Electrical panels in Nuclear power plants are usually designed to be rigid enough to reduce seismic response. However, design dynamic loadings for nuclear power plant are not only seismic loadings. The airplane crash (APC) load is also important dynamic load for nuclear power plant equipments. If the electrical panels are rigid enough for seismic loadings, the higher-mode vibrations of local floors due to the airplane crash will excite resonant vibration of electrical devices inside electrical panels, and so, the panels could lose its electrical functions. In this study, a vibration isolation system is applied to the electrical panels in order to reduce high frequency vibrations. The system consists of vertical and horizontal isolation rubbers which support four corners of lower end of electrical panels. Using this system, acceleration responses of panels during high frequency excitation due to airplane crash and so on, are reduced less than floor response. However, the rocking mode vibration is excited during an earthquake, because of its predominant frequency. Therefore, in the vibration isolation design, it is important to consider coupled vibration of horizontal and vertical mode and set the natural frequencies in the range that avoids spectrum peaks of acceleration, peaks arising from both the impact vibration and the seismic wave. In this paper, the design method and the vibration test are presented.
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