(A) parametric study of condensation-induced water hammer in nuclear power plants

Abstract

Condensation-induced waterhammer (CIWH) has a series of processes such as formation of water slug, trapping a steam cavity, depressurization due to steam condensation, accelerating slug caused pressure difference over it and final slug impact. These processes are dependent on water flow rate in a pipe, water temperature, water subcooling, steam pressure, length of slug and cavity, and heat transfer coefficient at interface between steam and water. First, the prediction of conditions to initiate water hammer has been made with full scale by applying the open channel flow theory. These conditions are expressed in terms of water flow rate according to changes of steam pressure, water subcooling and pipe diameter. The predictions of threshold flow rats to occur CIWHs were made and compared with event experienced and full scale tests in a real plant. Second, the effects of parameters which influence on slug impact pressure and cavity collapse rate have been studied with real scale. Also, the implact loads that may be applied to design were evaluated under various system conditions. The results of parametric studies show a good agreement with the values obtained by slug dynamics. From the results of this study, it can be concluded that the systems that have direct contact interface between steam and cold water always have the possibility of occurring CIWHs during system transients.