Development of a Three-Dimensional Momentum Source Model for Wire-Wrapped Rod Bundles

Abstract

Large uncertainties still exist in the treatment of wire-spacers and drag models for momentum transfer in current lumped parameter models. To improve the hydraulic modeling of wire-wrap spacer in a rod bundle, a three-dimensional momentum source term that spirals around each rod has been developed. The momentum source model that accounts for the wire geometry is derived from momentum conservation and is dependent on local velocity profiles. Simulations of both 7- pin and 37-pin bundle configurations have been completed using the commercial CFD code STAR-CCM+ to simulate the wire-wrapped pin bundle as a bare bundle with extra momentum sources. The calculated inter-subchannel cross flow velocities match very well in comparisons between bare-bundle and wire-wrapped bundle cases. It has been confirmed that the momentum source model works well if its affecting region is accurately imposed. The validity of the model is further verified by mesh and parameter sensitivity studies.