Study On Flow-induced Vibration Of5×5Rod Bundles With Spacer Grids

Rod bundles are often used in nuclear reactor design as fuel. It is mounted in parallel bythe plurality of sets of the fuel assembly at a high flow rate of cooling agent. The largerfluid-flow vibration may cause the rod bundles instability and failure.Under the background of the application of the rod bundles in the nuclear reactor fuel,we carried on an investigation into fluid-structure coupling vibration characteristics of the rodbundle fuel elements. We used hybrid mesh technology to generate the computation grids inthe liquid computed domain and calculated the flow-field by CFD methods, then wecompared the measured data with the computed value to verify the correctness of thecomputed results. Draw the following conclusions: The natural frequency of the fuel rodsdecreased with the increase of the flow rate. Different constraints had a great influence on thevibration characteristics of the rod. The calculated and measured lateral velocity was close tozero before passing the spacer grids. The mixing vane gave birth to cross flow after passingthe spacer grids. Measured and computed lateral velocity attenuated obviously downstream ofthe spacer grids, both of them were close to zero; Then spring which incident face was largermade a so strong block effect that caused axial velocity fluctuate largely. The mixing vane canblending and averaging the axial velocity.In addition to calculating and analyzing the natural frequency of the fuel rod and themixing, we calculated the displacement of the rod-appling one-way fluid-structure interactionand recomputed the flow-field after the displacement. Then we compared it to the results ofno displacement. We got that fluid-flow vibration has no effect on flow-field. And it can beneglected in thermal-hydraulic design.The rod vibration were analysed with time analytical method, considering fixed entrancevelocity, recurrent entrance velocity and stochastic entrance velocity. We got that the truebundle vibration was random and the spacer grids cannot cause vibration.