ABSTRACT
This troubleshooting case study concerns the primary reactor coolant pump configuration for a pressurized water nuclear reactor employed in many presently operating commercial nuclear power plants. It is an electric motor driven single-stage centrifugal pump employing a rigidly coupled vertical rotor configuration with three radial journal bearings. This pump configuration was found to have widely varying unit-to-unit rotor vibration characteristics which makes vibration-troubled units in nuclear plants quite difficult to root-cause diagnose and thus challenging to correct. The author's investigation of this led to the identification of the two contributing inherent root causes: (1) the absence of well-defined journal dead-weight loads inherent with vertical rotors, and (2) the statically indeterminate journal bearing loads because of having more than two radial bearings on a rigidly coupled shaft.
