Computational analysis of flow-induced vibrations in fuel rod bundles of next generation nuclear reactors

As our energy demand is ever increasing, new and preferably, cleaner energy sources are being developed. One of the on-going developments are the so-called 4th Generation nuclear reactors, which are significantly (up to 50 times) more efficient than current reactors. In one of the designs of such a reactor the coolant is lead-bismuth eutectic. Due to its high density and the dense packing of fuel rods, flow-induced vibrations might lead to damage. Flow-induced vibrations is a global term to indicate that the vibrations are caused by the interaction of a structural component and a surrounding fluid flow. It can be encountered in a number of fields including nuclear, aeronautical, civil, mechanical and biomedical engineering. This research focuses on the numerical prediction of key parameters of flow-induced vibrations. In contrast to existing approaches, no coefficients have to be tuned in these simulations. The model, which was developed during this research, was shown to accurately predict resonance characteristics (such as eigenfrequencies and damping) of slender structures in axial flow. Moreover, the simulations captured all dynamics including static and dynamic instabilities of a flexible cylinder in axial flow. It was demonstrated that changes in flow pattern were crucial to accurately capture these domains. Even in the stable regime small-amplitude vibrations are occurring, caused by turbulence in the flow. These small-scale vibrations might lead to long-term damage. Those vibrations were successfully predicted by means of Large-Eddy Simulations. The only drawback is that those simulations are very computationally demanding. As the computational power is increasing quickly, these types of simulations are anticipated to play an important role in the design against flow-induced vibrations.