Abstract
Comparing with other industrial structures, the nuclear reactors needs strengthen safety standard. In this research we focus on the reactor internal which are main components in the nuclear reactor. The reactor internal are classified as seismic category I which requires complete level of the seismic analysis. The seismic analysis of the reactor internal is generally performed with the numerical method such as the FE method. The main purpose of the seismic analysis of the reactor internal is to identify the accurate dynamic behaviors, and it requires thorough inspection of the fluid-structure interaction between internals and inner coolant. Thus, it needs detailed analysis model which can reflect accurate dynamic characteristics of the reactor internal for obtaining the reliable results. However, a numerous number of degrees of freedom in the detailed FE model causes large computation costs, thus, it needs to reduce the size of the FE model for performing the seismic analysis. In this thesis, we suggest to apply the model reduction methods, which reduce the overall degrees of freedom of the total system, in order to perform the seismic analysis efficiently. The final purpose of this thesis is constructing the vibration analysis model of the reactor internal using the model reduction method which satisfies accuracy and efficiency. To develop this, researches are progressed as follows. First we constructed detailed FE model of the reactor internal. In order to verify the FE model, the modal test with the scaled-down model which reflects the geometries and boundary conditions of the original reactor internal is performed. Second, the model reduction methods using this thesis are reviewed and application method for the reactor internal is introduced. The validity of the model reduction method is verified with the simple numerical examples and the detail application method is suggested. Then, it is applied to the reactor internal in the APR (Advanced Power Reactor) 1400 and the system-integrated small modular nuclear reactor (SMART; System-integrated Modular Advanced ReacTor), and the reduced models of the reactor internal are verified in the static and dynamic problems. Finally, the seismic analysis was performed with the suggested reduced model which most satisfies efficiency and accuracy. With the seismic analysis model, the time history analysis is performed to extract important seismic responses at the specified locations. Moreover, the stress analysis is also performed to identify that the reactor internal satisfy the seismic design, and design modification is suggested to reduce the stress intensity at the support locations. As a result, the reduced model shows reliable results compared with the full model, moreover, it shows great efficiency by reducing total computation time. The reduced model is expected for applying other types of vibration analyses such as the flow-induced vibration analysis and loss of the coolant accident analysis, and it can contribute to the improvement of structural integrity assessment of the reactor.
