Advancing Semantic Representation, Alignment, and Reasoning in Multi-Agent 6G Communication Systems
Semantic communications is an emerging and transformative research area, where the focus shifts from transmitting raw data to conveying meaningful information. While initial models and design solutions have laid foundational principles, they often rest on strong assumptions regarding the extraction, representation, and interpretation of semantic content. The advent of 6G networks introduces new challenges, particularly with the growing need for multi-agent systems where multiple AI-driven agents interact seamlessly.
In this context, the challenge of semantic alignment becomes critical. Existing literature on multi-agent semantic communications frequently assumes that all agents share a common understanding and interpretation framework, a condition rarely met in practical scenarios. Misaligned representations can lead to communication inefficiencies, loss of critical information, and misinterpretations.
This PhD research aims to advance the state-of-the-art by investigating the principles of semantic representation, alignment, and reasoning in multi-AI agent environments within 6G communication networks. The study will explore how agents can dynamically align their semantic models, ensuring consistent interpretation of messages while accounting for differences in context, objectives, and prior knowledge. By leveraging techniques from artificial intelligence, such as machine learning, ontology alignment, and multi-agent reasoning, the goal is to propose novel frameworks that enhance communication efficiency and effectiveness in multi-agent settings. This work will contribute to more adaptive, intelligent, and context-aware communication systems that are key to the evolution of 6G networks.
Development of an advanced grade of nano-reinforced austenitic steel for use under intense flux
Recent work has shown that it is possible to obtain ODS (Oxide Dispersion Strengthened) austenitic steels for use under intense flux. These new grades are beginning to be studied for nuclear applications around the world. They should have remarkable properties, particularly in terms of resistance to swelling under irradiation and creep, thanks to the addition of nano-reinforcements in exceptional density (10^23 to 10^24 m-3). These ODS steels are obtained by powder metallurgy, by co-grinding a metal powder with an oxide powder. The aim of this work is to succeed in manufacturing, using an innovative process, ODS austenitic steel cladding tubes. It will be necessary to master the recrystallization of these tubes, to propose a first critical evaluation by specifying the property/microstructure relationships and by evaluating, by irradiation with charged particles, the behavior under irradaition of this new material. The student will be trained in Scanning Electron Microscopy and the techniques that result from it (X-ray analysis, EBSD, etc.), in SAXS, in the performance and exploitation of mechanical tests. He will have to acquire good notions in Transmission Electron Microscopy and in Tomographic Atomic Probe. The understanding of the behavior under irradiation will be guided by simulations by cluster dynamics.
Study and simulation of phase entrainment in mixer-settler batteries
As part of the development of new liquid-liquid extraction separation processes, experimental tests are implemented to demonstrate the recovery of valuable elements sufficiently decontaminated from impurities. These tests are commonly carried out in mixer-settler batteries. However, depending on the operating conditions, these finished products may be contaminated by impurities. This contamination results from the combination of several factors:
-Hydrodynamic: Entrainment in the solvent of non-decanted aqueous drops containing impurities
-Chemical: the impurity separation factor is low (less than 10-3)
-Process: the entrainment of drops is amplified with the increase in the rate (reduction of the residence time of the drops)
This thesis aims to increase the understanding of the different phenomena responsible for these phase entrainments in order to estimate optimal operating parameters and to guarantee a contamination of the finished products below a fixed threshold. The aim will be to develop a macroscopic model to predict the flow rate of non-decanted droplets as a function of the operating conditions in the mixer-settler batteries. It will have to be based on hydrodynamic simulations coupling the resolution of a droplet population balance to a continuous phase flow. A coupling will be carried out between this hydrodynamic model and the PAREX or PAREX+ code to size the process diagrams. The qualification of the proposed models will have to be done by comparisons with experimental measurements (based on previous or future test campaigns).
Enhancing Communication Security Through Faster-than-Nyquist Transceiver Design
In light of the growing demand for transmission capacity in communication networks, it is essential to explore innovative techniques that enhance spectral efficiency while maintaining the reliability and security of transmission links. This project proposes a comprehensive theoretical modeling of Faster-Than-Nyquist (FTN) systems, accompanied by simulations and numerical analyses to evaluate their performance in various communication scenarios. The study will aim to identify the necessary trade-offs to maximize transmission rates while considering the constraints related to implementation complexity and transmission security, a crucial issue in an increasingly vulnerable environment to cyber threats. This work will help identify opportunities for capacity enhancement while highlighting the technological challenges and adjustments necessary for the widespread adoption of these systems for critical and secure links.
