Study of embrittlement and thermal fatigue of stainless steels
In order to study the behavior of nuclear materials under dynamic stress, CEA Valduc wishes to develop a new device integrated into a glove box. For this purpose, a collaboration with CEA GRAMAT and an industrial specialist in the field has been set up. During the experiments conducted with thisdevice, some components are subjected to very high temperatures and the presence of gaseous hydrogen for a very short time.
Initially, different grades of austenitic steels were tested under these severe conditions and a prototype was ordered and received at the industrial site.
The study has three objectives. The first is the acquisition of new experimental mechanical and microstructural data at the micrometric scale from the previously exposed steel batches. The second concerns the microstructural analysis of thermal fatigue. Finally, the third and final objective is the integration of these new data into a numerical tool for microstructural evolution simulation aiming at reproducing the global effect of aging, in thermal and pressure cycles by coupling, for example, CALPHAD-type codes and the use of multiphysical COMSOL-type codes.
The work will take place according to the three components carried out in parallel. It will also be requested from the post-doctoral student in charge of this study to:
- participate to the implementation and monitoring of collaborations with recognized experts in the fields of embrittlement, thermal fatigue, and microstructural analysis,
- synthesize and publish, as far as possible, the results obtained in the form of various documents and publications in international journals or conference communications
Synthesis of high-nitrogen heterocyclic molecules
One of the CEA DAM's objectives is the design of new explosive compositions with optimized properties. As such, the search for new molecules of interest, likely to be integrated into innovative formulations, is a fundamental activity.
The objective of the post-doctorate is to synthesize, on a laboratory scale, energetic molecules with structures capable of meeting the specifications in terms of performance and insensitivity. These are mainly highly nitrogenous heterocyclic molecules (pyrazoles, triazoles, oxadiazoles, etc.). The work will include both the synthesis of intermediates, whether they are considered energetic or not, and that of the final products.
This approach is supported by modeling work carried out upstream, intended to set up tools to propose new structures and evaluate their properties by calculation. This subject will require, in interaction with the modeling team, using these tools and putting them to good use to guide the choice of targets that will be studied experimentally in the laboratory.
Hydrodynamic and Magnetohydrodynamic Modelling of HED Plasmas
In the context of fusion, magnetized FCI utilizes external magnetic fields that are compressed during implosion, thereby magnetizing electrons and alpha particles. This reduces transverse heat losses and improves hot spot confinement, enabling ignition at lower surface densities, with slower and more stable implosions. CELIA, a recognized leader in magnetized implosion research [Plasma Phys. Control. Fusion 64, 025007 (2022)], coordinates multiple international and national programs (EUROfusion, NLUF, LBS, NIF Discovery Science, ANR).
Recent large-scale experiments conducted at Omega have demonstrated record-breaking compressed fields (~10 kT) and a temperature increase in hot spots of approximately 50%, thanks to K-layer spectroscopy of argon doping in DD nuclear fuel, enabling the characterization of plasma conditions in the compressed core [Phys. Rev. Research 6, L012018 (2024)].
Upcoming approved experiments include:
• Omega (February and August 2026): control of radiative cooling via argon concentration; multi-dopant spectroscopy; magnetized spherical implosions.
• NIF (May 2026): with 20 times the energy of Omega, study of triton confinement through the analysis of angular-resolved time-of-flight spectra of secondary neutrons, as a probe of magnetic field intensity and topology.
• LMJ (April 2026 and Q1 2027): with laser drive energy equivalent to that of NIF, but with smaller targets, magnetized cylindrical implosions aiming for a compression 3 times greater than that of Omega and NIF; spectroscopy of the double-doped K-layer for spatially resolved core conditions. The interpretation and predictive design of these experiments require advanced 2D/3D MHD simulations, which will be entrusted to the postdoctoral researcher
Numerical simulation of nanosecond laser pulse interaction with porous dielectric material
The context of this work concerns mechanical damage of porous ceramics induced by laser irradiation. The latter excites electrons of the material (energy gain), which in turn modifies its optical properties and the laser propagation itself. The pores in the material bulk also modify laser propagation, giving rise to interference and enhancement in the electric field, which then accelerate the electron dynamics and the laser energy deposition. The latter induces temperature and pressure gradients that form the shock wave responsible for damaging the material. Describing this system therefore requires coupling hydrodynamics with electronic and laser dynamics. The objective of this postdoctoral research is to model and study this complex system. The first part of the work consists in coupling existing codes describing laser energy deposition and hydrodynamics. The obtained code will then be used to carry out physical studies and understand the interaction mechanisms. In particular, the influence of porosity characteristics on shock formation will be studied.
Development of an electromagnetic jet material characterization probe
The subject falls within the scope of non-destructive testing of the electromagnetic properties of materials.
