Influence of Multi-Hole Sparger Geometry on the Chugging Regime

Several experimental tests have been carried out at the University of Pisa using the Large-Scale Experimental Facility simulating the behaviour of the Vacuum Vessel Pressure Suppression System of ITER fusion reactor. The experiments were carried out by injecting steam produced by an electric steam generator through a multi-hole sparger into a condensation tank, known as Experimental Test Tank, containing 55 m3 of water. Two spargers called sparger A (a reduced scale of ITER sparger) and sparger B (a full scale of ITER sparger) were used during the experimental campaign. The geometry of the two spargers differs for the arrangement of the holes at the external (injecting) surface. This study compares the behavior of the two spargers by analyzing two experimental tests. The unstable chugging regime was also considered. The image analysis of the videos permitted the comparison of the steam bubble dynamics. The geometry of sparger B leads to the coalescence of the entire steam mass, while the sparger A developed two distinct steam bubbles which do not coalesce together. The analysis of the strain gauges and accelerometer signal allowed to compare the structural-dynamic response of the steam bubble collapse. This preliminary analysis showed the strong influence of the sparger geometry on the steam bubble dynamics and on the developed load on the sparger.