Molecular Dynamics Simulation of Plutonium(IV) in Solution
With the revival of nuclear power in France, the CEA is playing a key role in the nuclear industry of the future. In this context, engineers and researchers are mobilised to meet the growing needs of this industry. Plutonium is a key element in the nuclear fuel cycle. Acquiring molecular data is crucial to optimising and rationalising the mechanisms involved in separating this element.
Plutonium(IV) is one of the most common cationic forms in the nuclear fuel cycle. Its study by theoretical chemistry presents difficulties both in ab initio modelling (occupied f-block orbitals) and in classical atomistic simulations. In classical molecular dynamics simulation, the models necessarily require the addition of the polarisation effect, and sometimes even the addition of charge transfer, in order to reproduce the system's behaviour correctly. As a result, classical simulations containing plutonium (IV) are almost completely absent from the scientific literature. In addition, the speciation of this cation is sensitive to the acidity of the medium, which has to be taken into account in the simulations, adding a further difficulty.
The aim of this thesis is to use molecular dynamics (classical and ab initio) to simulate solutions containing plutonium, taking into account the effect of acidity. The PhD student will be faced with two main issues: the choice or development of a force field for the Pu4+ cation, and the design of a method for including acidity in the solutions. A crucial step in the process will be to compare the results with the available experimental data in order to conclude on the ability of the models to reproduce the experimental data. This thesis will be carried out in a multidisciplinary laboratory, combining experimental chemistry and theoretical modelling, while conducting both applied and fundamental research.
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.
Radiolytic Degradation of N,N-dialkylamides: Effects on Metal Complexation
N,N-dialkylamides (or monoamides) are promising extractant molecules for the development of new processes for nuclear fuel reprocessing. In this context, these extractant molecules are exposed to radiolysis caused by ionizing radiation from radionuclides, which leads to the formation of new compounds through the breaking or modification of chemical bonds. Such changes in solution composition can alter the extractive properties, particularly in terms of efficiency and selectivity.
This thesis aims to study the impact of radiolysis on the speciation of actinide-ligand complexes in solution, in order to improve the understanding of the phenomena observed under ionizing radiation. We propose an approach combining experimental studies (chromatographic and spectroscopic techniques) with theoretical calculations (such as bond dissociation energies, identification of probable radical attack sites, stability of metal-ligand complexes, etc.) to describe the molecular speciation of species in solution. Organic compounds formed during radiation and the metallic complexes will be characterized to evaluate the modifications caused by radiation.
Perovskite devices for solar hydrogen production
Project Overview:
The PhD thesis is part of the ICARUS European project, aiming to develop efficient solar energy conversion systems for a carbon-neutral future. The project focuses on integrating photoelectrochemical (PEC) water splitting and photovoltaic (PV) power generation.
Key Objectives:
•Develop innovative metal halide perovskite solar cells with tunable bandgaps for broader light absorption.
•Optimize printed carbon-based solar cells and scaffolds for improved conductivity, mechanical resistance, and durability.
•Incorporate innovative carbon counter electrodes into perovskite devices.
•Upscale and manufacture solar modules.
•Integrate the developed modules into a final PEC prototype.
Research Focus:
The PhD candidate will primarily focus on:
•Printed carbon-based solar cells: Optimizing ink properties, investigating the behavior of printed conductive ink under various conditions, and characterizing conductivity and mechanical resistance.
•Perovskite devices: Incorporating innovative carbon counter electrodes and evaluating their performance and stability.
•Module manufacturing: Upscaling and manufacturing solar modules based on the developed technologies.
•PEC prototype integration: Contributing to the final integration of the PEC prototype.
Expected Outcomes:
The research is expected to contribute to the development of highly efficient and sustainable solar energy conversion systems, supporting the transition to a carbon-neutral future. The findings will have implications for both academic research and industrial applications.
