The Dynamic Characteristics Of The Rotor Immersed In Water In Heavy Nuclear Canned Pumps

Nuclear power is one of the most important clean energy.To improve the safety of the nuclear power and avoid the leakage of the coolant,the third generation reactor coolant pump is a kind of canned motor pump.Different from the regular motor,the canned motor gap between the rotor and stator is full of water instead of air.The rotor of the motor is immersed in the water and is supported by two journal bearing on the stator.The nuclear canned motor pump is hung below the steam generator by the inlet pipe.The particular installation style and the new environment of the rotor make the nuclear canned motor pump's dynamic characteristics be different from the traditional shaft-seal reactor coolant pump.In this dissertation,the interaction of the rotor surface and stator surface by the annular flow is studied.The lubrication characteristics of the water lubricated journal bearings and the special installation type of the nuclear canned pump are modeled and analyzed.Based on the rotor immersed in water,the dynamic model of the nuclear canned motor pump is built.The complex modal analysis method is used to decoupled the dynamic model.By using the Newmark numerical integration method,the unbalance response of the nuclear canned motor pump under normal work condition and the transient response during the earthquake of the nuclear canned pump are calculated.The research is aimed to provide technical support on the design of the nuclear canned motor pump.(i)The force effect of the annular flow between the rotor and statorThe cooling mode of the rotor and stator in the canned motor is changed from air cooling to water cooling.The change has great influence on the rotor dynamic characteristics.For moderate gap thickness,based on the bulk-flow theory and the wall friction coefficients,the control equations of the annular flow are established according to the continuum theory and momentum theorem.A finite element model based on the Galerkin method is proposed to study the steady and transient pressure distribution of the annular flow around the rotor.The force generated by the annular flow on the rotor is calculated.A test rig is built to validate the theoretical results.Based on the test rig,the distribution of the pressure in the annulus,the unbalance response of the rotor and the natural frequency of the rotor and stator are tested to validate the theoretical model.The added mass,damping and stiffness coefficients of the annular flow are affected by the gap ratio and the rotor eccentricity.When the amplitude of rotor vibration is large,the transient pressure in the annulus contains some high frequency components compared to the base frequency which is the rotor spinning velocity.The theoretical and experimental results indicate that the annular flow has negative stiffness effect and high added mass effect.Under the influence of the annular flow,the rotor's natural frequency reduces significantly and the damping of the system increase.The annular flow has great influence on the rotor's dynamic characteristic.(ii)Study of the hydrodynamic lubrication of the journal bearing and the transient response of the thermal shockBase on the turbulent Reynolds equation and energy equation,the water lubricated tilting pad journal bearings are studied.The stiffness and damping coefficients increase with the load almost linearly.The cross stiffness and damping coefficients of the tilting pad journal bearing are low and are good for the stabililty of the rotor.During the simulation,the effect of the force deformation and the thermal deformation of the pad on the hydrodynamic lubrication of the journal bearing are analyzed.Research shows that the pad force deformation reduce the pad's load capacity,especially for the heavy load.Compared to the oil-lubricated journal bearing,the increase of the temperature in water lubricated journal bearing is low for the high thermal capacity and low viscosity of water.When the nuclear canned motor pump's auxiliary cooling loop doesn't work,the temperature of the canned motor's coolant increase.The transient temperature field and the thermal deformation of the journal bearings' main components are calculated.The transient response of the journal bearing is analyzed.When the coolant's temperature in the canned motor increase rapidly,the deformations of the rotor and the journal base are small and can be ignored.The pad has curling deformation which can affect the water film thickness distribution.The pad steady angle increases.The pad load capacity decreases.(iii)The seismic response of the nuclear canned motor pumpConsidering the coupling of nuclear canned motor pump's rotor and stator by annular flow and the journal bearing,the dynamic finite element model of the nuclear canned pump is built.The model is based on the Timoshenko beam theory.The annular flow is represented by the mass,stiffness and damping matrix and the journal bearing is represented by the stiffness and damping matrix.These matrices are added in the matrices of the dynamic finite element model of the nuclear canned pump respectively.The dynamic characteristics and the unbalance response of the nuclear canned pump are obtained.According to the design acceleration spectrum of the Safe Shutdown Earthquake,the artificial accelerogram is generated.The transient seismic response of the nuclear canned pump are obtained.The possibility of the impact between the impeller and the stator is estimated.The work provides an effective method to evaluate the safety of the nuclear canned pump during the disaster period.The research shows that the bottom of the RCP has the largest the displacement response during the earthquake period.The journal bearing reaction forces change dramatically.The variation of the lower bearing's reaction force is much bigger than that in the upper journal bearings.The lower journal bearing are more vulnerable during the earthquake.The rotor and stator of the nuclear canned pump are coupled by the annular flow and the fluid film in the tilting pad journal bearings.In this dissertation,the method of building the dynamic model of the nuclear canned pump is researched.The influence of the annular flow on the natural frequency and stability of rotor system is analyzed.The steady and transient characteristics of the journal bearing is studied.The stiffness and damping coefficients are calculated.The cross stiffness and damping is low which may improve the stability of the rotor.Time domain analysis is carried out to investigate the transient response of nuclear canned pump when the base vibrates.The reliability of the nuclear canned pump under seismic load is assessed.These results offer technical guidelines for the parametric optimization of the nuclear canned pump design.