This doctoral project involves the study of fuel assembly dynamics under flow and external mechanical excitation (such as earthquakes). Experimental results are available via the HERMES (full-scale) or ICARE (reduced-scale) hydraulic loops at the Cadarache CEA center, as well as macroscopic models (homogenization, porous media) reproducing the predominant phenomena and enabling core-scale simulations.
Nowadays, the maturity of numerical simulation and the performance of clusters enable simulations to be carried out at an intermediate scale between experience and current models by directly representing a reduced-scale assembly and the surrounding turbulent fluid in 3D. The ensuing problem is hydraulic-mechanical coupling in the core in the above mentioned situations where assemblies or fuel rods undergo motion imposed by their boundary conditions.
In this context, the subject proposes to carry out best-estimate calculations of a moving assembly (reduced size) immersed in a flow to extend experimental results beyond the measurements and improve our detailed knowledge of fluid-structure interaction mechanisms. In particular, we will seek to understand the damping induced by the fluid flowing around a structure on its vibratory characteristics and the influence of grids and flow velocity on the characteristics of the fluid force (added mass, stiffness, and damping). These simulations will also contribute to the robust and accurate calibration of the macroscopic models (which inevitably rely on heuristics) needed for current engineering studies, also opening up a way towards characterizing and quantifying the uncertainties associated with them.