Resonant Metamaterials for high-frequency vibration mitigation in Nuclear Power Plants

Abstract

The paper explores the potential effectiveness of horizontally vibrating resonant metamaterials to mitigate high-frequency vibrations of critical equipment/components caused by vertically propagating horizontal shear waves. These components are housed in stiff and strong structures of high importance, such as the reactor vessel inside the reactor building of Nuclear Power Plants (NPPs). High-fidelity 3D Finite Element (FE) models of the reactor building with the resonant metamaterials embedded into the soil on the sides of the NPP reactor building in a strip-like configuration (1 x 6 x 22) are developed in the Real-ESSI Simulator. After describing the FE model, its individual components are verified. The preliminary analysis shows that properly tuned resonant metamaterials (i.e., resonant frequency at 19-20 Hz) with a total vibrating mass of only 4.3% of the NPP reactor building mass, can lead to 20% reduction of the in-structure response spectrum at the centre of the foundation, where the reactor vessel is located, at the critical vibration frequency of the reactor vessel of 20 Hz. The amplification effect of the metamaterials at lower frequencies, stemming from their in-phase vibration with the soil, could be avoided if they are designed as semi-active or active systems that vibrate exclusively at the desired frequency. Finally, it is shown that the effect of metamaterials in this high frequency range is very localized, vanishing rapidly within a distance of one unit cell, indicating that their geometric configuration could be optimized to increase their efficiency.