Seismic Performance And Fragility Analyses Of Water Intake Structure In Nuclear Power Station Based On OpenSees

As an important water supply facility of the cooling system, the water intake structure is the basic guarantee of the safe operation of nuclear power station. Therefore, seismic safety of the water intake structure is of much important significance. In this paper, seismic response performances of the water intake structure under strong earthquakes are investigated by use of the software OpenSees. The fragility curves of the water intake structure are built based on the structural reliability theory. The main contents and achievements of the thesis are as follows:(1) By use of the nonlinear program OpenSees with a fiber model for nonlinear reinforced concrete materials and a dynamic elasto-plastic model for soils, a two dimensional soil-structure plane strain finite element model is developed for the water intake structure and its surrounding soils of a nuclear power station. Based on the model, the dynamic elasto-plastic time history analysis is carried out and the seismic response and capacity of the water intake structure is investigated under strong earthquakes. The results show that the water intake structure and its surrounding soils exhibit large nonlinear deformations under the design basis earthquake. The soil deformation is mainly induced by shearing. The maximum internal force and the maximum shear demand capacity ratio occur at corners of the side wall and the bottom slab and at ends of the bottom slab, respectively. The inter-story displacement angle and the shear capacity of the structure can meet the requirement of seismic safety according to the seismic fortification criteria for nuclear power station. Moreover, there is an enough safety margin in the deformation and shear capacity of the structure.(2) The limit state response surfaces of the water intake structure are established by use of the response surface method and the reliabilities of the water intake structure are calculated with the central point method, design point method (JC method) and Monte-Carlo simulation method. Based on these results, the seismic fragility curves of the water intake structure are built. The results show that the calculating fragility curves of three methods are similar and the fragility of the water intake structure is determined by the inter-story displacement angle.(3) According to the seismic fragility model recommended by the nuclear regulatory commission (NRC) and the electric power research institute (EPRI), several seismic fragility curves with different confidences are built and structural high confidence of low probability of failure is calculated. The results indicate that the fragility curves with95%confidence are more conservative, while the mean fragility curves are moderate.