Microfluidics applied to the separation of actinides in nuclear samples by chromatography
The main objective of this post-doctoral position is to develop a method for separating the fission products, plutonium and uranium in nuclear samples by chromatography with a resin volume of 200 µL or less. This project is structured around three research axes.
The first one consists in optimising the miniaturised separation method. The resin packing protocol, the pressure applied during the separation and the eluant compositions will be studied by comparing the chromatograms and by calculating the associated decontamination factors. These developments will be carried out using simulated samples first, and then with plutonium-containing samples. Control over the redox adjustment step will be necessary to maximize the decontamination factors. A second development axis will focus on the conception of a user-friendly system, minimizing interventions in the glovebox in order to reduce the user's exposition to ionizing radiation. The experience of the laboratory in terms of experimental setup miniaturisation and micro-fabrication will be useful for this post-doctoral position. The third research axis consists in applying the developments of the first two axes to the determination of isotopic composition of nuclear samples by TIMS or MC-ICP-MS with a per-mil level of uncertainty in a radiation-controlled laboratory.
Robust path-following solvers for the finite element simulation of cracking in complex heterogeneous media: application to reinforced concrete structures
Path-following (or continuation) procedures are used to describe the unstable responses of structures exhibiting snap-back or snap-through phenomena. These methods consist in adapting the external load during the deformation process in order to satisfy a control constraint, by introducing an additional unknown, the load multiplier. Several variants exist depending on the controlled quantity: degrees of freedom, strain measures, or variables related to energy dissipation.
In addition to enabling the tracing of unstable responses, a major advantage of these approaches lies in improving the convergence of incremental Newton-type solvers by reducing the number of iterations required. This gain often compensates for the additional computational cost associated with the continuation algorithm. Some formulations have proven both efficient and simple to implement.
However, no objective criterion yet allows one to determine which formulation is best suited for the simulation of reinforced concrete structures, where multiple dissipation mechanisms coexist along with a strong spatial variability of the material properties.
The proposed postdoctoral work aims to develop robust path-following algorithms for such structures, building upon previous research carried out at CEA. It will include a critical analysis of existing formulations, an evaluation of their performance (monolithic or partitioned solvers), followed by their implementation. Finally, representative test cases of industrial structures will be simulated to assess the gain in robustness and computational cost compared to standard solvers.
Experimental and Thermodynamic Modeling of Corium Phases Formed During Severe Nuclear Accidents (24 months)
During severe accidents in pressurized water reactors, uranium dioxide (UO2) fuel reacts with zirconium alloy cladding and the steel vessel, forming a mixture of liquid and solid phases known as "in-vessel corium". If the vessel ruptures, this corium interacts with the concrete raft, forming "ex-vessel corium". This phenomenon occurred in the Chernobyl and Fukushima severe accidents. To simulate these stages, multi-physics codes require accurate thermodynamic and thermophysical data for the various phases of corium. This project aims to fill the data gap through experimental measurements and modeling. The work will involve synthesizing samples, measuring liquidus/solidus temperatures and liquid phase densities, and characterizing samples using advanced techniques. Moreover, the laser heating setup combined with aerodynamic levitation (ATTILHA) used to acquire data will be improved. Experimental results will be compared with thermodynamic models (TAF-ID database), and discrepancies will be resolved using the CALPHAD method. Thermophysical data will also be validated using atomistic simulations and other measurement techniques.
Accelerated development of materials resistant to molten chloride salts
The accelerated development of materials is a major challenge for all industries, and corrosion resistance is all the more important for resource conservation issues. This project therefore aims to estimate the corrosion resistance of FeNiMnCr alloys in chloride salt for use in molten salt nuclear reactors, in collaboration with the University of Wisconsin, which has demonstrated extensive expertise in the accelerated development of materials for molten fluoride and chloride salt reactors. As part of this post-doc, dozens of samples of quaternary FeNiMnCr model alloys will be synthesised by additive manufacturing at the University of Wisconsin, varying the composition in order to map the entire composition tetrahedron as accurately as possible. These samples, with a NiCr model alloy corroded in a wide range of molten chlorides salt chemistries, will then be corroded at the CEA. The aim of these experiments is, on the one hand, to obtain a large database on the corrosion of FeNiMnCr alloys in a very short time (1.5 years) and, on the other hand, to screen the effect of a wide range of salt compositions on a model NiCr alloy. Finally, these experiments will make it possible to target the best materials for studying their corrosion mechanisms.
TOMOGLASS: Gamma Emission Tomography Applied to the Radiological Characterization of Glass Residues from the Cold Crucible Vitrification Process
The TOMOGLASS project aims to develop an innovative gamma tomography system capable of operating in high-activity environments to characterize in three dimensions the glass residues resulting from the vitrification process of nuclear waste. The objective is to precisely locate platinum-group inclusions, which are poorly soluble in glass, in order to improve the understanding and control of the process. The system is based on a compact gamma imager integrating high-resolution pixelated CZT detectors, pinhole-type collimation, and mounting on a robotic arm. It will enable multi-isotopic reconstruction using advanced tomographic algorithms. This project is part of the modernization of the La Hague facilities and the integration of digital technologies within the framework of the factory of the future.
