Flow-Induced Vibration Characteristics of M310 and Novel Segmented Fuel Rods under Single-Spacer-Grid-Failure Conditions

A reduced-order Euler–Bernoulli beam model with four degrees of freedom per node is used to compare the flow-induced vibration responses of a conventional M310 fuel rod and a novel segmented-design fuel rod (NSDFR) under intact and complete single-spacer-grid-loss conditions. The numerical implementation is verified against published simply supported and elastically supported beam benchmarks; the largest difference in the first natural frequency is 3.57%. Model adequacy for the intended global-bending analysis is further assessed by effective modal mass, direct modal-truncation convergence, and axial-resolution sensitivity. Across the 18 structural states, the first 20 modes account for 0.872 to 0.920 of the lateral effective mass. Relative to the 20-mode solution, the maximum difference in spatial root-mean-square (RMS) response is 0.325% with 8 modes, 0.098% with 12 modes, and 0.004% with 16 modes. The flow excitation is prescribed using the experimentally informed transverse-velocity profile and semi-empirical response relations reported in the literature. For the intact state, the predicted total peak responses are 0.0601 mm for M310 and 0.0450 mm for NSDFR. Complete loss of the bottom grid produces the largest linear response indicator for both rods, whereas top-grid loss is markedly more severe for NSDFR than for M310. A damping sensitivity study changes response magnitude but not the ranking of critical cases. The model is intended for comparative screening of global bending and support-loss location.