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In reactor, the fuel is subjected to various loadings that can induce cracking and affects its mechanicals, physicochemical and transport properties. Thereafter, matter can diffuse inside the crack and clog it, which can restore the material’s rigidity. This phenomenon is commonly referred to as crack healing.Nuclear fuel for sodium fast reactor can be healed by diffusion welding (Salmon et al., 2026) or porosity migration (Barani et al., 2022).
This Ph.D. thesis aims at developing a multiphysics modeling of crack healing based on a coupling between fracture mechanics, matter transport in cracks and local physicochemical process which induce healing. Dedicated numerical method must be extended to couple damage gradient model, crack width and matter transport.
Model validation is a major challenge, notably because of the difficulty of distinguishing and characterizing the various mechanisms at play in irradiated nuclear fuel. To address this challenge, the project will also investigate cementitious materials, for which dedicated experiments on crack healing have been conducted.
This PhD project will be carried out within the MISTRAL Joint Laboratory, bringing together Aix-Marseille University, CNRS, Centrale Marseille and CEA, in collaboration between the IRESNE institute (CEA Cadarache site) and the ISAS institute (CEA Saclay site). The PhD student will be primarily based at Cadarache and will spend a period of 6 months to 1 year at the CEA Saclay site. The student will also benefit from the scientific environment of the Laboratoire de Mécanique et d’Acoustique (LMA). This collaboration aims to develop a generic model applicable to both nuclear fuels and cementitious materials.
The PhD student will showcase his results through publications and participation in conferences. He/she will have gained strong skills in multiphysics coupling, numerical method and numerical simulation, which will be a major asset in several fields, both in academic and industrial sectors.
(Barani et al., 2022) Barani T, Ramière I, Michel B (2022) Analysis of fabrication and crack-induced porosity migration in mixed oxide fuels for sodium fast reactors by the finite element method. J Nucl Mater 558:153341. https://doi.org/10.1016/j.jnucmat.2021.153341
(Salmon et al., 2026) Salmon, L., Blanc, V., Garajeu, M. et al. A thermo-mechanical cohesive zone model for damage and healing in brittle solids. Comput Mech 77, 501–520 (2026). https://doi.org/10.1007/s00466-025-02675-5
The management of gaseous inclusions or particles in glass is a challenge existing throughout the glass industry. Depending on the processes considered, their gravity-driven migration can be altered by natural convection movements. In this context, understanding the dynamics involved within multiphysics convective systems is essential. This subject proposes to model/simulate the transient evolution of a multiphase system representative of a fluid mixture with complex rheology (thermo-dependence and particle effects) containing particles and bubbles subjected to a thermal constraint in a cylindrical geometry. Doing so will allow to estimate the different evolution regimes, their transitions, and the characteristic quantities involved, such as characteristic times of stabilization of particles and bubbles, or their characteristic sizes and distribution zones. These results will be validated by experimental data from the corpus available within the DPME, which also has extensive experience in the development of vitrification processes and their modeling. The knowledge produced will be directly useful to the sector for the production of vitrified nuclear waste, as the processes must be optimized to take into account the presence of solid, liquid, and gaseous phases, which need to be characterized.
The French Alternative Energies and Atomic Energy Commission (CEA) is a major player in research and innovation in the field of low-carbon energy. In collaboration with EDF and Framatome, it conducts research combining simulation and experimentation to improve the safety of French reactors. The CEA is developing the PLEIADES simulation platform, which models the behavior of nuclear fuel using a multiphysical and multiscale approach.
This thesis focuses on studying the behavior of fuel rods during a hypothetical Loss Of Coolant Accident (LOCA) scenario in a pressurized water reactor. These rods consist of fuel pellets stacked within a zircaloy cladding, which serves as the first containment barrier for radioactive fission products. During a LOCA, the cladding temperature rises, while the internal pressure of the fuel rod exceeds that of the primary coolant system. Due to heat and oxidation, the cladding is weakened, this can lead locally to the cladding ballooning or even its rupture.
The resulting sudden depressurization can lead to the fragmentation of the fuel, which has already been fragmented into several pieces during its operation in the reactor. The fragments may then disperse into the primary coolant loop, altering the core cooling conditions—which constitutes a fundamental safety concern. The objective of this thesis is therefore to quantify the impact of cladding ballooning on fuel fragmentation and relocation, in order to predict its dispersion in the event of cladding rupture and thereby strengthen safety demonstrations.
This thesis work aims to develop a three-dimensional simulation approach for the release of fission products and the fine fragmentation of fuel observed under thermomechanical loads. Particular attention will be paid to the influence of the confinement exerted by the shell on fragmentation mechanisms. To this end, the Discrete Element Method (DEM) will be coupled with Cohesive Zone Models (CZM) to simulate crack propagation in an elementary volume composed of a few grains, under various loading, confinement, and geometric conditions. A multiscale approach will then be used to extend the simulations to fuel pellet scale. Volumes representative of the pellet’s different zones will be studied to gradually build a macroscopic-scale description, using cellular automata and/or full three-dimensional calculations. The models will be evaluated by comparing them with representative experimental data.
