CANDU Bundle Junction: Misalignment Probability and Pressure Drop Correlation

Abstract

The pressure drop over the bundle junction is an important component of the pressure drop in a CANDU fuel channel This component can represent from ~15% for aligned bundles to ~26% for rotationally misaligned bundles, an is dependent on the degree of misalignment. The geometry of the junction increases the mixing between subchannels, and hence improves thee thermal performance of the bundle immediately downstream. It is therefore important to model the junction's performance adequately. This paper summarizes a study sponsored by COG and an NSERC Industrial Research Grant, undertaken at CRL to identify and develop a bundle-junction model for potential implementation in the ASSERT subchannel code. The work reported in this paper consists of two components of this project: 1) an examination of the statistics of bundle misalignment, demonstrating that there are no preferred positions for the bundles and therefore all misalignment angles are equally possible, and 2) an empirical model for the single-phase pressure drop across the junction as a function of the misalignment angle. The second section of this paper includes a brief literature review covering the experimental, analytical and numerical studies concerning the single-phase pressure drop across bundle junctions.