High-throughput screening of catalysts for the direct conversion of CO2 into synthetic fuels
This doctoral project aims to develop an innovative high-throughput screening approach for catalysts for the direct conversion of CO2 into synthetic fuels, known as CO2-FTS. This approach will combine a catalyst screening platform with in situ/operando characterization techniques and artificial intelligence methods to accelerate the discovery and optimization of high-performance catalysts. It aims to identify doped FeOx-type catalysts for the CO2-FTS reaction (>50% conversion, high selectivity towards C8-C16). Several high-throughput screening campaigns will allow for iterative optimization of compositions and reactive conditions. A numerical model of the parametric landscape will then be developed. This model will subsequently be coupled with multi-scale modeling from the active site to the reactor level. The developed catalysts will contribute to the energy transition by enabling a circular carbon economy.
Bottom-up synthesis of nanographene and study of their optical and electronic properties
This project is part of an ANR project, which aims to synthesize perfectly soluble and individualized graphene nanoparticles in solution and incorporate them into spin electronics devices. To do this, we will draw on the laboratory's experience in synthesizing and studying the optical properties of graphene nanoparticles to propose original structures to several groups of physicists who will be responsible for studying the optical and electronic properties and manufacturing spin valve-type devices.
Tailored Peptide Ligands for Actinide Complexation: From Structure to Selectivity
The processes involved in the nuclear fuel cycle, such as the PUREX process designed to separate uranium and plutonium from fission products, rely on ligands capable of selectively complexing actinide cations to enable their extraction. The chemical functions carried by these ligands play a key role in determining both their affinity and selectivity toward metal cations. Studying the influence of these functional groups, such as carboxylic acids and phosphates, is therefore essential for the design of new extracting molecules, as well as for the development of decorporation strategies.
Over the past decade, cyclic peptides have been developed for their ability to complex uranyl ions with high selectivity over calcium. Organized in ß-sheet conformations, these peptides display a functional face bearing complexing groups (carboxylates, phosphates). Their amino acid composition can be tuned to finely adjust the chemical nature of the coordination site, making these cyclic peptides tailor-made molecular architectures for probing cation complexation. However, while their interaction with uranium is now well characterized, their ability to bind transuranic elements remains largely unexplored.
This PhD project aims to study the complexation of actinides such as plutonium and neptunium by various cyclic peptides. The combination of NMR spectroscopy and classical molecular dynamics simulations will provide detailed structural information on the formed complexes. Complementary techniques, including UV-Vis-nIR and EXAFS spectroscopies, ESI-MS mass spectrometry, and fluorescence spectroscopy, will deepen the characterization. By combining experimental and computational approaches, this work will enhance our understanding of ligand–actinide interactions while paving the way for the design of innovative extracting and decorporating molecules.
Investigation of autocatalysis phenomena occurring in nitric acid dissolution through electrochemical methods
The nuclear fuel recycling process, used at the La Hague plant in France, begins with the nitric dissolution of spent fuel, mainly composed of uranium and plutonium oxides. In a context of plant renewal and widespread of MOX fuel recycling, innovative new dissolution equipment are currently studied. The sizing of such devices is currently limited by the absence of a fully comprehensive model for the dissolution of mixed oxides, which is a highly complex reaction (three-phase involved, self-catalytic, heterogeneous attack, etc.). Despite substantial progress made in previous studies, a number of questions remain unanswered, particularly concerning the reaction mechanisms involved and the nature of the catalyst.
Electrochemical methods (cyclic voltammetry, electrochemical impedance spectroscopy, rotating electrode, etc.) have never been used to understand dissolution, yet they should prove relevant as already demonstrated by the studies carried out on this subject by CEA Saclay in the field of corrosion. Therefore, the aim of this thesis is to apply these experimental methods for the first time to the dissolution of nuclear fuels, through a phenomenological approach. To achieve this, the student will be able to rely on the teams and facilities of Saclay and Marcoule centers, specialized respectively in electrochemical methods for the corrosion studies and the physico-chemical modeling of dissolution.
This cross-disciplinary study, involving materials science, electrochemistry and chemical engineering, will follow a stimulating fundamental research approach, but will also take place in a highly dynamic industrial context. Initially, the work will be carried out on inactive model and noble materials (at the Saclay center), then on real materials containing uranium and/or plutonium (at the Marcoule center).
