Experimental analysis and two-region mixing coefficients development for a wire-wrapped tight lattice bundle

Abstract

Wire-wrapped tight lattice fuel assemblies are widely used in the design of advanced nuclear reactors for their advantages of higher power density and enhanced heat transfer capability. The flow mixing characteristics in this type of assembly are complicated due to the presence of the wire. In this study, a flow mixing experiment has been carried out in a 19-pin wire-wrapped tight lattice bundle with Reynolds numbers ranging from 5000 to 25,000. The mixing and crossflow effects were studied by injecting a tracer substance affecting the electrical conductivity of the fluid and measuring tracer concentration distributions using a wire-mesh sensor system. A set of flow mixing data has been obtained, and the experimental results indicate the mixing characteristics of a wire-wrapped bundle are insensitive to the Reynolds number. Combined with the measured data and the modified CTF code, the two-region mixing coefficients were determined by the least-square method and compared with the mixing coefficients in the literature. This work is an important supplement to the study of the mixing characteristics of wire-wrapped tight lattice bundles, and the data also can be used to validate the computational fluid dynamics codes and develop high-precision mixing models for subchannel analysis.