Modelling of actinide electrorefining
Modelling of an actinide electrorefining process
In the frame of the SACSESS European project CEA, ITU and CNRS are studying jointly a pyrochemical process for the reprocessing of spent nuclear fuels by electrolysis in molten chloride salts.
The main objective of the proposed post-doctoral work concerns the modelling of electrorefining runs onto aluminium cathodes using U-Pu-Zr-Am-Gd-Nd-Ce-Y metallic alloy. The modelling aims to evaluate the efficiency of this electrolytic process in terms of separation factors and to optimize the process flow sheets for a safe nuclear materials management.
Model reduction in dynamics : application to earthquake engineering problems
The complexity and refinement of the numerical models used to predict the behavior of structures under seismic loading often impose computation times of several days for solving the partial differential equations of the reference problem.
Furthermore, in the context of optimization , model identification, or parametric and stochastic analyses, the aim is not to predict the response of a unique model but of a family of models.
To reduce the computation time, model reduction techniques (Proper Orthogonal/Generalized Decomposition) may be considered. This post-doctoral study proposes to define and implement (especially in the FE code CAST3M) a technique suitable for the reduction of reinforced concrete type models subjected to seismic loading.
Droplets motion through modulation of surface energy gradient
Droplet motion through electro-wetting is nowadays largely studied and used in several systems and applications. In order to be useful, this technique needs an electrical field to monitor the droplet. For this post-doctoral fellowship, the main objective is to define an alternative method to the using of the electro-wetting technique in order to generate a droplet motion. The elaboration of surfaces with energy gradients conceived by thin film deposition or by laser ablation will be realized inside this study. The main difficulty is related to the patterns realization in order to obtain the appropriate hydrophilic/hydrophobic resolution. Apart from these “classical” techniques, an innovative method will be studied here by using switchable molecules. These molecules could modify the contact angle between a surface and a droplet, when acting on the potential of hydrogen (pH) or the wall temperature. For all the defined surfaces, the post-doctoral fellow will also analyze the coupling effect between the surface energy gradient and a thermal energy gradient on the droplet motion dynamics.
Study of aerosol transport through degraded materials
Radioactive Waste (RW) are produced during nuclear activities and are categorized as a function of their activities and their half-life in order to manage their conditioning, transport, storage… Mortar can be used in order to immobilize and/or create a safe barrier forming a Radioactive Waste Package (RWP) in order to protect the environment. It is important to study the efficiency of this mortar barrier for long term and safety assessment have to investigate the case of crack mortar formation as radioactive particles could then migrate in the cracks.
The LECD laboratory investigated this problematic by measuring the migration of CeO2 particle in mortar cracks using X-Ray microtomography. The cracks were synthesized by dissolving plastic molds (designed by 3D printing). This study showed the influence of particle interactions with tortuosity and roughness of the crack, but was limited to 40 µm particle diameter.
The aim of the postdoctoral work is to develop an experimental approach similar to the method developed to study the efficiency of HEPA filters, with particles of 0.05 - 5 µm diameter. Quantitative measurements will be performed on the particle flows on both sides of the cracked mortar sample. LECD has acquired an aerosol generator, a light-scattering aerosol spectrometer system for particle size analysis and concentration determination and an Universal Scanning Mobility Particle Sizers. The researcher will also develop modelling work using numerical tools as STARCCM+.
This project will be carried out under the format of an 12-month fixed-term contract at the Atomic Energy and Alternative Energies Commission (CEA), at the Cadarache site (Saint-Paul-lez-Durance, 13) at the Expertise and Destructive Characterization Laboratory (LECD) of the Expertise and Characterization CHICADE Service (SECC).
Contacts: ingmar.pointeau@cea.fr (R&D engineer) – Olivier.vigneau@cea.fr (Head of the Laboratory)
Batteries recycling :Development and understanding of a new deactivation concept of lithium ion domestic batteries
Domestic lithium ion batteries gather all batteries used in electronic devices, mobile phone, and tooling applications. By 2030, the domestic lithium-ion battery market will increase up to 30%. With the new European recycling regulation and the emergency to find greener and safer recycling process, it is today necessary to develop new deactivation process of domestic lithium ion batteries.
The process has to address several lithium ion chemistries, be continuous, safe, controllable and low cost.
To develop this new concept, the first step will be to define the most appropriate chemical systems. Then these chemical systems will be tested in a dedicated experimental laboratory setup using chemistry and electrochemistry, allowing the simulation of real conditions of domestic batteries deactivation.
