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.
Impact of fission products and microstructure on the thermophysical properties of LWR (U,Pu)O2-x fuel
In France, mixed oxide fuel (MOX, (U,Pu)O2) is currently deployed in several pressurized water reactors (PWRs) operated by EDF. To ensure continued low-carbon electricity production, a broader use of MOX fuel across the French nuclear fleet is expected to become essential in the near future. During reactor operation, U1??Pu?O2?? fuels undergo significant changes in their physical properties and microstructure, primarily due to the accumulation of dozens of lighter elements generated by plutonium’s fission, commonly referred to as fission products (FPs). Because of the high radiotoxicity of irradiated fuel, surrogate materials known as SIMMOX have been developed. In a previous PhD project, we established a synthesis route enabling the production of SIMMOX doped with up to twelve fission products, successfully reproducing the microstructure of irradiated PWR MOX fuel.
To maintain an adequate margin to fuel melting during irradiation, it is crucial to understand how the thermophysical and thermodynamic properties of MOX fuel evolve under these conditions. This PhD project aims to measure these properties on a representative MOX composition currently used in EDF reactors. The key properties of interest include thermal conductivity, heat capacity, and melting temperature. These measurements will be carried out at the JRC-Karlsruhe (Germany) during a research stay of approximately 12 months. Subsequently, the samples will be returned to CEA-Marcoule, where the impact of high-temperature exposure on actinide and fission product speciation, as well as on the microstructural evolution of the MOX fuel, will be investigated. In parallel, the experimental work will be complemented by thermodynamic modeling using the CALPHAD approach, in order to identify the mechanisms and phase equilibria governing high-temperature behavior during property measurements.
Simulation of flow in centrifugal extractors: the impact of viscous solvents on operation
Within the framework of nuclear spent fuel reprocessing, the CEA co-developed with ROUSSELET-ROBATEL liquid/liquid extraction (ELL) devices aimed at bringing two immiscible liquids into contact, one of which contains the valuable metals to be recovered and the other an extractant molecule. The multi-stage Centrifugal Extractor is one of the devices used to perform ELL at the La Hague plant. The future use of solvents potentially more viscous than current industrial standards may pose performance issues that need to be studied in advance in the laboratory to provide the necessary recommendations to restore the expected performance levels for the plant. The nuclear environment in which these devices operate makes in situ studies nearly impossible, thus depriving R&D of valuable information that is nevertheless essential for a deep understanding of the physicochemical mechanisms at the heart of the issues involved. To address this, the proposed study will rely on a numerical approach that will have been previously validated by comparison with either historical experimental data or data acquired from more recent ad hoc pilot systems. Thus, following a phase of literature review and capitalization of recent measurements, it is proposed to first create test cases that will be used to validate the numerical models. Based on this validation and in light of the knowledge acquired from previous theses concerning the effect of viscosity on flows, it is proposed to numerically explore the impact of an increase in solvent viscosity on centrifugal extractors. This will pave the way for a better understanding of the operation of the devices as well as operational or geometric improvements. The student will work at CEA Marcoule, in a research environment at the crossroads between a team of experimentalists and a team of numerical simulators. This experience will enable the student to acquire important skills in modeling liquid-liquid flows as well as solid knowledge on the development of liquid-liquid contactors.
Investigation of geopolymer durbility for radioactive wastewater treatment
The reprocessing of spent nuclear fuel generates radioactive effluents that require appropriate treatment. To meet industrial and regulatory challenges, the CEA is developing geopolymer-based adsorbent materials that are robust, cost-effective, and efficient for capturing Cs-137 and Sr-90. Their performance can be enhanced through the incorporation of selective adsorbents (such as zeolites) and through innovative shaping processes (3D printing, beads, foams) optimized for column adsorption.
The durability of these materials remains a critical issue, as their leaching and ageing mechanisms in column systems are still poorly understood. This PhD project will focus on studying these phenomena in order to assess the impact of effluent chemistry on the stability and efficiency of geopolymers. The work will include material synthesis, batch and column sorption tests, and the use of modelling tools to interpret alteration mechanisms. The scientific challenge is to identify the key physicochemical markers of geopolymer degradation in the targeted liquid effluents and to link them with column sorption performance.
The PhD candidate will join the Laboratory for Supercritical Processes and Decontamination (LPSD), renowned for its expertise in column-based ion extraction and adsorbent characterization. He/she will collaborate with specialists at CEA Marcoule and with the laboratory teams, and will regularly present project progress to the industrial partner. Upon completion of the PhD, the candidate will have developed recognized expertise at the interface of materials science, chemistry, and column adsorption processes. This work will open a wide range of opportunities: R&D positions in the nuclear sector, waste management, and functional materials; academic pathways (postdoctoral research, academia, teaching); or contributions to major energy and environmental challenges.
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).
