Cooperative Diglycolamides in Organic and Aqueous Phases for Selective and Stereodirected Extraction Applied to the downstream of the Nuclear Fuel Cycle
The recovery of elements of interest (uranium, plutonium, minor actinides, and platinum-group metals) generated by fission reactions involves a cascade of hydrometallurgical processes based on liquid–liquid extraction (LLE). Following dismantling, shearing, and leaching of spent nuclear fuel in concentrated nitric acid, the various elements are sequentially and selectively transferred into an immiscible phase, typically consisting of a lipophilic ligand dissolved in an organic diluent. Within the framework of the CEA’s accelerated research programme dedicated to downstream scientific and technological developments for nuclear energy, this PhD project will focus on a grouped actinide separation strategy following the preliminary extraction of uranium with a monoamide (PUMAS process). The objective is to develop an alternative to the GANEX process, enabling the selective partitioning of elements between the leachate and the solvent through competition between an organic phase containing a lipophilic diglycolamide (DGA)-type extractant or related diamide analogues and a water-soluble DGA dissolved in the aqueous leachate. The affinity and selectivity of these ligands will be controlled and tuned by modifying the topology and stereochemistry of their substituents, using lipophilic substituents for ligands in the organic phase and hydrophilic substituents for those in the acidic aqueous phase. Depending on the position of these substituents, either on the nitrogen atoms and/or on the methylene bridges of the DGA backbone, different stereogenic centres will be introduced. These structural modifications are expected to enhance both affinity and selectivity, as previously demonstrated.¹,2 In the first stage of the project, the PhD candidate will synthesise a series of chiral DGA derivatives in both unresolved and diastereomerically pure forms. Their ability to discriminate between actinides (thorium, the latter being used as a surrogate for plutonium), lanthanides, and other competing metals, including platinum-group metals, will then be evaluated. Elemental concentrations will be determined by ICP analysis of the aqueous phases and X-ray fluorescence (XRF) analysis of the organic phases. The molecular and supramolecular mechanisms associated with each diastereomer, including coordination and aggregation phenomena, will subsequently be investigated using both established and advanced characterisation techniques, including UV spectroscopy, IR spectroscopy, multinuclear NMR, density functional theory (DFT) calculations, X-ray scattering, neutron scattering, and extended X-ray absorption fine structure (EXAFS) spectroscopy.
The doctoral training provided through this project will equip the PhD candidate with a broad range of skills relevant to both academic and industrial careers, particularly in the fields of the nuclear fuel cycle and separation chemistry. The research will be carried out within the LISA laboratory at ICSM, which is recognised for its expertise in the chemistry and physical chemistry of extractants for hydrometallurgical applications. The PhD candidate will benefit from high-quality scientific supervision and a collaborative working environment alongside fellow PhD candidates, postdoctoral researchers, and research engineers, within a supportive and stimulating research setting.
Study of the Molecular Mechanisms of Selective Dissolution of Nuclear Fuels: Contribution of Structural Characterization
Classical nuclear fuel recycling processes, such as PUREX, rely on dissolution and separation steps to recover valuable elements (uranium and plutonium), enabling the production of new MOx fuels. However, with the development of 4th-generation reactors in France and the closure of the fuel cycle, there is a growing need for innovative reprocessing methods tailored to future fuels. This PhD thesis proposes exploring a promising approach: selective dissolution of uranium and plutonium, where these elements are dissolved in an organic phase while fission products remain in solid form within the residue. This process could simplify separation steps while optimizing waste management.
The thesis will focus on studying the selectivity of this dissolution process for uranium and plutonium relative to fission products, depending on initial conditions (fuel characteristics, solvent nature, and chemical environment), to optimize the recovery of valuable elements. Additionally, a detailed investigation of the speciation of dissolved cations and the residue will enhance the understanding of the underlying dissolution mechanisms. To achieve this, you will have access to state-of-the-art equipment in a nuclearized laboratory, including advanced characterization techniques. Your work will contribute to advancing knowledge in actinide chemistry applied to the development of innovative processes, while allowing you to develop expertise in a unique research environment.
