Present status of design improvements for high power operation of J-PARC neutron target vessel

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

no journal, , 

The maximum beam power for user operation of the present neutron target vessel is limited to 700 kW due to the allowable thermal stress. However, to allow the rated 1-MW operation, the next neutron target vessel changed the target structure and the water channel arrangement to reduce the thermal stress for achieving 1MW beam power. In the new target vessel design, the mercury vessel and water shroud were separated in the front half part of the target vessel where the heat generation density is high, and the water channel arrangement was optimized to reduce the thermal stress caused by the difference of thermal expansion between those two vessels. The fabrication design was changed to reduce the total parts number to be the minimum, and the number of welding lines was drastically reduced by fabricating each part from the block of stainless steel with wire electrode discharge machining. The welding deformation and the residual stress were also reduced by applying electron beam welding to part of the welds. Furthermore, the radiation tests and ultra-sonic tests were applied in the fabrication processes to check the soundness of welds. As for the cavitation damage caused by the pressure wave, the damage depth of the specimen cut out from the used neutron target vessel which was operated at the beam power of 150 kW to 200 kW was measured, and damage data to improve the damage evaluation under the non-bubble condition was obtained.