Vibration amplification mechanism and theoretical mitigation strategy for feedwater flow meter brackets in nuclear power plants

Excessive low-frequency vibration can impair the reliability of safety-class instruments in nuclear power plants. This study investigates vibration amplification in a feedwater flow meter bracket mounted on a steel grating platform in Unit 4. Field tests showed that the 10–50 Hz band contributed more than 56.1% of the mean-square acceleration at the transmitter and valve-group panels. An equivalent cantilever-beam model and a single-degree-of-freedom isolation model guided the retrofit. The design combined local reinforcement, a 250 mm reduction in effective cantilever length, and BE-40 rubber vibration isolators. Finite element response trends, laboratory tests, and field measurements all showed lower dynamic responses after the retrofit. The overall vibration acceleration level at the transmitter decreased by 18.4–26.4 dB over 10 Hz-8 kHz and met the applicable NB/T 25,081–2018 criterion. These results provide a practicable design route for mitigating vibration in lightweight instrument brackets mounted on flexible support platforms.