Seismic Behavior Analysis On Nuclear Power Plant Buildings

In the recent two decades, due to the demand of improving energy structure and transforming of economic growth mode, our country has formulated guidelines to develop nuclear power, so we has built a number of nuclear power plant units in coastal provinces. But all previous nuclear power plant accidents represented by Fukushima nuclear disaster indicate that seismic design of nuclear power plant is crucial among nuclear safety issues. Fuel building and safeguard buildings areⅠclass items which directly related to nuclear safety. They are usually reinforced concrete structures mainly composed of shear walls and have several frames. They are surrounding the reactor building and have a complex structural form with characteristics against seismic resistance such as large space and many holes. Fuel building and safeguard buildings have significant nuclear safety duties, so whether they can maintain a structural integrity and normal function under earthquake action are of great importance. Therefore, this paper did the finite element modeling of typical fuel building and safeguard buildings, aiming at analyzing the vibration characteristics, seismic response under linear and non- linear circumstance of fuel building and safeguard buildings, and then provided some reference bases for aseismic design of relevant plants. The major research achievements obtained are as follows:1. The elastic model of the building structure was built based on shell element to study its vibration characteristics through model analysis. The analysis results indicate that the building structure’s first three modes of vibration behave as monolithic translation, while monolithic rotation begins to appear from the fourth mode, and many partial vibrations appear from the eighth mode, so more modes should be chosen during aseismic calculation to ensure that the sum participation mass of the horizontal direction reach 90% of the total mass. The X and Y direction have approximate vibration periods and participating mass ratios, which indicates that the stiffness of the building structure in two horizontal directions is almost the same. The vibration period worked out by model analysis is similar to the result of the empirical equation, so the vibration period of this kind of building structure can be estimated by the vibration period equation of high-rise shear wall structure in early designing stage.2. By three-dimensional seismic input to the elastic model of building structure, I obtained the displacement and acceleration response under operational safety earthquake by spectral analysis and time history analysis, and calculated the earthquake effect value of each floor so these parameters can be estimations of equipment seismic behavior analysis. The displacement results indicate that under spectral and time-history seismic input with a horizontal peak ground acceleration of 0.15 g, the maximum inter-story drift of structure system is only 1/1156, so it is in elastic phase. The analysis results of floor response spectra indicate that the acceleration of the floors has significant amplification near the vibration period of the structure, but attenuates fast in higher and low frequency, so equipment on each floor should avoid having the similar vibration frequency of the structure.3. First I tried to build elastic-plastic model of the shear wall by multi- layer shell. I verified the feasibility of modeling shear wall by multi- layer shell by setting up two examples and comparing the skeleton curve and stress state of corresponding displacement of analytical model and experimental model. Based on this verification, three-dimensional artificial ground motion whose response spectra fits the accelerate response spectra of present national nuclear power plant seismic design code was input into the building structure modeled by multi- layer shell. The analysis results indicate that under seismic motion with peak ground acceleration of 0.3g, which is 1.5 times of ultimate safety ground motion, fuel building and safeguard buildings are in weak nonlinear phase, the maximum inter-story drift of structure system is 1/549, which is about 21.8% of ultimate elastic-plastic inter-story drift of shear wall structures ruled by the national seismic design code, so the there is only slight damages in the structure system. The result of Pushover of the structure indicate that the building structure has a good ductility, and the base shear force when the structure yields is much large than the maximum value of the non- linear time- history analysis, so the structure still has a great safety capacity under ultimate safety ground motion.