Dynamic diagnosis for nonlinear process. Application to a liquid-liquid extraction recycling unit.

Knowledge of the state of an industrial chemical process is a key-point for process control. Indeed, if hazards or operating changes occur, it is necessary to be able to detect their presence, their nature and possibly their amplitudes in order to maintain the process as close as possible to the target state. However, the uncertainties and errors affecting the collected measurements often make it difficult to estimate the process state. Specific treatment of the measured data is necessary to determine a consistent data set.

The proposed thesis consists in methodological developments aiming to extend existing results in order to take into account the dynamic regime of the process and its non-linear operation for its diagnosis. Two complementary aspects are to be developed, the first related to the data validation and the second dedicated to the detection and analysis of operating changes of a system.

The final tool would be able to follow the process at all times and able to detect any operational changes, like a real “digital twin” of the process. Such a tool would open up very interesting innovative perspectives for process control, as the state of the process would be known precisely at all times.

The candidate must hold a Bac+5 degree in chemical engineering, automatic control or mathematics (statistics). This thesis will enable him to acquire skills in these three areas, which will be greatly appreciated by companies, in particular to develop advanced monitoring and control tools.

Towards multi-physics and multi-scale modelling of pilot-scale photo-electrochemical cells for hydrogen production

The production of chemical molecules and synthetic fuel, from non-fossil resources and renewable energy, is one of the solution envisaged to face climate issues. In this context, the use of photo-electrochemical cells (PEC) solar-driven water splitting is seen as promising route for hydrogen production. Today, proofs of concept generally concern small objects (of the order of 1cm² of active surface) and operating-times limited to a few minutes or a few hours. It is therefore essential, in order to consider the rapid deployment of PECs, to be able to predict the influence of the architecture of the cell and scale-up on their performance, in terms of energy efficiency, kinetic efficiencies (volume and surface ), stability of operation and aging of materials.
The thesis is part of the development of a generic simulation tool for PECs, in support of R&D. It will be carried out in collaboration with ENGIE LabCRIGEN (CIFRE funding), )Institut Pascal (host laboratory) and CEA (ISEC, IRIG and INES).
You have a solid background in Chemical Engineering, Energy, Fluid Mechanics or Applied Mathematics, with particular attraction for modelling and simulation; you have also a strong capacity for collaborative work, and you want to contribute actively the energy transition? By choosing this thesis, you will join a multidisciplinary consortium and contribute to an active field of research, at the interface between fundamental research and industry.

Contribution of learning methods to separation and recycling processes: towards a numrical twin of a mixer-settler

Low-carbon energies (lithium batteries, photovoltaics, wind power) are largely based on rare earths (Dy, Nd, Pr, ...) and metals (Co, Ni, ...). Numerous studies are currently devoted to the development of liquid-liquid extraction processes adapted to their recycling, but their industrial transposition remains a major technological obstacle, which the thesis intends in part to overcome.
The performance of solvent extraction processes strongly depends on the exchange surface available between the two phases (generally an organic solvent and the aqueous dissolution medium) and through which the actual extraction takes place. However, this available surface is difficult to measure and predict because of the complexity of the phenomena involved. It is in fact strongly correlated with the physicochemical properties of the liquid-liquid system considered and with the properties of the turbulent flow generated by the stirring system used to create an interface between the liquids (dipersion of a phase in the form of droplets).
The objective of the thesis is to explore the potential of machine learning methods for the prediction of the exchange surface in a stirred tank, representative of a mixer-settler.
The experimental study will focus on the determination of the drop size distribution in the stirred tank (optical methods and image analysis), the numerical part will include the CFD simulation of the turbulent flow and the development of the learning model.
The thesis is located in Marcoule CEA research center, near Avignon, in a multidisciplinary team with a strong focus on processes for green transition. The applicant we are looking for is an engineer and/or master 2 having a generalist profile and interested in playing an active role in this field. At the end of this Ph.D., the candidate will have a first experience in machine learning methods applied to the present issues of recycling in circular economy. Such a type of versatile profile will undoubtedly be an asset for a future career in academia as well as in industry.

Development of a lensless microfluidic instrument for in-situ measurement of facies-dependent dissolution kinetics

This thesis is part of an ambitious program designated as a priority research program. This project identifies the subsoil as a major reservoir of resources necessary for the energy transition.
One of the major issues is the dissolution of ores in the context of mining and extractive metallurgy. In particular, with the objective of process industrialization, the dissolution kinetics of ores must be compatible with the footprint of the installations, biocompatibility and the volume of reagents consumed.
The observation today is the very strong mismatch between the volume of experimental data produced and those necessary to model the chemical processes essential to demonstrate the viability of industrial processes.
This thesis proposes to develop a millifluidic prototype bench for mass kinetic data acquisition using lensless imaging techniques. This will make it possible to measure dissolution reaction kinetics using 3D reconstitution techniques, in-situ, under stable chemical conditions and with statistical representativeness allowing the original properties of the solid to be taken into account.
A large part of the research will be directed towards the development of the lensless optical technique in a millifluidic device and the mass production of chemical kinetic data for catalytic dissolution models.
The desired profile is that of a general physics and chemistry student, with a strong desire to learn in areas they are least familiar with, such as microfluidics or optics. At the end of this thesis, the student will acquire solid professional experience in applied research and will learn to evolve in a multithematic environment.

