Characterisation of the physico-chemical properties of solid residues from biomass hydrothermal carbonisation
Hydrothermal carbonisation (HTC) is a thermochemical conversion process performed in pressurized water (2-6 MPa) between 180 and 260°C. The main product is a carbonaceous solid residue (hydrochar). Various applications are foreseen for hydrochar: combustion, gasification, adsorption, catalysis, soils amendment, hard carbon for Na-ion batteries, …, each of them requiring specific properties.
The objective of the thesis is to characterise and better understand the origin of several physico-chemical properties of biomass hydrochars. A special attention will be paid to hydrophobicity and drying capacity, to physical and textural characteristics of the particles (porosity, granulometry, specific surface), as well as to chemical characteristics (composition). The influence of biomass type and HTC conditions on these properties will be investigated.
The approach will consist in: experimentations in batch reactors on pre-selected biomass resources, together with use of different characterisation techniques for hydrochars; analysis of results aiming at determining links between the characteristics, elucidating the links between the resource and its hydrochar properties as a function of operational conditions.
Dual Active Bridge Topology Based on SiC Synthetic Switches for Ultra-Fast Active Stabilization of a Low-Inertia Converter-Dominated DC Grid.
With the massive deployment of direct current (DC) technologies on the grid, particularly photovoltaics and grid-connected battery energy storage systems (BESS), a growing share of electrical energy now flows through static power converters. Unlike classical grids dominated by rotating machines, which benefit from high natural inertia, power-electronics-dominated networks exhibit very limited inertia and may therefore experience highly dynamic voltage spikes, voltage drops, or even complete collapse. Some research focuses on synthetic inertia, emulated through specific control strategies implemented in static converters, but these approaches depend on equipment manufacturers and do not rely on established standardization. Another approach consists in designing dedicated equipment specifically intended for the active stabilization of low-inertia power systems, which is the direction explored in this PhD project.
A particularly demanding case concerns MVDC grids, which by construction rely entirely on static power converters, therefore exhibiting extremely low natural inertia, and requiring the use of converters based on specific technologies. Within the framework of this PhD, we propose the study and proof of concept of a converter connected to an MVDC electrical network operating between 6 and 12 kV, capable of injecting or absorbing very high levels of power in a transient manner, on the order of ten megawatts for durations ranging from 10 µs to 100 ms. The system will rely on an isolated Dual Active Bridge (DAB) topology, with a medium voltage capacitive DC bus at its primary.
This power electronics topic presents several technological bottlenecks. Synthetic switches (series-connected SiC devices, as investigated in a previous PhD in the laboratory) will have to be implemented in a real DAB converter. A highly isolated power supply for the gate drivers of these synthetic switches will need to be designed. The medium-frequency DAB transformer must be designed to transfer very high transient power while minimizing volume. Particular attention will therefore be paid to transient-oriented design, with the objective of identifying the key parameters that maximize, within a complex structure, the ratio between the converter rated power and its peak power.
Potential extensions toward other pulsed-power applications that could benefit from such a converter will be explored, taking into account their specific constraints.
Integrated waste treatment: design and optimisation of a multi-waste treatment scheme for a multi-purpose energy production
At the city scale, multiple waste streams such as household waste, compost, sewage sludge, yard waste, non-recyclable plastics, used oils, metals, glass, and others. All of these feedstocks exhibit variable seasonality and carbon content. Nowadays, the aforementioned streams are managed through recycling, and in some cases incineration or landfilling. Alternative treatment technologies, such as gasification, hydrothermal gasification, and anaerobic digestion, are being explored as potential pathways to improve the overall sustainability of waste management.
Existing scientific studies have largely focused on the conversion of individual waste types or on the application of a single technology to a specific waste stream, without accounting for regional integration, resource variability or systemic assessment. A city-scale analysis of waste streams could enable the identification of synergies between different waste types and the identification of optimal conversion pathways.
In this context, a key scientific challenge lies in the development of an integrated, multi-waste treatment framework capable of modelling, optimizing, and assessing a multi-waste, multi-product energy system at the city scale. The objective of this PhD project is to investigate waste treatment at the city scale, accounting for the seasonality of waste generation, waste stream composition, and local energy demand (heat, electricity, and gas). The work will consider local and European regulations (Waste Framework Directive, AGEC law, and RED III directive) as well as techno-economic and environmental aspects. The study will focus on one to three representative geographic areas and will establish a methodology that can be further applied to a broad range of territorial contexts.
