ULTRASONIC CHARACTERIZATION OF THE RADIUS OF CURVATURE AT THE ROOT OFA SURFACE-BREAKING AFS MARK

An ultrasonic method is proposed for estimating the root radius of cur vature of an abnormal fuel support (AFS) mark in a CANDU pressure tube . The method is based on characterizing the diffraction pattern result ing from a bulk shear wave impinging on the AFS mark root. To aid in t his study, a new type of ultrasonic reference block was developed for measurement of the diffraction pattern resulting from a mode-converted shear wave incident on a corner of finite radius at a metal-water int erface. Results on a set of simulated anomalies in a pressure tube spe cimen indicated that the root radius of a surface breaking anomaly can be estimated to within +/-25 percent, in the 70-400 mu m range.