Modeling of faults on low voltage DC networks in buildings, towards fault detection algorithms
The development of the use of renewable energies and energy storage as well as the progress made by power electronic components are gradually leading to a rethinking of the architectures of low voltage electrical distribution networks in buildings. These developments will allow the development of direct current or mixed alternating-direct current networks supplied by static converters. On this type of network, faults become more difficult to manage due to the power sources used. Indeed, the usual signatures of the short-circuit or the overload are no longer the same and will vary according to the converters used and the architecture of the network. For this, it is necessary to identify, by simulation, the most suitable protection topologies (by neutral systems for example) and to identify the typical fault signatures. Ultimately, these signatures will provide optimum detection devices.
Lean-Rare Earth Magnetic materials
The energy transition will lead to a very strong growth in the demand for rare earths (RE) over the next decade, especially for the elements (Nd, Pr) and (Dy, Tb). These RE, classified as critical materials, are used almost exclusively to produce NdFeB permanent magnets, and constitute 30% of their mass.
Several recent international studies, aiming to identify new alloys with low RE content and comparable performances to the dense magnetic phase Nd2Fe14B, put hard magnetic compounds of RE-Fe12 type as advantageous substitution solutions, allowing to reduce more that 35% of the amount of RE, while keeping the intrinsic magnetic properties close to those of the Nd2Fe14B composition.
The industrial developments of the RE-Fe12 alloys cannot yet be considered due to the important technological and scientific challenge that remain to be lifted in order to be able to produce dense magnets with resistance to demagnetization sufficient for current applications (coercivity Hc > 800 kA/m).
The aim of the post-doctoral work is to develop Nd-Fe12 based alloys with optimized intrinsic magnetic properties and to master the sintering of the powders in order to obtain dense magnets with coercivity beyond 800 kA/m, to fulfil the requirements of the applications in electric mobility. Two technological and scientific challenges are identified:
- understanding of the role of secondary phases on the coercivity. This will open the way to the implementation of techniques called "grain boundary engineering", well known for the NdFeB magnets to have remarkably improved the resistance to demagnetization.
- mastering the sintering step of these powders at low temperature (< 600°C) in order to avoid the decomposotion of the magnetic phase by grain boundary engineering
High efficiency silicon cell irradiations for space
Historically, photovoltaics was developed in conjunction with the growth of space exploration. During the 90's, III-V multi-junction solar cells were progressively replaced silicon, for their superior performance & radiation hardness. Today, the context is favorable to a revival of space Si: increasing PV power needs, missions with moderate durations & constraints (LEO), very low cost & high performance terrestrial Si cells (p-type > 26% AM1.5g). However, for Si cells, conventional irradiation ageing methods & sequences (ECSS) are less appropriate. As the literature mainly comes from 80s - 90s, it is necessary to revisit the topic for the latest generation of passivated contacts Si cells (developed at CEA INES) and the unique double beam irradiation facilities of JANNuS platform - CEA Saclay.
This work is part of the SiNRJs project, at the interface between two CEA departments, dealing with space photovoltaics & materials irradiation. The scientific & technological approach adopted: 1. fabrication of passivated contact Si cells (HeT and/or Poly-Si) 2. Si cells optoelectronic characterizations before irradiation (IV AM1.5/AM0, EQE, etc.) 3. Cells & samples proton irradiations, in situ characterizations (Raman & El) 4. Ex situ characterizations after irradiations (IV AM1.5/AM0, EQE, etc) 5. Results analysis and synthesis. From a scientific point of view, the key issues to be addressed concern the understanding of the mechanisms/dynamics of defect creation/healing under this double electronic and ballistic excitation.
Rhelogical properties of molten crystallized glass
Formulation of nuclear waste conditioning glass results from a compromise between waste loading, glass technological feasibility and its long-term behavior. Up to now borosilicate glasses formulated at CEA and elaborated at La Hague plant by Orano to condition nuclear waste are homogeneous when molten. That means that today glass formulation is determined such as solubility limits of each constituting elements of waste aren’t exceeded in order to avoid phase separation (implying typically Mo, S, P) and/or crystallization (implying typically Fe, Ni, Cr, Zn, Al, Ce, Cs, Ti…) leading to a two-phase molten glass (liquid-liquid or liquid-solid).Today CEA would like to explore the impact of solid particles in suspension in the molten glass and in the final glass canister on respectively the glass technological feasibility and its long-term behaviour.
