Development of a compact XRF for online analysis dedicated to process monitoring.
X-ray fluorescence (XRF) spectrometry is a well-known analytical technique for elemental analysis in an industrial context. In a simplified way, this technique is based on the measurement of X-radiation characteristics that are emitted by the atoms rearranging their electron cloud following an external stimulus. This is a non-destructive measurement relevant for the determination of chemical elements within liquid and solid mixture. In the 90s, the work conducted by the CEA has shown the relevance of XRF for the measurement of heavy elements using L-edge, (U, Pu, Am, Np, Cm, Pb) as well as lighter ones (Zr, Mo, Sr) using K-edge. Low detection limits (few mg/l) have been reached and the method has been implemented industrially for monitoring several processes (for instance at La Hague plant). However, operating a XRF requires heavy and cumbersome equipment, especially a nitrogen-cooled detector and a large X-Ray generator.
Recently the technology has been significantly improved on two key issues:
• The X-rays sources, which were miniaturized,
• The detectors thanks to new type of semiconductor of small volumes, operating at room temperature with a convenient spectral resolution (CdZnTe crystals for instance).
In this framework, the proposed subject concerns new R&D studies on potentialities offered by these improvements, regarding two application fields:
• On-line monitoring in reprocessing process.
• Screening of the contaminant in the polluted soils before remediation in a decommissioning context
Multiscale Modelling of Radiation Induced Segregation
Irradiation produces in materials excess vacancies and self-interstials that eliminate by mutual recombination or by annihilation at sinks (surfaces, grain boudaries, dislocations).
It sustains permanent fluxes of point defects towards those sinks. In case of preferential transport of one componant of an alloy, the chemical composition is modified in the vicinity of the sinks: a Radiation Induced Segregation (RIS). Its modelling requires a good description of the alloy properties: its driving forces (derived from the thermodynamics) and its kinetic coefficients (the Onsager matrix). The objectif on this project is to combine (i) atomic models (Kinetic Monte Carlo simulations and Self-Consistent Mean Field), fitted on ab initio calculations, that provide the Onsager coeffcients and the driving forces and (ii) a Phase-Field modelling that will give a description of the evolution of the alloy under irradiation at much larger time- and space-scales. The approach will be applied to Fe-Cr and Fe-Cu alloys, already modelled at the atomic scale. RIS will be first modelled near grain boundaries, then near dislocation loops. Special attention will be paid to the effect of elastic stresses on the RIS.
Optimal management of a tertiary energy system
In the solution concerning residential or tertiary sites that consume and produce electrical energy , the objective is to optimize the use of energy based on economic criteria or constraints networks (adaptation of the consumption) without introducing perturbations of user comfort. The purpose of this position is to develop a solution for "optimal management of the use of solar energy in a tertiary building integrating EV charging stations and storage." according to three objectives:
- Minimize the cost of consumption based on a dynamic tarif - Maximize the use of solar energy - Minimize the power demand of the network. Taking into account the LCOS (levelised Cost Of Storage) of battery . The Post- Doc will contribute and participate in: - Specification of tertiary system - Development of algorithms for managing a tertiary system - Deploy and test the proposed solution.
Development of methods for U quantification in cells after exposure to uranium
This project fits into the transverse Toxicology Program, led by CEA, whose purpose is to address by multidisciplinary approaches, the potential effects on living organisms of elements of strategic interest to the CEA. The objective is to provide some understanding on the mechanisms of uranium toxicity and behavior, in connection with its speciation in cells. Indeed, the radionuclides speciation governs their bioavailability, accumulation, biodistribution, toxicity, detoxification mechanisms and their interaction at the molecular level.
The post-doctoral project (12 months) consists in:
- Developing methods to quantify U accumulated in the cells as well as endogenous content of trace elements after exposure of cells to uranium.
- Developing methods to determine the precise isotopic composition of U in the cells after their exposure.
The candidate will be in charge of developing chemical purification and measurement methods for precise elemental and isotopic analyses. The analyses will be performed using inductively coupled plasma quadrupole mass spectrometer (ICP- MS Q) or inductively coupled plasma multi- collection mass spectrometer of the latest generation (ICP- MS MC), to achieve the lowest level of uncertainties.
Synthesis of inorganic monoliths functionalized with nanoparticles
Since 2008, the "Institut de Chimie Separative de Marcoule" (ICSM) and specifically the "Laboratoire des Nanomateriaux pour l’Energie et le Recyclage" (LNER) has developped specific skills in synthesis routes and studies of porous materials (BET, TEM, SEM, SAXS).
This post-doctoral position is devoted to the synthesis of inorganic monoliths using high internal phase emulsion (HIPE) as soft template, and particularly to the functionalization of these materials with nanoparticles (NP).
The use of an emulsion in the procedure allows to consider innovative ways of functionalizing the material. For example, the oil-water interface in the emulsion may be the site of adsorption of nanoparticles of interest for a given application. In our case the goal is to prepare an emulsion with high internal phase (> 50% vol) stabilized by both surfactants (required for mesoporosity) and NP of interest to functionalize the macroporosity. NPs are chosen to cover liquid effluent decontamination (zeolite, nonatitanate, clathrate)
Evolution of the surface layers resulting from the physico-chemical interactions between low pH concrete and clays: experiments and modeling
The design of an industrial facility for storage of radioactive wastes in geological environment is an important issue taken into account in the French nuclear energy sector. In this context the cementitious materials are an important (packages, structures).
