Shape optimization for innovation in nuclear fuels
Nuclear industry is currently developping enhanced Accident Tolerant Fuels" (ATF) [1]. These fuels feature enhanced physical properties; in particular, thanks to the addition of thermal conductors inside the fuel, they tend to be colder in standard as well as in accident conditions.
This thesis aims at developping numerical strategies (that will be programmed into a semi-industrial code) in order to propose new "shapes" of fuels (by "shape", we mean internal structures or microstructures), and to optimze already existing concepts. It will take advantage of recent numerical and mathematical techniques related to the so-called "shape optimization" [2]. Based on the previous work [3], more and more complex physical phenomena will be taken into account : first, thermal conductivity and mechanical behaviour in standard conditions, then gaz diffusion... Discussion with experts and modelization will be necessay in order to reformulate these physical behaviours into forms amenable to numerical simulation.
This thesis will take place at the CEA center of Cadarache in the fuel research department, in a laboratory devoted to modelling and numerical methods. The latter is affiliated to the Institute IRESNE for the research low-carbon energy production.
This project will be in collaboration with Nice University offering so an environment both academic and connected to application.
It also takes part in the PEPR DIADEM called Fast-in-Fuel, a national research project.
We search for excellent candidates with a solid background in scientific computing, analysis and numerical analysis of partial differential equations, as well as in optimization. Skills in physics (mechanics and thermics) will also be considered. The proposed subject aims at a concrete application at the intersection of various scientific fields, and it is largely exploratory. Hence, curiosity and creativity will also be highly appreciated.
[1] Review of accident tolerant fuel concepts with implications to severe accident progression and radiological releases, 2020.
[2] G. Allaire. Shape optimization by the homogenization method, volume 146 of Applied Mathematical Sciences. Springer-Verlag, New York, 2002.
[3] T. Devictor. PhD Manuscript, 2025 (in preparation)
Experimental Investigation and DEM Simulation of Actinide Powder Segregation During Transfer Processes
The fabrication of nuclear fuels based on actinide oxides (UO2, PuO2) involves numerous powder-handling operations, during which segregation phenomena may occur. These phenomena—arising from differences in particle size, shape, density, or surface condition—directly affect the homogeneity of the mixtures and, consequently, the quality and consistency of the resulting fuel pellets. Controlling these effects is therefore a major industrial challenge to ensure both process robustness and final product conformity.
This PhD project aims to deepen the understanding of the mechanisms driving powder de-mixing of UO2 during transfer stages, particularly during vibratory conveyor transport and gravitational discharge. The main scientific objective is to establish the relationship between the physical and rheological properties of the powders, the process operating conditions, and the intensity of the observed segregation phenomena. The work will combine experimental studies and numerical simulations using the Discrete Element Method (DEM) to identify the material and process parameters influencing segregation. Experimental setups will be developed to characterize the powders and quantify the degree of de-mixing, while simulations will serve to validate and extrapolate the experimental observations.
Conducted at CEA Cadarache, within the Uranium Fuel Laboratory (LCU) of the Institute for Research on Nuclear Systems for Low-Carbon Energy Production (IRESNE), and in collaboration with the TIMR laboratory at UTC, this project will provide recommendations to limit segregation during industrial operations and improve the prediction of segregation tendencies in powder mixtures, particularly in cohesive actinide powders.
The PhD candidate will disseminate their findings through publications and conference presentations. They will also have the opportunity to learn and refine several transferable techniques applicable to a wide range of materials science and engineering contexts.In particular, the issues related to the physics of granular materials, which form the core of this thesis, are of significant industrial relevance and are shared by many other sectors handling powders, such as the pharmaceutical, food processing, and powder metallurgy industries.
Three-Dimensional Fine Measurements of Boundary Layers in Turbulent Flows within PWR Fuel Assemblies
The production of electricity through nuclear energy is a key pillar of the energy transition due to its low carbon footprint. In a continuous effort to improve safety and performance, the development of new knowledge and tools is essential.
Fuel assemblies, which are components of a reactor core, face various challenges involving thermo-hydraulic phenomena. These include flow-induced vibrations, power transmission associated with critical fluxes, and fluid-structure interactions in cases of assembly deformation or seismic excitation. In all these situations, the behavior of the fluid near the wall plays a crucial role. The use of Computational Fluid Dynamics (CFD) allows for the simulation of these phenomena with the goal of obtaining predictive tools. The experimental validation needs required by today's simulations push classical measurement techniques to their limits. There is a strong need for refined experimental data in both time and space on complex geometries.
