Advanced acoustic detection system monitoring nuclear power plant components

An acoustic event detection system is presented, which was installed at all four Units of Paks Nuclear Power Plant in 2002, and since that it was modified several times to follow technical developments. It monitors the whole reactor coolant system including its components. The original aim of the system was to monitor and detect loose parts. Fortunately loose part occurs rather rarely, but several events have been registered since the beginning of its operation. Event detection is based on Sequential Probability Ratio Test (SPRT), which is the fastest method in the sense it requires the minimum number of samples to find the event. It is demonstrated, that SPRT can detect events buried in the background noise. Monitoring system is fully automated, collecting all abnormal occurrences, i.e. deviation from normal operation, deviation from usual background noises, etc. We also demonstrate the typical spectra of the operation of different components. During the 13 years of operation flow induced vibrations of motor operated valves were monitored continuously, movement of the control rod driving mechanism were registered. System automatically records the start of the main coolant pumps detecting small size loose parts named debris. Sensitivity is demonstrated with automated registration of the water flowing from the control rod bank during outage of the reactor.