Plasma and Fusion Research

Volume 18, 2405068 (2023)

Regular Articles

The Effect of the Grain Size of Divertor's Cooling Pipe on the Capability of High-Frequency Ultrasonic Tests to Evaluate the Quality of the Bond between Divertor's Cooling Pipe and Armor
Mohammadjavad FARIDAFSHIN, Noritaka YUSA, Ryouji SUZUKI1), Takashi FURUKAWA1), Masayuki TOKITANI2) and Suguru MASUZAKI2)
Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, 6-6-01-2 Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan
Nondestructive Evaluation Center, Japan Power Engineering and Inspection Corporation, 14-1 Benten-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0044, Japan
National Institute for Fusion Science, 322-6 Oroshi, Toki, Gifu 509-5292, Japan
(Received 5 January 2023 / Accepted 2 July 2023 / Published 10 August 2023)


This study evaluated the effect of the grain size of the divertor's cooling pipe on the capability of high-frequency ultrasonic tests to evaluate the quality of the bonded interface between the divertor’s cooling pipe and armor. First, simple oxygen-free copper and copper-chromium-zirconium block samples with different grain sizes were prepared and measured by an ultrasonic microscope with a 35 MHz probe. The results of the measurements confirmed that the non-uniformity of backwall echoes increased with the grain size of the samples. Samples with large grains provided distinctive signals that can be clearly confirmed on the ultrasonic C-scan images. Subsequently, two bonded samples consisting of 2.5 mm oxygen-free copper bonded with a block of pure tungsten that meets the material specifications of tungsten for ITER component which mimicked the basic design of a divertor's cooling pipe and a monoblock, were measured to evaluate their bonded interfaces. One of the bonded samples bonded at a high temperature provided distinctive signals due to the enlargement of the grain of the oxygen-free copper. Results confirmed that the grain enlargement is the reason for reduced defect detection capability of the high-frequency ultrasonic tests as was suggested previously. This study also revealed that the enlargement of grain caused by improper manufacturing would be non-destructively detectable by high-frequency ultrasonic tests.


nuclear fusion reactor, non-destructive inspection, bonded interface, diffusion bonding, heat treatment

DOI: 10.1585/pfr.18.2405068


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