Sonohydrothermal conversion of uranium(VI) compounds into UO2+x
The hydrothermal conversion of actinide carboxylates is a promising route for the synthesis of oxide powders intended for the manufacture of nuclear fuels. This method relies on the precipitation of a precursor at room temperature, followed by its conversion to an oxide under so-called “mild” hydrothermal conditions (T = 250°C, P < 100 bars). Simple An(IV)- oxalate systems and, more recently, U(VI)-oxalic acid mixtures have been studied for about a decade, particularly at the ICSM, and have shown that hydrothermal conversion allows for the quantitative precipitation of actinides from solution and yields a nanostructured powder suitable for densification. Nevertheless, the processes involved are generally characterized by slow kinetics and produce powders that are not well-suited for shaping and sintering.
The use of high-power ultrasound for the synthesis of materials is a rapidly growing field that has the potential to meet these requirements, particularly for hydrothermal syntheses—which are known to be time-consuming and energy-intensive but remain indispensable even on an industrial scale. The combination of ultrasound and hydrothermal conditions is a particularly innovative technique that we have been developing at the ICSM for the synthesis of catalytic materials for several years. In fact, our recent studies have shown that the synthesis of LTA-type zeolites is accelerated by an order of magnitude compared to conventional syntheses under silent hydrothermal conditions, while simultaneously reducing the particle size and polydispersity of the material.
This thesis topic aims to study the effect of sonohydrothermal treatment on the reductive conversion of uranium(VI) compounds into oxides, focusing on the mechanisms involved, their kinetics, and the characteristics of the powders obtained using various analytical techniques. It will also draw on the study of the mechanisms and kinetics of the phenomena observed under the innovative conditions employed—which generate both chemical and physical effects—in order to refine our understanding of the processes leading to the precipitation of the final oxide and to enable their future application to other systems of interest.
Molecular dynamics simulation of interfaces for U/Pu separation processes
The recycling of uranium and plutonium is a key challenge for closing the nuclear fuel cycle. It involves a stage based on a liquid-liquid extraction separation process, which consists of selectively transferring certain chemical elements from an aqueous phase to an organic phase. How do molecules organise themselves at the interface between these two phases to enable the separation of uranium and plutonium? This question is crucial for developing more efficient processes. This PhD thesis aims to understand, at the molecular level, how the structure of liquid–liquid interfaces controls the transfer of species between the two phases. The PhD student will develop molecular dynamics simulations and advanced computational methods to study various extraction systems, notably those based on monoamides and TBP. The objective will be to link the molecular organisation of the interfaces to the extraction mechanisms and to the thermodynamic and kinetic properties of the transfer, by comparing the simulations with available experimental data. Conducted at the CEA ISEC’s Laboratory of Actinide-Ligand Interactions, in collaboration with the Laboratory of Multi-Scale Theories and Methodologies at the Marcoule Institute of Separative Chemistry, this PhD research lies at the heart of the challenges facing the fuel cycle and the recycling of strategic metals. It will offer in-depth training in molecular modelling, physical chemistry, programming and scientific computing, within a multidisciplinary research environment and in collaboration with experimental scientists involved in process development. The PhD student, who will have a background in physical chemistry, theoretical chemistry or physics, and an interest in modelling, programming and scientific computing, will be encouraged to disseminate their scientific findings through publications and presentations at national and international conferences. The PhD will enable the candidate to acquire expertise in molecular modelling, physical chemistry, programming and numerical computation, with career prospects in academic research, research organisations and industrial R&D, particularly in the fields of nuclear science, materials and processes.
Reliable Perovskite/Silicon tandem photovoltaic cells and modules
Organic-inorganic hybrid perovskites (HOP) have emerged as one of the most promising photovoltaic technologies of the last decade, paving the way for the development of highly efficient and cost-effective solar panels. By combining a HOP cell with a silicon (Si) cell, a tandem cell can be formed to optimize light absorption. This technology has achieved a record efficiency of 35.5% , making it a highly promising candidate beyond the current generations of silicon-based photovoltaics, which have reached their optimization limits. The primary challenge for the full deployment of Si/HOP tandem panels is ensuring stability and reliability during operation.
