BRO-IA-GE: Multi-sensor instrumentation and hybrid modelling of ball milling processes
The Uranium Fuel Laboratory of the Institute for Research on Nuclear Systems for Low-Carbon Energy (IRESNE) at CEA Cadarache develops innovative tools to improve the understanding and control of nuclear fuel manufacturing processes. In the context of nuclear fuel cycle closure and the renewal of future industrial facilities, mastering powder processing operations has become a strategic challenge.
Ball milling is a key step in the production of UOX and MOX nuclear fuels, as it directly impacts powder homogeneity and particle size characteristics prior to pellet fabrication. Despite its industrial importance, the mechanisms of this process are still poorly understood due to the complexity of the fragmentation mechanisms and the interactions between particles with different properties.
This postdoctoral project aims to develop an in-depth understanding of milling processes through a combination of experimental instrumentation, signal processing, data analysis, and modelling. The successful candidate will rely on an instrumented experimental platform incorporating acoustic emission monitoring and high-speed imaging, as well as on an extensive experimental database currently being established using model materials such as alumina.
Particular attention will be devoted to multi-component powder systems in order to better understand the influence of powder properties on fragmentation, mixing, and homogenization mechanisms. The results will contribute to the development of predictive models and a digital twin of the milling process for real-time monitoring and process optimization.
The candidate will acquire expertise in advanced instrumentation, materials science, granular physics, artificial intelligence, and process modelling. These skills are highly transferable to many industrial sectors involving powders and granular materials, including energy, powder metallurgy, advanced ceramics, pharmaceuticals, and food processing industries.
Study of the Thermodiffusion of Small Polarons in UO2
The position is published on the CEA website at the following address:
https://www.emploi.cea.fr/job/emploi-post-doctorat-etude-en-ab-initio-de-la-thermodiffusion-des-petits-polarons-dans-UO2-h-f_36670.aspx
Calculation of the thermal conductivity of UO2 fuel and the influence of irradiation defects
Atomistic simulations of the behaviour of nuclear fuel under irradiation can give access to its thermal properties and their evolution with temperature and irradiation. Knowledge of the thermal conductivity of 100% dense oxide can now be obtained by molecular dynamics and the interatomic force constants[1] at the single crystal scale, but the effect of defects induced by irradiation (irradiation loop, cluster of gaps) or even grain boundaries (ceramic before irradiation) remain difficult to evaluate in a coupled way.
The ambition is now to include defects in the supercells and to calculate their effect on the force constants. Depending on the size of the defects considered, we will use either the DFT or an empirical or numerical potential to perform the molecular dynamics. AlmaBTE allows the calculation of phonon scattering by point defects [2] and the calculation of phonon scattering by dislocations and their transmission at an interface have also recently been implemented. Thus, the chaining atomistic calculations/AlmaBTE will make it possible to determine the effect of the polycrystalline microstructure and irradiation defects on the thermal conductivity. At the end of this post-doc, the properties obtained will be used in the existing simulation tools in order to estimate the conductivity of a volume element (additional effect of the microstructure, in particular of the porous network, FFT method), data which will finally be integrated into the simulation of the behavior of the fuel element under irradiation.
The work will be carried out at the Nuclear Fuel Department of the CEA, in a scientific environment characterised by a high level of expertise in materials modelling, in close collaboration with other CEA teams in Grenoble and in the Paris region who are experts in atomistic calculations. The results will be promoted through scientific publications and participation in international congresses.
References:
[1] Bottin, F., Bieder, J., Bouchet, J. A-TDE
Application of the Hybrid-High-Order (HHO) method for the treatment of non-local effects in crystal plasticity via a micromorph approach
Describing the behavior of materials at the crystalline scale is the subject of much academic research, and is of growing interest in industrial R&D studies. Classically, this description is based on behavior laws describing the local evolution of the material's microstructural state: (visco-)plastic deformation, dislocation density, etc.
The main driving force behind this evolution is resolved shear stress, the projection of the stress tensor on the slip systems.
The formalism of these local constitutive equations (as opposed to non-local constitutive
equations discussed hereafter) is now well established, whether we are considering
infinitesimal or finite transformations, and benefits from special support within the MFront code generator. Thanks to MFront, those constitutive equations can be used in various mechanical solvers at CEA (Manta, Cast3M , Europlexus , AMITEX_FFTP ) and EDF
(code_aster, Manta, Europlexus ).
However, the use of local constitutive equations does not allow to account for many effects.
The aim of the post-doc is to develop a robust numerical strategy for reliably solving
structural problems using non-local crystal plasticity laws, and guaranteeing the
transferability of the constitutive equations between the CEA and EDF codes.