Research on Calculation Method of Lower Radial Bearing Clearance of Main Pump of Nuclear Power Unit

For the Russian million-kilowatt pressurized water reactor (VVER) nuclear power units, the lower radial bearing clearance of the main pump cannot be directly monitored with installed sensors, and these units currently use Russian-supplied encrypted software for predictions. To solve the upgrading demand caused by equipment aging, it is necessary to research the calculation method of the lower radial bearing clearance of the main pump. Firstly, the finite element model of bearing-rotor dynamics was built. The radial vibration displacement response of the pump rotor under unbalanced excitation at different positions and amplitudes was calculated, which was further fitted to obtain the rotor vibration displacement relationship expression. Then, combined with the rotor radial displacement at the measured points, the calculation method of the minimum clearance of the lower radial bearing was established, and the calculation and prediction software of the lower radial bearing clearance of the main pump was developed. A comparison between actual measurement results and software calculations showed that the maximum absolute error was 0.017 mm (maximum percentage error: 11.3%), while the minimum absolute error was 0.001 mm (minimum percentage error: 0.8%).