Numerical Simulation of Countercurrent Gas-Liquid Flow in a PWR Hot Leg under Reflux Cooling

Abstract

In reflux cooling, the steam generated in the reactor core and the water condensed in a steam generator form a countercurrent flow in a hot leg. In order to investigate flow patterns in the hot leg under countercurrent flow conditions, countercurrent air-water tests were previously conducted using a 1/15 th scale model of a PWR hot leg. Numerical simulation results for the tests using a three-dimensional twofluid model in FLUENT6.3.26, implemented with an appropriate set of correlations for the gas-liquid interfacial friction, were in good agreement with the measured data. In the present study, further numerical simulations were carried out for a full-scale hot leg under PWR plant conditions to investigate the effects of pipe diameter and fluid properties. The predicted countercurrent flow limitation characteristics were well correlated with the Wallis parameters and agreed well with the measured data from the 1/15 th scale air-water tests as well as the full-scale steam-water UPTF tests. The results indicate that the set of correlations for the gas-liquid interfacial friction can be utilized to simulate countercurrent flows in the full-scale PWR hot leg.

Correlation for countercurrent flow limitation in a PWR hot leg

“…We found that the two-fluid model could reproduce CCFL characteristics under low pressure conditions and we confirmed that those in the hot leg could be well correlated with the Wallis parameters [13,14]. The two-fluid model, however, did not give good results for high pressures.…”

“…Based on the CCFL data from air-water tests with the diameter of 50 mm [9] and CCFL characteristics calculated for a full-scale model with the diameter of 750 mm using the two-fluid model, we proposed the following correlation for low pressures below 0.3 MPa [14].…”

“…In order to investigate effects of the shape and size of the flow channels simulating a PWR hot leg and the fluid properties on CCFL characteristics, we have done numerical simulations [13][14][15][16] using a two-fluid model and a volume of fluid (VOF) method implemented in the CFD software, FLUENT6.3.26. We found that the two-fluid model could reproduce CCFL characteristics under low pressure conditions and we confirmed that those in the hot leg could be well correlated with the Wallis parameters [13,14].…”

Effects of Liquid Properties on CCFL in a Scaled-Down Model of a PWR Hot Leg

“…The authors previously implemented numerical simulations using a two-fluid model in FLUENT 6.3.26 with an appropriate set of correlations for the gas-liquid interfacial drag coefficients, and carried them out for full-scale PWR plant conditions. (10) The predicted CCFL characteristics were well correlated with Wallis parameters for system pressures below 0.3 MPa, and showed no difference between different fluid property systems. On the other hand, the experiments conducted in the full-scale Upper Plenum Test Facility (UPTF) with steam/saturated water at pressures 0.3 and 1.5 MPa showed an apparent difference in CCFL curves at pressures between 0.3 and 1.5 MPa, (6) though the effects of fluid properties were not clearly mentioned.…”

“…Air at pressure 0.1 MPa was used for the gas phase in the simulations. Figure 15 compares predicted CCFL characteristics on the Wallis parameter diagram, in which the fitting curve of the measured CCFL correlation for air/water experiments in the same 1/15 th hot leg (10) is also shown. There is no significant difference in the predicted CCFL characteristics between the saturated water at 264 o C and the water at room temperature, while there is a clear difference between the GW 60 wt% and the water at room temperature.…”