Numerical study on a wire-wrapped fuel rod vibration induced by axial Pb-Bi coolant flow

Abstract

In this paper, the CFD analysis on the Pb-Bi axial flow around a wire-wrapped rod were performed and the vibrations of a wire-wrapped rod caused by the Pb-Bi axial flow were numerically studied. The effects of the pitches, flow rates and constraints on the vibration displacements and frequency were discussed. It was found that the transverse flow intensity increased twofold when the wire pitch was reduced from 400 mm to 200 mm. The augmentation of inlet flow rate from 1 m/s to 2 m/s resulted in an approximately fourfold amplification of the turbulent kinetic energy. The shear stress and pressure on the rod surface fluctuated significantly at the wire location. The force due to the wall shear stress was at least two orders of magnitude smaller than the pressure component. The vibration pattern of the fuel rod was consistent with the first-order vibration pattern and the main vibration frequency was close to the first-order natural frequency. The RMS of the fuel rod amplitude increased from 13.71 μm to 19.60 μm when the wire pitch decreased from 400 mm to 200 mm. When the inlet velocity increased from 1 m/s to 2 m/s, the RMS of the amplitude increased from 4.98 μm to 19.6 μm. When the both ends were restrained by completely fixed support, the vibration displacement at the center point decreased by 46 % compared to that in the case with circumferentially fixed in the upper end and completely fixed in the lower end. This study can provide the theoretical guide to the design of wire-wrapped fuel rods in the lead–bismuth cooled fast reactors.