Evaluation of Fluid-Structure interaction in multiple support cylinders of a liquid metal fast reactor

The support cylinder in a Liquid Metal Fast Reactor (LMFR) is a critical structural component essential for ensuring reactor stability and safety. Under extreme conditions, such as earthquakes, the liquid metal coolant significantly affects the added mass on the support cylinder, changing its modal frequency and vibration response. Previous research on the fluid–structure interaction of fast reactors mainly focused on the sloshing effect in rigid vessels. However, there is a gap in existing models for partially submerged, coupled cylinder systems in LMFRs that incorporate three-dimensional effects. This paper introduces a simplified fluid–structure interaction (FSI) mathematical model for a multi-cylinder system, based on potential flow theory, and employs a generalized single-degree-of-freedom (SDOF) system to simulate the dynamic characteristics of the support cylinder. By comparing experimental and numerical results, the model’s accuracy is validated with an error within 5% across multiple configurations. The paper examines the effects of water level changes, cylinder spacing, height-to-diameter ratio, and shape function choice on the added mass calculation. A three-dimensional correction formula for finite-length cylinders is proposed to improve calculation accuracy. The results show that the added mass coefficient increases with higher water levels and smaller cylinder spacing, while the height-diameter ratio has a nonlinear effect on added mass. This work provides a theoretical analysis and experimental verification of the FSI in LMFR support cylinders, which is important for the reactor’s seismic design and safety evaluation.