Supplementary development and close-to-reality testing of a novel technique for complete ultrasonic inspection of the nozzle field of the spherical bottom of BWR pressure vessels

The results of two measuring campaigns in a test stand using the phased array technique, and the subsequent on-site measurements in the spherical pressure vessel bottoms of the Brunsbuettel and Kruemmel reactors have shown that the phased array technique allows a significant enhancement of the testing performance in the bottom nozzle field. The enhancement does not reduce the sensitivity usually achieved for incipient cracking detection in the inner wall of the vessel bottom. Mechanical strength analyses indicate that crack formation is to be expected primarily at the inside surface, in the area of the control rod or instrumentation channel. (orig./DG)