Evaluation and Validation of Measurement Technique for Flow-induced Vibration Response of Fuel Rod

As core load-bearing and heat-transfer structures of nuclear reactor fuel assemblies, fuel rods endure persistent coolant scouring. Induced flow-induced vibration (FIV) directly governs long-term operational safety and service reliability of nuclear reactors. To fill the technical gap that single conventional testing tools fail high-precision, multi-dimensional synchronous characterization of fuel rod vibration in complex flow fields, this paper develops a collaborative testing framework integrating contact acceleration sensor measurement and non-contact digital image correlation (DIC) optical measurement. It conducts systematic comparative experiments on fuel rod FIV features, completes consistency verification of data from two measurement technologies, and uncovers amplitude distribution evolution rules of outer fuel rods under non-uniform constraint states. High-sensitivity biaxial acceleration sensors were embedded inside instrumented fuel rods. Vibration displacement and dynamic response parameters of rod bodies were extracted via acceleration integration algorithms. DIC non-contact optical measurement was introduced meanwhile. Multiple observation windows were deployed at upper, middle and lower axial typical zones of the test section. Synchronous collection and cross-check of vibration sensor signals and optical image datasets were realized under steady flow working conditions. Test outputs show high consistency between DIC optical measurement data and acceleration integration results. Cross-verification of dual measurement approaches greatly improves data credibility and forms a complete, trustworthy technical system for fuel rod FIV measurement. Fuel rod vibration responses display obvious spatial discrepancies. Frequency response RMS values of fuel rods at the middle window far exceed those at upper and lower zones. The root cause lies in uneven axial constraint stiffness: upper and lower regions adjoin rigid tube supports with high constraint stiffness, while weak restraints in the middle zone amplify structural vibration. First-order natural frequencies and frequency response RMS values of rod bundles within one observation window deliver excellent repeatability, which proves outstanding spatial uniformity of fuel rod vibration under flow excitation. Vibration response RMS values captured by both methods rise monotonically with stepwise flow rate growth. Such variation trends match standard FIV theoretical predictions perfectly. This finding validates theoretical adaptability and clarifies the positive correlation mechanism between flow excitation intensity and structural vibration amplitude. Vibration characteristic datasets acquired from this work supply vital experimental evidence for fuel rod vibration safety assessment. The established multi-tool collaborative testing framework provides solid methodological support for fuel rod FIV response measurement. It carries prominent engineering reference value for optimal structural design of nuclear reactor fuel assemblies, and offers scientific references for subsequent FIV test platform construction, testing scheme selection and experimental parameter calibration.