Assessment of subchannel flow mixing coefficients for wire-wrapped hexagonal fuel rod bundles

Convection heat transfer in upward flows of supercritical water in triangular tight fuel rod bundles is numerically investigated by using the commercial CFD code, ANSYS Fluent© 14.5. The fuel rod with an inner diameter of 7.6 mm and the pitch-to-diameter ratio (P/D) of 1.14 is studied for mass flux ranging between 550 and 1050 kg/m2s and heat flux of 560 kW/m2 at pressures of 25 MPa. V2F eddy viscosity turbulence model is used and, to isolate the effect of buoyancy, constant values are used for thermo-physical properties with Boussinesq approximation for the density variation with temperature in the momentum equations. The computed Nusselt number normalized by that of the same Reynolds number with no buoyancy against the buoyancy parameter proposed by Jackson and Hall’s criterion. Mentioned results are compared with V2F turbulence model whereas strong nonmonotonic variation of the thermo-physical properties as function of temperature have been applied to the commercial CFD code using user defined function (UDF) technique. A significant decrease in Nusselt number was observed in the range of 10-6<Grq/Reb3.425Prb0.8<5×10-6 before entering a serious heat transfer deterioration regime. Based on an analysis of the shear-stress distribution in the turbulent boundary layer and the significant variation of the specific heat across the turbulent boundary layer, it is found that the same mechanism that leads to impairment of turbulence production in concentric annular pipes is present in triangular lattice fuel rod bundles at supercritical pressure.

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SCADOP: Phenomenological modeling of dryout in nuclear fuel rod bundles

Nuclear Engineering and Design ◽

10.1016/j.nucengdes.2015.07.042 ◽

2015 ◽

Vol 293 ◽

pp. 127-137 ◽

Cited By ~ 6

Author(s):

Arnab Dasgupta ◽

D.K. Chandraker ◽

P.K. Vijayan

Keyword(s):

Nuclear Fuel ◽

Rod Bundles ◽

Phenomenological Modeling ◽

Fuel Rod

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Parametric Study on the Fluid Elastic Instability Factor of the Fuel Rod for a PWR Plant

ASME 2010 Pressure Vessels and Piping Conference: Volume 4 ◽

10.1115/pvp2010-25070 ◽

2010 ◽

Author(s):

Hyeong Koo Kim ◽

Sang Youn Jeon ◽

Kyou Seok Lee ◽

Jeong Ha Kim ◽

Sang Jong Lee

Keyword(s):

Parametric Study ◽

The Other ◽

Design Parameters ◽

Elastic Instability ◽

Direct Relation ◽

Spacer Grid ◽

Fuel Rod ◽

Flow Mixing ◽

Fuel Design ◽

Instability Factor

The main objective of this study is to estimate the effects of some considerable fuel design parameters on the fluid elastic instability behavior of the fuel rod. For the estimation, 6 fuel design parameters which seem to have direct relation with fluid elastic instability behavior of the fuel rod have been selected and examined using the PLUS7 fuel rod for OPR1000 PWR plants in Korea. Those are fuel rod creep-down, spacer grid stiffness, spacer grid spring relaxation, inactive spacer grid spring, intermediate flow mixing grid effect and fuel rod damping. As a result, the fluid elastic instability factors are insensitive with spacer grid stiffness, relaxation and intermediate flow mixing grid effect, but the other parameters need to be controlled and evaluated appropriately to maintain stability with proper margins.

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Mixing characterization in different helically coiled configurations by laser-induced fluorescence

Experiments in Fluids ◽

10.1007/s00348-020-03035-0 ◽

2020 ◽

Vol 61 (9) ◽

Author(s):

P. Kováts ◽

C. Velten ◽

M. Mansour ◽

D. Thévenin ◽

K. Zähringer

Keyword(s):

Cross Sections ◽

Quantitative Measure ◽

Laser Induced Fluorescence ◽

Helical Coil ◽

Mixing Coefficient ◽

Dean Vortices ◽

Flow Mixing ◽

Mixing Coefficients ◽

Mass Fractions ◽

Miscible Liquids

AbstractFlow Mixing of two miscible liquids has been characterized experimentally in three different helically coiled reactor configurations of two different lengths in the laminar flow regime at Re = 50…1000. A straight helical coil, a coiled flow inverter, and a new coiled flow reverser have been built, each in a 3-turn and a 6-turn configuration. Laser-induced fluorescence of resorufin has been used to visualize and quantify mixing in cross-sections throughout the reactors. A mixing coefficient is derived from the fluorescence images to allow for a quantitative measure and comparison of the six configurations. It becomes obvious from these experimental results, that an early flow redirection in the helical configuration is beneficial to mixing. The 3-turn reactors achieve nearly the same mixing coefficients as the 6-turn reactors with the double length. This can be explained by the stabilizing effect of the Dean vortices in the helix, which develop during the first two turns. After that, the liquid is trapped inside the vortices and further mixing is inhibited. Accordingly, the coiled flow inverter and coiled flow reverser configurations lead to much higher mixing coefficients than the straight helical coil. The results of these measurements are now used for validation of numerical simulations, which reproduce the geometrical and flow conditions of the experiments. Some exemplary results of these calculations are also shown in this article. Graphic abstract Mass fractions of tracer fluid at Re = 500 in the six examined helix configurations.

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