simulations are presented and discussed from the perspective to study the consequences of a surface mechanical treatment on the durability of a metallic material.