Development of solid porous siliceous supports for actinide sorption - Behaviour under irradiation
The aim of this research project is to study the densification of a mesoporous structure under the effect of irradiation damage produced by the presence of an actinide (238Pu) in the porous structure. To achieve this, siliceous materials based on mesoporous silicas modified by the addition of additive elements (B, Al, etc.) will be used. The purpose of adding these elements is to weaken the mesoporous structure in order to promote densification. The characteristics of the mesoporous structure (pore diameter, wall size, symmetry of the pore network) will be other parameters of the study. These materials will be functionalised with phosphonate ligands for actinide adsorption: thorium as a simulant in a preliminary stage, followed by plutonium. The final part of this work, which will continue beyond the thesis, will involve using various techniques (SAXS, BET, microscopy, etc.) to study the evolution of the mesoporous structure under the effect of irradiation damage as the material ages. This fundamental research work could have spin-offs in the field of nuclear waste conditioning materials: ageing of gels on the surface of nuclear glass, support material for decontaminating radioactive effluents. Part of the work will be carried out at CEA Marcoule's Atalante facility.
Impact of solvent nanostructure on uranium precipitation: a physicochemical approach for nuclear recycling
Recycling nuclear fuel is a major challenge to ensure a sustainable energy future. The CEA, in partnership with Orano and EDF, has been developing a new process for separating plutonium-rich fuels for several years. The goal is to replace the current TBP/TPH system with a redox-free process, better suited for the reprocessing of MOX or fast neutron reactors (FNR).
In this context, this thesis proposes to study the behavior of organic solvents loaded with uranium to understand and prevent the formation of precipitates, a phenomenon that could impact the performance of industrial processes. The scientific approach will focus on the supramolecular scale and compare different monoamides to evaluate the effect of alkyl chains on the physicochemical properties and nanostructure of the solutions.
The candidate should hold a Master's degree (Master 2) in chemistry, physical chemistry, or materials science. Skills in analytical chemistry, spectroscopy (NMR, FTIR), and scattering techniques (SANS, SAXS) will be highly valued. By joining this project, you will become part of the CEA's cutting-edge laboratories (ICSM/LTSM and DMRC/SPTC/LILA), equipped with world-class facilities for studying radioactive samples. You will benefit from multidisciplinary supervision, including opportunities for international collaborations. This thesis represents a major scientific challenge with direct industrial applications, offering you valuable experience in the field of nuclear separation and processing technologies.
Study of MOx and model compounds leaching in underwater storage conditions
This thesis deals with nuclear fuel recycling in France, with a focus on the multi-recycling of uranium and plutonium from MOX fuels, planned for 2040. Spent fuel is stored underwater in pools, where a cladding defect could lead to water contamination and complicate reprocessing. This thesis proposes to study the leaching of these fuels and the appearance of secondary phases under conditions simulating storage. The work is divided into three parts: preparation of model compounds, study of chemical durability of model and industrial materials, and analysis of secondary phases forming on the surface of irradiated fuels. The aim is to gain a better understanding of the stability of these phases as a function of chemical and irradiation conditions, as well as their transformation mechanisms. The results will enable us to develop models for the behavior of defective rods over several decades, contributing to safer and more efficient management of irradiated fuels.
Microemulsion model: Towards the prediction of liquid-liquid extraction processes
This multi-scale modeling thesis aims to develop innovative theoretical approaches and numerical tools to revolutionize strategic metal extraction processes, such as liquid-liquid extraction, whose underlying mechanisms remain poorly understood. To address these challenges, solvent phases will be represented as microemulsions through a synergy of mesoscopic and molecular modeling approaches.
The mesoscopic approach will involve the development of a code based on microemulsion theory using a random wavelet basis. This code will enable the characterization of the structural and thermodynamic properties of the solutions. The molecular approach will rely on classical molecular dynamics simulations to evaluate the curvature properties of the extractants, which are essential for bridging the two scales.
The new high-performance computational code may integrate artificial intelligence techniques to accelerate the minimization of the system’s free energy while accounting for all chemical species present with a minimal number of parameters. This will pave the way for new research directions, such as predicting speciation and calculating thermodynamic instabilities in ternary phase diagrams, thereby identifying unexplored experimental conditions.
This PhD thesis, conducted at the Mesoscopic Modeling and Theoretical Chemistry Laboratory at the Marcoule Institute for Separation Chemistry, will have applications in the recycling domain and extend to the broader field of nanoscience, thereby expanding the impact of this work.
The PhD candidate, with an academic background in physical chemistry, theoretical chemistry, or physics, and a strong interest in programming, will be encouraged to disseminate his/her scientific results through publications and presentations at national and international conferences. Upon completion of the thesis, the candidate will have acquired a wide range of skills in modeling and physical chemistry, opening numerous professional opportunities in both academic research and industrial R&D.
