Ultrasonic Guided Wave-Based Online Monitoring of Selective Leaching in NPP Underground Piping

The feasibility of an ultrasonic guided wave pitch-catch method for online monitoring of selective leaching in underground pipes is investigated. In this method, ultrasonic guided waves propagate along the length of the pipe to detect leaching. Numerical simulations of the underlying wave propagation are conducted to study salient features of this detection methodology. It is found that reflection and refraction induced by a small heterogeneity, representing leaching damage, result in amplitude changes in the recorded signal. This change in the amplitude of the received signal may be used for leaching damage detection. The effect of measurement noise and damage index threshold on detection accuracy is studied for two suitable damage indices. It is shown that for a known noise-to-signal ratio, a suitable damage index threshold could be chosen to maximize the detection accuracy. This investigation indicates that guided wave pitch-catch could be used for online monitoring of selective leaching in underground pipes.