Study of the Velocity-Vorticity-Pression formulation for discretising the Navier-Stokes equations.
The incompressible Navier-Stokes equations are among the most widely used models to describe the flow of a Newtonian fluid (i.e. a fluid whose viscosity is independent of the external forces applied to the fluid). These equations model the fluid's velocity field and pressure field. The first of the two equations is none other than Newton's law, while the second derives from the conservation of mass in the case of an incompressible fluid (the divergence of velocity vanishes). The numerical approximation of these equations is a real challenge because of their three-dimensional and unsteady nature, the vanishing divergence constraint and the non-linearity of the convection term. Various discretisation methods exist, but for most of them, the mass conservation equation is not satisfied exactly. An alternative is to introduce the vorticity of the fluid as an additional unknown, equal to the curl of the velocity. The Navier-Stokes equations are then rewritten with three equations. The post-doc involves studying this formulation from a theoretical and numerical point of view and proposing an efficient algorithm for solving it, in the TrioCFD code.
Modelling of prospective deployment scenarios for hydrogen in France and Europe M/F
One of the major energy transition leverages at the horizon 2050 is decarbonation of uses such as electricity production, transport or industry. If electrification of some uses is part of the solution, a potential is also foreseen in using decarbonized intermediate vectors such as hydrogen, produced by electrolysis, and which can be leveraged both as an energy vector and as a substitute molecule in carbon-emitting industries like chemistry, steel production, etc.
However, the potential high development of hydrogen creates underlying needs for electricity production, leading to questions about the sustainability aspects of such deployments, a possible criteria when choosing between different possible deployment options.
As part of a “PEPR Hydrogène” research project, the study aims at 1/ developing possible quantitative hydrogen deployment scenarios consistent between different geographic scales (from the French regions to the national and European level), in collaboration with project partners, 2/ assessing the consequences of these scenarios on the European electrical production system and consequently on the characteristics of the electricity used for the hydrogen production – in particular from the sustainability point of view (e.g. electricity cost and greenhouse gas emissions).
TREATMENT OF RADIOACTIVE ORGANIC EFFLUENTS
The ECCLOR project (Project labelled 'Investment for the Future') aims to find a management route for challenging radioactive organic effluents. A strategy under investigation is to make the effluents compatible with existing outlets by decontaminating them of radioelements by column filtration. This involves developing ion-selective extractants in a form suitable for use in columns.
Studies are being carried out at CEA to improve the treatment of radioactive aqueous effluents by developing processes capable of achieving "zero discharge" while producing a minimum of waste. The challenge of the ECCLOR project will be to transpose this work to contaminated organic solvents with various radiological compositions and rheological properties. A first post-doctoral contract was dedicated to the development of materials for this application. A number of inorganic supports (silicas, geopolymers, aluminas, etc.) were considered for decontaminating these organic effluents.
The performance of the various materials developed in previous work can be optimised in terms of actinide capacity and selectivity with respect to competitor ions. In particular, the performance of existing materials needs to be studied further on more complex simulated LORs, with the necessary adaptations to the analytical method.
This project is intended for a post-doctoral fellow wishing to develop skills in extraction mechanism comprehension and analytical methods, with an interest in advancing the field of radioactive waste management. It will be will build upon the expertise of two laboratories at CEA Marcoule: the Design and Characterization of Mineral Materials Laboratory for materials elaboration and characterization, and the Supercritical and Decontamination Processes Laboratory for materials grafting and decontamination experiments.
Development of a new generation of reversible polymer adhesives
Polymeric adhesives are generally cross-linked systems used to bond two substrates throughout the lifetime of an assembly, which may be multi-material, for a wide range of applications. At their end of life, the presence of adhesives makes it difficult to separate materials and recycle them. Moreover, it is difficult to destroy the cross-linking of the adhesives without chemical or thermal treatment that is also aggressive for the bonded substrates.
In this context, the CEA is developing adhesives with enhanced recyclability, by integrating recyclability into the chemical structures right from the synthesis of the polymer networks. The first approach involves incorporating dynamic covalent bonds into polymer networks, which can be exchanged under generally thermal stimulus (e.g. vitrimers). A second approach involves synthesising polymers that can be depolymerised under a specific stimulus (self-immolating polymers) and have the ability to cross-link.
The post-doc will develop 2 networks that can be used as adhesives with enhanced recyclability. A first network will be based on a depolymerizable chemistry under stimulus already developed on linear polymer chains, to be transposed to a network. A second vitrimer network will be synthesised on the basis of previous work at the CEA. Activation of the bond exchange in this network will take place via a so-called photolatent catalyst, which can be activated by UV and will make it possible to obtain a UV- and heat-stimulated adhesive. The choice and synthesis of these catalysts and their impact on the adhesive will be the focus of the study. The catalysts obtained could also be used to trigger depolymerisation of the first depolymerisable system under stimulus.
