Internal contact phenomena between fuel rod bundle and shroud-tube in ducted hexagonal fuel assemblies

Abstract

The paper is focused on internal contact phenomena between the fuel rod bundle and the shroud-tube in the ducted hexagonal fuel assemblies. Due to transverse clearances on all six sides of the hexagonal profile and the bowing of the fuel assembly (FA), contact may occur under operating conditions characterized by vibration excitation from coolant pressure pulsations. A comprehensive modelling approach is presented, which incorporates the effects of all relevant internal reactor components and interactions between the fuel rod bundle and the shroud-tube. This framework enables selecting the number of such bowed FAs, as well as the definition of FA bow shapes, clearances, modal properties of the FA components, and other key parameters. The practical implementation of the proposed method is demonstrated on PWRs, specifically VVER-440-type reactors, along with a broad range of analyses and results.