Study and implementation of photocatalysis in a Taylor-Couette reactor

Photocatalytic reactions are considered as a promising path in mitigating ecological impacts. In the case of heterogeneous reactions where the photoactive material is dispersed in the liquid phase (slurry), it is essential to identify and control the factors influencing efficiency, with a view to possible scale-up. These factors include the transmission of light in the system, the hydrodynamics of the reactor, the specific chemical reactions involved and, above all, the coupling of all these elements. In this PhD subject, the versatility of the Taylor-Couette flow will be exploited, which allows the flow to go from a plug flow to high turbulence in the same apparatus, while allowing high illumination thanks to a maximised surface/volume ratio, making it possible to study these different phenomena and their coupling. The study will rely on Monte Carlo and DNS (Direct Numerical Simulation) modeling to respectively describe the behavior of light and multiphase flow in the reactor. This will help identify and study influential parameters such as flow structure, spatial distribution of particles, photon transport, and photon-matter interactions within the reactor, not to mention the role of the gas phase. These models will be compared to experimental results obtained on a dedicated optical test rig and will contribute to a deeper understanding of the important processes at play in these photo(bio)reactors. The thesis is located in Marcoule CEA research center, near Avignon, in a multidisciplinary team with a strong focus on processes for green transition. The applicant we are looking for is an engineer and/or master 2 having a generalist profile and interested in playing an active role in this field. At the end of this Ph.D., the candidate will have a first experience in the present issues of low carbon energies in circular economy. Such a type of versatile profile will undoubtedly be an asset for a future career in academia as well as in industry.

Study of molten chloride salt fast reactor fuel synthesis and purification

Among a large variety of innovative reactor concepts used to decarbonize industry, a French fast reactor using molten chloride salts as fuel and primary coolant has been developed with a CEA-Orano collaboration. The reactor operates at temperature up to 600 °C in which actinides (An) are homogeneously dissolved in the liquid phase containing alkaline and alkaline earth chlorides. To feed it, an essential step is to produce the NaCl-MgCl2-AnCl3 fuel salt system without impurities to avoid corrosion and precipitations issues. The main aim is to study a way of producing molten salt fuel with a high purity level (as low contaminants content as possible). The first step is to synthesize and characterize actinide chlorides by a multi-scale approach (XRD, SEM, TGA-DSC, WDS…). Actinide chlorides are hygroscopic and easily absorb moisture from the environment. The reference synthesis route is a gas-solid reaction by hydrochlorination of actinide oxalate. The investigation of other synthesis methods is also planned in order to obtain less hygroscopic material. Synthesized products will studied by electrochemistry after dissolution in the molten salt phase to determine actinides purity and contaminants nature and content. A purification process is used as the last step to remove most of impurities from the molten salt. Purification issues are impurity content determination and the definition of salt purity criterion. Some physicochemical properties measurements could be performed with purified salts.

The applicant needs to have a master or engineer degree in materials and chemistry. He will join a multidisciplinary team dedicated to processes for the circular economy and work on a subject with strong international visibility and industrial potential. The student will benefit from scientific and technical expertise in the field of fuel recycling. The host laboratory is located at CEA Marcoule, near Avignon.

X-ray Emission spectroscopy: an alternative to X-ray absorption spectroscopy for studying the actinide’s physico-chemistry ?

Optimal exploitation of nuclear fuels is essential to maintain low-carbon energy production for decades to come. To this end, fuels such as mixed oxides U1-yPuyO2-x are being considered. However, the safety of their future use, requires an exhaustive multi-scale understanding of their behavior during both their manufacturing and their irradiation in reactor, as well as their compatibility with the dissolution processes necessary for their recycling. X-ray Absorption Spectroscopy (XAS) is a key technique for fuel characterization that is extensively employed at CEA Marcoule. A complementary approach to the latter is X-ray Emission Spectroscopy (XES). However, while XES studies are numerous in the context of 3d elements, only very few are available for actinides. Those studies suggest the possible access to new knowledge on the properties of fuels, while being characterized by a lower detection limit compared to XAS. The main objective of this thesis work is therefore the development of the methodology and instrumentation necessary for XES analyzes at the lab scale as well as the realization of experimental campaigns dedicated to the understanding of the links between experimental observations and the intrinsic properties of actinides. The thesis will be carried out in collaboration between CEA Marcoule and the University of Helsinki and will begin with a 1.5-year period in Helsinki before continuing at CEA Marcoule. The candidate would have a Master's degree in physics or chemistry of materials and a minimum level of B2 in English and will, if necessary, follow training course in French during his/her stay in Finland. By the end of this thesis, the candidate will have mastered a wide range of experimental techniques as well as the exploitation of the data acquired. These skills will open up a wide range of job opportunities in academic research or industrial R&D, both within and outside the nuclear sector.

