RSS export of vacancies - Seulement les offres à la une : No / Profil : Physique de l'état condensé, chimie et nanosciences, Défis technologiques

SL-DES-24-0167 - Physico-chemical coupling between a bubbles population and the oxido-reduction of glass-forming liquid

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
The calcination-vitrification process is the solution used in France for more than 30 years for the conditioning of high-level nuclear waste resulting from the reprocessing of spent fuel. During the vitrification process, the waste is incorporated into a borosilicate glass-forming liquid at more than 1000°C. The glass-forming liquid is homogenized in temperature and composition by stirring and gas bubbling. The incorporation of waste into glass-forming liquid can also lead to gas releases, including those of oxygen resulting from redox reactions between species dissolved in the liquid. It is important to properly control the impact of these gases on the glass and the process. The redox state of glass-forming liquid at equilibrium between the dissolved species has been the subject of various studies at the CEA in the context of the vitrification of nuclear waste [1, 2]. On the other hand, few studies have been devoted to the kinetics of gas reactions in glass-forming liquid [3, 4]. The objective of this thesis aims to study and model the impact of gas bubbles, whatever their nature, on the redox of melting and the kinetics of associated reactions. An approach combining experimentation and digital modeling will be adopted. A taste for experimentation, characterization and interpretation of results addressing different scientific fields is important to carry out this work. All experiments will be carried out on non-radioactive elements and will involve processing by digital modeling.

Physico-chemical coupling between a bubbles population and the oxido-reduction of glass-forming liquid

SL-DES-24-0110 - Direct precipitation of mixed oxides by reductive hydrothermal conversion

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
The development of new technologies of nuclear reactors implies to consider innovative methods for manufacturing (U,Pu)O2 MOx fuels. In this context, recent works focused on the hydrothermal conversion of tetravalent actinide carboxylates, in particular oxalates. This process enables hydrated actinide oxides to be obtained directly by using 'mild' conditions. The characteristics of the powders obtained can also be controlled by adjusting the experimental conditions. However, no study involving the uranyl cation UO22+ has been reported, although several studies have highlighted the reduction of U(VI) by organic matter in geological environments. The aim of this PhD thesis is therefore to address the direct precipitation, under reductive hydrothermal conditions, of UO2+x and associated solid solutions from uranyl-based solutions. The study of simple systems containing only U(VI) will first be undertaken by considering different sources of organic matter. A multiparametric study will specify the experimental conditions for the reduction of U(VI) to U(IV) and the quantitative formation of UO2+x, while the reduction mechanism will be studied using in situ XANES analyses on ESRF FAME and FAME-UHD beamlines. The second part of the work will concern the study of mixed systems initially containing uranium (VI) and a tetravalent cation. The U(VI)-Th and U(VI)-Ce(IV) systems will be studied as a first approach, in order to progressively increase the complexity of the redox behaviour of the samples. Finally, the study will be transposed to the U(VI)-Pu(IV) system at CEA Marcoule's ATALANTE facility, in collaboration with the DES/DMRC/SPTC/LSEM. Regardless of the chemical system studied, a complete physico-chemical characterisation of the solids obtained will be undertaken. The sintering of the powders prepared will also be studied. The aim of this thesis work is therefore to propose an alternative route for manufacturing/remanufacturing future-generation nuclear fuels, by offering the original possibility of reducing uranium(VI) in situ in the reactor, which constitutes a direct route from ions in solution to the final solid. The successful candidate will have a master's or engineering degree in radiochemistry, separative chemistry or materials chemistry. In the course of his/her work, he/she will be required to master numerous techniques relating to materials chemistry, microscopy and solution chemistry, which will enable him/her to develop skills not only in the nuclear field, but also more broadly in the field of ceramic materials development.

Direct precipitation of mixed oxides by reductive hydrothermal conversion

SL-DES-24-0080 - The Pd-Rh-Ru-Te-O system in nuclear glasses and its impact on the glass melt conductivity