A joint research proposal between Forschungszentrum Jülich (FZJ) and CEA for two PhD positions (1 PhD in Julich, 1 PhD in CEA) aims to accelerate towards a stable and reliable PV technology as required for market-relevant implementation. Both centers bring long-standing expertise across photovoltaic materials development and characterization as well as cell and module optimization to the consortium. FZJ is currently expanding a dedicated effort focused on the early stages of tandem innovation, including novel materials and emerging device architectures . CEA contributes its strong track record in realizing photovoltaic cells / modules and translating performance into robust, reliability-oriented device and module concepts. Together, the partners will establish a tightly coupled pathway that links rapid innovation with rigorous validation, in order to shorten development cycles and accelerate technology transfer into scalable tandem products.
Both PhD candidates will collaborate closely on selecting material and process conditions for single junction perovskite and then silicon–perovskite tandem photovoltaics using automated/AI protocols, materials characterization, and full device fabrication/characterization. In CEA, the PhD candidate will focus on device fabrication/characterization selected on the basis of automated/AI protocols (done in Julich by the other PhD), stability/lifetime testing using different stress factors (light and temperature particularly) and outdoor conditions after encapsulating the cells. A specific method will be developed to predict cells’ lifetime from short tests, in order to accelerate the development workflow. Data from aging experiments in CEA will provide quantitative feedback to Jülich on both performance and operational durability, as well as insights into degradation modes. Secondments are planned, with each PhD candidate spending at least three months at the other institute to be trained in the techniques employed in the twin study.
Causal Surrogate Modeling for High Performance Finite Element Earthquake Simulations
High-resolution earthquake simulations are essential for understanding seismic wave propagation in complex geological structures. However, finite element simulations require significant computational resources, particularly when exploring multiple scenarios or accounting for uncertainties. This PhD project aims to develop causal surrogate models that reduce computational costs while preserving the physical consistency of seismic simulations. The proposed approach combines causal machine learning, Bayesian statistics, and high-performance computing (HPC). Using data generated by large-scale finite element simulations, the research will investigate methods for identifying directed relationships between seismic variables across space and time. These causal relationships will then be used to construct surrogate models capable of approximating selected components of numerical simulators. Bayesian approaches will also be explored to quantify uncertainties in the learned causal structures and model predictions. The developed methods will be integrated into parallel simulation environments, particularly ArcaneFEM and PSD, to ensure their applicability to large-scale problems. The expected results include efficient causal learning algorithms, computationally scalable surrogate models, and hybrid simulation strategies combining numerical methods and artificial intelligence. Ultimately, this research aims to improve the efficiency of earthquake simulations and support uncertainty quantification, adaptive mesh refinement, and data assimilation.
Accelerated design of High Entropy Oxide thin films for carbon-free energies
Over the past decade, high-entropy oxides have emerged as a promising new class of materials for energy-related applications and corrosion resistance in extreme environments, both of which are central areas of CEA's activities.
However, their optimization remains limited by the vast compositional space that needs to be explored, leading most studies to focus on equimolar compositions.
This PhD project aims to overcome this limitation by combining combinatorial PVD using HiPIMS technology with artificial intelligence approaches based on Bayesian optimization, an approach that has not yet been explored for these materials.
The objective is to master the deposition of high-entropy oxides and optimize their properties for corrosion protection in high-temperature electrolyzers dedicated to low-carbon hydrogen production.
The deposited coatings will exhibit controlled stoichiometry, structure, microstructure, and texture, and will be characterized both in situ and ex situ using complementary techniques.
The project will provide a proof of concept for coupling combinatorial PVD with Bayesian optimization to accelerate the discovery and optimization of new materials.
This PhD project is part of the international doctoral programme of PEPR DIADEM and will bring together CEA (Saclay), ESRF (Grenoble), and NIMS (Japan).