In-operation modal analysis of containments using ambient vibration

► Ambient vibrations of four different containments were measured. ► Modal parameters of four different containments were extracted. ► At least one mode highly correlated to analytical mode was found for each containment. ► As many as four highly correlated modes were extracted using better equipments. The importance of preserving the structural integrity of a containment can never be overemphasized. Currently the structural integrity of the containment is evaluated periodically via various nondestructive inspection methods. However, these methods can only provide local integrity data, and cannot deliver continuous monitoring information on overall structural integrity. In this paper, the result of a feasibility study on utilizing ambient vibration measurements to monitor the structural integrity of a containment is presented. The ambient vibration testing was selected, because it can avoid the interruption of normal operation of power plants. For the purpose of the study, the ambient vibration of four different containments in Korea, i.e. Ulchin Unit 5, Wolsong Unit 2, Ulchin Unit 1, and Yeonggwang Unit 4, was measured and modal parameters were extracted via frequency domain modal analysis techniques. The experimental modes were then compared to the analytical modes estimated using finite element analysis to examine the correlation, and highly correlated modes were adopted in identifying structural parameters using a system identification method. The structural parameter selected in this study was the elastic modulus of the concrete, and the identified moduli were compared to design values and inspection results. The result shows the ambient vibration can be utilized in monitoring the structural integrity of a containment, though further extensive study needs to be conducted to identify and exclude the effect of ambient conditions such as temperature and humidity on resonant frequencies.