Ultrasound-assisted decontamination of Hg-bearing solids
Mercury is one of the most dangerous pollutants. Yet, it has been widely used in the industry, in particular in electrolysers (chlor-alkali process), resulting in many contaminated facilities. Existing methods to stabilise or decontaminate are either energy-consuming or limited in terms of speciation. The aim here is to develop a new method combining leaching and ultrasonic irradiation, to decontaminate porous solids (e.g. mortar). The characterisation of solids and liquids before/after decontamination will be performed using SEM-EDX, XRD and XRF.
The PhD study will be performed in Marcoule centre, located 30 minutes from Avignon. The two host laboratories are the Laboratory of Supercritical Processes and Decontamination (DMRC/STDC/LPSD) and the Laboratory of Sonochemistry in Complex Fluids (ICSM//LSFC). Marcoule site is served by bus and hosts many PhDs and post-docs. The candidate should hold a master degree with a chemical engineering background and desirable skills in analytical chemistry and inorganic chemistry. The candidate will gain initial experience in the field of decontamination, which is one of the major problems associated with the circular energy economy. Depending on the focus of the thesis, they will be able to pursue a career in academia or industry.
Nucleation, Growth, and Multi-Scale Structural Properties of Colloidal Nanoparticles of Actinide Oxides (Pu, U, Th)
Nanocrystalline oxides possess unique physicochemical properties, modulated by their size and local structure, making them promising for various technological applications. However, actinide oxide nanoparticles remain underexplored due to their radioactivity and toxicity. Nonetheless, studies dedicated to these species are growing, driven by environmental and industrial considerations, particularly for their involvement in current and future nuclear fuel cycles. This thesis focuses on plutonium, a key element in nuclear reactors. Its behavior in solution is complex, particularly due to hydrolysis reactions that lead to the formation of highly stable colloidal PuO2 nanoparticles. Although these species are now better described, the mechanisms leading to their formation remain largely unexplored.
The ambitious goal of this thesis is to uncover the fundamental mechanisms involved in the formation of these nanoparticles by adopting a systematic approach that combines a wide range of experimental parameters. These include the synthesis medium, temperature, reactant concentration, reaction time, and the contribution of sonochemistry. The focus will be on studying the nucleation and growth stages of these nanoparticles, as well as their structural properties in relation to the physicochemical conditions that influence their formation. Studies will be conducted at ICSM with Th, U, and Zr as analogs, and at the Atalante facility for Pu. In addition to standard laboratory techniques necessary for characterizing these systems, complementary experiments will be carried out on synchrotron lines (SOLEIL and ESRF) to thoroughly investigate the structural and reactive properties of these species and their precursors.
AI based prediction of solubilities for hydrometallurgy applications
Finding a selective and efficient extractant is one of the main challenges of hydrometallurgy. A comprehensive screening is impossible by the synthesis/test method due to the high number of possible molecules. Instead, more and more studies use quantum calculations to evaluate the complexes stabilities. Still, some important parameters such as solubility are lacking in this model.
This project thus aims to develop an AI based tool that provides solubility values from the molecular structure of any ligand. The study will first focus on 3 solvants: water, used as a reference as AI tools already exist, 3 M nitric acid to mimic nuclear industry applications and n-octanol, organic solvent used to measure the partition coefficient logP. The methodology follows 4 steps:
1) Bibliography on existing AI tools for solubility prediction yielding the choice of the most promising method(s)
2) Bibliography on existing databases to be complemented by the student's in-lab solubility experiments
3) Code generation and training of the neural network on the step 2 databases
4) Checking the accuracy of the predictions on molecules not included in the databases by comparing the calculated results with in-lab experiments
Biosourced alditol anhydrides, tunable molecular architectures for a sustainable approach to the uranium extraction
Although current applied processes for extracting uranium in sulfuric, phosphoric and nitric media, are efficient enough to justify their large-scale application, they require improvements to increase their efficiency and reduce their environmental impact. This doctoral project aims to improve these performances by focusing on the liquid-liquid extraction stage. This consists of selectively transferring uranium, extracted after crushing, grinding and leaching rocks, to an oil phase containing a lipophilic ligand compatible with the leachate medium. The ambition here is to develop new extractants analogous to trialkylamines (AMEX process), trialkylphosphines and phosphoric diesters (URPHOS process), and trialkylphosphates (refining). The PhD student will synthesize chiral amphiphilic extractants, derived from bicyclic anhydrides of biosourced alditols (isosorbide, isomannide and isoidide). He will evaluate their affinity towards uranium and their selectivity in the presence of competing ions. He will then characterize the molecular and supramolecular mechanisms of these new extractants (coordination, aggregation) using state-of-the-art methods such as UV, IR, multinucleus NMR, X-ray scattering and neutron scattering. The doctoral training will help the PhD student to integrate easily into academic or industrial environments, particularly in the fields of the nuclear fuel cycle, separative chemistry and formulation. Research will take place in the LTSM laboratory of the Institut de Chimie Séparative de Marcoule, renowned for its expertise in the chemistry and physical chemistry of extractants for hydrometallurgy. The PhD student will benefit from high-quality supervision and a collaborative working environment, surrounded by PhD students, post-docs and engineers, in a serene and stimulating setting.