Investigation of axial Flow-Induced vibration in a single fuel Sub-Assembly due to radial clearance

Abstract

A typical fast breeder reactor’s fuel sub-assembly (SA) has a radial clearance between the grid plate (GP) sleeve and SA bottom at the discriminator location. The radial clearance is maintained in the order of a few microns. In this work, axial flow with special emphasis on the influence of radial clearance on the dynamic behaviour of SA is studied. Since maintaining a precise clearance in the experimental setup is challenging, the full-scale axial flow experiment is conducted with zero clearance conditions, and the SA displacement amplitudes are measured. And then, the equivalent force from the experiment is applied to the numerical model to study the clearance effect. With and without radial clearance, cases are studied for various damping ratios. It is found that the displacement response of SA increases with increasing radial clearance up to a few microns corresponding to the given force. Further increasing radial clearance is not affecting the response of SA.