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
In France, the high-level nuclear waste is vitrified. The components of the waste are integrated in a vitreous borosilicate network and form a homogeneous glass. However, platinum group metals (PGM) Pd, Rh and Ru are very poorly soluble in the glass melt and they form particles, combined or not with oxygen or tellurium. These PGM particles may modify the physical properties of the glass melt and especially its electrical conductivity wich is paramount for the process control. Hence, the knowledge of the speciation and the morphology of the PGM elements is essential for the control of the vitrification process. Thereby, this PhD will be split in 2 interdependent approaches: the first one by thermodynamic Calphad calculations and the other one by experimentations. First, the experimental approache will aim to understand and quantify the reduction of (Ru,Rh)O2 and the solubilisation of Ru and Rh in Pd-Te thanks to elaborations and characterizations (SEM-EDS-WDS and XRD mainly) of glasses with PGM particles. The results will complete a Calphad database. Calculations will help to discuss experimental results and will enable to predict the PGM state in the glass melt during the industrial vitrification. Secondly, electrical conductivity measurements at high temperature will be implemented on the glasses previously made to determine the impact of Ru and Rh speciation on the global conductivity of the melt.

The Pd-Rh-Ru-Te-O system in nuclear glasses and its impact on the glass melt conductivity

SL-DES-24-0067 - Development of mixed oxide-based catalysts for the valorization of bioethanol into butanol

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
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. A modulation of the microstructure will also be studied by synthesizing these oxides using 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 ethanol conversion rates. but also the selectivity of the 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.

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

SL-DES-24-0088 - Investigation and use of uranium glasses for optical neutron detection

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
The Dosimetry, Sensors and Instrumentation Laboratory of the CEA Cadarache, develops, manufactures and operates neutron flux detectors used in the vicinity of and inside nuclear reactor cores. In addition to conventional detectors (fission chambers, collectrons, etc.), the laboratory is working on innovative measurement methods such as optical detectors, semiconductors, fiber scintillators, etc. As part of this PhD thesis, the laboratory wants to explore the potential of Uranium-doped glasses. These glasses are known to show bright fluorescence under various types of radiations. The main idea of this thesis is to try to exploit this fluorescence to detect the fission reactions induced when the glass is exposed to a neutron flux. This could enable the development of a new generation of optical neutron detectors halfway between a fission chamber and a scintillator. The thesis will focus on two main topics: - firstly, a detailed understanding of fluorescence mechanisms, and the synthesis of uranium glass with properties optimized for our needs (sensitivity, emission spectrum, isotopic vector, etc.). Synthesis will be carried out in partner laboratories; - secondly, the development of a dedicated instrumentation, probably in the form of optical fibers, to test these prototypes in a reactor.

Investigation and use of uranium glasses for optical neutron detection

SL-DES-24-0059 - Study of molten chloride salt fast reactor fuel synthesis and purification

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
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.

Study of molten chloride salt fast reactor fuel synthesis and purification

SL-DES-24-0049 - New cyclic extractant molecules for uranium/plutonium separation

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
This thesis subject is dedicated to the optimization of the uranium/plutonium separation process (PUREX) for spent nuclear fuels reprocessing. New extractant molecules based on cyclic monamide functions will be studied for targeted elements separation by liquid-liquid extraction from nitric acid medium. They should be soluble in industrial aliphatic diluents, adaptable to extraction technologies actually used in terms of density, viscosity, solubility and extraction kinetics. Their affinity and selectivity towards U and Pu should be adjusted to allow process flowsheet optimization. In order to help in the target molecules selection, theoretical DFT calculations (Density Functional Theory) will be investigated to make a comparative estimate of their affinity towards U and Pu elements. Then the student will have to determine the feasibility of organic synthesis and to propose and optimize synthesis pathways. Once the molecules will be purified and their structures and purity characterized, their separation performances will be assessed by liquid-liquid batch extraction tests involving radioelements of interest in active laboratories of ATALANTE facility. Their resistance towards hydrolysis and radiolysis will be evaluated after batch gamma irradiation tests. Finally, the structures of metallic complexes formed in organic phases with those new extractant molecules will be studied to better understand extraction mechanisms and propose new orientations for future synthesis.

New cyclic extractant molecules for uranium/plutonium separation

SL-DES-24-0037 - Development of lipophilic aminopoly(carboxylic) or hydroxamic acid ligands for ion separation

