This thesis focuses on the study of droplet fall in free volumes, as part of the continuous improvement of the physical models in the CATHARE code, used for safety studies of Pressurized Water Reactors. The current models are based on the work of Ishii and Zuber, who model the fall velocity of droplets in a two-phase fluid. The objective of the thesis is to refine the precision of this model by incorporating additional parameters and validating it through experiments such as those of Dampierre and CARAYDAS. The PhD candidate will be required to develop a more representative mechanistic model, based on experimental data or CFD simulations if necessary. The innovation lies in developing a more accurate model of droplet fall processes, paving the way for specific applications such as spray modeling, and thus contributing to the validation of the CATHARE code in additional fields.