Optical sensor development for in-situ and operando Li-ion battery monitoring
To improve the battery management system, it is required to have a better knowledge of the physical and chemical phenomena inside the cells. The next generation of cells will integrate sensors for deepest monitoring of the cell to improve the performances, safety, reliability and lifetime of the battery packs. The main challenge is thus to measure relevant physico-chemical parameters in the heart of the cell to get a direct access to the real state of the cell and thus to optimize its management. To address this challenge, a research project will start at CEA at the beginning of 2020 to develop innovative optical sensors for Li-ion battery monitoring. He / She will participate, in a first step, to the development of optical probes and their integration on optical fibres. The work will focus on the synthesis of a photo-chemical probe (nanoparticle and/or molecule) as active part of the sensor. Then, theses probes will be put on the optical fibre surface to form the sensor. The candidate will also participate to the realization of an optical bench dedicated to the testing of the sensors. In a second step, he / she will work on integrating the sensors into the Li-ion cells and test them in different conditions. The objective is to demonstrate the proof of concept: validation of the sensors efficiency to capture the behaviour of the cell and correlate it to electrochemical measurements.
Time-resolved in-situ study, by X-ray diffraction under synchrotron radiation, of structural evolutions in a high temperature oxidized zirconium alloys
In certain hypothetical accident situations in pressurized-water nuclear reactors (PWRs), the zirconium alloy cladding of fuel pallets, which constitutes the first barrier for the containment of radioactive products, can be exposed for a few minutes to water vapor. at high temperature (up to 1200 ° C), before being cooled and then quenched with water. The cladding material then undergoes numerous structural and metallurgical evolutions. In order to study these structural evolutions in a precise way, a first experiment campaign was carried out on the BM02 line of the ESRF on a prototype furnace allowing to perfectly control the atmosphere and the temperature. Two tasks will be entrusted to the candidate: continue and finish the analysis of the first experiment(phase fraction determination, residual constraints ...) and prepare a new complementary experimental proposal by mid 2020.
Strudy and processing of C/SiC composites
For different applications, we are looking for materials having superior mechanical properties at high temperature (1000 ° C or higher) and that are resistant to oxidation. The family of ceramic matrix composite materials (CMC), especially C / SiC, seems the most relevant to our needs. However, it is necessary to conduct studies to determine the most efficient solutions among the wide variety of fibrous architectures and possible matrix microstructures, while taking into account the constraints related to available processes and targeted geometries. This work will be conducted in collaboration with other CEA laboratories.
Data science for heterogeneous materials
In order to predict the functional properties of heterogeneous materials through numerical simulation, reliable data on the spatial arrangement and properties of the constitutive phases is needed. A variety of experimental tools is commonly used at the laboratory to characterize spatially the physical and chemical properties of materials, generating "hyperspectral" datasets. A path to progress towards an improved undestanding of phenomena is the combination of the various imaging techniques using the methods of data science. The objectives of this post-doc is to enrich material knowledge by developping tools to discover correlations in the datasets (for exemple between chemical composition and mechanical behavior), and to increase reliability and confidence in this data by combining techniques and physical constraints. These tools will be applied to datasets of interest regarding cementitious materials and corrosion product layers from archaeological artifacts.
Geophysical site characterizations of European seismic monitoring stations and contributions to the development of best-practices for noninvasive site characterization methods
In-situ geophysical characterizations of earthquake recording stations are essential toward the effective use of ground motion records by the earthquake engineering community to mitigate seismic hazards. The current methods used for seismic site characterization rely on array-based recordings of surface-waves. These methods determine the site dispersion curves from surface-wave phase velocity versus frequency (or wavelength) relations before inverting the curves to model the site shear wave velocity (VS) versus depth profiles. VS profiles are then used to calculate the site’s time-averaged VS of the upper 30 m (VS30) for use by engineers in developing ergodic GM regression models, and/or in combination with the site GM recordings, to directly estimate the site-specific seismic response. In recent years, an important effort was initiated by several countries to improve the state-of-knowledge about geophysical site characterization methods with the aim toward robust and consistent characterizations (VS, VS30, etc.). Much work still remains to be done with respect to the characterization of site conditions at network stations and the improvement of the methods selected and their implementation. The proposed post-doc position will consist of participation in the current effort of seismic station characterization, as well as the optimization of their implementation: 1/ The post-doctoral candidate is expected to participate in geophysical surveys of seismic stations located in European, 2/ The candidate is expected to improve acquisition parameters in order to optimized subsequent surveys 3/ Finally, the candidate is expected to be involved within the COSMOS guidelines project and assist organizers within the project advancement and guidelines writing coordination.