The aim is to upgrade an existing experimental device based on the use of a radiofrequency probe that extracts the magnetic permeability of the material covering an object from the measured reflection coefficient. Solving the direct problem using numerical simulations allows us to establish charts that are used to solve the inverse problem. The sensitivity to material properties, spatial resolution, and measurement uncertainties of the current device are limited by the antenna. Recent studies have demonstrated the value of using an electromagnetic jet-based probe for characterization with sub-wavelength resolution. Based on this work, the objective is to design and build a new probe that meets the desired performance requirements. The candidate will be responsible for the design and simulation work and then for monitoring the production of the prototypes. He/she will also be responsible for testing these prototypes on reference objects to demonstrate their advantages over the current solution. The new probe will then be integrated into the current measurement system and process
The postdoctoral research will proceed in three main stages. The first will consist of studying the principle of electromagnetic jet antennas and proposing a probe design suitable for the measurement method. Commercial simulation software will be used for the design, followed by internal codes for the validation of the selected prototype. The second stage will involve the manufacture of the prototype, followed by tests with reference samples to validate the concept. Finally, the probe will be integrated into the test bench and the calculation and extraction chain..
In-situ 4D tracking of microstructural evolution in atomistic simulations
The exponential growth of high-performance computing has enabled atomistic simulations involving billions or even trillions of particles, offering unprecedented insight into complex physical phenomena. However, these simulations generate massive amounts of data, making storage and post-processing increasingly restrictive. To overcome this limitation, on-the-fly (in-situ) analysis has emerged as a key approach for reducing stored data by extracting and compressing relevant information during runtime without significantly affecting simulation performance.
In this context, tracking the four-dimensional (space and time) microstructural evolution of materials under extreme conditions is a major scientific challenge. Atomistic simulations provide a unique spatial resolution to analyze crystalline defects such as dislocations, twinning, vacancies and pores, which govern dynamic phase transformations, melting, damage and mechanical behavior. By capturing their spatio-temporal evolution, it becomes possible to study their statistics, correlations and collective effects in out-of-equilibrium regimes, leading to more accurate predictive material models.
This project builds on advances of the exaNBody high-performance computing platform and a recently developed in-situ clustering method in the ExaStamp molecular dynamics code at CEA. This method projects atomic information onto a 3D Eulerian grid to perform real-time clustering. The objective is to extend this approach to full 4D tracking, enabling the time-resolved monitoring of clusters. This will allow dynamic graph-based analysis of their evolution, including changes in size, shape and temporal behavior, providing new insights into microstructural dynamics at the atomic scale.
Spin-lattice interactions in Machine Learning assisted ab initio simulations
The scientific field addressed by this postdoctoral project lies at the intersection of ab initio molecular dynamics, machine learning, and the thermodynamic characterization of materials under extreme conditions. Traditional AIMD simulations are a powerful tool to study temperature- and pressure-dependent properties from first principles, but their high computational cost limits their widespread use. By developing and applying machine learning-assisted sampling techniques like MLACS, this postdoc aims to drastically reduce the computational burden while retaining ab initio accuracy. This enables the efficient exploration of phase diagrams in high-pressure and high-temperature conditions. This research contributes to both fundamental understanding and practical modeling of materials, offering high-impact tools for the scientific community.
Simulation of landslides and the associated water waves by a 3D code
Until now, tsunamis generated by underwater landslides were modelled at the CEA using a 2D long wave code (Avalanche) that was adapted to the computing resources available at the time but now seems obsolete in the literature. An initial post-doctoral study (2023-2025) showed that the 3D OpenFoam tool could accurately simulate a landslide and the associated waves in the generation zone. During this post-doctoral fellowship, a coupling between the CEA's ‘2D’ propagation code (Taitoko) and the 3D code was developed in order to propagate waves over long distances. The work carried out will be continued. The first objective will be to familiarise with the tools developed and to publish the work carried out on the 80 Mm3 collapse that occurred in Mururoa in 1979. The main objective is then to carry out simulations of potential collapses in the northern zone, bearing in mind that the main difficulty lies in defining the geometry of these potential collapses. The propagation of waves over long distances is simulated by a ‘2D’ tsunami code coupled with the OpenFoam code.
Preparation and characterization of an oxide/oxide composite
Fiber-reinforced ceramic matrix composites (CMCs) are a class of materials that combine good specific mechanical properties (properties relative to their density) with resistance to high temperatures (> 1000 °C), even in oxidizing atmospheres. They are typically composed of a carbon or ceramic fiber reinforcement and a ceramic matrix (carbide or oxide.
The proposed study focuses on the development of a low-matrix oxide/oxide CMC with suitable dielectric, thermal, and mechanical properties.
This study will be conducted in collaboration with several laboratories at CEA Le Ripault.