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Research Papers: Nuclear Power

Comparison of Countercurrent Flow Limitation Experiments Performed in Two Different Models of the Hot Leg of a Pressurized Water Reactor With Rectangular Cross Section

[+] Author and Article Information
Christophe Vallée

Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V. (FZD), P.O. Box 51 01 19, 01314 Dresden, Germanyc.vallee@fzd.de

Tobias Seidel, Dirk Lucas

Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V. (FZD), P.O. Box 51 01 19, 01314 Dresden, Germany

Akio Tomiyama

Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japantomiyama@mech.kobe-u.ac.jp

Michio Murase

 Institute of Nuclear Safety System, Incorporated (INSS), 64 Sata, Mihama-cho, Mikata-gun, Fukui 919-1205, Japanmurase@inss.co.jp

J. Eng. Gas Turbines Power 133(5), 052917 (Dec 28, 2010) (9 pages) doi:10.1115/1.4002884 History: Received August 25, 2010; Revised August 26, 2010; Published December 28, 2010; Online December 28, 2010

In order to investigate the two-phase flow behavior during countercurrent flow limitation in the hot leg of a pressurized water reactor, two test models were built: one at the Kobe University and the other at the TOPFLOW test facility of Forschungszentrum Dresden-Rossendorf (FZD). Both test facilities are devoted to optical measurement techniques; therefore, a flat hot leg test section design was chosen. Countercurrent flow limitation (CCFL) experiments were performed, simulating the reflux condenser cooling mode appearing in some accident scenarios. The fluids used were air and water, both at room temperature. The pressure conditions were varied from atmospheric at Kobe to 3.0 bars absolute at TOPFLOW. According to the presented review of literature, very few data are available on flooding in channels with a rectangular cross section, and no experiments were performed in the past in such flat models of a hot leg. Commonly, the macroscopic effects of CCFL are represented in a flooding diagram, where the gas flow rate is plotted versus the discharge water flow rate, using the nondimensional superficial velocity (also known as Wallis parameter) as coordinates. However, the classical definition of the Wallis parameter contains the pipe diameter as characteristic length. In order to be able to perform comparisons with pipe experiments and to extrapolate to the power plant scale, the appropriate characteristic length should be determined. A detailed comparison of the test facilities operated at the Kobe University and at FZD is presented. With respect to the CCFL behavior, it is shown that the essential parts of the two hot leg test sections are very similar. This geometrical analogy allows us to perform meaningful comparisons. However, clear differences in the dimensions of the cross section (H×W=150×10mm2 in Kobe, 250×50mm2 at FZD) make it possible to point out the right characteristic length for hot leg models with rectangular cross sections. The hydraulic diameter, the channel height, and the Laplace critical wavelength (leading to the Kutateladze number) were tested. A comparison of our own results with similar experimental data and empirical correlations for pipes available in literature shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross sections. However, some limitations were noticed for narrow channels, where CCFL is reached at lower gas fluxes, as already observed in small scale hot legs with pipe cross sections.

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Figures

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Figure 1

Comparison of the flooding characteristics obtained from data by Zapke and Kröger (2000) with different characteristic lengths for the calculation of the liquid Wallis parameter

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Figure 2

Schematic view of the TOPFLOW hot leg model test section (dimensions in millimeter)

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Figure 3

Schematic view of the Kobe University hot leg model test section (dimensions in millimeter)

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Figure 4

Comparison between the test section profiles of the hot leg models at the Kobe University and at TOPFLOW, both represented at the NPP full scale

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Figure 5

Comparison of the flooding characteristics obtained at the Kobe University and TOPFLOW plotted in terms of the Wallis parameter with different characteristic lengths

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Figure 6

Comparison of the present data (plotted in terms of the Wallis parameter with L=Dh) with different CCFL correlations and experiments obtained in hot leg typical geometries with pipe cross section

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Figure 7

Comparison of the present data plotted in terms of the Wallis parameter with L=H with different CCFL correlations obtained for hot leg typical geometries

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Figure 8

Comparison of the present data plotted in terms of the Wallis parameter with L=H with previous CCFL experiments performed in hot leg typical geometries

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