Research Papers: Nuclear Power

Experimental and Numerical Modeling of Transition Matrix From Momentum to Buoyancy-Driven Flow in a Pressurized Water Reactor

[+] Author and Article Information
Thomas Höhne

Forschungszentrum Dresden-Rossendorf (FZD), Institute of Safety Research, P.O. Box 510119, D-01314 Dresden, Germanyt.hoehne@fzd.de

Sören Kliem, Roman Vaibar

Forschungszentrum Dresden-Rossendorf (FZD), Institute of Safety Research, P.O. Box 510119, D-01314 Dresden, Germany

J. Eng. Gas Turbines Power 131(1), 012906 (Oct 02, 2008) (10 pages) doi:10.1115/1.2983137 History: Received July 21, 2008; Revised July 23, 2008; Published October 02, 2008

The influence of density differences on the mixing of the primary loop inventory and the emergency core cooling (ECC) water in the cold leg and downcomer of a pressurized water reactor (PWR) was analyzed at the Rossendorf coolant mixing (ROCOM) test facility. This paper presents a matrix of ROCOM experiments in which water with the same or higher density was injected into a cold leg of the reactor model with already established natural circulation conditions at different low mass flow rates. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the cold leg, upper and lower part of the downcomer. A transition matrix from momentum to buoyancy-driven flow experiments was selected for validation of the computational fluid dynamics software ANSYS CFX . A hybrid mesh with 4×106 elements was used for the calculations. The turbulence models usually applied in such cases assume that turbulence is isotropic, whilst buoyancy actually induces anisotropy. Thus, in this paper, higher order turbulence models have been developed and implemented, which take into account that anisotropy. Buoyancy generated source and dissipation terms were proposed and introduced into the balance equations for the turbulent kinetic energy. The results of the experiments and of the numerical calculations show that mixing strongly depends on buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation with lower mass flow rates and/or higher density differences. The ECC water falls in an almost vertical path and reaches the lower downcomer sensor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with the ECC injection in PWR and should be also considered in pressurized thermal shock scenarios. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.

Copyright © 2009 by American Society of Mechanical Engineers
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Figure 11

Upper and lower downcomer—Experiment versus CFX, E5

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Figure 12

Time dependent mixing scalar distribution at the cold leg sensor, E3 (local position 0312)

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Figure 1

Bird’s eye view of the ROCOM test facility

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Figure 2

Test matrix of ECC injection experiments, classification of the ROCOM tests, and isolines of Froude numbers

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Figure 3

Flow domain with inlet boundary conditions

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Figure 4

Mixing scalar evolution in the downcomer in ROCOM buoyancy-driven mixing tests (uppercase—no density difference E1 and lowercase—10% density difference E6) and CFX-Experiment

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Figure 5

Classification of ROCOM tests with density differences with respect to the downcomer Froude number (Eq. 2), calculated cases

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Figure 6

Upper and lower downcomer—Experiment versus CFX, E1

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Figure 7

Upper and lower downcomer—Experiment versus CFX, E2

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Figure 8

Upper and lower downcomer—Experiment versus CFX, E6

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Figure 9

Upper and lower downcomer—Experiment versus CFX, E4

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Figure 10

Upper and lower downcomer—Experiment versus CFX, E3

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Figure 13

Mixing scalar distribution in the circumferential positions of the cold leg sensor, 25s, E3



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