Influence of chromium doping of UO2 fuel on fission product speciation under accidental conditions
The development of nuclear reactors is part of a drive to improve safety, with, for example, the deployment of nuclear fuels with improved properties in terms of their behavior under accident conditions, the so-called E-ATF (Enhanced Accident Tolerant Fuel). Industrial operator FRAMATOME is developing the Cr2O3-doped UO2 fuel as E-ATF. However, very little data is available on the behavior of fission products from Cr-doped fuel under accident conditions.
This thesis proposes to develop a synthesis process for Cr-doped UO2 fuel that simulates irradiated fuel, in order to study the behavior of the elements (Cr and fission products) at different temperatures and under different oxygen partial pressures. The methodology is based on an experimental approach combining synthesis of model materials and in-depth chemical characterization, complemented by a theoretical approach (thermodynamic calculations) enabling thermal sequences to be dimensioned and the proposed reaction mechanisms to be confirmed.
The thesis will be carried out at CEA Cadarache (France), within IRESNE (Research Institute on Nuclear Systems for Low-Carbon Energy Production). The PhD student will be hosted in a laboratory dedicated to the study of uranium-based compounds in the Department of Fuel Studies (DEC). Depending on the densification processes chosen, experiments of various duration may be carried out in other laboratories in France or Europe.
The PhD student will have the opportunity to learn advanced characterization techniques for ceramic materials, gain access to experiments on large-scale instruments (synchrotron) and take part in exchanges with the academic community(CNRS, Universities, JRC). He or she will be able to promote his work through publications and participation in conferences.
At the end of this thesis, the PhD student will have acquired skills in materials science and solid state characterization that he/she will be able to use in various materials fields, as well as experience in the nuclear environment of interest to the nuclear industry.
Phenomenological study of the coupled effects of iodine and oxygen on Iodine induced Stress-Corrosion-Cracking (I-SCC) of zirconium alloys
The Pressurized Water Reactor (PWR) core is composed of fuel assemblies, for which the fuel cladding is the first barrier for the confinement of the fuel and the fission products. Pellet Cladding Interaction (PCI) occurs during increases in the reactor power and results in the expansion of the pellets that produces a thermomechanical loading on the fuel cladding. In conjunction with iodine expelled from the pellet, it can, in theory, lead to the failure of the cladding by Iodine Stress Corrosion Cracking (I-SCC).
The objective of this PhD is to study the phenomenology of I-SCC, in mechanical and chemical conditions as close as possible to the conditions seen by the PWR cladding in PCI (in terms of the oxygen and iodine partial pressures).
The PhD has three main parts. The first part will focus on the study of the effect of the stress on the I-SCC susceptibility of zirconium, at different partial pressures of iodine and oxygen. The tests will be simulated and analyzed using numerical models of the I-SCC process. The second part will focus on the effect of the temperature on I-SCC as a function of the stress, and the partial pressures of iodine and oxygen. The third part will focus on the effect of a thick zirconia layer, at the inner wall of the cladding, on the I-SCC susceptibility of the cladding.
Development of a digital twin of industrial equipment: coupling chemistry / thermo-hydraulics / corrosion
This PhD subject is part of CEA R&D aimed at developing and improving decarbonized technologies for energy production, in response to climate issues. More specifically, it is part of the spent fuel reprocessing stage used in current nuclear reactors. The simulation of the operation and aging of this equipment is a major challenge for the sustainability of the activities of fuel reprocessing plants.
The objective of the thesis is to respond to these challenges, by developing a modeling of the corrosion of one or more equipments in the plants based on their operation. This will require coupling chemical reaction models (in solution and corrosion) with thermo-hydraulic models. These developments will be carried out using modeling tools developed by the CEA.
By making it possible to simulate the corrosion of equipment, the development of such a model will make it possible to optimize its lifespan (by seeking to optimize its operation, for example) or to accurately estimate (and therefore anticipate) the time needed for its replacement.
Brittle fracture of low alloy steels: sensitivity of mesosegregation regions to quenching and tempering conditions
The pressure vessels of the primary circuit of French nuclear power plants are made by assembling low-alloy steel components, forged from high-tonnage ingots (> 100t) that solidify in a non-uniform manner. The high thickness of the component also implies that the evolution of temperature during post-forging heat treatments vary significantly depending on the position in the thickness of the component. These two effects contribute to producing heterogeneous microstructures that can significantly weaken the material.