The main objective of the proposed study is to characterize alterations of the materials in the concrete-clay interfaces, caused by chemical exchanges. At the current stage, a comprehensive approach was initiated taking into account simultaneously the chemistry of the storage site and concrete considered for this application, based on commercial cements or innovative binders (low pH) formulated specifically. On these low pH materials in particular, questions remain as to their mineralogical and microstructural evolution. An experimental program (dedicated testing, microscopic characterization), supplemented by digital simulations, will increase the essential knowledge for use of these materials.
This project will involve both of the specialists of cementitious materials of the CEA, and researchers at the laboratory Hydrasa of the University of Poitiers.
Crystalline materials for the selective extraction of monovalent metal cations: understanding the link between the crystalline structure and the selectivity
The selective extraction of monovalent metal cations from aqueous solutions have complex compositions is a key step in many energy-related fields. In this work, specific adsorbents for Cs, to decontaminate effluents produced by the nuclear industry, and for Li, to extract this strategic metal for the development of batteries, will be studied. Due to their modularity in terms of porosity and structure, crystalline oxides (as zeolites) are promising for the selective extraction of such cations. With a view to understand the role of their microstructure on their sorption/desorption performances and mechanisms, identify the selective sorption sites within these crystal structures is crucial.
For that purpose, the objective of this research work is, on the one hand, to synthesize crystal structures allowing the selective sorption of Cs or Li. Then, by using fine characterization techniques at the atomic scale as well as structures reconstruction effort, we will identify the location of selective sorption sites within these materials and, in this way, better understand their sorption mechanisms and properties.
For this post-doctoral position, we are looking for a PhD in material science with strong skills in synthesis and characterization of crystalline materials by X-ray diffraction. Experience in the study of crystalline oxides, such as zeolites, would be an advantage.
Micro-energy sources for biomedical applications
There is a growing interest towards wireless implantable systems for in vivo biomedical applications. However, such implantable systems have a limited lifetime determined by the battery capacity. CEA LITEN is working on innovative miniaturized systems integrating an energy harvesting component with a rechargeable battery. This type of micro-systems will be used for powering sensors or other implantable medical devices. The post-doctoral researcher will work on the design, the fabrication and the characterization of demonstrators consisting of the energy harvesting component, the battery and a power management circuit. Numerical simulations could also be performed, with the help of specialized engineers. The characterization of the demonstrators and the numerical simulation results will allow the post-doctoral researcher to propose innovative solutions for optimizing the system. The post-doctoral researcher will work in a multi-disciplinary team, which requires strong abilities for team working and communication.
Nonlinear dynamic analysis of a reinforced concrete structure subjected to seismic loadings: Deterministic and probabilistic study of response spectra
The proposed work is based on the experimental campaign of the ENISTAT project and is composed of three parts:
1. Calibration and enhancement of the numerical model (5 months)
Based on the nonlinear numerical model that has been realized in CEA, the applicant will have to compare the results to those provided by the experimental campaign. The potential gaps will be interpreted and the model should be calibrated (and/or enhanced) to ensure a satisfactory accordance with the experimental results and observations.
2. Deterministic and probabilistic analysis of response spectra (5 months)
Based of the numerical model that will have been calibrated, the response spectra will be computed in given points. They will be compared the demand spectra prescribed by the design rules such as the EC8. Based on probabilistic methods that are developed in CEA for seismic applications, the uncertainties not only of the input parameters but also of the seismic signals will be taken into account. The induced variability of the response spectra will be quantified and discussed. One can notice that the knowledge of these data is particularly interesting since design rules in seismic engineering are based on them.
3. Study of the effect of the thermic brick elements
Thanks to the experimental results, not only experimental but also numerical, a discussion on the effect of the thermic brick elements will be realized with the aim to draw first conclusions on their effect on the overall structural behavior under seismic loading.
Development of a Metal Supported Cell for Hydrogen production by High Temperature Steam Electrolysis
The development of Metal Supported Cells (MSC) for High Temperature Steam Electrolysis (HTSE) constitutes an interesting innovation able to reduce the degradation of this component under operation. An increase in the cell life time would be a valuable contribution to cost reduction and is able at positioning HTSE as an alternative process to other hydrogen production technologies. However, some progresses in the elaboration of MSCs are still required. Within the current process, functional ceramic layers of the MSC are joined to the metallic substrate at elevated temperature (> 1000 °C). Mismatch of the mechanical properties of the materials as well as the reducing conditions fixed by the metal substrate during sintering lead to MSCs having insufficient electrochemical performances. The post-doctorate aims, on the one hand, at obtaining a better understanding of the mechanisms that occur in the multilayer structure during sintering and, on the other hand, at proposing and testing technological solutions able to improve to reliability of MSC elaboration.