Synthetic methodologies towards functionalized azaheterocycles and application to energetic molecules
The objective of the PhD is to develop new synthesis and/or functionalization methods to obtain functionalized heterocyclic molecules. These molecules are based on 5- or 6-member azaheteroaromatic rings (diazines, triazines, triazoles, tetrazoles, etc.). The targeted structures make it possible to envisage high densities and enthalpies of formation, while maintaining low sensitivity (thermal, mechanical, etc.). They find applications in the energy field, notably propulsion, explosives and gas generators (airbags). In addition, these heterocyclic compounds as well as the intermediates are also structurally close to families of biologically active products and/or likely to exhibit fluorescence properties, as already shown in a previous PhD in the laboratory.
Chemical recycling of oxygenated and nitrogenated plastic waste by reductive catalytic routes
Since the 1950s, the use of petroleum-based plastics has encouraged the emergence of a consumption model focused on the use of disposable products. Global plastic production has almost doubled over the last 20 years, currently reaching 468 million tons per year. These non-biodegradable plastic are the source of numerous forms of environmental pollution. Since the 1950s, only 9% of the wastes have been recycled. The majority have been incinerated or sent to landfill. In the current context of this linear economy, health, climate and societal issues make it essential to transition to a circular approach to materials. This evolution requires the development of recycling methods that are both effective and robust. While the most common recycling methods currently in use are mainly mechanical processes that apply to specific types of waste, such as PET plastic bottles, the development of chemical recycling methods appears promising for treating waste for which no recycling channels exist. These innovative chemical processes make it possible to recover the carbonaceous material from plastics to produce new ones.
Within this objective of material circularity, this doctoral project aims to develop new chemical recycling routes for mixed oxygen/nitrogen plastic waste such as polyurethanes (insulation foam, mattresses, etc.) and polyamides (textile fibres, circuit breaker boxes, etc.), for which recycling routes are virtually non-existent. This project is based on a strategy of depolymerizing these plastics by the selective cleavage of the carbon-oxygen and/or carbon-nitrogen bonds to form the corresponding monomers or their derivatives. To do that, catalytic systems involving metal catalysts coupled with abundant and inexpensive reducing agents will be developed. In order to optimize these catalytic systems, we will seek to understand how they proceed and the mechanisms involved.
Study of plutonium oxalate formation mechanisms – Application to molten salt reactors
Molten salt reactors (MSRs) offer a promising alternative for sustainable nuclear energy production, thanks to their intrinsic safety and their ability to close the nuclear fuel cycle, notably through the use of a fast neutron spectrum. This type of reactor can use liquid chloride salts containing plutonium and other actinides as fuel. As part of the development of this nuclear pathway, the CEA supports the development of a PuCl3 production process. The synthesis of this chloride has already been carried out at small scale at the CEA and elsewhere in the world. Several starting materials can be used for the synthesis of the trichloride, notably plutonium metal, plutonium oxide and plutonium oxalate. The most industrially promising synthesis route is the oxalate route, because it can be transferred to the equipment already present at the La Hague site. This process consists of converting the oxalate into plutonium chloride via a gas–solid reaction with a chlorinating agent, such as HCl for example. However, the reaction mechanism and the decomposition of the oxalate in a chlorinated environment are still poorly understood. A detailed understanding of this transformation would make it possible to optimize operating conditions and facilitate the scale-up of this synthesis. The topic will initially focus on determining the reaction mechanism of Ce oxalate (a surrogate for Pu) to the chloride. Small-scale studies will be performed to identify the various reaction intermediates using analytical techniques such as X-ray diffraction (XRD), thermogravimetric analysis / differential thermal analysis (TGA/DTA) and analysis of the gases produced during the reaction. The kinetics as well as the enthalpy changes will also be studied in order to obtain key data for modelling a large-scale process. Subsequently, an optimization of the PuCl3 synthesis at the scale of a few tens of grams will be carried out. These studies will first be conducted under non-radioactive conditions on a surrogate to validate the experimental approach, before being transposed to radioactive conditions.
