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• Low detectability of high-frequency ultrasonic tests for original screw pipe. • Interference of the echoes from the interface and original screw pipe's inner surface. • Adjusting the height of the grooves in the screw pipe reduces echoes' interference. • Employing step-like grooves in the screw pipe improves the detectability of the tests. This study investigated the applicability of high-frequency ultrasonic testing to inspect the tungsten-copper bonded interface between a divertor's mono-block and a cooling pipe called the "screw pipe." Mock-up samples simulating the interface were fabricated by diffusion bonding of a 2.5 mm thick oxygen-free copper plate to a 12 mm thick tungsten block that satisfied the ITER material specifications. After making the bond, grooves were machined on the oxygen-free copper side of the samples. High-frequency ultrasonic tests were performed before and after machining the grooves using an ultrasonic scanner with a 30 MHz probe in the immersion pulse-echo setting. The testing results showed that the original screw pipe has a low capability for inspection with high-frequency ultrasonic testing. The visibility of a defect at the interface decreased because of the reflection of ultrasonic waves from the slope of the grooves and interference by the echoes from the interface and the grooves' surfaces. These issues were addressed by proposing geometrical modifications for the grooves and testing with high-frequency ultrasonic testing. The proposed modifications considerably increased the visibility of a defect at the interface and improved detectability by high-frequency ultrasonic tests. [ABSTRACT FROM AUTHOR]

This study evaluated the applicability of a high-frequency ultrasonic test to the inspection of the bonded interfaces between a divertor monoblock and a cooling pipe. This study prepared a tungsten block bonded with 1 mm of oxygen-free copper and 1.5 mm-thick CuCrZr plates, which simplifies one of the fundamental designs of a divertor: a tungsten monoblock bonded with a cooling pipe with a copper interlayer. The samples were fabricated using a high-temperature vacuum furnace for diffusion bonding. A high-frequency ultrasonic immersion test using a 30 MHz probe was performed from the CuCrZr surface to simulate inspecting the interface from inside the pipe. Ultrasonic images obtained by the test were consistent with the actual bonding condition revealed by sectioning the samples; whether a flaw exists on the interface between CuCrZr and the oxygen-free copper or that between the oxygen-free copper and tungsten was clearly distinguished. The results of this study also suggested the possibility of detecting the growth of crystal grains caused by improper bonding such as too high bonding temperature. [ABSTRACT FROM AUTHOR]