Modal Optimization And Effect Analysis Of A Nuclear Level Of The First Stage Pneumatic Cut-off Valve

A nuclear power plant(NPP)is a place where steam is heated by the use of nuclear fission or nuclear fusion to heat water to generate steam.And the steam through a pipe into a steam turbine,to drive a turbine generator to generate electricity,and to produce and output power.There are a large number of equipment in the nuclear power plant,and the safety of the nuclear reactor is an important guarantee for the safe operation of the nuclear power plant.The nuclear level of the first stage pneumatic cut-off valve is an indispensable basic equipment in the nuclear power plant.Huge of energy released by the earthquake is transmitted in the form of seismic waves,which can cause ground motion.This ground vibration will cause serious damage to the system structure and the internal structure of the structure.When the ground motion is transferred to the nuclear level of the first stage pneumatic cut-off valve,the displacement,speed and acceleration will be magnified,which may lead to the stress and deformation of the structure of the equipment exceeding the permitted range,which eventually leads to the equipment loss of its due working performance and produces serious safety accident problems.In this paper,the ANSYS Workbench finite element analysis software is used to perform the modal analysis of the nuclear level of the first stage of pneumatic cut-off valve.And its basic frequency is 21.8047 Hz.Because of the maximum frequency of seismic wave is 33 Hz.And the resonance may be damaged during the earthquake,which affects its working performance.Through the analysis,the modal optimization method for the nuclear level of the first stage of pneumatic cut-off valve is given.By comparing the effects of different optimization methods,an optimization method to improve the basic frequency of the valve is selected,and the fixed constraint is added to the bottom of the valve cover.Through the harmonic response analysis for the nuclear level of the first stage of pneumatic cut-off valve,it is found that only the seismic waves along the horizontal direction of the vertical pipe can cause the resonance of the valve,and the resonance frequency is 22 Hz.The artificial earthquake response spectrum is designed by “Code for seismic design of buildings”.And the curve of power spectrum is achieved through the MATLAB programming.The curve of power spectrum show that the artificial earthquake response spectrum can used to the requirements.The response spectrum analysis for the nuclear level of the first stage pneumatic cut-off valve was analyzed by the artificial ground motion response spectrum.The optimization results of the nuclear level of the first stage pneumatic cut-off valve were very obvious by comparing the results before and after the optimization.The research in this paper can provide guidance and experience for modal optimization of small caliber nuclear grade pneumatic cut-off valves,and has good practical significance.