Activated conductive materials for energy conversion and energy storage through capacitive effect
Energy production from renewable sources requires efficient storage systems to address imbalances between supply and demand. This project aims to develop cost-effective supercapacitors using composite electrodes derived from industrial by-products. Mineral binders, such as geopolymers or Alkali Activated Materials (AAM), made conductive by dispersing carbon black, are being studied for energy storage or heat generation applications. Based on a recently filed patent, we propose a detailed study of these conductive composites. Their performance will be evaluated depending on formulation and shaping parameters. Additionally, the porous network and the dispersion of conductive charges in the material will be thoroughly characterized. Finally, material shaping tests will be conducted, and supercapacitors will be assembled to study the impact of the process (3D printing) and geometries.
Stabilization of secondary phases in nanoreinforced ferritic steels: High-throughput screening approach of chemical compositions
Ferritic steels reinforced by oxide dispersion strengthening (ODS) are considered for use in 4th Generation and fusion nuclear reactors due to their excellent thermomechanical properties and stability under irradiation. However, these steels are weakened by secondary phases resulting from complex interactions between alloying elements and interstitials (C, N, O) introduced during their processing. Some alloying elements (such as Nb, V, Zr, Hf) could potentially stabilize these undesirable phases and mitigate their detrimental effects on the mechanical behavior of ODS steels. This thesis aims to develop a high-throughput screening method to identify optimal alloy compositions by combining rapid fabrication and characterization techniques. The PhD student will synthesize various compositions of ODS steels through powder metallurgy and carry out chemical, microstructural, and mechanical characterizations. This work will enhance the understanding of interstitial stabilization mechanisms and propose effective methodologies for characterizing new materials. The PhD student will gain in-depth knowledge in metallurgy and data processing, providing opportunities in industry, nuclear start-ups, and research.
Kinetics of segregation and precipitation in Fe-Cr-C alloys under irradiation : coupling magnetic, chemical and elastic effects
Ferritic steels are being considered as structural materials in future fission and fusion nuclear reactors. These alloys have highly original properties, due to the coupling between chemical, magnetic and elastic interactions that affect their thermodynamic properties, the diffusion of chemical species and the diffusion of point defects in the crystal. The aim of the thesis will be to model all of these effects at the atomic scale and to integrate them into Monte Carlo simulations in order to model the segregation and precipitation kinetics under irradiation, phenomena that can degrade their properties in use. The atomic approach is essential for these materials, which are subjected to permanent irradiation and for which the laws of equilibrium thermodynamics no longer apply.
The candidate should have a good background in statistical physics or materials science, and be interested in numerical simulations and computer programming. The thesis will be carried out at CEA Saclay's physical metallurgy laboratory (SRMP), in a research environment with recognised experience in multi-scale modelling of materials, with around fifteen theses and post-doctoral contracts in progress on these topics.
A Master 2 internship on the same subject is proposed for spring 2025 and is highly recommended.
Understanding the mechanisms of oxidative dissolution of (U,Pu)O2 in the presence of platinum group metals
The treatment of MOx fuel, composed of a mixed uranium and plutonium oxide (U,Pu)O2, is aimed at recycling plutonium. Plutonium dioxide (PuO2) is notably difficult to dissolve in concentrated nitric acid. However, by introducing a highly oxidizing agent, such as Ag(II), into the nitric acid, plutonium can be solubilized with fast dissolution kinetics—a process known as oxidative dissolution. The fission products present in irradiated MOx, particularly platinum group metals, can potentially impair the effectiveness of plutonium’s oxidative dissolution through side reactions. For the industrial deployment of this method, it is therefore crucial to understand how platinum group metals influence the dissolution kinetics. Yet, there is currently very limited data on this subject.
This thesis aims to address this knowledge gap. The proposed research involves a parametric experimental study of increasing complexity: initially, the impact of platinum group metals on Ag(II) consumption will be investigated separately, followed by their effect during the dissolution of (U,Pu)O2. These findings will enable the development of a kinetic model for the dissolution process based on the studied parameters.
By the end of this thesis, the candidate, with a strong background in physical or inorganic chemistry, will have gained expertise in a wide range of experimental techniques and advanced modeling methods. This dual competence will open up numerous career opportunities in academic research or industrial R&D, both within and beyond the nuclear sector.
