This thesis is part of the general framework of safety studies associated with Severe Accidents in Sodium-cooled Fast Neutron Reactors. More specifically, it focuses on the modelling of corium debris beds and associated phenomena, which are specific to this reactor technology. In particular, it aims to produce physical models describing the self-levelling of these beds by following an upscaling approach based on the so-called volume averaging method. Based on the results of previous work, and on a simulation tool coupling LBM (Lattice Boltzmann Method) and DEM (Discrete Element Method), the proposed research will follow a two-scale approach. First, the phenomena of interest will be simulated at the pore scale, selecting the most significant closure problems. It will be followed by the proper upscaling to propose new physical laws for the most influential effective properties of the debris bed.
The work carried out here in the context of the safety of sodium fast reactors is generic and the establishment of the methodology for determining closure relationships (in this case, effective properties of the medium) for a larger-scale numerical tool is innovative and will find applications in many other contexts dealing with problems related to fluid/grain interactions.
This work participates in the revival of nuclear power with a flourishing of start-ups based on sodium reactors and collaboration with Japan on the safety of this type of reactor.
A master internship is proposed by the team in addition to the thesis.