Chemical and mechanical properties of N-A-S-H aluminosilicates of geopolymer
Management of low- and medium-level nuclear waste relies primarily on cements, but their limitations with regard to certain types of waste (reactive metals, oil) require the exploration of new, more effective materials. Geopolymers, particularly those composed of hydrated sodium aluminosilicates (Na2O–Al2O3–SiO2–H2O, or N–A–S–H), appear to be a promising alternative thanks to their chemical compatibility with certain types of waste.
However, despite the growing interest in geopolymers, scientific obstacles remain: 1) The available thermodynamic data on N-A-S-H is still incomplete, making it difficult to predict their long-term stability via modeling, 2) The role of their atomic structure in regard to their reactivity remains unclear, and 3) The links between chemical composition (in terms of Si/Al ratio) and mechanical properties are not established, limiting the representativeness of the models created.
By combining experimentation and modeling in order to link atomic structure and properties, this thesis aims to obtain robust and novel data on the chemical and mechanical properties of N-A-S-H. The thesis is organized around three major objectives: 1) determining the impact of N-A-S-H composition on dissolution and establishing thermodynamic solubility constants, 2) characterizing their atomic structure (aluminols, silanols, and hydrated environments) using advanced NMR spectroscopy, and 3) linking their mechanical properties, measured by nanoindentation, to their structure and composition using molecular dynamics modeling.
Development of extracting systems for the isotopic enrichment of chlorine
Chlorine (Cl) is naturally composed of 76% 35Cl, which through neutron capture forms 36Cl, a long-lived gamma emitter (t1/2 = 301 000 years), and sulfur 36S, which accelerates corrosion phenomena, and 24% 37Cl with a drastically lower neutron capture section. A supply of 37Cl is therefore necessary in order to operate these reactors. Techniques currently exist that enable the enrichment of chlorine, such as ultracentrifugation, liquid-phase thermal diffusion, or laser isotope separation. The enrichment of chlorine by liquid-liquid extraction technics has been recently developed within CEA. The objective of the thesis is to identify and implement chemical systems allowing the 37Cl enrichment by a separative chemistry process. The thesis subject aims to identify on the basis of literature data initially, the families of ligands and, within these families, the best candidates for the 37Cl enrichment. Next, the synthesis and purification of the selected molecules will be carried out in the laboratory. Finally, the enrichment properties of the successfully synthesised ligands will be evaluated by separative chemistry, by quantification of chlorine isotopes using Inductively coupled plasma mass spectrometry (ICP-MS).
The thesis will be carried out at the recycling and energy recovery processes laboratory (LRVE) at the CEA in Marcoule.
The ideal candidate will be a Master's student in their second or third year of engineering school, studying chemistry, organic chemistry or analytical chemistry. The multidisciplinary nature of the skills acquired and the rigour developed by the student during the experiments undertaken will be valuable assets for the future PhD student.
Understanding the mechanisms of oxidative dissolution of (U,Pu)O2 in the presence of Ag(II) generated by ozonation
The recycling of plutonium contained in MOx fuels, composed of mixed uranium and plutonium oxides (U,Pu)O2, relies on a key step: the complete dissolution of plutonium dioxide (PuO2). However, PuO2 is known to dissolve only with great difficulty in the concentrated nitric acid used in industrial processes. The addition of a strongly oxidizing species such as silver(II) significantly enhances this dissolution step—this is the principle of oxidative dissolution. Ozone (O3) is used to continuously regenerate the Ag(II) oxidant in solution.
Although this process has demonstrated its efficiency, the mechanisms involved remain poorly understood and scarcely documented. A deeper understanding of these mechanisms is essential for any potential industrial implementation.
The aim of this PhD work is to gain insight into the interaction mechanisms within the HNO3/Ag/O3/(U,Pu)O2 system. The research will be based on a parametric experimental study of increasing complexity. First, the mechanisms of generation and consumption of Ag(II) will be investigated in the simpler HNO3/Ag/O3 system. In a second phase, the influence of various parameters on the oxidative dissolution of (U,Pu)O2 will be examined. The results will lead to the development of a kinetic model describing the dissolution process as a function of the studied parameters.
At the end of this PhD, the candidate—preferably with a background in physical chemistry—will have acquired advanced expertise in experimental techniques and kinetic modeling, providing a strong foundation for a career in academic research or industrial R&D, both within and beyond the nuclear sector.