Résumé
During a Loss of Coolant Accident (LOCA), fuel rods are heated by the residual power. The resulting increase of internal pressure leads to a ballooning of the cladding which allows the fuel to relocate and, if there is a rupture, to disperse into the primary circuit.Here, we propose to assimilate the fragmented fuel to a granular medium and implement a Discrete Element Method (DEM) to model the behavior of fragments within the rod. The aim is to describe their relocation through the analysis of packing fraction along the rod. This model echoes previous DEM-focused numerical simulation works on fragment relocation. Some of these models have limitations in terms of representation which we aim to overcome by creating a realistic 3D model to describe the main features of the fuel rod during a LOCA: • The complex shape of the fragments; • The deformation of the cladding and the interaction of fragments with the inner wall; • The interaction of fuel fragments with fission gases and the confinement gas;The initial developments aimed to adapt the discrete element method and extend it to arbitrary polyhedral geometries, adopting a method based on sphero-polyhedra. This method allows to facilitate the contact detection stage, which is challenging to implement for complex geometries.Verification and validation test cases of the polyhedral DEM method have been conducted. They serve as benchmarks for applied simulations aimed at studying the effect of size and shape distribution of fragments on relocation in the case of a dry granular medium.Further developments are in progress to address the effects of fragment interaction with cladding walls and fission gases. Various coupling methods with DEM are being explored, and their selection is the subject of current research efforts.