In the hypothetical conditions of a reactivity initiated accident in a nuclear power plant, some
of the cylindrical rods, that contain the fuel, could break. If fuel fragmentation occurs, hot fuel particles and pressurized gas could be ejected out of the rod and then interact with the surrounding fluid. The consequences of this interaction are studied by IRSN (Institut de radioprotection et de sûreté nucléaire). The violence of this interaction depends particularly on the discharge rate of the fuel particles. The aim of this thesis, was to study this dynamics.We simulated the fuel particles and gas ejection dynamics by the flow of a dense granular material and a gas from a confined space toward an open space. We focused on the experimental
study of the stationary discharge of a silo composed of monodisperse spherical glass beads, with an orifice either lateral or at the bottom of the silo, with or without air flow. The measured parameters were the mass flow rate and the pressure along the silo, whereas the controlled parameters were the size of particles, the size of orifices, and the flow rate of air. To understand the underlying physical mechanism, discrete and continuous numerical simulations were also performed and compared to the experimental results. For the case of a lateral orifice, when the form of the orifice is rectangular, we identified two regimes that depend
on the ratio of width to height. For the case with air flow, we found that the flow rate increases significantly with the air flow. We used a simple physical model to describe the grains and gas ejection taking into account the pressure gradient imposed by the fluid on the particles around the orifice. This pressure gradient depends strongly on the permeability of the granular media, therefore the dependance of the flow rate on the particle size becomes important, unlike in the dry case. Finally, we performed a numerical study of the discharge of a bidisperse granular media from a silo. We showed that the flow rate can be described by a
simple mixture law on the particle density.