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
The subject of this thesis has been defined with the aim of proposing new liquid-liquid extraction (LLE) processes applicable to the recycling of lanthanides and actinides at downstream of the nuclear fuel cycle. The proposed methodology relies essentially on the availability of lipophilic ligands derived from highly polar chelating agents such as poly(aminocarboxylic) acids (PACA) or hydroxamic acids (HA). As a first step, the PhD student will be involved in a major organic synthesis project, building up a library of several of these different derivatives. During the first phase of the thesis, the candidate will be allowed to develop his activity based on knowledge and results already acquired in this field at LTSM. In subsequent phases, he or she will be asked to develop new, more efficient and, in some cases, stereoselective (enantio- and/or diastereoselective) synthesis strategies when several stereoisomers can be obtained. Concomitantly to this, the candidate will be asked to characterize the extraction properties (affinity and selectivity) of the yielded ligands towards valuable lanthanides and actinides. This will be carried out using well proven approaches, enabling quantitative and qualitative monitoring of ELL performed on a scale of a few milliliters. The PhD student will be supervised throughout his thesis by two co-directors and a supervisor, who will provide him with multidisciplinary expertise.

Development of lipophilic aminopoly(carboxylic) or hydroxamic acid ligands for ion separation

SL-DES-24-0077 - X-ray Emission spectroscopy: an alternative to X-ray emission spectroscopy for studying the actinide’s p

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
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.

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

SL-DES-24-0038 - Comportement d’un bloc de verre fracturé en phase vapeur

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
L’altération du verre au cours du temps est largement étudiée dans de multiples domaines d’application, dont un majeur : le stockage des déchets radioactifs en couche géologique profonde. En effet, ces déchets sont vitrifiés en vue d’un stockage à très long terme dans des galeries à 500 m de profondeur. Il est prévu que l’eau liquide n’atteigne pas les colis de verre avant une centaine de milliers d’années. Néanmoins, durant cette période, une certaine humidité relative est attendue dans l’espace de stockage. Ainsi, l’impact de la vapeur d’eau sur le verre doit être pris en compte pour prédire le comportement du colis de verre sur toute la période de décroissance radioactive des radionucléides. Le colis est intrinsèquement fracturé ; en cause : des gradients thermiques lors du refroidissement après coulée. Les fissures développées accroissent la surface réactive du matériau. Mais à quel point ? Quelle est la contribution des fissures dans l’altération globale du bloc en phase vapeur ? Est-ce que de l’eau condense au sein du réseau de fissures, induisant l’altération du matériau en milieu liquide ultra-confiné ? Si oui, dans quelles proportions ? De ces questions découlent d’autres problématiques à aborder telles que l’évolution de l’altération au cours du temps dans ce système potentiellement biphasique, ainsi que le comportement du bloc de verre lors de l’arrivée de l’eau liquide. Cette thèse se propose donc de répondre à ces questions en menant des études sur des verres simulants non radioactifs. Des systèmes de fissures modèles ainsi que des blocs de verre fracturés seront utilisés. Au cours de ce travail, le doctorant sera donc amené à élaborer des verres au laboratoire et à réaliser des expériences en exposant des échantillons à la vapeur d’eau dans des chambres atmosphériques. La thèse comportera trois parties constituées de 1) l’étude de la condensation au sein du réseau de fissures, 2) l’étude de l’altération et de son évolution au cours du temps et 3) le comportement de ces systèmes lors de la remise en eau liquide. Un large panel de techniques d’analyse sera déployé pour caractériser les échantillons solides et liquides. Au sein même du service, le doctorant pourra être formé à la manipulation du DVS (études de sorption de l’eau), du MEB-EDS, de la DRX, du spectromètre Raman ainsi qu’au spectromètre UV-Visible. Des collaborations sont envisagées pour mener des analyses par MET, de la tomographie, de l’AFM ou encore de la RMN. Pour ce travail, le candidat devra présenter des compétences solides dans le domaine de la science des matériaux. Il devra être curieux, ouvert et dynamique car il sera amené à interagir avec de nombreuses personnes, voire potentiellement à collaborer avec des intervenants dans un cercle plus élargi que le domaine du verre (concernant les milieux fissurés d’autres matériaux). Cette thèse apportera au doctorant de larges compétences techniques au vu du nombre d’outils analytiques prévus. Par ailleurs, ce travail lui fournira une connaissance poussée du matériau qui pourra être valorisée dans de nombreux domaines d’activités.

