Electricity production in France relies mainly on nuclear energy and is one of the most decarbonized in the world, emitting approximately 50 g/kWh. This production is ensured by 56 pressurized water nuclear reactors commissioned between 1978 and 1999. Extending the lifespan of these reactors is crucial to guarantee electricity supply in the years to come, especially considering the perspective of increasing electrification of society and potential tensions in European energy supply. The nuclear industry is exploring the possibility of extending the operation of some reactors beyond 50 or even 60 years. This prospect raises questions regarding the aging of components, particularly those in the primary circuit. Among these components, the reactor vessel is of particular importance as it contains the reactor core and is not replaceable. The vessel is made of low-alloy steel (16MND5) and is subject not only to thermal aging but also to irradiation aging. Interfacial segregation of solutes, notably phosphorus, is one of the mechanisms of steel embrittlement. This segregation, which refers to the accumulation, by solid-state diffusion, of solute atoms at grain boundaries of a material, can occur during manufacturing heat treatments as well as during reactor operation. It is in this context that the SIRA chair aims to improve understanding of the aging by segregation of steel components in the primary circuit of nuclear reactors. This initiative responds to a demand from Framatome and EDF, the main players in the nuclear industry in France. Segregation predictions, integrated into the design and operation codes of nuclear equipment, are currently obtained using the so-called "Druce model." This model is based on several simplistic, even unrealistic assumptions, and its predictions are not validated by recent segregation measurements made as part of laboratory aging programs. The work of this chair aims to improve understanding (1) of the effect of initial microstructures, including welding microstructures, on intergranular segregation and associated embrittlement, and (2) of the thermodynamic and kinetic aspects of segregation, taking into account the chemical interactions of phosphorus with alloying elements. Methodological developments are also planned to improve measurements of intergranular segregation by Auger spectroscopy on fracture and by energy-dispersive analysis in transmission electron microscopy (STEM-EDX). The work program will be supported by three CIFRE theses and 116 months of post-doc research. Beyond the scientific aspect, the chair holds strategic importance for the French nuclear industry. The knowledge developed will contribute to component maintenance programs in service, particularly in the perspective of reactor extension, and to the optimization of component manufacturing for new reactors (EPRs). This initiative will also help maintain a level of equipment and skills in both academic and industrial sectors commensurate with the challenges related to component aging.

Strain localization in deformed polycrystalline materials is of major importance for a large number of physical phenomena occurring during the lifetime of a material, such as fatigue, rupture or corrosion cracking. The elastic-plastic transition of a material is of strong interest on the one hand because it constitutes severe loading conditions, and on the other hand because particularly strong strain heterogeneities occur, as only some grains deform plastically. In this project, we will first develop a methodology for 3D strain measurements in polycrystalline materials. Two materials will be used: Al-0.1wt%Mn and 316L steel, which are expected to develop different local behaviours. As strains cannot be measured directly in 3D, we will adopt an inverse approach, consisting of deriving the plastic strains from one of their microstructural consequences: the local lattice reorientations. Two high-energy X-ray diffraction techniques will be used for measuring lattice reorientations in 3D during deformation: 3D-XRD and 6D-DCT. For validation of the method, a 2D configuration will also be adopted, where the lattice reorientations at the surface of a sample will be followed by high angular resolution EBSD and the real, surface deformation measured by standard digital image correlation techniques. The strains measured in the 3D case will be compared to full-field crystal plasticity finite element simulations using the experimental microstructure. Using both the experimental and simulation results, the strain heterogeneity will then be analysed at gradually increasing strains, by focusing on specific aspects: the early state of plastic deformation and the influence of elastic anisotropy, the spatial distribution of the strain "hot spots" and grain interaction effect, the strain propagation as strain increases and relation to orientation gradients.

