We have previously done numerical simulations using the two-fluid model implemented in the CFD software FLUENT6.3.26 to investigate effects of shape of a flow channel and its size on CCFL (countercurrent flow limitation) characteristics in PWR hot leg models. We confirmed that CCFL characteristics in the hot leg could be well correlated with the Wallis parameters in the diameter range of . In the present study, we did numerical simulations using the two-fluid model for the air-water tests with ？m to determine why CCFL characteristics for ？m were severer compared with those in the range, . The predicted CCFL characteristics agreed with the data for ？m and indicated that the CCFL difference between ？m and m was caused by the size effect and not by other factors. 1. Introduction Reflux condensation by steam generators (SGs) is considered as one of the possible core cooling methods under hypothetical accident conditions in pressurized water reactors (PWRs). During the reflux condensation, the water condensed in SG U-tubes has to flow countercurrent to the steam generated in the reactor core. The core cooling performance heavily depends on the occurrence of countercurrent flow limitation (CCFL) in the hot leg which consists of a horizontal pipe, an elbow, and an inclined pipe. As reviewed by Al Issa and MacIan [1], many experiments have been conducted to investigate the CCFL characteristics in the hot leg, and empirical correlations have been proposed using Wallis parameters [2]. The review showed that many differences between CCFL data were simply due to geometrical effects. To compare CCFL characteristics in hot leg models, Vallée et al. [3] selected three geometrical factors: the horizontal pipe length to diameter ratio , the inclined pipe length to diameter ratio , and the elbow angle . They showed that even for similar geometrical factors, there was clear deviation between CCFL characteristics due to size effects. In order to evaluate effects of size better, numerical simulation using CFD (computational fluid dynamics) software is expected to be useful. In order to investigate effects of shape of a flow channel and its size on CCFL characteristics in hot leg models, we have previously done numerical simulations using a two-fluid model implemented in the CFD software FLUENT6.3.26 [4–6]. 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 in the region of m [6]. On the other hand, CCFL characteristics for m
References
[1]
S. Al Issa and R. MacIan, “A review of CCFL phenomenon,” Annals of Nuclear Energy, vol. 38, no. 9, pp. 1795–1819, 2011.
[2]
G. B. Wallis, One-dimensional Two-phase Flow, McGraw Hill, New York, NY, USA, 1969.
[3]
C. Vallée, T. Seidel, D. Lucas, A. Tomiyama, and M. Murase, “Comparison of counter-current flow limitation experiments performed in two different models of the hot leg of a pressurized water reactor with rectangular cross-section,” Journal of Engineering for Gas Turbines and Power, vol. 133, article 052917, 2011.
[4]
N. Minami, M. Murase, D. Nishiwaki, and A. Tomiyama, “Countercurrent Gas-Liquid Flow in a Rectangular Channel Simulating a PWR Hot Leg (2) Analytical Evaluation of Countercurrent Flow Limitation,” Japanese Journal of Multiphase Flow, vol. 22, no. 4, pp. 413–422, 2008 (Japanese).
[5]
N. Minami, M. Murase, and A. Tomiyama, “Countercurrent gas-liquid flow in a PWR hot leg under reflux cooling (II) numerical simulation of 1/15-scale air-water tests,” Journal of Nuclear Science and Technology, vol. 47, no. 2, pp. 149–155, 2010.
[6]
I. Kinoshita, M. Murase, Y. Utanohara, N. Minami, and A. Tomiyama, “Numerical simulation of countercurrent gas-liquid flow in a PWR hot leg under reflux cooling,” Journal of Nuclear Science and Technology, vol. 47, no. 10, pp. 963–972, 2010.
[7]
A. Ohnuki, H. Adachi, and Y. Murao, “Scale effects on countercurrent gas-liquid flow in a horizontal tube connected to an inclined riser,” Nuclear Engineering and Design, vol. 107, no. 3, pp. 283–294, 1988.
[8]
H. J. Richter, G. B. Wallis, K. H. Carter, and S. L. Murphy, “Deentrainment and Countercurrent Air-water Flow in a Model PWR Hot-leg, NRC-0193-9,” U. S. Nuclear Regulatory Commission, 1978.
[9]
F. Mayinger, P. Weiss, and K. Wolfert, “Two-phase flow phenomena in full-scale reactor geometry,” Nuclear Engineering and Design, vol. 145, no. 1-2, pp. 47–61, 1993.
[10]
G. Geffraye, P. Bazin, P. Pichon, and A. Bengaouer, “CCFL in hot legs and steam generators and its prediction with the CATHARE code,” in Proceedings of the 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH '95), pp. 815–826, Saratoga Springs, NY, USA, September 1995.
[11]
M. A. Navarro, “Study of countercurrent flow limitation in a horizontal pipe connected to an inclined one,” Nuclear Engineering and Design, vol. 235, no. 10–12, pp. 1139–1148, 2005.
[12]
N. Minami, D. Nishiwaki, T. Nariai, A. Tomiyama, and M. Murase, “Countercurrent gas-liquid flow in a PWR hot leg under reflux cooling (I) air-water tests for 1/15-scale model of a PWR hot leg,” Journal of Nuclear Science and Technology, vol. 47, no. 2, pp. 142–148, 2010.
[13]
J. G. M. Andersen, “Interfacial shear for two-fluid models,” American Nuclear Society Transactions, vol. 41, pp. 669–671, 1982.
[14]
A. Minato, K. Takamori, and N. Ishida, “An extended two-fluid model for interface behavior in gas-liquid two-phase flow,” in Proceedings of the 8th International Conference on Nuclear Engineering (ICONE '00), Baltimore, Md, USA, 2000.
[15]
M. Ishii and K. Mishima, “Two-fluid model and hydrodynamic constitutive relations,” Nuclear Engineering and Design, vol. 82, no. 2-3, pp. 107–126, 1984.
[16]
Y. Kataoka, H. Suzuki, and M. Murase, “Drift-flux parameters for upward gas flow in stagnant liquid,” Journal of Nuclear Science and Technology, vol. 24, no. 7, pp. 580–586, 1987.
