Turbulent mixing in a rod bundle with vaned spacer grids: OECD/NEA–KAERI CFD benchmark exercise test

Abstract

An experimental study titled the 2nd International Benchmark Exercise (IBE-2) has been conducted to provide high-precision data of detailed turbulent flow mixing in a rod bundle for validating the CFD codes being used widely in the nuclear power industry. A 5×5 rod bundle having mixing spacer grids was adopted as a test rig, and was contained in a square flow housing with a 170mm side length and 4670mm length. The 25 rods in a bundle have dimensions of 25.4mm in outer diameter and a 3863mm length. The benchmark experiments have been performed at the MATiS-H water loop facility in KAERI. The axial bulk velocity in a rod bundle was maintained at about 1.50m/s (equivalent to Re ∼50,000) with loop conditions of 35°C and 1.57bar measured upstream of the spacer during the experiments. Detailed measurements of the turbulent flow in the subchannels were accomplished using 2-D LDA at four different distances (0.5, 1, 4 and 10DH) from the downstream of the mixing spacer grid. The upstream flow profiles also have been measured at the inlet of the mixing spacer grid for the inlet boundary condition. Precise measurements of the lateral and axial velocities in the subchannels are presented at four downstream distances, as well as the inlet from the mixing spacer grid of two types. Turbulence intensities and vorticities in the subchannels are also evaluated from the velocity measurements.