In-bore ultrasonic testing of cooling pipes in lower divertor cassette of JT-60SA

We have developed an in-bore ultrasonic testing (UT) tool to inspect piping welds from inside the pipes of the inboard target in the first actively-cooled divertor cassette covering a 10 degrees sector in the toroidal direction in JT-60SA. Because the cooling water pipes were enclosed by the cassette frame, they should be cut, welded and inspected from the inside. The inner diameter of the cooling pipe was 54.2 mm, and the wall thickness was 2.8 mm. The UT probe was mounted on the welding tool with elevation, rotation, and tilt mechanisms. In the measurement of a pipe with a known internal defect, the peak intensity, indicating the axial length of the defect, was 80%. By moving the probe in the circumferential direction, the circumferential length of the defect was measured to be 2.5 mm, it is possible to clearly detect internal defects of 0.5 mm or more. In the first divertor cassette of JT-60SA, the maximum circumferential defect lengths of the two butt welds and the two lap welds to connect the inboard target were 1 mm and <0.5 mm, respectively. This method is new in that it uses UT of narrow piping from the inside without completely filling the piping with water.