Development of under-sodium three-dimensional visual inspection technique using matrix-arrayed ultrasonic transducer

We have developed an advanced under-sodium ultrasonic visual inspection tec hnique in order to observe in-vessel structures in a Fast Breeder Reactor ( FBR) whose reactor vessel is filled with opaque liquid sodium. The final go al of this work is achievement of resolution equivalent to that of an image obtained by optical fiber scope. The under-sodium ultrasonic visualizing system consists of a matrix-arrayed transducer and a signal-processing device. The matrix-arrayed transducer, in which 36x36 piezoelectric elements are arranged with 5 mm interval and s ealed by a thin metal diaphragm, can realize a 3-dimensional image with hig h resolution. Regarding signal processing, the 3-dimensional image syntheti c processing and the cross correlation processing for the purpose of improv ing S/N ratio of ultrasonic echoes are implemented on a high-speed parallel processor. Under-sodium imaging test was carried out, and it was confirmed that a S-dimensional image of the blind target, which was prepared without information beforehand, could be visualized clearly with less than 2.0 mm resolution under-sodium.