This doctoral project aims to address this need by leveraging the latest advancements in optical measurements for turbulent flows. By combining index matching techniques, panoramic cameras, and Particle Tracking Velocimetry (PTV), it is possible to measure the velocity field in a representative volume (approximately 1 cm³) with a spatial density of around 10 micrometers. This allows for the simultaneous measurement of flow in the boundary layer and the hydraulic channel.
The thesis will primarily be conducted at the Hydromechanics Laboratory (LETH) at the IRESNE Institute (CEA Cadarache) and will involve collaboration with the Thermo-Fluids Lab at George Washington University. Travel to the USA will be required.
Numerical modelling of large ductile crack progagation and assessment of margins comparing to engineering approach
Predicting failure modes in metal structures is an essential step in analyzing the performance of industrial components where mechanical elements are subjected to significant stress (e.g., nuclear power plant components, pipelines, aircraft structural elements, etc.). To perform such analyses, it is essential to correctly simulate the behavior of a defect in ductile conditions, i.e., in the presence of significant plastic deformation before and during propagation.
Predictive numerical simulation of ductile tearing remains an open scientific and technical issue despite significant progress made in recent years. The so-called local approach to fracture, notably the Gurson model (and its modified version GTN), is widely used to model ductile tearing. However, its use has limitations: significant computation time, simulation stoppage due to the presence of completely damaged elements in the model, and non-convergence of the result when the mesh size is reduced.
The aim of this thesis is to develop the ductile tear simulation model used at LISN so that it can be applied to large crack propagation on complex structures. It also aims to compare the results obtained with engineering methods that are simpler to implement.
Towards automated and reconfigurable microfluidic platforms for the study and development of nuclear fuel recycling processes
The main objective of this PhD project is the design and development of the first automatic and reconfigurable microfluidic platform dedicated to research and development on the nuclear fuel cycle. In a context where mastering nuclear processes remains a key challenge, both for energy production and for the sustainable management of nuclear materials, microfluidic devices represent a particularly promising approach. These autonomous laboratories on a chip have already demonstrated their potential in various fields, such as chemistry, materials science, and biology. Their application to nuclear processes would help reduce radiation exposure risks, minimize waste generation, and optimize resources by enabling a larger number of experiments to be performed safely, quickly, and reproducibly. For about a decade, the DMRC has been conducting phenomenological studies on the main stages of the nuclear process (dissolution, solvent extraction, precipitation, etc.) using microfluidic devices. In parallel, it has developed PhLoCs (Photonic-Lab-on-Chips), which allow the miniaturization of several analytical techniques (UV-Vis spectroscopy, LES, holography, etc.) and their integration for online monitoring of the investigated phenomena. Nevertheless, no truly autonomous and fully automated platform currently exists that combines process execution with integrated analytical monitoring.
The aim of this PhD work is therefore to make a decisive step by designing a modular device where several functional chips can be assembled, some dedicated to process operations (e.g., uranium/plutonium separation) and others to online measurements, within a flexible configuration adapted to nuclear environments. In addition, the research will focus on integrating new instrumental techniques directly on chips, such as FTIR and UV-Vis-NIR spectroscopies, which are crucial for studying critical process steps, including solvent degradation. This project thus aims to establish the foundations of next-generation microfluidic platforms that combine safety, modularity, and performance to advance nuclear fuel cycle research. At the end of the PhD, the candidate will have developed unique expertise in microfluidics applied to nuclear processes, combining optical instrumentation and automation. These skills will offer strong career opportunities in research and advanced process engineering.
Fatigue crack growth modelling with residual stress - Improvement of the Gtheta method
Residual stresses are self-balanced stress fields found in certain mechanical components in the absence of external loading. Caused by welding, for example, these stresses can potentially affect the behaviour of the structure and its resistance to fracture. When demonstrating the integrity of a mechanical component, particularly in the context of nuclear safety, it is crucial to precisely understand the role of these stress fields on the component's resistance. In the case of fatigue crack propagation, to accurately model all the phenomena involved (stress redistribution, evolution of plasticity, closure effect), it will be necessary to improve numerical tools, such as meshing and crack propagation methods (AMR, X-FEM...) and the J-integral interpolation in the case of through-cracks (Gtheta method). The thesis will consist of two complementary parts: (a) numerical development aimed at improving the Gtheta method in Castem FE code, associated with a 3D crack propagation modelling using AMR, and (b) continuation of component scale tests on fatigue crack propagation in different configurations of residual stress fields.
