Development of Acoustic Leak Detection in a Primary Cooling System

Abstract

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 MP a and ~280 degrees C. In parallel with the experiments, noisy AEs have been measured on inlet feeder piping of the FUGEN 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 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 ~13 dB. The signal levels decay in a simulated inlet feeder pipe, rapidly at first, exponentially at the rate of 1.16 ± 0.06 dB/m after a distance of 1 m from a leakage point. The insulator does not affect these attenuation characteristics.

The level of continuous noisy AEs under the power operation is lower than electronic noise level of 5 μVrms. On the other hand, burst-type noisy AEs with large amplitude(< 2.5 mV) but short duration time (< 1 sec) are frequently detected during the heatup or cooldown process.