Thermal hydraulic design of double-walled mercury target vessel

二重壁ターゲット容器の熱流動設計

羽賀 勝洋  ; 直江 崇   ; 涌井 隆  ; 粉川 広行  ; 木下 秀孝   ; 二川 正敏  

Haga, Katsuhiro; Naoe, Takashi; Wakui, Takashi; Kogawa, Hiroyuki; Kinoshita, Hidetaka; Futakawa, Masatoshi

J-PARCの1MW核破砕中性子源の水銀ターゲット容器では、大強度のパルス陽子ビーム入射に伴い水銀中で発生する圧力波で誘起される容器壁面のキャビテーション損傷が、容器寿命を左右する重要な要因となる。これまでの解析的及び実験的研究や、米国のSNS施設の運転経験により、壁面近傍の速い水銀流れがキャビテーション損傷を抑制する効果を持つことが分かってきた。同様な効果を得るために、J-PARCのターゲット容器において陽子ビームが入射する壁面(ビーム窓部)の内側に壁を設けて二重壁構造とし、幅2mmの狭隘流路を形成した。計算コード(ANSYS Fluent)を用いた解析の結果、狭隘流路内では水銀流速を4m/sにまで高められることが分かった。また、内壁に円形の穴を設けたモデルをつくり、損傷による影響を解析および水実験で調べた結果、穴の大きさが10mm程度なら狭隘流路内の水銀流速への影響は小さく、外壁(ビーム窓部)へのキャビテーション損傷の抑制効果は維持できる可能性のあることを見い出した。

For the mercury target of a pulsed spallation neutron source of J-PARC, cavitation damage of the target vessel wall which is caused by the pressure wave in mercury induced by high power pulsed proton beam of 1 MW is the crucial issue. So far, the analytical and experimental studies and the operational experiences of SNS suggest that the rapid mercury flow can mitigate the cavitation damages. In order to include this effect into the target design of J-PARC, we adopted doubled-walled structure to the beam window of the target vessel. The mercury flow channel with a narrow gap of 2 mm was made by adding an inner wall to just inside of the beam window. In order to investigate the mercury flow distribution and flow field, numerical simulations were carried out using the conventional code, ANSYS FLUENT. While the mercury velocity outside of the narrow channel was 1.2 m/s, the mercury velocity in the narrow channel increased to almost 4 m/s, which was promising to suppress the cavitation damages. The effect of the inner wall failure of the narrow channel on the mercury flow was also evaluated. The round hole was created on the inner wall at the center of the beam window. The simulation results and the water experimental results showed that the mercury flow velocity in the narrow channel was almost the same with the case without a hole if the hole diameter is around 10 mm.