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For the passive natural circulation systems (PNCSs) in offshore floating nuclear plants, the ocean environment is usually regarded as the final heat sink. Condensation-induced water hammer (CIWH) may occur as the saturated steam released into the ocean by natural circulation. This study aims to develop a CFD model to analysis the CIWH phenomenon induced by direct contact condensation (DCC) in the PNCSs. In the model framework, the two-phase interface is tracked explicitly by the volume of fluid method; the interface heat transfer is acquired by the hybrid Heat Transfer Coefficient model based on the Surface Renewal Theory; the condensation heat and mass transfer rate are obtained by user-defined functions (UDF). The condensation model is firstly validated with the PMK-2 experimental data, showing consistency with the measured temperature evolutions. Then, the model is applied to investigate the CIWH events in the horizontal pipe geometry of the passive natural circulation systems. The simulation results indicate that the reverse flow of subcooled water triggers the formation of the CIWH events, by increasing the condensation rate and forming the entrapped bubble. The reverse flow periodically occurs afterwards, inducing multiple CIWHs. The increase of inlet stream velocity lengthens the reverse flow period and the distance, thus strengthening the interfacial condensation and the pressure impulse of CIWH.

Numerical investigation on direct contact condensation-induced water hammer in passive natural circulation system for offshore applications