Comportement d’un bloc de verre fracturé en phase vapeur

SL-DRT-24-0016 - Advanced modeling of Gas Diffusion Layers for Fuel Cells: ink impregnation and drying, 3D phase distribu

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
In the frame of advanced H2 solutions for the energy transition, the Proton Exchange Membrane Fuel Cell (PEMFC) is a relevant solution for the production of low-carbon electrical energy. The European Project DECODE proposes to develop a fully digital chain of design tools, including raw material properties, manufacturing and assembly of the different components, to predict the performance of such ‘virtual’ stack. This will help reducing the development cost and time of improved materials/components suitable for different applications in the future. The component considered in this thesis is the Gas Diffusion Layer (GDL), which is a combination of a fibrous microporous substrate and of a micro/nano porous layer (MPL for microporous layer). The work will be split into different steps: a) based on (real or virtual) 3D images of the substrate, simulation of the hydrophobic and MPL coating and drying to derive the 3D distribution of the components (fibers, hydrophobicity and MPL); b) simulation of single and two-phase transport properties of the GDL to supply inputs to upper scale performance models; c) sensitivity analysis of the main manufacturing processes (ink properties, drying parameters…)

Advanced modeling of Gas Diffusion Layers for Fuel Cells: ink impregnation and drying, 3D phase distribution, and effective properties

SL-DRT-24-0005 - Learning Fine-Grained Dexterous Manipulation through Vision and Kinesthetic Observations

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
Fine-grained dexterous manipulation presents significant challenges for robots due to the need for precise object handling, coordination of contact forces, and utilization of visual observations. This research aims to address these challenges by investigating the integration of vision and kinesthetic sensors, sim2real techniques, and generalization through embodiment. The objective is to develop end-to-end algorithms and models that enable robots to manipulate objects with exceptional precision and adaptability. The research will focus on learning from large-scale data, transferring knowledge from simulations to real-world scenarios, and efficiently generalizing through low-shot fine-tuning.

Learning Fine-Grained Dexterous Manipulation through Vision and Kinesthetic Observations

SL-DRT-24-0030 - Scenario-Based Testing for Automated Systems: Enhancing Safety and Reliability in Compliance with Regula

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
This research aims to investigate the effectiveness of scenario-based testing as a comprehensive and robust approach for evaluating ASs' performance while enhancing their safety and reliability with respect to regulations and standards. The primary objective of this thesis will be to investigate the benefits of scenario-based testing for automated systems and its compliance with regulations and standards. The following sub-objectives will be pursued: - Conduct an in-depth review of relevant literature and industry practices on ASs testing methodologies, with a focus on the unique challenges posed by ASs' complex decision-making algorithms and interaction with the dynamic environment. - Develop a scenario-based testing framework for systematic identification, generation, selection, and execution of realistic and diverse scenarios, for automated systems - Analyze gaps or areas of non-compliance about the key concepts and requirements outlined in regulations and standards and examine their applicability, implications and improvments for scenario-based testing. - Conduct extensive validation of the proposed scenario-based testing framework through different real-world and near-realistic transportation applications (various types, varying levels of automation, and diverse real-world scenarios) to evaluate the practical applicability and benefits of the methodology. The findings and recommendations from this research will ultimately guide AV manufacturers, regulators, and stakeholders in developing and validating ASs that comply with the regulatory framework, fostering the safe and responsible deployment of automated systems in the future.

Scenario-Based Testing for Automated Systems: Enhancing Safety and Reliability in Compliance with Regulations and Standards

SL-DRT-24-0026 - Deep Neural Network Uncertainty Estimation on Embedded Targets

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
Over the last decade, Deep NeuralNetworks (DNNs) have become a popular choice to implement Learning-Enabled Components LECs in automated systems thanks to their effectiveness in processing complex sensory inputs, and their powerful representation learning that surpasses the performance of traditional methods. Despite the remarkable progress in representation learning, DNNs should also represent the confidence in their predictions to deploy them in safety-critical systems. Bayesian Neural Networks (BNNs) offer a principled framework to model and capture uncertainty in LECs. However, exact inference in BNNs is difficult to compute. Thus, we rely on sampling techniques to approximate the true posterior of the weights for computing the posterior predictive distribution (inference). In this regard, relatively simple though computationally and memory expensive sample-based methods have been pro posed for approximate Bayesian inference to quantify uncertainty in DNNs, e.g., Monte-Carlo dropout or Deep Ensembles. Efficient DNN uncertainty estimation in resource-constrained hardware platforms remains an open problem, limiting the adoption within applications from highly automated systems that possess strict computation and memory budgets, tight time constraints, and safety requirements. This thesis aims to develop novel methods and hardware optimizations for efficient and reliable uncertainty estimation in modern DNN architectures deployed in hardware platforms with limited computation resources.

