arXiv subjects

Lionel Desgranges

Publications and source records attributed to Lionel Desgranges.

6 recordsLinked to original sources

arXiv2025

Kitaev interactions of the spin-orbit coupled magnet UO2

Uranium dioxide, UO$_2$, is a canonical example of a magnetic material with strong spin-orbit coupling. Here, we present a study of the magnetic diffuse scattering measured on a polycrystalline sample of UO$_2$, which we interpret in terms of its magnetic interactions between U$^{4+}$ magnetic moments. By refining values of the magnetic interaction parameters to magnetic diffuse-scattering data measured above the magnetic ordering transition temperature, we show that the dominant magnetic coupling in UO$_2$ is a bond-dependent interaction analogous to the Kitaev model of honeycomb magnets. We compare our experimental results with published theoretical predictions and experimental measurements of the magnetic excitation spectrum. Our results suggest that magnetic materials with $f$-electron magnetic ions, particularly actinides, may be promising candidates for realising Kitaev magnetism, and highlight the role that magnetic diffuse-scattering data can play in identifying such materials.

cond-mat.str-el↗

arXiv2024

A Simple Modeling for Gas Release During Annealing of Irradiated Nuclear Fuel

We have developed a gas flow model in the spent nuclear fuel during the annealing. It postulates that the gas release during an isothermal plateau at 1200{\textdegree}C corresponds to the equilibrium between overpressure gas reservoirs in the fuel sample connected to the free surface at atmospheric pressure.

cond-mat.mtrl-sci↗

arXiv2013

Influence of the U3O7 domain structure on cracking during the oxidation of UO2

Cracking is observed when a UO_{2} single crystal is oxidised in air. Previous studies led to the hypothesis that cracking occurs once a critical depth of U_{3}O_{7} oxidised layer is reached. We present some μ-Laue X-ray diffraction results, which evidence that the U_{3}O_{7} layer, grown by topotaxy on UO_{2}, is made of domains with different crystalline orientations. This observation was used to perform a modelling of oxidation coupling chemical and mechanical parameters, which showed that the domain patterning induces stress localisation. This result is discussed in comparison with stress localisation observed in thin layer deposited on a substrate and used to propose an interpretation of UO_{2} oxidation and cracking.

cond-mat.mtrl-sci↗

arXiv2013

Specific Aspects of Internal Corrosion of Nuclear Clad Made of Zircaloy

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^{\circ}C on the internal surface of the clad, a layer of oxidised Zircaloy is formed with a thickness ranging from 5 to 15 $μ$m. 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.

cond-mat.mtrl-sci↗

arXiv2010

Internal Interface Strains Effects on UO2/U3O7 Oxidation Behaviour

The growth of a U3O7 oxide layer during the anionic oxidation of UO2 pellets induced very important mechanical stresses due to the crystallographic lattice parameters differences between UO2 and its oxide. These stresses, combined with the chemical processes of oxidation, can lead to the cracking of the system, called chemical fragmentation. We study the crystallographic orientation of the oxide lattice growing at the surface of UO2, pointing the fact that epitaxy relations at interface govern the coexistence of UO2 and U3O7. In this work, several results are given: - Determination of the epitaxy relations between the substrate and its oxide thanks to the Bollmann's method; epitaxy strains are deduced. - Study of the coexistence of different domains in the U3O7 (crystallographic compatibility conditions at the interface between two phases: Hadamard conditions). - FEM simulations of a multi-domain U3O7 connected to a UO2 substrate explain the existence of a critical thickness of U3O7 layer.

cond-mat.mtrl-sci↗

arXiv2009

A thermodynamic approach of the mechano-chemical coupling during the oxidation of uranium dioxide

The aim of the present work is to introduce a thermodynamic model to describe the growth of an oxide layer on a metallic substrate. More precisely, this paper offers a study of oxygen dissolution into a solid, and its consequences on the apparition of mechanical stresses. They strongly influence the oxidation processes and may be, in some materials, responsible for cracking. To realize this study, mechanical considerations are introduced into the classical diffusion laws. Simulations were made for the particular case of uranium dioxide, which undergoes the chemical fragmentation. According to our simulations, the hypothesis of a compression stress field into the oxidised UO2 compound near the internal interface is consistent with the interpretation of the mechanisms of oxidation observed experimentally.

physics.chem-ph↗