Learning Interpretable Models for Stress Corrosion of Stainless Steels Exposed in the Primary Environment of PWRs
Stress corrosion cracking (SCC) of austenitic alloys in water-cooled nuclear reactors is one of the most significant component degradation phenomena. SCC occurs due to the synergistic effects of tensile stresses, environment and material susceptibility. For reactor life extension, understanding this mechanism is essential. The methodology most frequently employed to investigate SCC cracking is an experimental one, requiring lengthy and costly tests of several thousand hours. Furthermore, the considerable number of critical parameters that influence susceptibility to SCC cracking and coupling effects have resulted in test grids increasing in length and complexity. This thesis proposes a novel approach based on the use of interpretable models that are driven by the artificial intelligence of fuzzy logic. The aim is to reduce the length and cost of research activities by focusing on relevant tests and parameters that can improve environmental performance. The key issues here will be to add the performance of artificial intelligence to the experimental approach, with the aim of defining susceptibility domains for the initiation of SCC cracks as a function of the critical parameters identified in the model, and providing data for the development of new materials by additive manufacturing. The thesis will develop a numerical model that can be used as guidance in decision-making regarding the stress corrosion mechanism. The future PhD student will also carry out experimental work to validate this new numerical approach.
Numerical twin for the Flame Spray Pyrolysis process
Our ability to manufacture metal oxide nanoparticles (NPs) with well-defined composition, morphology and properties is a key to accessing new materials that can have a revolutionary technological impact, for example for photocatalysis or storage of energy. Among the different nanopowders production technologies, Flame Spray Pyrolysis (FSP) constitutes a promising option for the industrial synthesis of NPs. This synthesis route is based on the rapid evaporation of a solution - solvent plus precursors - atomized in the form of droplets in a pilot flame to obtain nanoparticles. Unfortunately, mastery of the FSP process is currently limited due to too much variability in operating conditions to explore for the multitude of target nanoparticles. In this context, the objective of this thesis is to develop the experimental and numerical framework required by the future deployment of artificial intelligence for the control of FSP systems. To do this, the different phenomena taking place in the synthesis flames during the formation of the nanoparticles will be simulated, in particular by means of fluid dynamics calculations. Ultimately, the creation of a digital twin of the process is expected, which will provide a predictive approach for the choice of the synthesis parameters to be used to arrive at the desired material. This will drastically reduce the number of experiments to be carried out and in consequence the time to develop new grades of materials
Simulation of the evolution of dislocation microstructures in UO2: impact of dislocation climbing at high temperature
Carbon neutrality requires the development of low-carbon energy production systems, including nuclear power. The safety analysis of nuclear reactors requires the containment of fission products in all operating conditions, including the integrity of the first barrier made up of the fuel elements. For rod-type designs, which consist of a stack of fuel pellets in a metallic cladding, the mechanical behavior of uranium dioxide (UO2), pellet material, plays an important role in the cladding integrity assessment. During power transients, fuel-cladding contact increases mechanical stresses on the cladding, and fuel creep can accommodate swelling deformations, thereby reducing the stresses induced the cladding. One of the challenges is to understand and predict this phenomenon of UO2 creep, and in particular the mechanisms that drive it at the polycrystalline microstructural scale.
The main objective of the thesis will be to provide simulation methods and reference results in support of multi-scale modeling of the mechanical behavior of fuel at high-temperature, which is highly dependent on dislocation climbing mechanisms. To this end, a computational scheme will be developed, based on the coupling of a dislocation dynamics code (NUMODIS) and a code for solving nonlinear partial differential equations by FFT (AMITEX-FFTP), in order to describe the evolution of a dislocation microstructure (NUMODIS) under the effect of dislocation climbing induced by vacancy diffusion (AMITEX-FFTP). Simulations based on this approach will then be used to quantify the recovery of stored dislocation density with the effect of climbing mechanisms in different configurations (temperatures, stresses, etc.). Ultimately, this work will improve and validate the existing micromechanical modeling implemented in the CEA's PLEIADES simulation platform.
This thesis will be carried out under the joint supervision of the Département d'Etude des Combustibles (Institut IRESNE, CEA Cadarache) and the Département de Recherche sur les Matériaux et la Physico-chimie (Institut ISAS, CEA Saclay), and in collaboration with IM2NP at Aix Marseille Université. The thesis work will be carried out at the LM2C (Cadarache) and LC2M (Saclay) laboratories, in an environment that provides access to extensive expertise in multi-scale materials modeling. The research work will be promoted through publications and participation in international conferences in the materials field.
