This PhD thesis is part of the optimization of nuclear fuel fabrication processes, which rely on the powder metallurgy of uranium dioxide (UO2) and plutonium dioxide (PuO2). These powders exhibit a hierarchical microstructure composed of crystallites forming rigid aggregates, themselves agglomerated into larger structures. The morphology and interactions between aggregates play a key role in the macroscopic behavior of the powders—particularly their flowability, compressibility, and agglomeration capacity—and directly influence the quality of the fuel pellets obtained after pressing and sintering. However, the experimental characterization of these aggregates remains complex and does not yet allow for the establishment of a predictive link between synthesis processes and morphological properties.
The objective of this thesis is to combine experimental and numerical approaches to achieve a detailed characterization of the aggregates in a reference powder. Experimentally, techniques such as Scanning Electron Microscopy (SEM), specific surface area measurement (BET), and laser granulometry will be used to determine particle size, roughness, and size distribution. In parallel, numerical simulations based on the Discrete Element Method (DEM) will be employed to construct a granular digital twin consistent with the experimentally measured properties. This digital twin will allow the reconstruction of the internal structure of the aggregates, the evaluation of interparticle adhesion forces, and the analysis of agglomeration and densification phenomena under controlled conditions.
The PhD will take place at CEA Cadarache within the Institute for Research on Nuclear Systems for Low-Carbon Energy Production (IRESNE). The student will be assigned to the PLEIADES Fuel Development Laboratory (LDOP), which specializes in simulating nuclear fuel behavior (from fabrication to in-reactor performance) and in multi-scale numerical methods. The work will be carried out in collaboration with the CNRS/LMGC in Montpellier, internationally recognized for its research on granular materials, and with the Uranium Fuel Laboratory (LCU – CEA Cadarache), which has extensive experience in the experimental characterization of uranium powders.
The PhD candidate is expected to demonstrate strong skills in numerical simulation and in the physical analysis of results. He will share its results through publications and conference presentations and will have the opportunity to learn or further develop various experimental and numerical techniques that can be applied in other contexts.In particular, the issues related to the physics of granular media — which constitute the core of this PhD — are of significant industrial relevance and are common to many other sectors handling powders, such as pharmaceuticals, agri-food, and powder metallurgy.

[Hebrard2004] S.Hebrard, Etude des mécanismes d’évolution morphologique de la structure des poudres d’UO2 en voie sèche, thèse de doctorat, CEA-LSG2M-COGEMA), 2004.

[Pizette2010] P. Pizette, C.L. Martin a, G. Delette, P. Sornay, F. Sans, Compaction of aggregated ceramic powders: From contact laws to fracture and yield surfaces, Powder Technology, 198, 240-250, 2010.

[Tran2025] T.-D. Tran , S. Nezamabadi , J.-P. Bayle, L. Amarsid, F. Radjai , Effect of interlocking on the compressive strength of agglomerates composed of cohesive nonconvex particles, Advanced Powder Technology 36, 2025.