Development of microbubble generator for suppression of pressure waves in mercury target of spallation source

Kogawa, Hiroyuki  ; Naoe, Takashi   ; Kyoto, Harumichi*; Haga, Katsuhiro  ; Kinoshita, Hidetaka   ; Futakawa, Masatoshi  

MW-class mercury target for the spallation neutron source is subjected to the pressure waves. Propagation of the pressure wave causes negative pressure which causes cavitation erosion and degrades the vessel. Microbubbles injection into mercury is an effective technique to suppress the pressure waves and cavitation erosion. The bubble-generator utilizing swirl flow of liquid (swirl-type bubble-generator) is suitable for a mercury target system. However, when the single generator was used, swirl flow remains at downstream. The remaining swirl flow causes the coalescence of bubbles which results in ineffective suppression of pressure waves. To solve this concern, a multi swirl-type bubble-generator, which consists of several single generators arraying in the plane perpendicular to mercury flow direction, was invented. The multi swirl-type bubble-generator generated the microbubbles with the sufficient size to suppress the pressure waves.