Yuanzineng kexue jishu (Feb 2023)
Study of Isolation Effectiveness of Nuclear Reactor Building with Three-dimensional Seismic Base Isolation
Abstract
In recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. In order to study the application of 3D seismic base isolation in nuclear power plants (NPPs), the new 3D combined isolation bearing (3D-CIB) composed of laminated rubber bearing with lead-core coupled with combined disk spring bearing (CDSB) was proposed. Four different combinations of CDSB were designed and employed as the vertical isolation component, based on the advantage that the constitution of CDSB can be flexibly adjusted according to its bearing capacity and stiffness requirement. CDSB and laminated rubber bearing with lead-core were respectively connected in series to form four kinds of 3D-CIB with different vertical stiffnesses, which was firstly applied to isolate nuclear reactor building from both the horizontal and vertical components of seismic motion beneath the raft foundation. The influence of different vertical stiffnesses of 3D-CIB on the 3D isolation effectiveness was investigated. A comparative study of modal analysis in terms of main frequencies and mode shape, and the seismic response in terms of acceleration floor response spectra (FRS), acceleration and relative displacement response was carried out, respectively. The results show that the main frequencies of the 3D isolated nuclear reactor building for the degrees of freedom of both translation and torsion are significantly reduced compared with that of the non-isolated structure, and the first mode of the 3D isolated superstructure is not purely horizontal motion along the x-axis but a combination of rocking and horizontal motion. 3D-CIB can effectively reduce FRS and acceleration response in both the horizontal and vertical direction. Overall, the horizontal isolation effectiveness of 3D-CIB is less affected by vertical stiffness, and the smaller vertical stiffness of 3D-CIB, the better the vertical isolation effectiveness is, while the horizontal and vertical displacement response of superstructure increases correspondingly, including the rocking effect. The concept of rocking rate is introduced to quantitatively analyze the rocking effect, and the decrease in the vertical stiffness may significantly increase the rocking, which cannot be ignored. Hence, the vertical stiffness of 3D-CIB should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. Besides, 3D-CIB always remains in a stable compressed state in the whole process of earthquake, so that the isolated superstructure has the stable robustness without risk of overturning. This study of 3D isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of NPPs in the future.
