Improvement of design and fabrication technique of J-PARC mercury target vessel for increasing structural durability

Haga, Katsuhiro  ; Wakui, Takashi  ; Wakai, Eiichi  ; Kogawa, Hiroyuki  ; Naoe, Takashi   ; Takada, Hiroshi   

In 2015, we experienced failure in the water shroud of the mercury target vessel while they were in operation with the proton beam power of 500 kW, and since then investigations for the failure cause were carried out. As a result, it revealed that the target failures had been resulted from conditions which were difficult to examine by analytical approaches at the stage of target design, e.g., those relating to the bonding/welding processes. In order to prevent such troubles and to improve the reliability and soundness of the target vessel, we decided the design strategies to minimize welding part by using wire EDM and to increase radiographic and ultrasonic test during fabrication process. For the front part of the target vessel where the heat density by proton injection is high, the mercury vessel and the water shroud will be cut out from a block of stainless steel. The components of the rear part will also be decreased and total welding length will be reduced by 70 %.