Prediction of pressure oscillation characteristics in condensation induced water hammer within a horizontal steam pipe of equal-height-difference passive heat removal system

The passive heat removal system (PHRS) on the secondary side of advanced marine nuclear reactors is vulnerable to condensation induced water hammer (CIWH), a phenomenon characterized by abrupt condensation that triggers high-frequency, transient pressure oscillations. These pressure oscillations pose a considerable threat to the pipe integrity and jeopardize the safe operation of system. Therefore, this present study aims to develop a three-dimensional numerical simulation model of CIWH and to examine the pressure oscillations under various multi-parameter coupled conditions. Firstly, the local countercurrent flow—coupled with the interfacial wave generated by Kelvin–Helmholtz (K H) instability—triggers the CIWH phenomenon, thereby inducing the reverse flow of cold water. Subsequently, dimensionless parameters are systematically employed to characterize the occurrence location, frequency, and peak amplitude of pressure behaviors under various operating conditions. Finally, based on the influences of the various dimensionless parameters on pressure behaviors, segmented empirical correlation equations are formulated to predict the average occurrence position, frequency, and peak intensity. The corresponding prediction errors were found to range from −15.2% to +13.5%, −17.7% to +18.9%, and − 23.3% to +19.6%, respectively. These findings offer valuable theoretical insights for the suppression, prediction, and valuation of the CIWH phenomenon in advanced marine nuclear reactors.