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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

A Numerical Study on the Effect of the Mixing Vane Arrangement Patterns on the Heat Removal Capability inside the Fuel Assembly

Gong Hee Lee
Korea Institute of Nuclear Safety 62 Gwahak-ro, Yuseong-gu, Daejeon, 34142, Republic of Korea

Ae-Ju Cheong
Korea Institute of Nuclear Safety 62 Gwahak-ro, Yuseong-gu, Daejeon, 34142, Republic of Korea

Abstract

In a PWR (Pressurized Water Reactor), the appropriate heat removal from the surface of the fuel rod bundle is important for thermal margins and safety. A spacer grid that supports the fuel rods in a fuel assembly is equipped with mixing vanes that play a role in improving the heat transfer from the hot surfaces of the fuel rods to the coolant flow as the turbulence-enhancing devices. Because a spacer grid may cause rigorous mixing as well as greatly increased local turbulence levels inside the sub-channel, prediction of sub-channel flows, even in isothermal condition, is very difficult. In general, sub-channel analysis codes such as COBRA or VIPRE have been used to predict the flow and enthalpy distributions within fuel assemblies. However, these sub-channel codes rely on geometrically dependent mixing factors and empirical correlations to close the governing equations. The advantage of a CFD software for sub-channel flow predictions is that it does not rely to the same extent on these empiricisms. Therefore, CFD results have the potential for wider applicability to capture the essential features of the turbulent structures downstream of the spacer grid. In previous studies, authors had conducted the simulations the commercial CFD software, ANSYS CFX R.14 under the isothermal condition, and compared the predicted results with the measured data from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. Although there were locally differences between the prediction and the measurement, ANSYS CFX R.14 predicted the time averaged velocity field in the reliable level. The predicted horizontal and vertical velocity components were more in agreement with the measured data than the axial velocity component. While the effect of both the swirl flow and the cross flow was dominant for the split-type mixing vane arrangement, the effect of the cross flow was not significant for the swirl-type one. In this study, in order to examine the effect of the mixing vane arrangement patterns on the heat removal capability inside the fuel assembly, simulations were conducted with the same CFD software, ANSYS CFX R.14 under the heating condition and the predicted results will be explained.

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