Multidimensional simulations of Fuel-Rod Appendage Effects on Pressure Drop and Heat Transfer in an Annulus Flow

Abstract

It is well known that fuel-bundle appendages affect the pressure drop and heat-transfer characteristics of a typical CANDU fuel channel. The price paid for higher heat-transfer rates is an increase in pressure drop. To account for these effects in thermalhydraulic analyses utilizing system codes like CATHENA or subchannel codes like ASSERT, adequate characterization of individual appendage contributions to these effects is required. As experimental quantification of these contributions may be difficult even for single-phase flows, we are using Computational Fluid Dynamics tools, as an alternative to experimental testing, to estimate the important parameters from simulations alone. This paper discusses the initial phase of a study undertaken to predict the fuel-rod appendage effects on heat-transfer enhancement and pressure-drop penalty in CANDU fuel channels. The general purpose CFD code, Harwell-FLOWSD, has been used to predict these effects for an obstruction approximating the Bruce-type bearing pad in a single-phase flow through a concentric annular channel at typical CANDU operational conditions.