From angstroms to microns: a nuclear fuel microstructure evolution model whose parameters are calculated at the atomic scale
Controlling the behavior of fission gases in nuclear fuel (uranium oxide) is an important industrial issue, as fission gas release or precipitation limit the use of fuels at extended burn-ups. The gas behavior is strongly influenced by the material’s microstructure evolution due to the aggregation of irradiation-induced defects (gas bubbles, dislocation loops and lines). Cluster dynamics (CD) (a kind of rate theory model) is relevant for modelling the nucleation/growth of the defect clusters, there gas content and the gas release. The current model has been parameterized following a multiscale approach, based on atomistic calculations (ab initio or empirical potentials). This model has been successfully applied to annealing experiments of UO2 samples implanted with rare gas atoms and has emphasized the impact of the irradiation damage on gas release. The aim of this PhD thesis is now to improve the model, particularly the damage parameterization, and to extend its validation domain through in depth comparison of simulation with a large set of recently obtained experimental results, such as gas release measurement by annealing of sample implanted in ion beam accelerator, bubble and loop observation by transmission electrons microscopy, and positron annihilation spectroscopy. This global analysis will finally yield an improved parameterization of the CD model.
The research subject combines a “theoretical” dimension (improving the model) with an “experimental” one (interpreting existing experiments or designing some new ones). The variety of techniques will introduce the candidate into the experimental world and thus broaden his scientific skills. The candidate will also have to manage collaborations for the experiments analysis, for the model development and for the specification of additional atomistic calculations. He will be at the interface of atomistic techniques, large-scale simulation and various experimental techniques. Therefore, he will develop a broad view of irradiation effects in materials and of multi-scale modelling in solids in general.
This project is an opportunity to contribute to the overall development of numerical physics applied to multi-scale modeling of materials, occupying a pivotal position and adopting a global viewpoint. This will allow experiencing oneself the way computed fundamental microscopic data finally helps solving complex practical issues.
Further readings:
Skorek et al. (2012). Modelling Fission Gas Bubble Distribution in UO2. Defect and Diffusion Forum, 323–325, 209.
Bertolus et al. (2015). Linking atomic and mesoscopic scales for the modelling of the transport properties of uranium dioxide under irradiation. Journal of Nuclear Materials, 462, 475–495.
Development of thin film negative electrodes for Li-free all-solid-state batteries
The aim of this work is to develop 'Li-free' negative electrodes for new generations of high energy density all-solid-state lithium batteries. The function of this type of electrode is to provide a significant gain in energy density in the battery, to facilitate its manufacture by eliminating the need to handle lithium metal and, most importantly, to enable the formation of a homogeneous, dendrite-free lithium film when the battery is charged.
These electrodes will be based on the functionalisation of a metal collector with thin-film materials comprising at least one lithiophilic material (typically a compound that can be alloyed with lithium) and an inorganic ionic conductor. These electrodes are prepared by physical vacuum deposition processes such as sputtering or thermal evaporation. It will therefore be necessary to study the influence of the composition and structure of the lithiophilic layer on the nucleation and growth mechanism of the lithium film and on the evolution of the electrode during charge/discharge cycles. The role of chemical/mechanical interactions with the ionic conducting layer will also be investigated.
This work, which is part of a national CEA/CNRS joint project, will be carried out at the CEA Tech site in Pessac, which has a full range of vacuum deposition and thin film characterisation equipment, in close collaboration with ICMCB CNRS in Bordeaux. It will benefit from the many characterisation resources (confocal optical microscopy, SEM/cryo FIB, ToF-SIMS, SS-NMR, µ-XRD, AFM,...) available in the various partner laboratories involved in the project.
MOCVD growth of 2D ferroelectric In2Se3 films for high density, low consumption nonvolatile memories
Room temperature ferroelectric thin films are the key element of high density, low consumption nonvolatile memories. However, with the further miniaturization of the electronics devices beyond the Moore’s law, conventional ferroelectrics suffer great challenge arising from the critical thickness effect, where the ferroelectricity is unstable if the film thickness is reduced to nanometer or single atomic layer limit. Two-dimensional (2D) materials, thanks to their stable layered structure, saturate interfacial chemistry, weak interlayer couplings, and the benefit of preparing stable ultra-thin film at 2D limit, are promising for exploring 2D ferroelectricity and related device applications. So far, proof of concept demonstrating 2D ferroelectricity has predominantly utilized small flakes (less than a few hundred µm) mechanically exfoliated from a bulk crystal. In particular, atomically thin alpha (or gamma)-In2Se3 lamellar semiconductor preserves a ferroelectric character at 2D limit.
Given the imperative for wafer-scale electronics applications, there is a pressing need for large area growth of high quality 2D materials using bottom-up processes. The objective of this PhD project is to develop the growth of lamellar In2Se3 in its alpha or gamma phase crystal structures by chemical vapor phase epitaxy (MOCVD) on large silicon substrates (200 mm). The proof of concept of a ferroelectric memory cell will be performed by directly depositing a metal electrode on the surface of the 2D ferroelectric material without damaging it.