Description of the evolution of grain size and dislocation density during ODS steels consolidation
Steels reinforced with a dispersion of nanometric oxides (generally referred to as ODS steels) are currently considered especially as potential material for combustible cladding for 4th generation reactors. Up to now, these materials are conventionally produced by powder metallurgy. The evolution of the microstructure during processing is not well described, yet. Recent work in the laboratory has focused on the evolution of nano-precipitation during processing. The objective of the post-doctoral work is therefore to refine the description of this evolution, more precisely with regard to the grain size and the density of dislocations. This subject combines an experimental approach, through analyses in electron microscopy and X-ray diffraction, and a numerical approach, aiming to define an optimized method for the treatment of the evolution of dislocations.
Stability of the oxide/metal interface of a coated 6061-T6 aluminium alloy
The aluminium alloy, named 6061-T6, is used as core component for the Jules Horowitz French experimental reactor (RJH). In order to improve the corrosion resistance, and to prevent the alloy from wear degradation, a coating is deposited at the surface of the alloy. The coating layer that is 50 µm thin is obtained by oxidation of the aluminium alloy.
The RJH core component will be subjected to neutron irradiation that may modify the microstructure of both the 6061-T6 alloy and the coating layer. Concerning the 6061-T6 alloy, the irradiation damages are well known: neutron irradiation induces the formation of dislocation loops, and causes the dissolution of the nano-precipitates. However, the effect of irradiation on both the coating layer and the interface metal/oxide remains unknown. One of the deleterious effect that may occur in reason of irradiation could be the peeling of the oxide coating and consequently the loss of the corrosion properties. Thus, the understanding of the irradiation response of the coating layer remain a key issue to guarantee a safe use of the coated aluminium alloy. Therefore, the aim of the study is to characterize the irradiation damage of ion irradiated coated aluminium alloys.
Modeling of the spent fuel alteration mechanisms in a water-saturated environment with temperature effect
Modeling the alteration of spent nuclear fuel in the eventuality of an underwater interim storage in pools or a deep geologic disposal is essential for long-term prediction. In the event of a failed spent fuel assembly, corrosion processes can lead to a deterioration of the failed rod and to a radionuclide release into water. A geochemical model coupling chemistry to transport (reactive transport) was the subject of first developments in connection with deep geological disposal conditions using the CHESS-HYTEC code developed by the Ecole des Mines de Paris. This model makes it possible to take into account the main alteration mechanisms and associated kinetics while relying on robust thermodynamic data. It remains important to pursue these developments by studying the effect of temperature between 20 and 70 °C. Adapting this model to other alteration conditions like an underwater of spent fuel in dedicated pools for several decades is also a short-term objective.
Wood modifications by supercritical CO2
In order to replace current high environmental impact construction materials, CEA leads research work on chemical functionalization of wood (from French local forests) to improve its properties and make them a viable substitute of these construction materials or imported construction wood.
In this frame, chemistry under supercritical CO2 appears to be an efficient way to carry innovative chemistries while liùmiting the environmental impact & VOCs emissions of such processes.
Thus, you will be in charge of the development of new processes of chemical modification of local wood species under supercritical CO2. You will lead the research project by perfroming the state of the art, making technical propositions (around the adapted functionalization chemistries), carrying out the eperiments & the characterizations and will be in charge of respecting the deadlines & redacting the associated deliverables.
Use and extension of the Alien solver library with the proto-application Helix
First, the post-doc candidate will have to integrate the solver Library Alien into Helix to carry out performance and usability assessments in iterative or direct solver configuration. These assessments will be done on different computer architecture from desktop computer to national supercomputer with thousands of cores.
In a second time, the candidate will deal with the possibility to add new functionalities in the Alien library to solve non-linear systems composed with equations and inequations to be able to solve, in an HPC context, mechanical problems like phase field problem or contact problems, problems often still opened in the community. The results will be compared to the classical test cases and benchmarks of the state of the art in the domain.
The candidate will join the Helix development team, formed by 3/4 developers for the moment in the laboratory LM2S (15 persons). A transversal program between CEA directions finances the post-doc and the candidate will collaborate with the Alien library developers at the DAM of CEA.
Modelling of valley winds by statistical downscaling
To model and monitor atmospheric emissions in an area with significant relief, it is essential to represent the winds at the scale of this relief. Cadarache's operational meteorological model only has a horizontal resolution of 1km, which does not allow it to resolve the orographic effects of the valley.
However, obtaining simulation results with a high resolution model requires calculation times that are still incompatible with the constraints of operational weather forecasting (6 hours of calculation on our servers for 1 hour of forecast for Cadarache in 2020). This constrains the horizontal resolution of the calculations and does not make it possible to resolve the orographic valley effects.