Thermodynamic and Structural properties of alkaline and/or alkaline-earth, actinyl(VI) with carbonates
The triscarbonato uranyl solid phases containing alkaline (Alk = Na, K) alkaline earth (Ae = Mg, Ca) are known since mid-19th century. The evidence of equivalent complexes in solution Ca-UO2-CO3 has only occurred during the 1990s. Their importance is recognised as major in certain natural environments, from surface waters down to deep underground disposal sites of nuclear waste disposal. Using theoretical calculations, the formation of Alk-Ae-U(VI)-CO3 complexes has been proposed but without any experimental confirmation. This PhD work, in collaboration between Laboratory for Analytical, Nuclear, Isotopic, and Elementary development (DES/ISAS/DRMP/SPC/LANIE) in the Saclay centre, and the Laboratory for the Ligand Actinide Interactions (DES/ISEC/DMRC/SPTC/LILA) in the Marcoule centre, is proposing to couple the advantages of time-resolved fluorescence (or luminescence) of uranium(VI) complexes (LANIE) and theoretical calculations and X-ray spectroscopy (LILA) to guide the experiments to evidence the eventual Alk-Ae-U(VI)-CO3 complexes in solution.
The candidate must already dominate, or quickly acquire, a competence in solution chemistry with a strong tendency upon the acquisition of thermodynamic constants and functions of reactions, with a knowledge of the concepts linked to the ionic strength correction and SIT. Adaptability to, of even better knowledge, of different spectroscopic techniques will be an undeniably asset. The inclination to multidisciplinary team work will be essential.
Hydrogen transport and trapping in austenitic alloys coupling experiments and simulations.
Molecular hydrogen H2 is an alternative energy carrier to traditional fossil fuels, gas or oil. It meet the current energy and environmental challenges, i.e. the need to store greenhouse gases free energy produced by intermittent means such as wind turbines or solar panel. Nevertheless, its safe storage and transportation is one of the keys to its use. The containers or pipes that carry the hydrogen must be leaktight and maintain their integrity over time, for both economical and safety reasons. Understanding and predicting the behavior of hydrogen in container/pipeline alloys and the associated mechanical degradation – such as embrittlement – is therefore crucial for the development of the hydrogen industry. These issues are also generic to all alloys exposed to a source of hydrogen, in corrosion or in the metallurgical industries where the hydrogen simply comes from contact with water, or in the oil&gas industry where hydrogen comes from hydrogen sulphides present in hydrocarbons.
If many experimental works have identified hydrogen embrittlement as the origin of the degradation of alloys exposed to hydrogen, large gray areas still remain on the mechanisms at work due to experimental difficulties and the great variability of the observed phenomena. In addition, the transport and trapping of hydrogen prior to mechanical degradation are poorly known and poorly documented at the nanoscale.
The objective of the thesis is to explore the mechanisms of hydrogen trapping / transport in austenitic materials, as well as its distribution in volume, prior to cracking in order to be able to report and explain the experimental observations.
To achieve this objective, the thesis work will be dedicated to the study of pure nickel, a model system for the austenite phase. The study will be carried out in three stages: (i) thermodesorption measurements and (ii) atomic scale simulations using molecular dynamics, both feeding chemical kinetics modeling coupled with Fick's law at the mesoscopic scale.
Modeling the CSS growth of CsPbBr3
Lead-halide perovskites, particularly CsPbBr3, are emerging as promising materials for X-ray detection in medical applications. This technology requires their deposition in thick layers (>100 µm), and close-space sublimation (CSS), initially developed by CEA-Liten, has shown highly encouraging results. However, this process remains poorly understood at the microscopic scale, and the relationship between microstructure and performance remains a major scientific and industrial challenge.
This thesis, in partnership with the SIMAP laboratory, aims to develop a comprehensive thermodynamic model of the CSS process. The candidate will (i) experimentally generate the essential thermodynamic data for modeling, (ii) simulate growth mechanisms, and (iii) validate them experimentally using dedicated instrumented growth furnaces and advanced characterization techniques. Machine learning tools will be implemented to establish predictive correlations between deposition parameters and layer properties.
The results will enable optimization of CsPbBr3 growth for more sensitive and stable X-ray detectors, with a strong impact on medical imaging. This work will also provide opportunities for high-impact publications and patents in a highly competitive field.
