Triangulation of Local Coolant Boiling by Cross-Correlating Acoustic Noise Signals

Unambiguous and early detection of anomalous coolant boiling in nonboiling liquid-cooled reactors, especially in liquid-metal fast breeder reactors, is of great significance from the viewpoint of reactor safety. Acoustic detection of boiling is promising but is often hampered by existing background noise. Cross-correlating noise signals may alleviate this problem and also locate the anomaly. The characteristics of the cross-correlation functions of acoustic boiling noise were investigated experimentally. A pair of hydrophones detected local boiling of water in a container tank. The nucleate local boiling was generated in the tank by electrically heating a small segment of simulated fuel rod. Measurements were taken in pure water as well as in a heterogeneous medium with simulated rod bundles. In general, acoustic boiling noise signals with duration times of <50 msec successfully located the boiling site from the observed peak shifts of the cross-correlation functions when the signals were used in the off-resonance frequency region.