Experimental research on characteristics of condensation induced water hammer in natural circulation systems

Condensation induced water hammer (CIWH) is a common phenomenon possibly appearing in industrial pipelines, which may cause pipeline oscillation and even serious damage to the components. Previous research on the CIWH mostly focuses on the steam-water counterflow under forced flow conditions. For new floating nuclear power plants proposed recently, the CIWH may occur in some passive natural circulation safety systems. Nevertheless, the CIWH in natural circulation systems (NCS) has never been reported publicly yet. In this paper, a series of experiments are performed to investigate the flow characteristics during the CIWH in a NCS. The basic flow and temperature characteristics of the CIWH caused by counterflow of saturated steam-water mixtures and subcooled water in the NCS are studied in detail. Thereinto, the steam condensation induced flashing (SCIF) along with CIWH is firstly observed and analyzed. Moreover, the influences of CIWH on the flow behavior of the system are discussed under natural circulation and forced circulation conditions. The experimental results indicate that the occurrence of CIWH can result in further reverse flow of the subcooled water, which causes a sudden decrease in the flow rate of NCS. Moreover, the flow rate is more unstable under natural circulation than under forced flow.