In the framework of the contribution of nuclear power to a decarbonized energy mix, reactors safety is of paramount importance. In the event of an earthquake, dynamic loads experienced by a reactor core could lead to collisions between fuel assemblies. The presence of turbulent flow inside the core has a significant effect on the dynamic behaviour of the assemblies. Recent tests have revealed an additional effect of the flow on impact forces between structures, possibly caused by a high-speed fluid sheet phenomenon.

The objective of this thesis, divided into three parts, is to understand and characterise this high-speed fluid sheet phenomenon in the specific case of a fuel assembly geometry.
A first part will be dedicated to CFD simulations taking into account the deformation of the fluid domain mesh using the Arbitrary Lagrange-Euler (ALE) method [1]. In addition, ambitious experimental campaigns will allow measuring, as close as possible to the impact, the effect of structures displacement on flow velocity field (using optical methods such as Particle Image Velocimetry [2]) and the resulting impact forces. The findings will be translated into an analytical modelling of the phenomenon.

The candidate will be hosted by the laboratory leading work on fluid-structure interactions within CEA Cadarache research centre. He/she will be integrated into a research environment with international outreach (collaboration with George Washington University - USA), will publish his/her research outcomes in leading journals in the field, and will participate in international conferences.

[1] A computationally efficient dynamic grid motion approach for Arbitrary Lagrange-Euler simulations, A. Leprevost, V. Faucher, and M. A. Puscas, Fluids, 8(5), 2023.
[2] Longo, L., Capanna, R., Ricciardi, G., & Bardet, P. (2024). Threshold of Keulegan-Carpenter instability within a 6 × 6 rod bundle, Experimental Thermal and Fluid Science