Considering Gaps Between Tubes and AVBs for U-Shaped Tube Bundle in Steam Generators Using Seismic Linear Analysis Method

Abstract

Abstract Ensuring seismic resistance of the tube bundle of steam generators is very important. In order to predict the vibration behavior of the tube bundle, a linear analysis method was developed by modeling all the components of the tube bundle such as tubes and Anti-Vibration Bars (AVB). First natural frequency and its seismic response calculated using the linear analysis were very consistent with the seismic test results. However, since the calculated tube strain distribution was smaller than the results obtained from the test, we developed a nonlinear analysis model that can take into account gaps between tubes and AVBs. Natural frequencies and seismic response, however, cannot be obtained based on this nonlinear analysis. In seismic response evaluations, since focusing on the first order mode of the tube bundle is important, the strain of the tubes was assessed by simulating the deformation of the first order mode, based on a static analysis that uses horizontal inertial acceleration so that the seismic response can be determined by the linear analysis model. In this study, an improved linear analysis model was developed in which tubes and AVBs were connected by linear springs only at contact points. A nonlinear analysis model was used to grasp contact points when the tube bundle was deformed due to seismic load. First natural frequency and its stress distribution in the tube array calculated using the improved linear analysis model were very consistent with the test results obtained from U-shaped tube bundles with both triangular and square arrays. Therefore, it has been concluded that the improved linear analysis model can be applied to seismic analysis for both arrays in steam generator.