Water experiment for assessing vibroacoustic beamforming gain for acoustic leak detection in a sodium-heated steam generator

Abstract

In an intent to improve the monitoring of steam generators, a technique based on vibration measurements is developed for the detection of a water leak into sodium. Background noise can mask the leak-induced vibrations. In order to increase the signal-to-noise ratio (SNR), a beamforming technique may be considered. In the purpose of studying the feasibility and the efficiency of this technique for the present configuration, experimental investigations have been performed on a mock-up composed by a straight cylindrical pipe coupled to a hydraulic circuit through two flanges. A sound emitter introduced in the pipe simulates the source to detect, whereas a flow speed controls the background noise vibrations. Beamforming is applied on the signals measured by an array of accelerometers externally mounted on the pipe. Two different kinds of beamforming are considered: the conventional (Bartlett) one and an advanced one based on SNR maximization (MaxSNR). After an analysis of the vibroacoustic behaviour of the mock-up, one studies the efficiency of the two beamforming treatments for narrow bands and broad bands.

Spatial coherence of pipe vibrations induced by an internal turbulent flow

“…One would then presume very weak correlation between sensors beyond 300 Hz, but this is not what was observed in Fig. 6 of Kassab et al [22]. Yet there is an important difference between the experiments in [22] and previous works in literature.…”

“…6 of Kassab et al [22]. Yet there is an important difference between the experiments in [22] and previous works in literature. The latter mostly focus on the pressure induced by a TBL on a rigid wall, whereas the former focuses on the pipe shell vibrations induced by the TBL.…”

“…This behaviour was observed in the frequency range [1kHz-3 kHz] for a flow rate of 140 l/s (4.5 m/s) as shown in Fig. 6 of [22]. Such a strong coherence significantly reduced the performance of the Bartlett beamforming approach, which relies on the assumption that the background noise is uncorrelated [29].…”

“…The current work has significant applications for vibroacoustic beamforming techniques. In fact, it was mainly motivated by unexpected results from beamforming measurements in [22], to detect sodium-water reactions in the steam generator unit (SGU) of a liquid sodium fast reactor (SFR). Sodium/water reactions can lead to severe damage if appropriate action is not taken quickly.…”

“…The numerical results by Moriot et al [28] showed that vibroacoustic beamforming using a fixed linear array of accelerometers on the external surface of the cylindrical shell can be used to localize an acoustic monopole, as well as to increase the signal-to-noise ratio when the vibratory background noise is uncorrelated. To validate these results, an experiment on a laboratory mock-up was performed by Kassab et al [22]. The experimental setup comprised a cylindrical pipe filled with a heavy fluid connected to a hydraulic circuit by two flanges (see Fig.…”