Study of the synthesis and thermodynamic properties of the (An,Zr)O2 and (Zr,An)SiO4 compounds
In the event of a serious nuclear accident, the fuel in the reactor core may melt, resulting in the formation of a compound known as corium. Cases of major accidents and prototypical corium formation experiments have identified the formation of key compounds such as mixed oxides (U,Zr)O2 formed by interaction of the fuel with the zircaloy cladding and silicates (Zr,U)SiO4 formed by interaction of the corium with structural materials. In the case of MOx, (U,Pu)O2 fuels, corium formation could lead to the formation of equivalent phases with significant plutonium contents. However, experimental thermodynamic data on such compounds, which would enable their behaviour to be assessed, are currently non-existent. In this context, determining the conditions for synthesising such compounds with a good degree of purity is essential for acquiring such data. The synthesis of (Zr,Pu)O2 and (Zr,Pu)SiO4 solid solutions is therefore an essential first step before studying (Zr,U,Pu)O2 and (Zr,U,Pu)SiO4 systems.
The aim of this PhD thesis will be to determine the conditions suitable for the synthesis of these compounds, to carry out a series of characterisations enabling their purity to be assessed and their thermodynamic properties to be established. To achieve this, experiments will be carried out on the ATALANTE facility and a multi-technique characterisation approach will be chosen (XRD, Raman and infrared spectroscopies, SEM, synchrotron characterisation techniques, etc.). Solubility tests in a controlled environment will then be set up and calorimetric measurements carried out as part of international collaborations.
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.
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).
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.
Thermoelectric energy conversion control via coordination chemistry of transition metal redox ions in ionic liquids
Thermoelectricity, a materials’ capability to convert heat in to electric energy has been known to exist in liquids for many decades. Unlike in solids, this conversion process liquids take several forms including the thermogalvanic reactions between the redox ions and the electrodes, the thermodiffusion of charged species and the temperature dependent formation of electrical double layer at the electrodes. The observed values of Seebeck coefficient (Se = - DV/DT, the ratio between the induced voltage (DV) and the applied temperature difference (DT)) are generally above 1 mV/K, an order of magnitude higher than those found in the solid (semiconductor) counterpart. The first working example of a liquid-based thermoelectric (TE) generator was reported in 1986 using Ferro/ferricyanide redox salts in water.
However, due to the low electrical conductivity of liquids, its conversion efficiency was very low, preventing their use in low-temperature waste-heat recovery applications. The outlook of liquid TE generators brightened in the last decade with the development of ionic liquids (ILs). ILs are molten salts that are liquid below 100 °C. Compared to classical liquids, they exhibit many favorable features such as high boiling points, low vapour pressure, high ionic conductivity and low thermal conductivity accompanied by higher Se values. More recently, an experimental study by IJCLab and SPEC revealed that the complexation of transition metal redox couples in ionic liquids can lead to enhancing their Se coefficient by more than a three-fold from -1.6 to -5.7 mV/K, one of the highest values reported in IL-based thermoelectric cells. A clear understanding and the precise control of the speciation of metal ions therefore is a gateway to the rational design of future thermoelectrochemical technology.
Based on these recent findings, we proposes to further study the coordination chemistry of transition metal redox ions in ILs and mixtures. A long-term goal associated to the present project is to demonstrate the application potential of liquid thermoelectrochemical cells based on affordable, abundant and environmentally safe materials for thermal energy harvesting as an energy efficiency tool.
Synthesis and optical properties of quantum dots
Graphene as a constituent of graphite was close to us for almost 500 years. However, it is only in 2005 that A. Geim and K. Novoselov (Nobel Prize in 2010) reported for the first time the obtaining of a nanostructure composed by a single layer of carbon atom. The exceptional electronic properties of graphene make it a very promising material for applications in electronic and renewable energies.
For many applications, one should be able to modify and control precisely the electronic properties of graphene. In this context, we propose to synthesize chemically graphene nanoparticles and study their absorption and photoluminescence properties. We will focus on families of elongated nanoparticles, with the aim of studying how size can enable us to observe and control multiexcitonic processes in these materials. This project will be developed in collaboration with Physicists so the candidate will work in a multidisciplinary environment.