The proposed study focuses on the molten glass technological feasibility. The presence of solid heterogeneities in the melt is known to lead to a modification of some of its physical properties – notably its rheology, as well as thermal and electrical conductivities, and can generate settling phenomena. Yet these properties are in the heart of vitrification process control and modelling. This study will then investigate the impact of crystals in the molten glass on vitrification process control and modelling.
Synthesis by 3D printing of functionnalized geopolymer membrane for the treatment of complex radioactive effluents.
In the field of the treatment of liquid radioactive wastes on solid supports, the development of new composite materials synthetized by 3D printing under filtre shape is of primary of importance to decontaminate some radioactive effluents.
In this phD proposal, we propose to develop a membrane allowing to produce, from effluent containing somes traces of micronic solids in suspension and ionic species, a clarified effluent compatible with a nuclear outlet pipe. The challenge is to study the shaping of a material in a form of a filtration membrane allowing to trap in a single step an effluent containing some solids in suspension and some ionic species. In order to develop both functionnalities, 3D printing will be used to synthetise multiscale porous ceramic composites such as some geopolymers functionnalized by a selective adsorbants. The candidate, mainly based at CEA/ISEC Marcoule, could first formulate a functionnalized geopolymer paste with suitable rheological properties compatible with the constraints of the 3D printing process. A cross-flow filtration membrane with a controled macroporous network will be then printed by optimizing the geometry of the mesh. Finally, some sorption and cross-flow filtration tests will be performed on some model effluents containing calibrated solid in suspension and ions of interest such as Cs and Sr. The relevance of the printed membrane architecture will be assessed in relation to the capture of the solids and radioelements.
The candidate must have skills in the field of rheology, process and modeling. From this research work, job opportunities either in the field og 3D printing of materials or in the field of liquid waste treatment and depolution are potential options.
Robotics Moonshot : digital twin of a laser cutting process and implementation with a self-learning robot
One of the main challenges in the deployment of robotics in industry is to offer smart robots, capable of understanding the context in which they operate and easily programmable without advanced skills in robotics and computer science. In order to enable a non-expert operator to define tasks subsequently carried out by a robot, the CEA is developing various tools: intuitive programming interface, learning by demonstration, skill-based programming, interface with interactive simulation, etc.
Winner of the "moonshot" call for projects from the CEA's Digital Missions, the "Self-learning robot" project proposes to bring very significant breakthroughs for the robotics of the future in connection with simulation. A demonstrator integrating these technological bricks is expected on several use cases in different CEA centers.
This post-doc offer concerns the implementation of the CEA/DES (Energy Department) demonstrator on the use case of laser cutting under constraints for A&D at the Simulation and Dismantling Techniques Laboratory (LSTD) at the CEA Marcoule.
Etudes et développement d’un système laser dans l’UV pour la démonstration à l’échelle laboratoire de l’épuration isotopique du palladium (naturel).
Le palladium est un métal rare dont la demande mondiale est en forte augmentation. Or, il est présent en tant que produit de fission dans les combustibles nucléaires usés qui sont retraités en France. Il serait donc intéressant de recycler ce métal. Pour cela, il est nécessaire de procéder à une épuration isotopique, afin de supprimer un des isotopes du palladium, le 107, qui est un radionucléide artificiel à vie longue émetteur béta. Dans le cadre d'un nouveau projet sur 4 ans construit en réponse à l'appel d'offre du Plan d'Investissement et d'Avenir de l’État, le Service d’Etude des Procédés d’Enrichissement propose un contrat post-doctoral portant sur le développement d’un système laser dans l’UV pour le procédé de séparation isotopique du palladium par Lasers actuellement en cours de développement. L’objectif principal du projet est la démonstration finale de la faisabilité de séparation de palladium naturel (et non radioactif) pour la phase suivante de développement d’un premier pilote.