The object of the post-doc is therefore to develop a downscaling model applied to a 3D mesh of the valley, with a sufficient resolution to, at the same time, model the aerology of the valley and follow a pollution plume using an atmospheric dispersion model. It will be implemented through the use of an artificial neural network, the learning of which will be based on measurements of local climatology and aerology, supplemented by synthetic data using a local high-resolution model.
The candidate will work within a small, attentive and benevolent CEA team while remaining connected to university research via the Toulouse Aerology Laboratory. He will be able to both become a specialist in applied research in the meteorological field and acquire digital and scientific skills that can be used in business.
Optimization of energy transition scenarios through a dynamic Life Cycle Assessment approach
The modelling of the energy transition, with a projection until 2050 and adaptable to different countries or strategies, is complex in terms of LCA because it involves many parameters:
- a dozen possible energies, with evolutionary inventories of construction of electricity generation/storage infrastructure
- a difficulty to estimate the future of technologies for a given sector
- electricity generation in connexion with national consumption
- very contrasting scenarios, including more or less rapid increases in renewables and a decrease in nuclear power, offset or not by gas-fired combined cycle power plants
- a need to provide for several forms of electricity storage depending on the size of the unmanageable energy stock, with power levels depending on the storage time
- the correlation or not of storage power with the level of interconnection of European electricity networks.
The work will consist of analysing the inventories available in the Ecoinvent database linked to Simapro, modifying them according to the foreseeable technologies for the medium term, continuing modelling in Python language to include all the parameters.
The objective is to determine the best possible environmental trajectories for the French energy transition.
Modelling of uranium precipitation kinetics as a function of pH. Application to fluidized bed reactor
The Orano plant in Niger (Somaïr) precipitates its uranium concentrate in a fluidized bed reactor by adding sodium hydroxide. The concentrate obtained contains around 6% sodium which leads to converter penalties. Orano carried out tests at the end of 2019 on a fluidized bed in the laboratory to change the operating point of precipitation and preferentially form UO3 via a change in pH. To refine the management of the industrial unit, it is necessary to model the precipitation reactions of uranium. The candidate will have to propose and calibrate a competitive precipitation model for Na2U2O7 and UO3 based on the equilibrium constants and reaction kinetics, as a function of the pH within the reactor. In particular, the model should make it possible to understand the impact of pH on the distribution of the two main species identified in the concentrate: Na2U2O7 and UO3. This chemical model should serve as input to an existing physical model of the fluidized bed reactor. An extension of the model to other precipitation reagents, in particular magnesia, could also be studied.
Synthesis and structural analysis of reference uranium minerals for the identification of uranium-bearing phases in mining environment by TRLFS.
In the frame of the collaborative project between the ICSM , CEA and Orano, a study is conducted in order to detect and identify minerals containing uranium (VI) by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS). This technique showed its efficiency in order to identify the presence of uranyl in natural assemblies through the probing of the local environment of uranium. However, it requires the establishment of a database from synthetic and natural samples fully characterized. Therefore, in order to achieve this goal, we intend to synthesis, and thoroughly characterize a variety of compounds containing uranyl groups within the crystal structure. We can cite the families of oxi-hydroxide, sulfate, and silicates based compounds. Then, TRLFS spectra will be collected in order to complete the database and to evidence the impact of the local structure of uranyl cation on the intensity and the position of the emission bands. The obtained data will be also compared to a collection of natural samples.
Dynamic monitoring by light scattering of mass transfer between two phases in multiphase flows
The understanding and the modeling of recycling processes studied at CEA, require the measurement of both local and average properties of multiphase flows involved in chemical engineering devices. Moreover, as the R&D studies are generally conducted on small-scale experiments, access to these quantities is often difficult, especially considering that measurement methods should not disturb the observed system. In this context, optical methods, associated to extensive and rigorous physical simulations of light/particles interactions, are particularly relevant and, accordingly under specific developments since several years. Therefore, the DMRC/LGCI (CEA Marcoule), in collaboration with the laboratory IUSTI (CNRS and Aix-Marseille University), develops two optical interferometric techniques suitable for R&D studies: the Digital In-line Holography (DIH) and the Rainbow Refractometry (RR). Previous works have shown that DIH allows a simultaneous measurement of 3D-positions, shape and size of flowing particles, even considering astigmatic geometries, while RR gives access to the size and refractive index of each particle or of set of particles, which considering linear optics is directly linked to their composition. This study aims to go further in multiphase flows characterization with these two technics by following three main objectives: 1) propose original solutions for the characterization of materiel compositions thanks to DIH, 2) deepen inverse methods in RR to allow the study of clouds of particles with variable compositions and to take into account gradients of concentration around a sessile drop, 3) evaluate the relevance of these technics for lab on chip systems.