The student will be based at the IRESNE Institute (CEA-Cadarache) in the Laboratory of multi-type fuels expertise and performance code validation (LEVA) within the Fuel Study Department (DEC). This doctoral research will be conducted jointly at : 1) LEVA and 2) the Laboratory of Mechanics and Civil Engineering (LMGC, University of Montpellier). The doctoral student will build upon the findings of previous doctoral research as well as the high-performance computational tools ExaDEM and the proven LMGC90 tool. The doctoral student will develop skills at the intersection of mechanics, materials science, and nuclear engineering, within a research environment that combines scientific expertise, academic collaboration, and industrial partnerships. The work may be showcased through publications and presentations at international conferences.
A. Nusslé « Modélisation de la fragmentation fine du combustible UO2 lors d’un Accident de Perte de réfrigérant Primaire », Thèse de doctorat, Université de Montpellier, 2026
V. Richefeu & al., Advanced strategies for discrete simulations with three-dimensional R-shapes in rockable framework. Computer Physics Communications, 320, 109997, 2026.
Safety studies for Pressurized Water Reactors (PWRs) require demonstrating the absence of fuel melting by maintaining its temperature below the melting threshold in all operating conditions. In this context, the melting behavior of the fuel and the solidus/liquidus temperatures are critical input data. However, the available experimental data, which are limited and outdated, show significant variability, particularly for the solidus temperature, demanding substantial safety margins. As a consequence, the current safety approach ensures the absence of fuel melting by accounting for sufficient power margins, but research aimed at improving the understanding of the underlying mechanisms could pave the way for optimization and operational margin gains.
This PhD thesis has two main objectives: clarifying the impact of fission products on solidus/liquidus temperatures; to finely characterize the microstructural evolution during this transition. To achieve this, the Ph.D. student will develop a high-temperature measurement method (>2700°C) with a thermal gradient on the CEA's laser platforms, in collaboration with the Fresnel Institute. The method must ensure sufficient precision for the unambiguous characterization of solid-liquid phase transition temperatures. Tests will use SIMFUEL samples (fresh UO2 doped to simulate irradiated fuel). A detailed characterization of the samples before and after testing (optical microscopy, SEM, EDX) will provide clear indicators of microstructural evolution. The predesign and interpretation of the experiments will rely on thermochemical calculations to consolidate modeling in support of the understanding the melting behavior of irradiated UO2.
This project, to be carried out at CEA Cadarache within the Institute for Research on Nuclear Systems for Low-Carbon Energy Production (IRESNE) in close collaboration with the Fresnel Institute in Marseille, will provide an opportunity to develop strong expertise in the behavior of composite materials, thermochemistry, as well as high-temperature instrumentation and optics, opening up a wide range of career opportunities in the energy and materials sectors.
1/ D. Manara et al., Journal of Nuclear Materials, 342, 148–163, 2005. DOI : 10.1016/j.jnucmat.2005.04.002.
2/ V. D’Ambrosi et al., Nuclear Technology, 210, 285–307, 2024. DOI : 10.1080/00295450.2023.2253660.
Precision measurements at the Large Hadron Collider (LHC) require a detailed understanding of the particles produced in each collision and the relationships between them. However, reconstructing the underlying physics process remains extremely challenging. Different decay chains can produce similar experimental signatures, several particle assignments may be compatible with the same event, and undetected particles leave incomplete information. A representation connecting these observations to different possible physical interpretations could improve reconstruction and provide a common basis for multiple analyses.
In this project, we propose to develop a hierarchical representation of collision events within the HEP Foundry programme led by the supervisors. This representation will connect reconstructed particles, composite objects, and possible decay chains within a unified machine-learning model. The model will first be trained on a diverse range of simulated processes and then adapted to specific reconstruction tasks. The objective is to retain several physically compatible interpretations of an event and quantify their uncertainties. Higgs boson pair production (HH), particularly in the four-bottom-quark final state, will serve as the main physics case study. This process probes the Higgs self-coupling and the shape of the Higgs potential, making it a major objective of the LHC physics programme. Its challenging reconstruction and large backgrounds will provide a stringent test of the proposed framework.
This PhD project will naturally fit within the ScienceFace initiative, notably by contributing to the development of shared software tools for scientific data curation and the construction of scientific foundation models.
Current batteries primarily rely on the use of liquid electrolytes composed of flammable solvents that are unstable in contact with lithium metal, posing safety issues. The development of gel polymer electrolytes (GPEs) is expected to lead to new generations of safer batteries. To maintain their environmental relevance, these new batteries should ideally be made of bio-based materials, have an extended lifespan, and be recyclable. In this context, this thesis aims to develop bio-based GPEs cross-linked by vitrimer chemistry that allows for their recyclability. The swelling of electrolytes in green, non-flammable deep eutectic solvents (DESs) is considered to achieve ionic conductivities greater than 10-4 S.cm-1 at room temperature. The PhD student will study the influence of the chemical structure of the polymer and the DES on the physicochemical, mechanical, and electrochemical properties of these eutectogels to optimize their formulation for integration into a complete pouch-cell system.