Study of the prototypical corium solid state containing fission products crystallographic and microstructural analysis impact on weathering and leaching mechanisms

In a moderated and/or water-cooled nuclear reactor, a loss of cooling systems may result in partial or total melting of the core, which may then interact with any water present in the vessel or outside the vessel, as it happened during the Fukushima-Daiichi nuclear accident in 2011. The study of the interactions between corium and water is now a prerequisite for defining the source terms for radionuclides in the course of serious accidents that may escape from the containment by alteration and leaching, whether with residual water from the reactor or by a later voluntary injection of water or with environmental water. This requires a better knowledge of the crystallographic structures of coriums concretes incorporating fission products and their mechanism of interaction and release during contact with water.
In order to provide answers, this thesis project is part of an original experimental approach by combining structural and microstructural studies on prototypical coriums concrete in which stable isotopes simulating fission products present in corium have been introduced, to leaching tests. The materials based on siliceous and silico limestone concrete developed on the PLINIUS Platform of the CEA Cadarache, will be characterized at the LMAT laboratory of the CEA of Marcoule by the use of different techniques in surface analysis (MEB, EDS, WDS Castaing microprobe for elementary measurement of contents less than 1% mass). The study of phase formation in coriums concretes (segregation, crystalline and amorphous forms) can be conducted by crystallographic analysis performed by diffraction techniques at the SOLEIL synchrotron and by neutron diffraction at the ILL. Fine crystallographic analysis will implement the Rietveld method. The properties of the micro texture can be qualified on solid material and thin film by EBSD, TKD, DRX, and by Laue micro diffraction in the ESRF synchrotron. First leaching tests under oxidative conditions will be carried out with the LEMC laboratory of the CEA of Marcoule in parallel to the characterization campaigns in order to identify the main mechanisms of weathering. This knowledge will feed into a database of "serious accident materials" useful for the management of coriums during the accident and beyond. The skills acquired by the doctoral student around the characterization of materials may be valuable for the doctoral student in many fields in materials science. The profile of the student will require knowledge of materials and instrumentation. The theme «serious accident» and interaction with water will also be of interest to the doctoral student in the field of environment and more particularly discharges.

Synthesis and shaping of Metal-Organic Frameworks for the capture of noble gas (Xe, Kr)

The design of new nuclear reactors named MSR, for Molten Salt Reactor, is currently being studied at the CEA, but also internationally. During their operation, gaseous fission products are generated and must be extracted, in particular Xe and Kr. For this purpose, adsorption on solid support in fixed bed columns are considered, but such processes require the development of very selective materials with high sorption capacities. Recently, Metal-Organic Framework (MOF) materials have demonstrated exceptional selectivity for noble gas trapping. However, such materials are generally synthesized in a fine powder form, which is not compatible with an application in fixed bed processes.
This PD works aims to synthesize MOFs and develop a shaping technique, so that they can be used in columns for the trapping and separation of noble gases. Firstly, the most promising MOF structures will be identified in the literature and synthesized in laboratory. Then a process allowing their granular shaping will be developed. This shaping will optimize the application of MOFs in a fixed bed column process and their capture performances will be determined using a gas separation pilot.
The student must have a strong interest in experimentation. He/she will develop skills in synthesis and characterization of materials (SEM, XRD, nitrogen adsorption-desorption, etc.). More generally, the student will have the opportunity to address the complexities linked to a gas treatment process using fixed bed columns.

Development of mixed oxide-based catalysts for the valorization of bioethanol into butanol

The production of biobutanol from bioethanol via the Guerbet reaction is an important process for improving the valorization of biomass into new generation biofuels. The objective of this thesis is to develop new catalysts based on mixed oxides which allow this reaction in the liquid phase. The starting formulation is the CuMgAl mixed oxide of hydrotalcite type. Partial or total substitutions in the Cu and Al sites by Ni and/or Co and Ce and/or La respectively will be studied as well as a modulation of the microstructure via the use of different synthesis routes (NPG, alginate, etc.). ). Once synthesized, the oxides will be characterized by classic XRD, SEM, BET/BJH, ATG, high-resolution TEM methods, but also by TDP of NH3 and CO2 in order to determine the quantity of acidic and basic sites. The synthesized catalysts will then be tested in the Guerbet reaction of ethanol in the liquid phase, in a batch reactor, the products being analyzed by gas chromatography coupled with high resolution mass spectrometry to determine the conversion rates but also the selectivity of conversion to butanol. After an initial screening, complete kinetic studies will be carried out on the 2 or 3 most promising formulations by varying all the parameters (temperature, quantity of catalysts, moisture absorber, etc.). Post-reaction characterizations will be carried out to study possible deactivation of the catalysts by coking phenomena. Finally, it will be considered to develop a continuous process in order to overcome the disadvantages of a discontinuous batch process. This thesis subject therefore presents a multidisciplinary dimension with a material aspect and an organic chemistry component, in the context of heterogeneous catalysis. The profile of the candidate sought must therefore allow them to address these different experimental aspects. An interest in chemical engineering will be a plus for the definition of a continuous process, the last part of this work. Valuation in the form of patents and then communications in international conferences or A-rank scientific journals will be sought, allowing good integration into the professional environment in the buoyant energy transition market.

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