Deep Neural Network Uncertainty Estimation on Embedded Targets

SL-DES-24-0166 - Kinetics and mechanisms of corium leaching

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
During a severe nuclear accident, significant quantities of 'volatile' fission products are released during core degradation. A further significant proportion of radionuclides (RN) from degraded nuclear fuels are incorporated into solidified materials (corium and fuel debris), and their medium- to long-term stability is of major importance for accident site safety. Depending on the progress of the accident and subsequent interactions with different materials (cladding, internal structures, vessel materials and concrete), corium may have different structures and compositions. Generally speaking, it is a highly heterogeneous, multiphase material within which the distribution of radionuclides is poorly understood. In this context, the aim of this thesis is to improve our understanding of the mechanisms of corium leaching and radionuclide release into water, through parametric studies on model materials. This work, carried out with a view to increasing the complexity of the materials studied, will enable us to prioritize the influence of different parameters (temperature, solution composition, presence of oxidizing radiolytic species) on the transfer of RNs into solution. Taken together, these results will improve our understanding of the evolution of the RN inventory contained in a corium in an underwater cooling scenario, and our knowledge of the chemical durability of the different phases it contains.

Kinetics and mechanisms of corium leaching

SL-DRT-24-0017 - Exploring the Future of Satellite Communications: Dual-Band Electronically Reconfigurable Flat Lens Ante

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
CEA Leti offers a PhD topic to develop new electronically scanning antennas for efficient data transmission in satellite communications (Satcom). Novel efficient electronically scanning antennas are essential for future satellite communications (Satcom). Electronically reconfigurable flat lens antennas, also known as transmitarrays, are a promising architecture to achieve high scanning performance. Each element of the flat lens introduces an optimized phase shift on the impinging wave emitted by a primary source, to steer and shape the radiation pattern. The phase profile over the lens can be dynamically modified by adding reconfigurable devices in the cells, such as switches (e.g. pin diodes) or varactors. Compared to phased arrays, these antennas attain high-gain beam-steering with a significantly lower power consumption and architectural complexity. The Ph.D. work aims to propose and experimentally demonstrate novel concepts and design methods for wideband/multi-band electronically beam-steering flat lens antennas. The main research goals are: . Study of new approaches for designing unit cells with broad radiation patterns, stable performance under oblique incidence and wideband/multiband operation. . Electrically thin subwavelength cells and Huygens’ radiating elements will be investigated to tailor the angular and frequency response of the cell. . Novel design solutions to enable a fine electronic control of the phase shift introduced by the cells. Multilayer cells comprising either pin diodes or varactors, or a combination of both, will be analyzed. The trade-offs between phase resolution, bandwidth, power consumption, number of reconfigurable devices and bias lines, will be studied. . Development of dedicated synthesis procedures to enable the independent control and shaping of the radiation pattern at two or multiple frequencies. . Experimental demonstration of high-gain dual-band fixed-beam and electronically 2-D beam-steering prototypes achieving extremely wide scan ranges (±60° or greater). The demonstratators will be optimized to work in typical Satcom bands (e.g. around 20 GHz and 30 GHz).

Exploring the Future of Satellite Communications: Dual-Band Electronically Reconfigurable Flat Lens Antennas with Ultra-Wide Scan Range

SL-DRT-24-0055 - New sustainable electrode materials for High Temperature Electrolysis

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
High temperature electrolysis is considered as the high efficiency technology for hydrogen production with low carbon emissions. The electrolysis reaction occurs in a solid oxide cell (SOC) composed of a dense electrolyte of yttria stabilized zirconia (YSZ), sandwiched between two porous electrodes. The most common hydrogen electrode material is a cermet of Ni and YSZ, and the oxygen electrode is a perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). To make the high temperature electrolysis more sustainable to better support the European eco-system towards the achievement of the Sustainable Development Goals and the objectives of the Paris Agreement, there is a critical need to reduce reliance on critical raw materials (CRM). The objective of the thesis is therefore to limit the use of CRM in the oxygen electrode material. Critical elements such as cobalt will be substituted by new cations on the A and/or B site of the crystal lattice, while maintaining equivalent performance and long-term stability. At the same time, in order to limit losses during synthesis, a part of the work will be carried out on the synthesis process efficiency and on the increase in capacity of the synthesis method. After a bibliographic study on oxygen electrode materials for high temperature electrolysers, the proposed work will initially be focused on the synthesis by chemical routes as well as on fine characterization of the perovskites. The thermal and chemical compatibility with the other materials constituting the cell will be studied, then this work will lead to the shaping of the materials with the most interesting properties in order to test them electrically and electrochemically. The electrochemical behaviour of the electrodes will be analysed in order to understand the influence of substitutions and to determine the electrochemical performance of the different compositions studied.

