In Pressurized Water Reactors (PWRs), the fuel consists of uranium oxide (UO2) pellets stacked in metallic cladding. During a Loss of Coolant Accident (LOCA) scenario, the rapid temperature increase can cause deformation and sometimes rupture of these claddings. This phenomenon can potentially lead to the ejection of fuel fragments into the primary circuit. This phenomenon is known as FFRD (Fuel Fragmentation, Relocation, and Dispersal). Since the cladding is the first safety barrier, it is crucial to evaluate the amount of dispersed fuel. Experimental studies have shown that the size, shape of the fragments, shape of the breach, and internal pressure significantly influence the ejection. However, the speed of the initial depressurization phase makes direct measurements difficult. Numerical approaches, particularly through fluid-grain coupling (LBM-DEM), offer a promising alternative. The IRESNE Institute at CEA Cadarache, through the PLEIADES software platform, is developing these tools to model the behavior of fragments. However, the compressibility of the gas needs to be integrated to accurately reproduce the initial depressurization. In this context, the laboratory M2P2 of the CNRS, a specialist in modeling compressible flows with the LBM method and developer of the ProLB software, brings its expertise to integrate this effect. The thesis therefore aims to design and improve a compressible model in the LBM-DEM coupling, to conduct a parametric study, and to develop a 3D HPC demonstrator capable of leveraging modern supercomputers.
This CEA thesis will be conducted in close collaboration between the Fuels Research Department (DEC) of the IRESNE Institute at CEA Cadarache and the laboratory M2P2 (CNRS). You will be primarily located at M2P2 but will make regular visits to CEA within the Fuel Simulation Laboratory, to which you will be affiliated. The approaches developed in this thesis ensure a high scientific level with numerous potential industrial applications both within and outside the nuclear field.