Stability Analysis for Reactor Coolant Pump With Vertical Rotor Supported by Fluid Film Bearings

A special dynamics model for a vertical rotor-bearing system with two fly wheels is developed, imitating a sort of reactor coolant pump (RCP) under design. The stability and the process of reaching that condition are of special interest since the rotor is supported vertically other than horizontally. And the classical Jeffcott rotor dynamics model is not quite appropriate because the real pump has its two fly wheels outside the region between the two journal bearings and it has a thrust bearing right under the lower fly wheel. A set of dynamics coefficients are introduced to the rotor dynamics model, taking account of the flow confinement in the reduced gap of the canned pump. The stability characteristic is clearly changed due to the additional dynamics coefficients. Numerical simulation shows that the critical speed of the RCP is lowered. The moment of the thrust bearing, which is ignored customarily in rotor dynamics analysis, also influences the dynamic behavior of the rotor system. The stability of the rotor is enhanced while the thrust bearing has its stiffness and damping values in certain ranges.