Impact of ultrasound on the flow properties of complex suspensions
Nuclear industry generates radioactive wastes of various nature such as solids, liquids but also sludges coming from effluent treatment facilities or historical residues stored in pool or tanks. The physico-chemical nature of those sludges leads to a complex flow behaviour making it difficult to handle and convey prior their immobilization in a conditioning matrix. In order to fluidize these suspensions of varying compositions, the mechanical action of power ultrasound is envisaged. It has recently been shown, thanks to a set-up coupling power ultrasound and rheology, that it is possible to significantly reduce the yield stress and viscosity of the slurry by applying ultrasound. The aim of this thesis is to pursue the studies already undertaken (physical chemistry, microstructure, ultrasound and rheology) on reconstituted sludge or simplified model suspensions, focusing more specifically on two aspects. The first, more fundamental, will aim to gain a better understanding of the interaction between power ultrasound and matter, with a particular focus on the origin of the effects observed (interfaces vs. volume). The second aspect will be more applied, with the development of original larger-scale experimental devices capable of generating flows closer to industrial situations. For this phD work, we are looking for a motivated, serious and curious candidate. Given the multidisciplinary character of the subject, mixing physics, physico-Chemistry and experimental development, the candidate could valorize his new skills in various industrial fields such as nuclear, civil engineering and depollution domain.
The thesis will be conducted in a laboratory at CEA Marcoule, which provides the scientific, technical, and human resources necessary to carry out the research. Short stays are planned at the physics laboratory of ENS Lyon. This PhD topic, combining both fundamental understanding and applied aspects, offers dual career prospects: either pursuing a postdoctoral position or entering a career in industry.
On the fluid distribution for liquid thermocline - From experimental work to reduction of models
Thermocline heat storage (stratified tank) is an industrial solution for recovering waste heat and integrating intermittent energy sources. However, its performance remains limited by poorly controlled phenomena: non-uniform fluid distribution, partial thermal cycling, and real-world operating conditions (fluctuating inputs, incomplete cycles).
The proposed doctoral research builds upon the PhD work of Alexis Ferré and the postdoctoral research of Martin Rudkiewicz, which focused on the modeling and characterization of thermocline storage systems. These studies led to the development and validation of a comprehensive physical model implemented in ANSYS Fluent, enabling detailed investigation of the physical phenomena governing the formation and subsequent transport of the thermocline within a storage tank.
A partially validated CFD numerical model, together with a fully operational experimental facility, will therefore constitute the foundation of this PhD project. The main objectives are:
• to further advance the experimental characterization of liquid thermocline storage behavior, with particular emphasis on the influence of flow distribution (including distributor type and design parameters), thermal cycling, and initial conditions on storage performance;
• to validate the CFD physical model against newly acquired experimental data;
• to reduce the high-fidelity CFD model to a comprehensive system-level model incorporating the distributor, the storage tank, and the extraction process;
• to provide the scientific and industrial communities with currently unavailable datasets that are essential for model validation under varied and realistic operating conditions.
Development of an innovative anode based on non-critical and sustainable materials for anion-exchange membrane electrolysis
Anion-exchange membrane water electrolysis (AEMWE) is a recent and promising technology for producing green hydrogen, but it still faces major challenges in terms of performance and durability. Currently, the anodes used in AEMWE electrolyzers consist of two layers: a porous transport layer (PTL), which enables the circulation of electrolyte and gases, and an active layer made of catalysts and binders, where the electrochemical reactions take place. This configuration limits reactant diffusion and reduces the available active surface area, which negatively impacts overall performance.
This PhD project aims to develop an innovative anode based on non-critical materials by combining the advantages of both layers while minimizing their drawbacks. The idea is to functionalize the PTL directly by adding catalyst nanoparticles and/or by applying a surface activation treatment, in order to confer electrochemical activity. These modifications are expected to improve electron and reactant transport while increasing the active surface area for the oxygen evolution reaction (OER).
The work carried out in this thesis will involve functionalizing a pre-selected PTL and characterizing the resulting anodes through structural and electrochemical analyses. The expected outcomes include the development of an optimized anode with enhanced performance and limited degradation, as well as a deeper understanding of the limiting phenomena in AEMWE anodes. This project is part of a broader effort to develop sustainable technologies essential for the energy transition.
Contribution in the study of Power Partial Converters in Energy sources Hybridization
One of the key areas for reducing the carbon footprint is transport, particularly the development of electric mobility, which is currently growing rapidly. In this context, the hybrid electric transport market is growing. Hybridization applications have seen their power increase and with it that of power electronics converters allowing to adapt the voltage levels of energy sources and the energy exchanges between them. This increase in power is accompanied by higher losses to be evacuated, resulting in a significant impact firstly on the size of the converters, and therefore of the overall system, and then on the energy efficiency of the entire chain. Efforts have already been made at CEA-LITEN to develop high-efficiency DC-DC converters (in particular by using interleaved DC-DC converters). The objective of the thesis will be to go further by studying the so-called partial power converters (PPC). The different architectures/topologies will be studied for hybrid applications associating a fuel cell and a battery on the one hand, and applications associating 2 batteries (one power type battery and the other, energy type battery) on the other hand. The work aims to determine the best architecture/topologies for each of the typical applications allowing a significant reduction in the size of the converters and the improvement of the efficiency of the whole system