Study of homogeneous SIMMOX synthesis and dissolution based on hydroxide pathway
The dissolution of spent nuclear fuel is an essential first step in its reprocessing. The kinetics of irradiated (U,Pu)O2 (MOX) dissolution currently hinders industrial-scale reprocessing and therefore requires a better understanding of the mechanisms involved in order to overcome this industrial obstacle. However, studying the dissolution of irradiated MOX fuel in order to identify and model the various stages and mechanisms involved is hampered by the high radiotoxicity of such material and the representativeness of the available samples. In order to simplify these studies and establish representative models, numerous tests have been carried out on model compounds (e.g., non-irradiated UO2 and MOX). Among these, SIMfuel (U,Pu)O2 compounds doped with up to 11 fission products aim to represent the chemical complexity of irradiated fuels. The conventional approach to manufacturing SIMfuel by mixing solid-phase reagents requires sintering of fuel pellets at high temperatures (>1600°C). In order to reproduce the behavior of fission products (reduction-oxidation, distribution, etc.) for irradiated fuels at lower temperatures, an alternative approach has been developed based on the synthesis of oxides via the hydroxide route. This method allows for the simultaneous and homogeneous precipitation of numerous metal cations and significantly lowers the sintering temperature. This approach has already enabled the study of SIMfuel incorporating rare earths, platinoids, and molybdenum under representative conditions. However, this approach has never been implemented for the synthesis of SIMfuel containing both plutonium and all fission products relevant to the study of dissolution.
The objective of this thesis is to implement such syntheses, based on recent results obtained concerning the synthesis of MOx by the hydroxide route. To this end, SIMfuels will be synthesized to represent spent MOx-type fuels (SIMMOx). To represent the different zones present in spent fuel, SIMMOx with different Pu/(U+Pu) ratios will be considered. These SIMMOx will undergo dissolution tests to characterize their behavior during this stage.
TRANSIENT LIQUID PHASE SINTERING OF UOX AND MOX FUEL PELLETS
The subject is related to the manufacture of UOX and MOX fuels. The main objective is to identify dopant pairs that allow the formation of a transient liquid phase during the fuel sintering step. For this, phase diagram calculations using the CALPHAD method will have to be carried out, also taking into account the requirements related to the irradiation phase once the fuel is loaded into the reactor. The most promising pairs will then be evaluated in the context of the manufacture of a UOX fuel and a MOX fuel. The experiments to be carried out will essentially be: the preparation of a powdery material, the shaping by pressing of this material in the form of cylinders representative of fuel pellets and the study of the high-temperature sintering of these UOX and MOX formulation cylinders. After sintering, a very important step will be the characterization at the macroscopic and microscopic scales of these pellets. The first year of the thesis will take place at the CEA center in Cadarache. The next two will take place at the CEA site in Marcoule. The first year of the PhD will take place at the CEA Cadarache center within the ICPE Uranium Fuel Laboratory. The following two years will be spent at the INB Atalante facility on the CEA Marcoule site. The candidate will work in two facilities unique in Europe and will be able to develop experience working in a nuclear environment with a highly innovative approach that will lead to the publication of original scientific results.
Study of new concepts for miniaturizable and parallelizable liquid-liquid extractors
In the process of developing procedures, their miniaturization represents a major challenge for upstream research and development (R&D). Indeed, the miniaturization of procedures offers numerous advantages in terms of reducing the volume of raw materials, waste management, screening possibilities, automation, and safety for personnel.
To date, the counter-current liquid-liquid extraction process does not have a convincing miniaturization solution, although the applications are numerous: in pharmacy, chemical synthesis, nuclear, or nuclear medicine.
The CEA-ISEC in Marcoule has developed new microfluidic tools to perform these operations in a simple and operational manner, based on a fine understanding of the instabilities of two-phase flows in capillaries.
This 3-year study topic proposes:
- To experiment, understand, and finely model the flows and mass transfers;
- To optimize and then transpose the phenomena to industrially significant volumes;
- To publish and participate in international conferences.
The doctoral student will benefit from learning about the world of research in a team that values quality in the supervision and future of its doctoral students, in a multidisciplinary team ranging from process engineering to instrumentation, with projects ranging from research to industry.
General competencies in chemical engineering and mass transfer are required. Competencies in collaborating with our academic partners will be essential to the success of the study project.
INFLUENCE OF THE DRY GRANULATION ON THE MANUFACTURING OF SFR MOX FUELS
The subject is related to the manufacture of MOX U,Pu)O2 fuel for Fast Neutron Reactors. The current process integrates a co-grinding step of uranium and plutonium dioxides to generate a powder medium which is then shaped by uniaxial pressing to generate cylindrical fuel pellets which are then sintered at high temperature. The collected powder medium has poor flowability which limits the rates of shaping by pressing. The objective of the thesis is therefore to evaluate the impact of mechanical granulation of the powder medium on the flowability, the pressing step and the microstructure obtained after sintering. Dissolution tests in nitric acid will also be carried out on certain very specific microstructures. The thesis will be based on a formal experimental plan developed using specific software (JMP). The PhD will take place at the INB Atalante facility on the CEA Marcoule site. The candidate will work in a unique facility in Europe and will be able to develop expertise in working in a nuclear environment with a highly innovative approach that will lead to the publication of original scientific results.