Influence On Radial Force Of Relative Position Between Impeller And Hydraulic Static Component Of Nuclear Reactor Coolant Pump

The Nuclear Reactor Coolant Pump(RCP),is the“heart”of the nuclear power plant.The long-term operation at high speed of rotation in the high temperature,high pressure and strong radiation environment means,if an fatigue damage event occurs,the heat in reactor core will not be taken away,so that a serious nuclear reactor accident will happen.While,the radial force on the impeller can cause eccentricity vibrations,which is one of the main reasons lead to the damage of the pump axle.In order to improve the evaluation of the reliability of the impeller,a further investigation of radial force is necessary.In this paper,numerical calculations of the scaled CAP1400 RCP model pump are performed to obtain the hydraulic performance,the flow field characteristics,the pressure pulsation,the radial force and the axial force,meanwhile,a test of hydraulic performance is completed to prove the reliability of the numerical methods.Firstly,simplify the clearance structures between the impeller and the stationary components one by one,and discuss the reasonability of the simplifications.And then change the sizes of the clearances of wear-rings and the shape of the front cavity,to find out the influents on the flow field in the front cavity and the radial force,which helps to gather experience for the optimal design of the dynamic and static clearance.Secondly,numerical investigations on the models with different circumferential positions of vanes are finished,through comparing the variations of flow field and radial force,some advice on designing the match of blades and vanes are proposed.Finally,numerical calculations on radial force in the idle process under the Small Break Loss of Coolant Accident(SBLOCA)conditions are performed,which can provide reference data of the evaluation of impeller reliability under extreme operating conditions.The results indicate that:(1)The simplification of clearances will add to error of the simulation results,only the meshes of the back cavity can be simplified to improve the calculation efficiency when investigating radial force.The size reduce of the clearances of wear-rings will cause less impeller force,and radial force pulsation is best when the front and the back clearances are 0.3,0.5mm,respectively,which is better for the vibration rules and the stability of the long-term operation.The shape of the front cavity will change the pressure distributions on the external shroud surfaces,and the radial force decreases with the increase of the volume of the cavity,but the axial force increases.According to the impact of the difference,radial force should be considered as the main factor in the design.(2)The variation of the circumferential vane position leads to a difference of 13.3%between the maximum and minimum radial force and little impact on other factors.In the cases of?=0~°and?=4.62~°,the radial force reaches maximal values with minimal pulsations,which can make the vibration track of axle head more relaxed,so that the pump operates more smoothly.(3)In the idle process of SBLOCA,the head and efficiency drop sharply,and the vortexes appear in the pump.The flow becomes most chaotic at 29th second,the becomes circumferentially uniform later.The vibration of pump was the most intense when the radial force pulsation fluctuated most at 29th second.Therefore,the axle fracture accident caused by radial force is most likely to occur at about 29th second after a SBLOCA occurs.