Vibration- and pressure signals as sources of information for an on-line vibration monitoring system in PWR power plants

Higher demands with regard to the safety and reliability of reactor primary components require methods to get an idea of the mechanical state of the plant at any time during operation and to recognize failures already in their developing phase. Reactor vibration monitoring systems are being developed which are based on the analysis of vibration signals, neutron noise and pressure fluctuation signals. The special role vibration and pressure signals can play in such a system is investigated by the analysis of extensive preoperational tests at different PWRs. The theoretical foundation for the application of these signals to vibration monitoring are developed in the special case of the Stade nuclear power plant. The pressure vessel of this reactor performs pendular and verical vibrations. They are excited mainly by pressure fluctuations generated by the coolant flow, by standing waves, or by the revolution of the coolant pumps.

For interpreting the spectra measured during the preoperational test and during power operation and for clearing up changes of these spectra, which will signalise incipient failures, model investigations are of predominant importance. Two mechanical models, a pendular and a vertical one, simulate the two kinds of vibration sufficiently which can be seen in comparing the calculated frequency response with the measured vibrations.