Modeling of Lateral Flow in CFD for Subchannel Analysis

Abstract

This paper is aimed at the application of computational fluid dynamics (CFD) calculations for lateral flow modeling in rod bundles of Russian-type pressurized water reactors with hexagonal fuel rod lattice by subchannel analysis under a constant temperature. The subchannel code SUBCAL and CFD code ANSYS Fluent with the Reynolds stress turbulence model, which is capable of solving the anisotropic flow present in rod bundles, are used. Both methods are compared in terms of calculations in rod bundles. The literature review of available experiments of rod bundles suitable for CFD calculation validation follows. This paper describes the created CFD models on a triangular lattice, which are subsequently validated on selected experimental data in a wide range of Reynolds numbers $2.0\cdot {10}^4\le Re\le 1.8\cdot {10}^5$ and geometry (pitch-to–rod diameter ratio) $1.06\le P/D\le 1.50$ together with mesh sensitivity analysis. The main part of this work is to develop a new equation for the lateral flow resistance coefficient for the subchannel code based on CFD calculations. Within these calculations, the turbulent mixing coefficient β for hydraulically smooth rod bundles, which is related to the geometry, and the momentum-energy transfer analogy correction factor ε are also evaluated and for which the equation is subsequently proposed.

Keywords:

• Computational fluid dynamics
• subchannel analysis
• lateral flow
• triangular rod bundle
• lateral flow resistance coefficient

Nomenclature

$A$ =	=	area (m2)
$C_2$ =	=	loss coefficient per unit length (m−1)
$D$ =	=	rod diameter (m)
$F$ =	=	linear force (N/m)
$G$ =	=	mass flux (kg/m2/s)
$g$ =	=	gravitational acceleration (m2/s)
$K_{ij}$ =	=	lateral flow resistance coefficient
$l$ =	=	control volume length (m)
$\dot{m}$ =	=	mass flow (kg/s)
$P$ =	=	rod pitch (m)
$p$ =	=	pressure (Pa)
Re =	=	Reynolds number
$s$ =	=	gap width (m)
$T$ =	=	temperature (°C)
$t$ =	=	time (s)
$u$ =	=	velocity (m/s)
$v$ =	=	cross-flow velocity (m/s)
$w$ =	=	diversion cross-flow rate (kg/m/s)
$w{ }^{\mathrm{\prime }}$ =	=	turbulent interchange (kg/m/s)
$z$ =	=	axial length (m)
Greek	=
$\beta$ =	=	turbulent mixing coefficient
$\epsilon$ =	=	correction factor
$\zeta$ =	=	local resistance coefficient
$\theta$ =	=	angle (deg)
$\mu$ =	=	dynamic viscosity (kg/m/s)
$\xi$ =	=	friction coefficient
$\rho$ =	=	density (kg/m3)

Acknowledgments

This paper was written based on the author’s dissertation at Department of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, and the author would like to acknowledge the contribution of UJP Praha (Jiří Čížek), which provided the subchannel code SUBCAL.

Disclosure Statement

No potential conflict of interest was reported by the author.