The third step will be to characterize, understand and validate the electrochemical and physico chemical mechanisms. The last step will be to participate to the validation of the deactivation concept on a real object (a lap top battery) in representative conditions (on the abuse tests plateform of CEA).
Modelling of interstitial cluster evolution in bcc metals after helium implantation
Under irradiation, structural materials inside nuclear reactors undergo changes in mechanical properties, which result from the formation of point defect clusters, such as cavities (clusters of vacancies) and interstitial dislocation loops (clusters of self-interstitial atoms). Understanding the formation processes of such clusters is thus of prime importance. Recently, three-dimensional interstitial clusters, known as C15 clusters, have been shown theoretically to be highly stable in iron [1]. In order to detect such clusters experimentally, an idea is to make them grow, as shown for dislocation loops after helium implantation [2].
This approach will be carried out experimentally in various bcc metals in the framework of the ANR project EPigRAPH, in collaboration with Chimie ParisTech, GEMaC and LPS.
In this project, the following modelling tasks will be performed by the postdoc:
- DFT calculations will be done to obtain the energetic properties of point defects and point defect clusters in the bcc metals envisaged in the project.
- These data will then be used to parameterize a kinetic model based on cluster dynamics [3]. This formalism is particularly well adapted to simulate the evolution of point defect clusters over long physical times.
The modelling work will be performed in close collaboration with another postdoc working on the experimental part.
[1] M. C. Marinica, F. Willaime, J.-P. Crocombette, Phys. Rev. Lett. 108 (2012) 025501
[2] S. Moll, T. Jourdan, H. Lefaix-Jeuland, Phys. Rev. Lett. 111 (2013) 015503
[3] T. Jourdan, G. Bencteux, G. Adjanor, J. Nucl. Mater. 444 (2014) 298
Predictive design of heat management structures
Heat management is a paramount challenge in many cutting edge technologies, including new GaN electronic technology, turbine thermal coatings, resistive memories, or thermoelectrics. Further progress requires the help of accurate modeling tools that can predict the performance of new complex materials integrated in these increasingly demanding novel devices. However, there is currently no general predictive approach to tackle the complex multiscale modeling of heat flow through such nano and micro-structured systems. The state of the art, our predictive approach “ShengBTE.org”, currently covers the electronic and atomistic scales, going directly from them to predict the macroscopic thermal conductivity of homogeneous bulk materials, but it does not tackle a mesoscopic structure. This project will extend this predictive approach into the mesoscale, enabling it to fully describe thermal transport from the electronic ab initio level, through the atomistic one, all the way into the mesoscopic structure level, within a single model. The project is a 6 partner effort with complementary fields of expertise, 3 academic and 3 from industry. The widened approach will be validated against an extensive range of test case scenarios, including carefully designed experimental measurements taken during the project. The project will deliver a professional multiscale software permitting, for the first time, the prediction of heat flux through complex structured materials
of industrial interest. The performance of the modeling tool will be then demonstrated in an industrial setting, to design a new generation of substrates for power electronics based on innovating layered materials. This project is expected to have large impacts in a wide range of industrial applications, particularly in the rapidly evolving field of GaN based power electronics, and in all new technologies where thermal transport is a key issue.
Simulation of silicon solar cells based on n-type material : modelling and architecture optimisation.
INES is actually developping new fabrication technologies for n-type silicon solar cells. Working on simulation of photovoltaic solar cells enables the speed-up of the developement of new technologies: physical interpretation of characterisation results, support to device design, optimisation of processing steps and evaluation of original designs.
This subject open for post-doc position is focused on the study of semi-empirical models for materials and process steps for n-type solar cells. These basic road-blocks will be assembled in a complete model by using a multi-scale simulation tool. In the end, this global model will allow optimising of the p-type emitter geometrical structure, the efficiency of carrier collection on the back side or the geometry of metallisation for electrical contacts.
Electrochemical device for purifying hydrogen in a reformed gas
This project aims to establish a new research and development on purification devices for fuel reformers for hydrogen fuel cells. This work is of prime importance for fuel cell systems fed by different sources of hydrogen. Used in "power full" or "range extender" modes, the reformer and gas purification system are elements of the chain that have to be optimized.
Objective is to develop an electrochemical device for purifying the gas from a reformer whose basic principle is similar to that of a PEM electrolyzer. The gases from the reformer undergo a selective electrocatalytic oxidation to separate hydrogen and conventional pollutants directly power a fuel cell.
The project will focus on selection and characterization of catalysts electrocatalytic performance and the achievement of functional prototypes. These developments will assess the economic relevance of the device vis-à-vis other systems and identify areas of research to develop thereafter.