Vibration Monitoring of Nuclear Power Plant Containment Buildings During the Integrated Leakage Rate Test for Structural Condition Assessment

This study investigates the use of the operational vibrations produced during the Integrated Leak Rate Test of nuclear power plant containment buildings for further informing on its mechanical condition. The experiment is performed on a 1:3-scale containment building mock-up. The results show that meaningful vibrations were generated during the pressurization test. Different features were extracted from the vibration signals and analyzed as a function of the internal pressure. Experimental modal analysis was performed and demonstrated that several frequency peaks generated during the pressurization cycle effectively corresponded to the eigenmodes of the containment building. The identified operational frequency modes exhibited remarkable hysteretic dependencies on the internal pressure. The latter was phenomenologically described through a simplified two-dimensional (2D) finite element model of the vessel. Besides, a surrogate statistical model based on the Principal Component Analysis of the vibration data was proposed as a baseline and so detect abnormal behavior. Then, different synthetic damage scenarios were created by subtlety altering the recorded signals and ultimately substantiate the capability of the statistical model to detect these odd signals. Finally, conclusions were drawn regarding the possibility of using mechanical vibrations for assisting in the licensing process of nuclear power plants and monitor the structural health condition of in-service containment buildings.