Progress of specimen cutout and damage inspection for used mercury target vessel at J-PARC

Naoe, Takashi   ; Kinoshita, Hidetaka   ; Wakui, Takashi  ; Kogawa, Hiroyuki  ; Haga, Katsuhiro  ; Takada, Hiroshi   

A liquid mercury target system for the spallation neutron source has been in operation at J-PARC. In the mercury target, pressure waves are generated due to abrupt heat deposition by the proton beam injection, inducing cavitation. A 3-mm-thick beam window portion of the enclosure vessel made of 316L stainless steel, so-called target vessel, is severely damaged by the cavitation. To observe the cavitation damage inside the target vessel, the beam window was cut out with an annular cutter. In 2017, some tests were conducted to optimize cutting conditions for cutting out a sample from the target No.2. As a result, the cutting was smoothly done with a water soluble lubricant. Since dose rate of the sample was extremely high for direct observation with a microscope, a replica method was adopted to observe the cavitation damage on the cut specimen. In the presentation, progress in the beam window cutting and cavitation damage observation by remote handling will be reported.