Leak detection in the primary reactor coolant piping of NPP by applying a beam-microphone

A microphone leak detection method has been applied for the inlet piping of ATR-prototype reactor Fugen. Further analysis shows that sensitivity and reliability of the microphone leak detection system cna be relatively improved via spatial selectively of the methods applied. In particular, the cross-correlation method can be applied to detect a small leakage at its early stage. However, application of such technique is limited due to significant distortion of the signals on the reactor site. As one of the alternative methods, a beam-microphone provides the necessary spatial selectivity and its performance is less affected by signal distortion. A prototype of beam-microphone has been developed and then tested in Oarai Engineering Center (JNC). The site test of the beam-microphone was carried out in the inlet piping room of RBMK reactor on Leningrad NPP (Russia). A leak imitator has been used to simulate the leakage sound with the equivalent leak flow rate of 1-3gpm; (0.23-0.7m3/h). An analysis showed that signal distortion would not seriously affect the performance of this method but the sound reflection would result in appearance of ghost sound sources. The test results showed that the influences of sound reflection and background noise were smaller at the high frequencies where leak location could be estimated with the angular accuracy of 5 degrees. This accuracy is within the localization accuracy required for the leak detection system. (author)