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.
Modeling the impact of defects in Steel–Concrete Structures. Identification of critical defects through metamodeling and optimization algorithms
To meet growing constructability challenges, steel–concrete (SC) structures are emerging as a promising alternative to conventional reinforced concrete structures. These elements are composed of infill concrete, two external steel plates, and steel shear studs that ensure composite action. While such structures present a clear interest due to their overall mechanical behavior, the presence of the steel plates prevents visual inspection of the concrete casting quality. It is therefore essential to characterize the impact of possible defects. This is the context of the proposed PhD research. Building upon recent results obtained in the laboratory, the goal is to develop a numerical framework to account for defects in steel–concrete structures. The thesis will be structured in several stages: validation of a modeling strategy for the mechanical behavior of defect-free SC structures, introduction of defects in the simulations and assessment of the applicability of the numerical approach, development of a metamodel and sensitivity analysis, and identification of critical defect configurations through optimization algorithms. One of the operational objectives of this doctoral work is to provide a tool capable of identifying critical defect configurations (size, position, and number) with respect to a given target quantity of interest (such as loss of strength or reduction in average stiffness). The research will therefore rely on the use and further development of state-of-the-art numerical tools in the fields of finite element modeling, optimization techniques, sensitivity analysis, and metamodeling. The thesis will be carried out within a rich collaborative environment, notably in partnership with EDF.
Multiphysic modeling of sintering of nuclear fuel pellet: effect of atmosphere on shrinkage kinetics
Uranium dioxide (UO2) fuels used in nuclear power plants are ceramics, for which solid-phase sintering is a key manufacturing step. The sintering stage involves heat treatment under controlled partial O2 pressure that induces coarsening of UO2 grain and then consolidation and densification of the material. Grain growth induce material densification and macroscopic shrinkage of the pellet. If the green pellet (powder obtained by pressing, manufacturing step before sintering) admit a highly heterogeneous density, this gradient leading to differential shrinkage and the appearance of defects. Furthermore, the sintering atmosphere, i.e., the gas composition in the furnace, impacts grain growth kinetics and thus the shrinkage of the pellet. Advanced simulation is the key to improving understanding of the mechanisms observed as well as optimizing manufacturing cycles.
The PhD thesis aims at developing a Thermo-chemo-mechanical modeling of sintering to simulate the impact of the gas composition and properties on the pellet densification. This scale will enable us to take into account not only the density gradients resulting from pressing, but also the oxygen diffusion kinetics that have a local impact on the densification rate, which in turn impacts the transport process. Therefore, a multiphysics coupling phenomenon has to be modelled and simulated.
This thesis will be conducted within the MISTRAL joint laboratory (Aix-Marseille Université/CNRS/Centrale Marseille CEA-Cadarache IRESNE institute). The PhD student will leverage his results through publications and participation in conferences and will have gained strong skills and expertise in a wide range of academic and industrial sectors.
Design and Optimisation of an innovative process for CO2 capture
A 2023 survey found that two-thirds of the young French adults take into account the climate impact of companies’ emissions when looking for a job. But why stop there when you could actually pick a job whose goal is to reduce such impacts? The Laboratory for Process Simulation and System analysis invites you to pursue a PhD aiming at designing and optimizing a process for CO2 capture from industrial waste gas. One of the key novelties of this project consists in using a set of operating conditions for the process that is different from those commonly used by industries. We believe that under such conditions the process requires less energy to operate. Further, another innovation aspect is the possibility of thermal coupling with an industrial facility.
The research will be carried out in collaboration with CEA Saclay and the Laboratory of Chemical Engineering (LGC) in Toulouse. First, a numerical study via simulations will be conducted, using a process simulation software (ProSIM). Afterwards, the student will explore and propose different options to minimize process energy consumption. Simulation results will be validated experimentally at the LGC, where he will be responsible for devising and running experiments to gather data for the absorption and desorption steps.
If you are passionate about Process Engineering and want to pursue a scientifically stimulating PhD, do apply and join our team!