| The control rod driving mechanism(CRDM)is a significant action unit to ensure the safety and controllability of the nuclear reactor.The electromagnet CRDM is generally adopted by the pressurized water reactor.However,its movement is step by step which can’t be fine adjustment.In this paper,a new style servo piston hydraulic control rod driving mechanism(SHCM)is designed by using servo control elements,which has many advantages such as continuous movement,low energy consumption,strong ability to resist disturbance,and self balancing capacity.The numerical analysis and the experimental research on its operating characteristics is carried out.The design project of SHCM is determined firstly in this paper,and then the experimental platform is built up.The 3D model of SHCM is established based on the design parameters.The numerical simulation of the internal flow field and the core components are carried out respectively by the numerical calculation software ANSYS.The applicability of each grid model and turbulent model are evaluated according to the experiment data.The pressure property,the resistance property and the structural strength property of the driving mechanism are obtained.The calculation results show that the pressure loss in the driving cylinder mainly concentrates in the variable throttle mouth.The resistance coefficient of the variable throttle mouth decreases with the servo disk diameter increasing.There is a difference of the inlet pressure and the pressure in the cylinder.The results not only show the reliability of numerical simulation that is used in hydraulic driving mechanism analysis,but also supplement more detailed data which are lacking in experiment.The numerical simulation lays the foundation for subsequent theoretical analysis and the experimental research.The double-acting hydraulic driving mechanism is designed by structure improvement of the single hydraulic driving mechanism,whose movements and dynamics equations are established.The relationship between the static flow and the cylinder pressure changing with the gap of the variable throttle mouth are researched.Furthermore,the influence of the fixed orifice resistance coefficient to the piston movement is analyzed.The change rules of the critical flow and the critical speed are summarized further,which are influenced by the structural parameters of the driving mechanism and the working conditions.The stable flow rate increases slightly and the differential pressure in cylinder fell sharply,while the gap of the variable throttle mouth increases.The working zero clearance of the variable throttle mouth should be greater than 3.0 mm.Decreasing the diameter of the upper cylinder fixed throttle mouth can reduce the work flow and increase the lifting force of SHCM.The critical lifting speed can be improved greatly while the diameter of the lower cylinder fixed throttle mouth increases.In order to reveal the working mechanism of SHCM further,the static process and the dynamic process mathematic models of the system is established respectively according to the working principle and the geometric construction of SHCM.The theoretical calculation and analysis on the control rod performance of holding,lifting,and inserting are also carried out.The dynamic responses of the system parameters in the work process of SHCM are researched.The influence of the operation parameters and the structure parameters on the performance of the drive mechanism are analysed.The simulation results show that the servo disk can achieve synchronous movement with the control rod in a very short time,and then the system parameters achieve the equilibrium state.This changing process is validated by the experimental results.The diameters of the drive cylinder and the deflector hole on the piston have obvious effects on the driving mechanism performance.Moreover,the larger working temperature will lead to bigger flow rate.During the experimental research of SHCM,the development law of the working pressure and the flow rate,and the effects of the working parameters on the driving mechanism are analyzed and summarized.The experimental results show that the differential pressure in the cylinder increases and the flow rate decreases at the beginning of the lifting stage,and then they tend to a stable value respectively.The quality and the movement speed of the control rod affect the performance of SHCM obviously.The force of the servo disk reaches the maximum in the starting and braking stage,and the electric actuator power is between 23 ~ 35 W that can meet the design requirements.The resistance coefficient of SHCM increases gradually in the lifting process,and then reaches to a certain value.No matter in the process of lifting or declining,the servo disk can realize accurately positioning of the control rod,and the working pressure has no influence on the positioning accuracy.Moreover,stopping the pump can accelerate the rod drop.The research proves that the design idea has great value of development and application.The hydraulic driving mechanism can be used in the project implementation,which provides a new concept for the design domain of CRDM. |
