Numerical calculations for steam-water CCFL tests using the 1/3rd scale rectangular channel simulating a PWR hot leg

In reflux cooling, steam generated in the reactor core and water condensed in a steam generator (SG) form a countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. At Forschungszentrum Dresden-Rossendorf (FZD), both countercurrent air-water and steam-water tests were previously carried out using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, numerical calculations for the steam-water CCFL tests at FZD were conducted using the CFD code, FLUENT6.3.26. The numerical calculation region included the reactor vessel simulator, hot leg and SG inlet chamber, in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. The CCFL characteristics calculated by the 2F and VOF models agreed with the steam-water CCFL data at FZD and showed the same trends with the data for fluid properties.