The first phase of the project will consist in demonstrating the feasibility of implementing a spectro-imager prototype in a constrained environment, building on existing technological components: detection modules and acquisition electronics based on the HiSPECT technology, and image reconstruction algorithms developed at CEA-Leti. The work will focus on conducting a multi-parameter study through numerical simulations (Monte Carlo calculation code) to design an optimized measurement system, and to generate simulated datasets for various representative measurement configurations. Once the concept has been validated, the work will continue in year N+1 with the assembly of the prototype components and their integration on a robotic arm. Experimental tests may then be carried out to demonstrate the system in a representative environment.
Development of an innovative instrumentation architecture using an array of magneto-resistive sensors to create a fast tomography system for fuel cells
Developing an innovative instrumentation architecture using an array of magneto-resistive sensors to create a rapid tomography system for fuel cells.
The goal is to develop a TRL 4 demonstrator in the laboratory to demonstrate a proof of
concept on a low-temperature fuel cell stack. This will include four measurement boards
with several dozen of synchronized magnetic sensors for simultaneous acquisitions. Experimental results and a description of the instrumentation system will be published. Historical data will be used to validate current density resolution algorithms and compare their performance to solutions based on Physics Informed Neural Network. Estimated current density results will be used for an additional publication.
The instrumentation system will be integrated into a CEA test bench dedicated to optimal control, transient observation, fault detection and exploration of defect propagation phenomena. This approach will offer dynamic and non-invasive observation of current distribution in the fuel cell, thereby improving the understanding of its operation and facilitating the optimization of its performance and lifespan.
Synthesis, Characterization, and Molecular Modeling of M-(A)-S-H
The main hydration product of Mg/silicate cements is magnesium silicate hydrate (M-S-H), whose composition evolves with time and environmental interactions [refs 1,2], with Mg/Si ratios ranging from 0.67 to 1.5, variable water content, and potential Al incorporation. Atomistic models of M-(A)-S-H remain largely unexplored [ref 4], and most of their properties are still unknown, making it difficult to establish composition–property relationships.
This project aims to elucidate the atomic-scale structure of (alumino)silicate magnesium hydrates (M-(A)-S-H) by combining experimental techniques and atomistic simulations, and to estimate their mechanical properties. The study will focus on M-(A)-S-H compositions relevant to nuclear applications or new low carbon cement matrices.
Modelling and analysis of prospective scenarios for the deployment of hydrogen infrastructure in France and Germany
The use of hydrogen produced by electrolysis or of molecules derived from electrolytic hydrogen (synthetic methanol, synthetic kerosene, etc.) is one of the solutions envisioned to decarbonise certain sectors such as the steel industry and long-distance sea and air transport.
The development of a Europe-wide hydrogen transport infrastructure is considered to facilitate the development of electrolytic hydrogen production on the continent. This infrastructure could provide access to massive underground hydrogen storages unevenly distributed across Europe, facilitate exchanges between regions with high solar or wind energy potential and major industrial hubs and, in certain areas, limit the cost of reinforcing the electricity transmission network.
The goal of the CrossHy project is to analyse the possible deployment pathways for hydrogen transport infrastructure in France and Germany. Two complementary modelling tools (REMix, ANTARES) are going to be used and to develop a European-scale model and a regional-scale model of a cross-border-region.
Regular physical meetings between the French and German research teams are planned during the project; the post-doc will include a 3-month visit to Stuttgart to work and exchange with the DLR team involved in the project.
Decomposition of Fission Fragment Energy from Microscopic Approaches to Provide Input Data for the FIFRELIN Code
The FIFRELIN code (FIssion FRagment Evaporation modeLINg), developed since 2009 at the CEA, simulates the formation and decay of nuclear fission fragments. It contributes to the enrichment of the European nuclear data library JEFF, which is used for reactor simulations. The calculation proceeds in two steps: the generation of fission fragments (with their physical properties), followed by their decay using a Monte Carlo Hauser-Feshbach approach. At the moment of scission into two fragments, the total energy is split between kinetic energy (TKE) and excitation energy (TXE). The TXE is further divided into deformation energy and intrinsic excitation energy, which govern the emission of neutrons and photons. Accurate knowledge of both TXE and TKE is essential to improve FIFRELIN’s performance. Microscopic theoretical approaches (such as Hartree-Fock-Bogoliubov and the Generator Coordinate Method) are used and developed within DES to provide theoretical input supporting evaluated nuclear data. This postdoctoral position aims to use and enhance these models to gain a more detailed understanding of nuclear properties at scission. The desired candidate has several years of experience (3 years or more) in nuclear mean-field theory (such as Hartree-Fock-Bogoliubov, relativistic mean-field, etc.) or in the generator coordinate method.