Saturated fatty acids (SFA) and trans-Fatty acids (TFA) and are a major public health issue because they increase the risks of cardiovascular diseases. TFA and SFA are found mainly in solid fats, and form crystalline triacylglycerol. This crystallinity plays an essential role to texture the lipid phase in food products, i.e. to give its solid-like behavior. But public health authorities harden regulations to lower the intake of these solid fats especially TFA. Facing these legislation and health issues, food industry aims at replacing these solid fats by healthier products, but able to solidify the lipidic phase. Oleogels are the most promising and studied substitutes. They consist in vegetable liquid oils (usually healthy), gelled by small molecules called oleogelators. These compounds self-assemble at low concentration in a network of fibrillar aggregates, which provides the mixtures the sought mechanical properties. A few clinical and in vitro studies have been conducted with oleogels, but focus mainly on digestion. They show a decrease of after-meal triglyceridemia and a decrease of the extent of lipolysis during digestion in vitro. These results are encouraging but not enough to assess the benefits of oleogels on health. One needs to address the effects on metabolism, on guts and microbiota. Moreover, the observed effects have not been correlated so far with physicochemical or mechanical quantities. For instance, which properties slows lipolysis: structure of the gel, elastic moduli their surface tension, their solubility which slows digestion? In this context, we have shown that some fatty amides like palmitoylethanolamide gel edible oils. These compounds are endogenous (i.e. naturally present in the body) and have beneficial effects on health. In the corresponding gels, oil is less hydrolyzed during digestion in vitro than when it is liquid. The objective of this proposal are: 1) to synthesize and develop as new oleogelators, endogenous fatty amides, and to study the structure of the formed gels; 2) to know and predict their thermo-mechanical behavior: for this purpose, we will map and model their phase diagrams, measure their complex viscosity, yield stresses and interfacial tensions; 3) to correlate these quantities with the extent of lipolysis; 4) study the impact of oleogels on the physiology and metabolism of the lipids, on the inflammatory response of the guts and on the microbiota. The ultimate goal is to correlate the physiological effects with the thermo and mechanical properties of the gels. We will address these questions in 4 different work-packages. In the first one, we will synthesize a series of endogenous compounds and test their ability to gel rapeseed oil. We will study the structure of the oleogels by electron microscopy, small angle scattering and FTIR. In order to measure the shape and sizes of the aggregates and the intermolecular interactions. In the second work-package, we will select oleogelators with low gel concentrations and we will measure both their rheological properties and map their c-T phase diagrams. The transitions will be studied by rheology, turbidimetry, microDSC, VT-NMR and IR-microscopy experiments. In parallel, the phase diagrams will be modelled by activity coefficient models (NRTL-SAC) or residual approaches (SAFT or PC-SAFT based models). In the third work-package, we will study the rate and extent of the digestion in vitro of the oleogels. The interfacial tension of the gels in the used physiological buffers will be measured. Then, we will identify the thermodynamical, rheological or interfacial quantities impacting the digestion and we will try to correlate it quantitatively with the rate of lipolysis. In the last work-package, we will study in mice the impact of gelation on the lipid metabolism, the gut inflammation and microbiota. The results will be analyzed and correlated with the rheological, structural and thermodynamical properties measured from the previous tasks.

The large-scale use of renewable energy, in particular solar energy, requires the development of energy storage technologies to compensate for the intermittent availability of solar radiation. Among all storage methods, the thermochemical storage of energy appears to be particularly interesting due to its high storage density and its potential ability to avoid energy losses. A charge reaction stores the solar energy whereas the reverse discharge reaction gives back this energy whenever it is needed the most. Among the different reactors allowing one to do this for Concentrated Solar Power (CSP), Solar Rotary Kilns (SRK) appear to be particularly promising as they can potentially allow the continuous and uninterrupted storage of energy unlike batch and semi-batch reactors. There are, however, two main aspects that need to be further explored. On the one hand, the modelling of solar rotary kilns is still at its infancy and a realistic understanding of the interaction between granular flow, heat transfer and chemical kinetics has yet to be reached. On the other hand, the construction of a directly irradiated SRK with the possibility of adjusting the solid flow rate to the fluctuating radiance of the sun would be highly beneficial. The purpose of the project MULTITHERMO will be to develop a realistic and physically and chemically sound multiphysics model describing all aspects of heat storage in a rotary kiln and to validate it based on the data from a new prototype of SRK and from an already existing electrical rotary kiln and an already existing rotary drum. It will be mainly based on the reduction of BaO2(s) as a promising heat-storing reaction. This reaction will be also studied during the projetc in order to master its chemical kinetics.

The aim of this project is to carry out a coupling of experiments and numerical simulations, allowing a better understanding and modelling of the links between microstructural evolutions and the mechanical properties of a two-phase Titanium alloy, and thus to improve the cold forming process of some of these alloys. The TA3V alloy, which has an intermediate strength between pure titanium and the TA6V alloy while offering excellent cold formability, was chosen as a paradigm because it usually presents a high microstructure variability, a high anisotropy, an important springback and has been little studied until now, despite its great potential for high added value applications (mainly for aeronautics, sport and energy). Through the implementation of non-standard thermomechanical treatments for this alloy, innovative microstructures will be created and then "digitized" to enable their use in finite element calculation codes integrating crystalline plasticity (CPFEM). In parallel, a multi-scale modeling approach, based mainly on Dislocation Dynamics (DD) will be developed in order to integrate by stages into the crystalline constitutive law all the microstructural elements that can influence the cold behavior of the material (texture, morphology, phase percentages, distribution of particular grain boundaries, ...) as well as the influence of the alloying elements on the activation of the different possible deformation systems. A back and forth between experiments and simulations will first allow to validate the modeling approach, then to optimize the forming process, by numerically determining the forming limit curves for various microstructural states. This project therefore aims both to develop more predictive numerical simulations by integrating physically based constitutive laws, rather than purely phenomenological ones, and to better understand the behaviour of a titanium alloy during complex thermomechanical treatments.