Development of acoustic leak detection in a primary cooling system

Developments have been made on quick and early leak detection, especially for pressure-tube-type reactors, using acoustic emission (AE) sensors. Laboratory experiments have been conducted to clarify characteristics of AE associated with leakage of water at 7 MPa and approximately 2800C. In parallel with the experiments, noisy AEs have been measured on inlet feeder piping of the FUGEN reactor under normal reactor operation. Signal levels for leaks through circular holes increase proportionally with the square root of leak rate. The signal levels for leaks through circumferential cracks, however, show somewhat complicated characteristics, and are approximately 4 - 7 dB higher than the corresponding values for leaks through circular holes for a given leak rate. An asbestos heat insulator reduces the signal levels by approximately 13 dB. The signal levels decay in a simulated inlet feeder pipe, rapidly at first and exponentially at the rate of 1.16 +- 0.06 dB/m after a distance of l m from a leakage point. The insulator does not affect these attenuation characteristics. The level of continuous noisy AEs under power operation is lower than electronic noise level of 5 μVsub(rms). On the other hand, burst-type noisy AEs with large amplitude (< 2.5 mV) but short duration time (< l sec) are frequently detected during the heatup or cooldown process