Effect of inner wall craking on the mercury flow induced vibration

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

Cavitation damage is one of the issues for the mercury spallation target, which threatens the structural integrities of the target vessel wall. To reduce such cavitation damages, Japan Atomic Energy Agency (JAEA) tried to prevent the cavitation bubble growth using the "flow effect". To arrange the environment for the use of the "flow effect", a narrow channel was newly installed by adding an inner wall to the mercury target head. Moreover, the microbubble injection technique to the mercury was also used to reduce the pressure waves which is one of the causes of the cavitation bubble formation. Consequently, the damage could be almost weakened. However, the damage on the inner wall can still be accumulated gradually during the practical target operation. Then, the inner wall might be penetrated by such damage accumulation: wall cracking might happen to the inner wall. Therefore, development of a diagnostic technology for such inner wall cracking should be important. So, the purpose of this study is to clarify the flow field in the target head with wall cracking conditions. Effect of the wall cracking on the flow field in the target head was investigated by CFD analysis. For simplicity, the flow channel near the target head was simulated as two-dimensional models. As the results, the continuous vortices shedding was recognized in the cases of any cracking conditions. And, pulsation flows in the narrow channel were observed in the cases of the cracking width larger than 4 mm.