Development and characterization of an oxide/oxide composite material
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with excellent high-temperature resistance (> 1000 °C), even in an oxidizing atmosphere. They generally consist of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide).
The proposed study focuses on the development of a fabrication process for oxide/oxide CMCs with long and/or short fibers that possess suitable dielectric, thermal, and mechanical properties.
Synthesis, Characterization, and Molecular Modeling of M-(A)-S-H
The main hydration product of Mg/silicate cements is magnesium silicate hydrate (M-S-H), whose composition evolves with time and environmental interactions [refs 1,2], with Mg/Si ratios ranging from 0.67 to 1.5, variable water content, and potential Al incorporation. Atomistic models of M-(A)-S-H remain largely unexplored [ref 4], and most of their properties are still unknown, making it difficult to establish composition–property relationships.
This project aims to elucidate the atomic-scale structure of (alumino)silicate magnesium hydrates (M-(A)-S-H) by combining experimental techniques and atomistic simulations, and to estimate their mechanical properties. The study will focus on M-(A)-S-H compositions relevant to nuclear applications or new low carbon cement matrices.
Study of the Thermodiffusion of Small Polarons in UO2
The position is published on the CEA website at the following address:
https://www.emploi.cea.fr/job/emploi-post-doctorat-etude-en-ab-initio-de-la-thermodiffusion-des-petits-polarons-dans-UO2-h-f_36670.aspx
PV module designed for repair and recycle using ultrasonic delamination
PV panels, crucial for producing decarbonized electricity, have a limited lifespan due to performance degradation, failures, or economic factors. In the next decade, millions of tons of PV panels will become waste, posing significant environmental and societal challenges. Europe has recognized this problem through the WEEE directive (Waste Electrical and Electronic Equipment) to manage electronic waste, including PV.
PV modules are complex devices containing critical materials such as silver and long-life pollutants like fluorinated polymers. On top of that, the glass sheet and the silicon solar cells show a high carbon footprint, making the reuse essential to mitigate environmental impact. Various dismantling techniques have been explored in R&D labs to obtain pure fractions of metals, polymers and glass, but these methods require further improvement. Key objectives include selectivity and purity, material yield and control of residual pollution. To boost the sustainability of photovoltaic energy, managing module lifespans in a circular economy vision is essential.
The LITEN institute is leading research into delamination and separation methods to enhance the quality of recycled materials. In this postdoc opportunity, we will explore the implementation of ultrasonic waves for dismantling or repairing PV modules. The development of a numerical model to understand vibration phenomena in PV panels will support the design of a tool for efficient wave coupling. Beside modelling ant tool set-up, we will explore new PV architectures based on "design to recycle" and "design to repair" principles, focusing on composite layers sensitive to ultrasound. Evaluating various phenomena induced by these layers, such as optical transmission and thermo-mechanical behaviour, will be a key aspect of the study. The research will leverage a high-level scientific environment, with expertise in thermo-mechanical numerical modelling, PV module design and prototype’s fabrication.
New semiconductor materials for neutron detection
The candidate will work at CEA LITEN on the development of organic-inorganic perovskite single crystals. The solution-growth protocols will be inspired by preliminary work from several internships and PhD. The student will vary the material's structure, chemical composition, or doping in order to optimize scintillation and direct detection performances for fast neutron detection. The best compositions selected based on their structural, optical properties, and responses under X-rays will then be integrated into detectors and characterized under various neutron fluxes and energies. Their performances and durability under irradiation will be studied and benchmarked to existing materials.
Holder of a PhD in materials science or chemistry, with the ability to work with multidisciplinary teams (collaboration with the teams at CEA LETI in Grenoble, IRESNE in Cadarache, and LIST in Saclay), good autonomy, and strong organizational skills will be major assets to successfully carry out this mission.
Development of a new generation of reversible polymer adhesives
Polymeric adhesives are generally cross-linked systems used to bond two substrates throughout the lifetime of an assembly, which may be multi-material, for a wide range of applications. At their end of life, the presence of adhesives makes it difficult to separate materials and recycle them. Moreover, it is difficult to destroy the cross-linking of the adhesives without chemical or thermal treatment that is also aggressive for the bonded substrates.
In this context, the CEA is developing adhesives with enhanced recyclability, by integrating recyclability into the chemical structures right from the synthesis of the polymer networks. The first approach involves incorporating dynamic covalent bonds into polymer networks, which can be exchanged under generally thermal stimulus (e.g. vitrimers). A second approach involves synthesising polymers that can be depolymerised under a specific stimulus (self-immolating polymers) and have the ability to cross-link.