Impact of Microstructure in Uranium Dioxide on Ballistic and Electronic Damage
During reactor irradiation, nuclear fuel pellets undergo microstructural changes. Beyond 40 GWd/tU, a High Burnup Structure (HBS) appears at the pellet periphery, where initial grains (~10 µm) fragment into sub-grains (~0.2 µm). In the pellet center, under high temperatures, weakly misoriented sub-grains also form. These changes result from energy loss by fission products, leading to defects such as dislocations and cavities. To study grain size effects on irradiation damage, nanostructured UO2 samples will be synthesized at JRC-K, using flash sintering for high-density pellets. Ion irradiation experiments will follow at JANNuS-Saclay and GSI, with structural characterizations via Raman spectroscopy, TEM, SEM-EBSD, and XRD. The postdoc project will take place at JRC-K, CEA Saclay, and CEA Cadarache under expert supervision.
Modeling of the MADISON fuel irradiation device for the future JHR reactor
The Jules Horowitz Reactor (RJH), currently under construction at CEA's Cadarache site, will irradiate materials and fuels in support of the French and international nuclear industry, as well as producing radioelements for medical use. To carry out its missions, the reactor will be equipped with numerous experimental devices. In particular, the MADISON device, currently under design, will irradiate 2 or 4 fuel samples under nominal stationary or operational transient conditions. The loop is representative of light-water reactor operating conditions, with single-phase and two-phase forced convection.
The main objective of the Post-Doc is to model the MADISON device and all associated heat exchanges precisely, in order to help determine the overall heat balance during the test and thus improve the accuracy of the linear power imposed on the samples. To this end, a coupled thermal model (describing the fuel rods and device structures) / CFD thermal-hydraulic model (describing the coolant) will be established using the NEPTUNE_CFD/SYRTHES code. The modeling will be validated based on results obtained from similar modeling carried out on the ISABELLE-1 and ADELINE single-rod devices in the OSIRIS and RJH reactors. The proposed approach fits in with the logic of developing digital twins of the RJH experimental devices.
In-situ measurement of liquid composition by digital in-line holography
This postdoctoral position is part of the ANR ATICS project (Advanced Tri-dimensional Imaging of Complex Particulate Systems), which aims to develop a set of advanced tools and methods for modeling and reconstructing holograms to enhance the practical capabilities of three-dimensional imaging through digital inline holography. This is a collaborative research project lasting four years, involving four university laboratories, the CNRS, grandes écoles, and the CEA. Within this framework, the objective of the postdoctoral work is to provide physical knowledge and data to other team members and to demonstrate the contributions of the theoretical and numerical developments made in ATICS in two research areas in which the partners are regularly involved: multiphase flows and recycling processes. To achieve this, new experimental devices for measuring the composition of liquids will be developed, leveraging the potential of inline digital holography at various scales, from microfluidics to the study of sprays in acoustic levitation. The work will be conducted in close collaboration with the teams at the IUSTI laboratory of Aix-Marseille University.
Thermochemical and thermodynamic study of chloride molten salts
In today’s climate emergency, access to clean and cheap energy is more important than ever. Several ways have been envisaged for several years now, but a number of technological issues still need to be overcome before they can be put into practice, as they represent breakthroughts. Whether for energy storage than for fourth generation nuclear reactors, molten salt environment used as coolant and/or as fuel is highly corrosive requiring a complexe choice of structural materials.
The aim of this subject proposed in the Corrosion and Materials Behavior Section is to study in depth the chemical properties of different chloride molten salts : the basic ternary salt (NaCl-MgCl2-CeCl3) but also the corrosion/fission/activation products that can be produced (MxCly with M=Cr, Fe, Te, Nd, Ni, Mo,…). The activity coefficients and solubility limits of these metallic elements will be determined using various techniques such as electrochemistry and Knudsen cell mass spectrometry. If required, this study can be completed by the phase transition temperature and heat capacity measurements using differential scanning calorimetry.
Optimizing phytotechnologies for the remediation of contaminated nuclear sites
CEA is recruiting a postdoctoral researcher for a research project aimed at optimizing phytotechnologies for the remediation of contaminated nuclear sites. This research is part of the risk management and remediation of contaminated soils, in particular those resulting from the decommissioning of nuclear facilities. The aim of the project is to develop an advanced mechanistic model of soil-plant transfers, in order to gain a better understanding of contaminant mobility in lightly contaminated soils, and to optimize the use of suitable plants to stabilize these contaminants.
Development of new Potassium-ion cells with high performances and low environmental impact
Lithium ion batteries are considered as the reference system in terms of energy density and cycle life and will play a key role in the energetic transition, especially concerning electric vehicles. However, such a technology involves the use of a large amount of critical elements and active materials are synthesised using energy intensive processes.
In this way, our team is developing a new Potassium-ion batteries technology with high performances but with a low environmental impact.
For this innovative and ambitious project, CEA-LITEN (one of the most important research institute in Europe) is looking for a talented post-doctoral researcher in material chemistry. The post-doctoral position is opened for a young researcher with a high scientific level, interested by valorising her/his results through different patents and/or scientific publications.