Abstract
Grid-to-rod fretting (GTRF) caused by flow induced vibration is one of the most important mechanisms of fuel rod failure in PWRs, which has a strong impact on the economy and safety of nuclear power plant. To avoid rod failure due to GTRF, several verification tests which are high costs and long term are always carried out for new design fuel assemblies. So as to deal with the disadvantages of tests and speed up progress in fuel design, a progressive analysis method to predict GTRF performance of fuel rod is developed, and systemic tests are carried out to verify the analysis method. The method consists of three main parts, including flow field analysis, structure vibration analysis and wear analysis. In the first part, the flow field excitation force is obtained by the large eddy simulation method, and this CFD method is verified by a particle image velocimetry (PIV) test with a 5 × 5 fuel bundle. In the second part, to get the vibration response of fuel rod, a nonlinear vibration model which can consider end-of-life gaps is established. Full scale fuel rod vibration in air and water conditions are tested to validate the predicted fuel rod response from analysis. In the third part, the fuel rod wear is estimated by tribological theory with fuel rod vibration response, the wear coefficient and the typical feature of wear scar. The GTRF method is finally verified by a long-term wear test of full-scale fuel assembly. It turns out that this method can effectively predict the wear characteristics of fuel rod cladding at the early stage of design. It provides a feasible solution for rapid design iteration of fuel assembly, and could reduce the development costs and risks.
