Study on vortex-induced vibration of the tubes in a nuclear engineering test reactor

The nuclear engineering test reactor in this paper is a small nuclear reactor designed and manufactured in China. The structure of this nuclear reactor is different from the normal pressurized water reactors. Especially, these are some tubes in the nuclear reactor, which are named radiation tube, neutron tube and temperature tube. The vibration induced in the flexible tubes by vortex shedding is practical importance, which is related to the safety of this nuclear reactor. However, it is difficult to obtain the natural frequencies and the dynamic characteristics of the tubes with the undetermined boundary conditions only by numerical analysis. In this paper, a 1/2 scaled-down model of this nuclear reactor was manufactured, and the modal experiment was made to obtain the natural frequencies both in air and in water. Based on the results of the modal test in air and water, the restraint stiffness of the tubes was calculated. Then, CFD analysis was made to calculate the velocities and the vortex shedding frequencies of the flow near the tubes and the vibration equations of the tubes were presented to calculate the dynamic responses of the tubes. A dynamic test was also made to verify the accuracy of the calculation. Compared the results of numerical calculation to the results of dynamic test, it is obvious that the numerical analysis method can reflect the dynamic characteristics of the scaled-down model with a valid margin of error.