Le post-doctorant devra développer des lasers prototypes de procédé à haute cadence en partant du visible (système lasers colorant) jusqu’à l'UV. Le passage dans l’UV se fait par doublage de fréquence avec des objectifs élevés en terme de performance. Il s’agit d’utiliser un cristal doubleur de fréquence de type BBO, LBO, KDP ou autre. Pour ce faire, le post-doctorat participera à la définition de ce cristal, mais aussi au développement de l’environnement du cristal doubleur (comportement, performances attendues et la tenue au flux des différents matériels). Des échanges seront mis en place sur ce sujet spécifique avec des spécialistes reconnus au sein de la Direction de la Recherche Fondamentale du CEA. La programmation (en Python et/ou sous Labview) de ces outils ou asservissements est à développer également. Une attention particulière sera portée sur les publications à réaliser essentiellement dans le cadre du doublage de fréquence, sujet complexe très étudié mondialement.
Development of a digital twin of complex processes
The current emergence of new digital technologies is opening up new opportunities for industry, making production more efficient, safer, more flexible and more reliable than ever. The application of these technologies to the vitrification processes could improve the knowledge of the processes, optimise their operation, train operators, help with predictive maintenance and assist in the management of the process.
The SOSIE project aims at providing a first proof of concept for the implementation of digital technologies in the field of vitrification processes, by integrating virtual reality, augmented reality, IoT (Internet of Things) and Artificial Intelligence.
This project, carried out in collaboration between the CEA and the SME GAMBI-M, is a READYNOV project. GAMBI-M is a company specialised in the reconstruction of complex environments and in digital engineering. The work will be carried out in close collaboration with the CEA teams developing the vitrification processes for nuclear waste.
The project consists of developing a digital twin of 2 vitrification processes, and will be implemented on 2 platforms in parallel, one in a conventional zone, the other in a high activity zone. The first step will be to develop a visual digital twin, the virtual 3D model of each cell, which will allow the user to visit the cells and access any point virtually. Based on this reconstructed model, an "augmented" twin will be developed and connected to the supervisory controller. Finally, the last step will be to develop the "intelligent twin" by exploiting existing databases on the operation of the process. By training machine learning algorithms on these data, a predictive model of nominal operation will be generated.
Publications are expected on the implementation of virtual reality and augmented reality tools on shielded chain operations, as well as on the development of deep learning methods for the assistance to the control of such complex processes.
Decentralized Solar Charging System for Sustainable Mobility in rural Africa
A novel stand-alone solar charging station (SASCS) will be deployed of in Ethiopia. Seeing as 45% of Sub-Saharian Africa’s population lacks direct access to electricity grids and seeing as the the infrastructure necessary to reliably harness other energy sources is largely non-existent for many such populations in Ethiopia, introducing the SASCS among some of the country’s rural communities is a necessary effort. It could ostensibly invigorate communities’ agricultural sector and support those whose employment is rooted in farming. A SASCS could also serve to integrate renewable energy within the country’s existing electricity mix. CEA INES will act as a consulting Partner for the design and implementation of the solution (second life batteries, solar will be investigated). In addition, because of CEA INES’s established expertise in the installation of solar tools within various communities, the initiative will also provide know-how for the installation of the SolChargE in Ethiopia as well as cooperate on workshops for students and technicians employed by the project.
Natural convection at high Ra numbers for nuclear safety: 2nd year
Thermal exchanges at very high Rayleigh numbers (Ra) exist on geophysical scale, at civil engineering scale and increasingly in industrial applications and here particularly in the energy sector. At this point, we mention the cooling of solar panels or the heat removal from nuclear power plants under accidental conditions. In fact, the passive safety concept of Small Modular Reactors (SMR) is based on the transfer of residual heat from the reactor to a water pool in which the reactor is placed. Since the outer reactor vessel is very high, heat exchange occurs by natural convection at Rayleigh numbers (Ra) between 1010 and 1016. Reliable heat transfer correlations exist to date only up to about Ra < 1012 with very high uncertainties in the extrapolation to higher Ra. Understanding the heat transfer at very high Ra is thus of fundamental and practical interest. The associated challenges are twofold:
• Numerical challenges: CFD codes cannot model turbulent heat transfer at very high Ra with sufficient accuracy and appropriate calculation time. Improved physical and numerical models are required, which use high performance computing (HPC) capabilities.
• Experimental challenges: Detailed experiments are essential for code validation. Since experiments in water require impractical huge dimensions, cryogenic experiments with helium are planned at CEA, based on the interesting physical properties of this fluid in the range of 5 K (high thermal expansion associated to low viscosity and thermal conduction).