This project will establish atomic layer deposition (ALD) as a versatile surface engineering approach for superconducting resonators, addressing two complementary objectives for particle accelerators and quantum technologies.
The first objective is controlled doping of bulk niobium superconducting radiofrequency (SRF) cavities. Conformal films up to 10 nm thick will provide solid dopant sources, followed by high-vacuum annealing to tailor dopant profiles within the RF-active region. This strategy aims to improve uniformity, explore alternative dopants and eliminate subsequent electropolishing. Particular attention will focus on suppressing hydride formation while preserving the superconducting energy gap. Target performances include quality factors of 8 × 10¹° at 2 K and accelerating gradients of 40–45 MV/m. Supported by the European EPITA project, this work addresses requirements for future accelerators, including the Future Circular Collider.
The second objective is developing protective coatings with minimal dielectric losses by mitigating defects, particularly two-level systems. Building on CEA treatments combining dielectric oxide coatings and annealing that achieved record quantum-regime quality factors, alternative compounds will be investigated.
Ultimately, one treatment could enhance performance across quantum and accelerator operating regimes. Tunneling spectroscopy, X-ray spectroscopy and TOF-SIMS will correlate local superconducting properties with surface chemistry and dopant distributions. Two ALD systems will support development on coupons and transfer to resonators, building on demonstrated coating uniformity inside cavities. RF measurements will be conducted at CEA and partner laboratories, with Fermilab evaluating promising treatments at millikelvin temperatures. These investigations will clarify performance-limiting mechanisms and guide the rational design of optimized superconducting surfaces for both application domains.
Design of an industrial process aiming at the production of boron 10 (10B) enriched boron carbide (B4C) is key to reach PPE 3 general strategic goals. Indeed, production of new Evolutionary Power Reactors (EPR) for electrical power output and Rapid Neutron Reactor (RNR) to ensure fuel cycle closure will put a tremendous strain on 10B enriched stocks.
Isotopic fractionation by means of boric acid liquid chromatography over an ad hoc material could be an industrially viable process. If anionic resins are strong historical candidates for this purpose the Laboratoire des Procédés Supercritiques et de Décontamination (LPSD) at CEA Marcoule focuses at developing original hybrid materials with enhanced properties.
The PhD work will focus on the synthesis and characterization (NMR, IR, LC-UV, GC) of organic molecules for the separation of boric acid boron isotopes. These molecules will be grafted over silicas to obtain hybrid materials with fine tuning of their physicochemical properties (SEM, BET, TGA, XRB, microscopy). Separative properties will be evaluated by column chromatography foreshadowing the industrial process.
This offer is aimed at a final year MSc student in organic synthesis or materials chemistry interested in the field of analytical and process development. The candidate should be meticulous and demonstrate analytical thinking. This is an opportunity to develop an expertise in organic synthesis applied to the production of hybrid material applicable to the development of an industrial process.
Due to their unique physicochemical properties, PFAS used in numerous industrial applications pose a problem regarding their accumulation in groundwater. This situation highlights the need for innovative treatment technologies aimed at minimizing PFAS levels in effluents. Various methods (thermal, biological, chemical) have been investigated, but they suffer from drawbacks such as high energy consumption or the generation of toxic secondary effluents. In this context, hydrothermal oxidation (HTO) offers a promising alternative, achieving PFAS mineralization rates exceeding 99.9% at temperatures of 600°C and above. Under these conditions, water becomes a reaction medium conducive to the mineralization of organic compounds. However, applying such operating conditions at an industrial scale presents a technological challenge due to significant heat loss and the *in situ* formation of HF, which can cause corrosion issues. This thesis aims to investigate the HTO process using a co-fuel and the *in situ* use of a silica-based material designed to sequester all fluoride ions. Defining the process's operating regime requires a detailed understanding of mass balances as well as the mechanisms of PFAS oxidation. Elucidating these mechanisms will require the implementation of a precise and rigorous analytical protocol to quantify all residual organofluorine compounds. Modeling high-pressure/high-temperature phase equilibria for fluorinated species can be performed using PhreeQC and Prosim Simulis software. Finally, the process's versatility regarding other organofluorine waste streams will also be considered. The candidate will work within the Supercritical Processes and Decontamination Laboratory, in collaboration with the Measurement, Safety, and Environment Laboratory (LITEN/Grenoble) and in interaction with technicians, engineers, and doctoral students. They will benefit from the expertise of these laboratories in hydrothermal processes and the analysis of perfluorinated compounds. The skills acquired during the PhD will open up numerous career opportunities in academic research and industrial R&D within the fields of chemistry and the environment..