Effect of inner wall cracking on the cavitation bubble formation in the mercury spallation target at J-PARC

Ariyoshi, Gen  ; Saruta, Koichi   ; Kogawa, Hiroyuki  ; Futakawa, Masatoshi  ; Maeno, Koki*; Li, Y.*; Tsutsui, Kihei*

Cavitation damage on a target vessel due to proton beam-induced pressure waves is one of the crucial issues for the pulsed neutron source using a mercury spallation target. As a mitigation technique for the damage, the helium microbubble injection into the mercury has been carried out by using a swirl bubbler in order to utilize compressibility of bubbles. Moreover, double-walled structure, which consists of an outer wall and an inner wall, has been applied as the target head structure. In this study, we aim to develop an abnormality diagnostic technology to detect the inner wall cracking, which is caused by such cavitation damage, from the outside of the target vessel. The mercury flow fields in the case with the cracking are evaluated by computational fluid dynamics analysis based on finite element method. And then, effect of the cracking on the flow field is discussed from the point of view of the flow-induced vibration and the acoustic vibration.