STUDY ON THE MECHANISM OF FLOW-HOLE BLOCKAGE OF STEAM GENERATOR TUBE SUPPORT PLATES UNDER PWR SECONDARY CONDITIONS

摘要

Flow-hole blockage has been experienced in the Steam Generator of PWR power plants which have adopted quatrefoil type flow-hole support plate structure. The growth of flow-hole blockage can lead to cause the oscillation of the water level. To prevent this phenomenon, various countermeasures, i.e., chemical cleaning and high pH AVT etc., are being employed. However, the root cause of flow-hole blockage has not been clarified, yet.In this study, the effect of flow rate on flow-hole blockage was examined under AVT chemistry conditions at 270°C using a high-velocity scale adhesion test loop. The numerical analyses around the flow hole were also carried out to clarify the phenomenon of flow-hole blockage. The amount of scale deposition due to iron oxide (Fe_3O_4) adhesion was observed at the inlet of quatrefoil type flow hole. Flow analyses result showed that the localized pressure drop and turbulent kinetic energy were increased at the inlet of quatrefoil type flow-hole. The scale adhesion test and flow analyses results indicated that the increase of amount of scale deposition at the inlet of quatrefoil type flow hole might be correlated with the pressure drop and localized increase in turbulent kinetic energy.