The annular fuel has a closely arranged structure, and the coolant flow at both the gap between the stringers and the near wall surface is small, which is unfavorable to the coolant mixing between the subchannels and the uniform circumferential temperature distribution.

This study aims to explore the effect of the ratio of gate spacing to gate diameter on the distribution of temperature along the circumference direction.

Based on the software code ANSYS FLUENT, a computational fluid dynamics (CFD) analysis model for annular fuel assemblies was established. Then, the calculations in hydromechanics and the numerical simulation using operating parameters of typical pressurized water reactor (PWR) were performed to analyze the coolant flow and heat transfer characteristic when the annular fuels in square or hexagonal arrangement under different grid ratios. The circumferential non-uniformity of annular fuel outer temperature distribution was investigated under circumstances of various pitch-to-diameter ratio.

Computational results show that an appropriate increase of grid ratio is beneficial to the uniform circumferential temperature distribution of stringers. The appropriate grid ratio of square component is between 1.07 and 1.09, and the non-uniformity of circumferential temperature distribution of triangle component is slightly lower than that of square component. Therefore, the appropriate grid ratio is between 1.06 and 1.09.

The temperature distribution at the bar gap is improved most obviously by increasing the grid ratio and the improvement in the near surface takes the second. The results of this study provide a reference for the subsequent optimization design of the grid ratio of annular fuel.