The post-doc will develop 2 networks that can be used as adhesives with enhanced recyclability. A first network will be based on a depolymerizable chemistry under stimulus already developed on linear polymer chains, to be transposed to a network. A second vitrimer network will be synthesised on the basis of previous work at the CEA. Activation of the bond exchange in this network will take place via a so-called photolatent catalyst, which can be activated by UV and will make it possible to obtain a UV- and heat-stimulated adhesive. The choice and synthesis of these catalysts and their impact on the adhesive will be the focus of the study. The catalysts obtained could also be used to trigger depolymerisation of the first depolymerisable system under stimulus.
Impact of Microstructure in Uranium Dioxide on Ballistic and Electronic Damage
During reactor irradiation, nuclear fuel pellets undergo microstructural changes. Beyond 40 GWd/tU, a High Burnup Structure (HBS) appears at the pellet periphery, where initial grains (~10 µm) fragment into sub-grains (~0.2 µm). In the pellet center, under high temperatures, weakly misoriented sub-grains also form. These changes result from energy loss by fission products, leading to defects such as dislocations and cavities. To study grain size effects on irradiation damage, nanostructured UO2 samples will be synthesized at JRC-K, using flash sintering for high-density pellets. Ion irradiation experiments will follow at JANNuS-Saclay and GSI, with structural characterizations via Raman spectroscopy, TEM, SEM-EBSD, and XRD. The postdoc project will take place at JRC-K, CEA Saclay, and CEA Cadarache under expert supervision.
Adapting the Delayed Hydride Cracking (DHC) experience to irradiated materials
The objective of this study is to nuclearize the Delayed Hydride Cracking (DHC) experiment developed as part of Pierrick FRANCOIS PhD research (2020-2023). This experiment enables the reproduction of the DHC phenomenon in Zircaloy cladding under laboratory conditions to determine the material's fracture toughness in case of DHC: KI_DHC.
The term "nuclearize" refers to the adaptation of the experiment to test irradiated materials within dedicated shielded enclosures (called hot cells), where materials are handled using remote manipulators. The experimental protocols described in Pierrick FRANCOIS' thesis must therefore be modified, and ideally simplified, to allow for their implementation in hot cells. This will require close collaboration with the personnel responsible for the tests and the use of numerical simulation tools developed during the same PhD research.
The development of this hot cell procedure will be used by the postdoctoral researcher to assess the risk of HC during dry storage of spent fuel assemblies by quantifying the fracture toughness of irradiated claddings.
Preparation and characterization of an oxide/oxide composite
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with resistance to high temperatures (> 1000 °C), even in oxidizing atmospheres. They are typically composed of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide.
The proposed study focuses on the development of a low-matrix oxide/oxide CMC with suitable dielectric, thermal, and mechanical properties.
This study will be conducted in collaboration with several laboratories at CEA Le Ripault.
Modeling the corrosion behavior of stainless steels in a nitric acid media with temperature
Controlling the aging of equipment materials (mainly stainless steel) of the spent nuclear fuel reprocessing plant is the subject of constant attention. This control requires a better understanding of the corrosion phenomena of steels by nitric acid (oxidizing agent used during the recycling stages), and ultimately through their modeling.
The materials of interest are Cr-Ni austenitic stainless steels, with very low carbon content. A recent study on Si-rich stainless steel, which was developed with the aim of improving the corrosion resistance of these steels with respect to highly oxidizing environments [1 , 2 ]; showed that the corrosion of this steel was thermally activated between 40 °C and 142 °C with different behavior below and above the boiling temperature (107 °C) of the solution [3]. Indeed, between 40°C and 107°C, the activation energy is 77 kJ/mol and above boiling point, it is much lower and is worth 20 kJ/mol. This difference may be due to a lower energy barrier or a different kinetically limited step.
The challenge of this post-doctoral subject is to have a predictive corrosion model depending on the temperature (below and beyond boiling). With this objective, it will be important to analyze and identify the species involved in the corrosion process (liquid and gas phase) as a function of temperature but also to characterize the boiling regimes. This model will be able to explain the difference in activation energies of this Si-rich steel below and above the boiling temperature of a concentrated nitric acid solution but will also make it possible to optimize the processes of the factory where temperature and/or heat transfer play an important role.