New sustainable electrode materials for High Temperature Electrolysis

SL-DES-24-0143 - Study of rheological phenomena occurring during thermal treatment for waste encapsulation into a glassy

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
Operations of decontamination and dismantling generate highly diverse waste in terms of chemical composition and physical form. It can take the form of solid deposits, powders, sludges or liquid solutions. To condition them, encapsulation with a glassy binder seems promising because of its lower working temperature than conventional vitrification processes. The process involves heating mixtures of waste and vitreous adjuvant between 800 and 1200°C, which requires a deep understanding of the rheological behavior of the system at temperature. Three research directions will be explored during the thesis: the influence of waste loading and nature of the adjuvant on the flow behavior, the behavior of volatile species in mixtures made of wet waste and adjuvant, and the impact of potential reactivity between the waste and the adjuvant on the system properties. Final objective will be, on one hand, to optimize the container filling rate while maximizing the waste loading rate, on the other hand, to guide the choice of the most suitable vitreous adjuvant. The PhD student will benefit from the recognized skills of the host laboratory in the field of rheology of complex systems from low temperature (slurries, bitumens, cements) to high temperature (homogeneous and crystallized glass melts), and from all the characterization resources required for the successful completion of the thesis. The entire thesis will be carried out in a non-nuclear environment, using inactive simulants.

Study of rheological phenomena occurring during thermal treatment for waste encapsulation into a glassy matrix

SL-DES-24-0142 - Rheology of partially-crystallized glass melts: from experimental data acquisition to modeling

Wed, 11 Oct 2023 02:15:11 Z

Category : Condensed Matter Physics, chemistry, nanosciences
Contract : Thèse
Thesis topic details :
The formulation of a radioactive waste packaging glass is the result of a compromise between waste loading, technological feasibility and chemical durability. Maximizing the waste loading rate allows us to reduce the number of vitrified packages produced, and consequently the volume and cost of the underground disposal. On the other hand, increasing this loading rate beyond a certain threshold is likely to lead to the presence of crystals in the vitrification furnaces. However, such an evolution of glass formulations requires, among other things, verification of the impact of the presence of these crystals on the properties of the glass during its production (at 1100-1200°C), in particular its rheology, a key property for the good operation of vitrification furnaces. The aim of the proposed thesis is therefore to measure and then model the effect of crystals on rheology, as a function of time, temperature, and nature and morphology of the crystals, and to take into account the risk of sedimentation. To do this, experimental data will have to be acquired, then modelled using models proposed in the literature, which may need to be adapted.

Rheology of partially-crystallized glass melts: from experimental data acquisition to modeling

SL-DRT-24-0004 - Study of inversion methods based on simulation and machine learning for defect characterisation in ultra

Wed, 11 Oct 2023 02:15:11 Z

Category : Technological challenges
Contract : Thèse
Thesis topic details :
The thesis work is part of the activities of CEA-List department dedicated to Non-Destructive Testing (NDT), and aims to study simulation-based inversion methods to characterise defects from ultrasonic images, such as TFM (Total Focusing Method) or PWI (Plane Wave Imaging) images. The inversion methodology will rely on machine learning algorithms and numerical training databases generated with the CIVA software platform. A first part will study the ability of such an inversion method to characterise a defect (location, size, orientation...) without any a priori information, by exploiting the noise and reconstruction artefacts due to the use of unsuitable propagation modes. In a second part, the simulation-based inversion will be evaluated in more realistic situations where images are of poor quality due to uncertainties on the properties of the component and/or on the experimental setup. In order to reduce the generation time of the training database, and to gain in robustness and accuracy, the feasibility of inverting fast imaging (e.g.: combining PWI and fast reconstruction algorithms in the Fourier domain) will be studied, as well as the feasibility of directly inverting signals or spectra without the need to compute images. The inversion method will be experimentally evaluated with different mock-ups representative of industrial components and, at the end of the thesis, a real-time proof of concept will be demonstrated by implementing the imaging and inversion algorithms in a laboratory prototype system.

Study of inversion methods based on simulation and machine learning for defect characterisation in ultrasonic array imaging