The scientific objective of this thesis is to evaluate which elements within the microstructure are responsible, and in what proportion, for increased embrittlement of the material for certain unfavorable heat treatment conditions. Conversely, better identifying the range of heat treatment conditions for which this embrittlement of the material remains contained, for a given initial microstructure, is an objective with high industrial stakes. Several heat treatments have already been applied to coupons from a rejected industrial component before subjecting them to Charpy impact toughness tests, in the field of the brittle to ductile transition of the material. Instrumented mechanical tests will be conducted as well as advanced fractographic and microstructural analyses in order to identify the evolution of the nature of the initiation sites according to the heat treatment conditions. These elements will then be integrated into a local approach to fracture model developed specifically to account for the effects of microstructural variations on the resistance to brittle fracture of low-alloy steels.
Flotation for Li-ion active materials recycling : limitations and influence of hydrodynamics and interfacial physico-chemistry on their selective separation
Battery recycling is now a major geopolitical, economic and environmental issue for the EU. Graphite, which makes up the anode of Li-ion batteries, is very rarely recycled. It is concentrated in a fraction called blackmass, where it is mixed with metal oxides of high commercial value. This graphite is then considered as an impurity and causes oversizing of hydrometallurgical operations. Since natural graphite is considered critical by EU and in order to reduce the operating and investment costs of hydrometallurgical processes, it is proposed to carry out a pre-treatment step on the blackmass in order to valorize the graphite directly. This stage is carried out by flotation. This process for separating solids suspended in water uses gas in the form of air bubbles to separate the particles according to their difference in wettability and therefore their attachment to the air bubbles. The complexity of the flotation process, linked to the dependence on both the nature of the interfaces and the hydrodynamic conditions, requires in-depth understanding of the mechanisms involved.
The aim of the proposed project, which follows on from two internal projects, is to identify the mechanisms at work during flotation, using methods of interfaces characterization, stability and rheology of foam fraction, imaging, etc., with a view to improving the performance of the flotation stage and extending it to other recycling challenges.
The PhD thesis work will be carried out at the Laboratoire des technologies de Valorisation des procédés et des Matériaux pour les ENR (LVME) at CEA Grenoble and in close collaboration with the Laboratoire de Caractérisations Avancées pour l'Energie (LCAE) at CEA Grenoble, the Laboratoire des Procédés Supercritiques et décontamination (LPSD) and the Laboratoire de développement des procédés de recyclage et valorisation pour les systèmes énergétiques décarbonnés (LRVE) at CEA Marcoule (30). In parallel with the experimental work, the models and mechanisms involved and the associated technical solutions will have to be proposed.
The scientific and industrial interest of the subject guarantees that the work will be promoted through international communications. After the PhD, you can join one of the best academic or applied research teams, or pursue an R&D career directly in industry.
Numerical simulation of the impact between immersed structures in a compressible liquid using immersed boundary type approaches.
Many industrial systems involve structures immersed in dense fluids. Examples include the submarine industry, or, more specifically, certain 4th generation nuclear reactors using coolant fluids such as sodium or salt mixtures. The effect of the interaction of the surrounding fluid on the contact forces between structures is a phenomenon of primary importance, particularly during accidental transient scenarios that can generate large displacements of structures whose residual integrity must be demonstrated for safety purposes.
In the context of this thesis, we are particularly interested in modeling the rapid impact of a structural fragment immersed in a fluid against a wall, resulting, for example, from an explosive phenomenon in a nuclear reactor vessel cooled by sodium. In this context, the sodium, modeled as a compressible fluid, is treated numerically using a volume-finite approach. The reactor's internal structures are treated using a finite-element approach. In order to deal with large structural displacements and possible fracturing, “immersed boundary” techniques are used for fluid-structure interaction.
The aim of this thesis is to define an innovative numerical method to better simulate the fluid film between two structures that come into contact in this context. Initially, we will focus on identifying the physical characteristics of the flow at the level of the fluid film (compressibility, viscosity, etc.) that have the greatest influence on the kinematics of the structures. Secondly, the main challenge of this thesis will be to improve current numerical methods in order to represent the flow characteristics of the fluid film as accurately as possible.
The proposed thesis will be carried out at CEA Saclay, in close collaboration with the EM2C laboratory at CentraleSupélec, within the environment of the Université Paris-Saclay. The PhD student will be immersed in a team with recognized expertise in transient simulations of fluid-structure interaction.