Ultrasonic inspection technique for weld part of mercury target vessel for spallation neutron source

Wakui, Takashi  ; Wakai, Eiichi  ; Naoe, Takashi   ; Kogawa, Hiroyuki  ; Haga, Katsuhiro  ; Takada, Hiroshi   ; Shintaku, Yohei*; Li, T.*; Kanomata, Kenichi*

A mercury target vessel has been used for the spallation neutron source at J-PARC. It has a complicated multi-layered structure composed of a mercury target and a surrounding double-walled water shroud, which is assembled with thin plates (minimum thickness of 3 mm) by welding. Thus, welding inspection during the manufacturing process is important. We investigated the applicability of new ultrasonic inspections using specimens (thickness of 3 mm) with defects to improve the accuracy of welding inspection for the mercury target vessel. Immersion ultrasonic testing using a probe (frequency of 50 MHz) could detect a spherical defect with a diameter of 0.2 mm. The size was smaller than target value of 0.4 mm. The length of unwelded region estimated using the phased array ultrasonic testing corresponded with the actual length (0.8 - 1.5 mm).