Experimental investigation of the frictional pressure drop of steam-water two-phase flow in AP1000 surge line

The Steam-Water Co-Current Flow (SWCOCF) in the AP1000 Pressurizer Surge Line (PZR SL) are important phenomena during the depressurization stage of the Small Break Loss-of-Coolant Accidents (SB-LOCAs), which affect the predictions of SWCOCF pressure drop in PZR SL and safety analyses. To investigate the pressure drop characteristics of SWCOCF in the PZR SL of AP1000, a PZR SL test model made of stainless steel is designed and a test loop is also established. The test section is mainly composed of a long inclined tube with a short acrylic visual section, a whole surge line tube and a vertical section. Two experiments were conducted: the single phase water experiment and the SWCOCF experiment. The total friction factor and the full-liquid two-phase friction multiplier as well as the liquid-only two-phase friction multiplier of the PZR SL tube were obtained, separately. The research results show that: the whole surge line two-phase friction multiplier increases with the increasing of mass quality, and decreases with the increasing of pressure. Two prediction models of two-phase friction multiplier for the surge line were developed based on the Martinelli-Nelson and Lockhart-Martinelli method, respectively. The fitted full-liquid two-phase friction multiplier model and the liquid-only two-phase friction multiplier model can predict the two-phase friction pressure drop in PZR SL very well. This paper may provide contributions to the design and safety analysis of AP1000 surge line.