Sensitive analysis of water levels and air intakes on natural frequency of AP1000 nuclear island building considering FSI effects

Abstract

AP1000 is an advanced generation III+ nuclear power plant which utilizes a series of passive safety features. The main component of AP1000 is nuclear island which consists of containment vessel, shield building and auxiliary building. Water storage tank and air intake are two of the most important components of nuclear island for cooling down the containment vessel when an accident happens. The fluid–structure interaction effects and the locations of air intakes may affect the vibration characteristics of the nuclear island. In a previous paper, the influence of water level and elevation of air intakes on dynamic characteristics of shield building was studied. A more detailed model of AP1000 nuclear island including auxiliary and internal structures should be built and analyzed to obtain more reliable results due to the complex shape and arrangement of AP1000.The purpose of this paper is to investigate the influence of various water levels and different locations of air intakes on natural frequency of the overall nuclear island of AP1000 by modal analysis considering fluid–structure interaction effects. The results of finite element analysis indicate that the first two natural frequencies decrease as the water levels increase while the 3rd and the 4th frequencies are almost constant, and the elevation of air intake has an insignificant impact on the natural frequencies of the nuclear island building. In addition, the height ratios of h1/H and h2/H also influence the vibration characteristics of nuclear island building. The variation of stiffness as location of air intake is very small compared to the integral rigidity of the overall nuclear island.