Signature analysis of the primary components of the Koeberg nuclear power station

Abstract

In line with its commitment to safe nuclear power generation, the Koeberg Nuclear Power Station (KNPS) replaced the outdated vibration monitoring system with a modern on-line vibration monitoring system. This will allow plant personnel to monitor components on a continuous basis which will provide faster response time in the scenario of excessive vibrations of the primary components. This study focuses on the analysis of the vibration of the primary components of the KNPS by analysing the frequency spectra of the vibration signals of the primary components and comparing these to reference signatures obtained during similar operating conditions. The condition of the vibration sensors will also be evaluated. In order to obtain a deeper understanding of the vibration behaviour and hence vibration signatures of the KNPS primary reactor components, a simplified mathematical model of the primary components is developed, based on the system of elasto-dynamic equations. The equations are solved numerically and used to simulate the KNPS vibration monitoring system. The mechanical system is modelled. Time series are generated and Fast Fourier Transforms (FFT) are calculated to simulate the new KNPS monitoring system. In the simulation mechanical degradation of the primary components as well as sensor degradation is simulated. The purpose of this study is to indicate whether mechanical degradation has occurred in the primary components of the plant and to validate the vibration signals. At the same time the study aims to lay a foundation for future monitoring and interpretation of vibration signatures by simulating the vibration and the monitoring signals. It was found that the primary components had not been affected by mechanical degradation as no deviations in resonances were detected in the frequency signatures. A small number of vibration sensors were found to have deteriorated; hence replacement / maintenance was proposed. The mechanical model and the simulation of the monitoring signals proved to be useful to understand and interpret the vibration of the KNPS primary components.