Experimental study and sub-channel analysis on the transverse mixing of the helical cruciform fuel assembly

The helical cruciform fuel (HCF) is characterized as self-mixing and self-supporting, which has promising applications in advanced nuclear power devices. In the presented work, the transverse mixing behaviors of the 4 × 4 HCF assembly with the Reynolds number scope of 5.90 × 10 2 to 1.13 × 10 4 were investigated by mixing experiment and sub-channel analysis. The wire-mesh sensor (WMS) device for the complex-structured rod bundle channel was designed, which was utilized for the concentration measurement in the range of 0.01352 mol/L to 0.02916 mol/L. The one-way mixing at rod gap type Ⅰ and two-way mixing at rod gap type ⅠⅠ were revealed by the evolution of sub-channel concentration profile along the axial height of HCF assembly. The mixing coefficient of the HCF assembly was found to be a geometry depended constant, which was 0.022 for the 4 × 4 HCF assembly. It is confirmed that the transverse mixing of HCF assembly is dominant by flow sweeping effect rather than the turbulent mixing. The flow sweeping mixing model for the HCF assembly was developed, which involves two sets of momentum equations. In general, the presented work provides the fundamental experimental data and applicable mixing model for the development of sub-channel code for HCF assembly. • WMS device for complex-structured bundle channel is developed. • One-way mixing and two-way mixing are described by momentum equations. • A flow sweeping mixing model is developed for HCF assembly.