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.
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.
Tools and diagnostic methods for the reuse of electronic components
The Autonomy and Sensor Integration Laboratory (LAIC) at CEA-Leti has the primary mission of developing sensor systems for the digitalization of systems. The team's activities are at the interface of hardware (electronics, optronics, semiconductors), software (artificial intelligence, signal processing), and systems (electronic architecture, mechatronics, multiphysics modeling).
In a context of exponential growth in electronics and scarcity of resources, the reuse of electronic components from end-of-life systems represents a promising avenue to limit environmental impact and support the development of a circular economy. The objective of this project is to develop an advanced diagnostic methodology to assess the health status of electronic components, particularly power components, to reintegrate them into a less constraining second-life cycle.
The postdoctoral researcher will be tasked with developing a comprehensive approach to evaluate the reuse potential of electronic components, with the aim of reintroducing them into second-life cycles. This will include:
- Identifying relevant health indicators to monitor the performance evolution of components (e.g., MOSFETs, IGBTs, capacitors, etc.);
- Setting up test benches and sensors adapted to measure electrical, thermal, or mechanical parameters, with the goal of detecting signs of aging;
- Analyzing degradation modes through experimental tests and failure models;
- Developing algorithms for predicting the remaining useful life (RUL) adapted to different usage scenarios;
- Contributing to scientific publications, the valorization of results, and collaboration with project partners.
Analysis of Gas Effluents for More Eco-Responsible Plasma Etching Processes
Traditionally used fluorinated gases, such as CF4 and C4F8, exhibit extremely high Global Warming Potentials (GWPs), significantly contributing to climate change. To address these environmental challenges, the project aims to promote the use of alternative low-GWP gases in combination with efficient exhaust abatement systems at the reactor outlet, while maintaining high-performance plasma etching processes. In this context, the postdoctoral researcher will be responsible for the analysis and characterization of gaseous species in an industrial plasma etching reactor using mass spectrometry. These measurements will be compared with the gas effluent at the outlet of the pumping and abatement systems. The main objectives are (i) to quantify the Destruction Removal Efficiency (DRE) of high and low GWP fluorocarbon gases during plasma processing and within the pumping and abatement stages, and (ii) to identify and propose innovative, environmentally responsible alternatives to minimize the release of high-GWP gaseous effluents.
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.
Multipoint initiation of explosives. Experiments and simulations.
The design of high-performance and increasingly safe systems requires new solutions for initiating the explosives that make up their charge. One possible approach is to replace the electrical ignition of detonators with optical ignition in order to eliminate the risks associated with parasitic electrical sources.
Another possible way to improve safety is to use multipoint initiation so that the explosive only detonates when all initiation points are activated synchronously.
The objective of the postdoctoral contract will be to conduct an in-depth study of the mechanisms governing multipoint optical initiation. To this end, after conducting exhaustive bibliographic research, the candidate will propose the most relevant configurations and test them both experimentally and by performing hydrodynamic simulations using a code developed at the CEA. Understanding the phenomena involved is essential in order to be able to choose an initiation configuration suited to each need.
Diamond-based electrochemical sensors for monitoring water pollution in urban environments
This postdoctoral position is offered by CEA List as part of the European UrbaQuantum project ("A novel, Integrated Approach to Urban Water Quality Monitoring, Management and Valorisation"), part of the HORIZON-CL6-2024-ZEROPOLLUTION-02 call for projects. The main objective of this project is to develop, in response to climate change, sensors, models, and protocols for better management of the water cycle in urban environments.
At the Sensors and Instrumentation for Measurement Laboratory (LCIM)of CEA List the postdoctoral fellow will contribute to the development of electrochemical sensors based on synthetic diamond and associated measurement protocols for the detection of pollutants such as pharmaceuticals, heavy metals, PFAS, and pesticides. These sensors will be miniaturized and integrated into a microfluidic cell, in partnership with CEA-Leti, then tested under real-world field conditions.