Study of a transient regime of helium dispersion to simulate an accidental release of hydrogen from a fuel cell.
CEA and industrial partners want to improve their knowledge, models and risk mitigation means for the conséquences of an accidental release of hydrogen from a H2 Fuel Cell. The dispersion of helium as a replacement for hydrogen takes place in a private garage and the transient state will be studied. Different scenarios of release are considered: from a cubic idealized fuel cell, then with different aspect ratios and finally with varying main dimension. The goal is to study some scaling effects. For the first case, we will measure helium concentration with katarometres and possibly velocity fields with PIV methods. Then mitigation processes will be tested. At last comparisons with models and numerical simulations will be performed.
Structural characterization, reactivity and physico-chemical properties of Pu(IV) colloidal suspensions
Pu(IV) is known to be highly prone to hydrolysis leading to the formation of extremely stable Pu(IV) colloidal suspensions (known as intrinsic colloids). The lack of knowledge concerning the speciation and reactivity of these Pu colloids hinders the development of reliable models allowing to predict their behavior in industrial and environmental systems. The behavior of these colloidal species towards dissolution, complexation, or aggregation has been very poorly described in the literature. It thus appears essential to study and characterize Pu(IV) colloids and in particular their surface charge properties which ensure their stability and their interactions with their environment. This pioneering project in the nuclear field aims to study and characterize colloidal Pu(IV) suspensions whose size, concentration and dispersion medium can be controlled by our approaches. It comprises: (i) the preparation of intrinsic Pu(IV) colloidal suspensions and the study of their chemical and sonochemical reactivity; (ii) the electrophoretic characterization of various colloidal suspensions and the study of their behavior under the influence of an electric field; (iii) the characterization of their multi-scale structural properties by small and large angle scattering (SAXS / WAXS) coupled with EXAFS / XANES measurements (MARS line, SOLEIL synchrotron).
Analysis of low abundance 144Ce and 106Ru isotopes by mass spectrometry
The aim of this project is to develop the high precision analysis of 144Ce and 106Ru by mass spectrometry in irradiated samples for the qualification of neutronic calculation codes. These two isotopes are present at low abundances in the samples of interest and display significant isobaric interferences with 144Nd and 106Pd respectively. To complete this project, the candidate will carry out the appropriate analytical developments in conventional laboratory on inactive samples. Then the procedure will be transposed in the active laboratory for validation with the analysis of real samples. In the case of 144Ce, the implementation of a coupling between high performance liquid chromatography (HPLC) and ICPMS-MC, combined with the isotope dilution technique for the precise determination of atomic contents is envisaged. For 106Ru, the 101Ru concentration will first be determined by ICPMS-Q and the 101Ru/106Ru ratio will be determined by HPLC/ICPMS-Q or HPLC/ICPMS-MC coupling to remove the 106Pd/106Ru interference.
Simulation of supercritical helium flows in the cooling circuits of tokamaks
Future fusion reactors such as tokamaks (ITER, DEMO) will have to demonstrate the safety of their systems, validated by thermal hydraulic codes. To meet this requirement, the CATHARE code has been chosen as scientific computing tool. The work will consist in adapting the CATHARE code to helium at low temperatures and then to benchmark it with other thermal hydraulic codes used by the DRF (Direction de la Recherche Fondamentale), as well as with experimental data available at CEA Grenoble.
The study will be threefold. The first phase will be dedicated to a literature survey on the thermal hydraulics of helium, featured by closing equations for monophasic helium (friction and heat transfer coefficients). In a second step, the engineer will implement these laws in the code and perform some validations tests. The last part will focus a benchmark based on three applications: the study of a cryo-pump, the study of a supercritical helium discharge and the study of a superconducting cable.