Study On The Dynamic Characteristics Of The Hold-down Spring For Nuclear Reactor Vessel Internals

The safety of nuclear power equipment has always been the focus of nuclear power issues and has received widespread attention.Among them,vibration is one of the issues that affects the safety of nuclear power.When the reactor is operating normally,cooling water flows in the reactor from the water inlet at the upper part of the gondola,which generates impact vibration,which is called flow-induced vibration.The Holddown spring is located between the flange of the top cover of the pressurized water reactor and the flange of the core support barrel(CSB).When there is flow-induced vibration,the CSB with its internal structure and the cooling water form a mass body.The Hold-down spring has an impact on the boundary conditions and vibration response of the mass.In this paper,the free vibration response of the Hold-down spring-mass system is discussed.The man contents include:(1)In view of the variable characteristics of the Coulomb damping force in the Hold-down spring vibration system,a free vibration response dynamics model for the compression spring vibration system is proposed.The model considers the adhesion characteristics of Coulomb damping force,discusses the expression of Coulomb damping,and solves the free vibration response analytically with linear fixed stiffness according to the equation of motion of the vibration system.(2)Based on the calculation model of the large deflection of the Hold-down spring,the software is used for programming,and the free vibration response numerical calculation is performed with variable stiffness.(3)The free vibration response of the Hold-down spring vibration system was simulated by finite element,and compared with the analytical solution of linear fixed stiffness and the numerical calculation of nonlinear variable stiffness.The three results have high consistency.(4)The boundary conditions of the mass in the vibration response are discussed in this article when the Hold-down spring is used as an elastic element.Due to the viscous effect of the friction force,if the pulsating load is smaller than the initial preload,the contact between the mass and the Hold-down spring should be regarded as the rigid axial displacement boundary,otherwise it should be regarded as the elastic axial displacement boundary.(5)In the vibration response process of the vibration system,if the boundary is an elastic boundary,the rigidity of the Hold-down spring and the natural frequency of the vibration system should be calculated separately according to whether the Hold-down spring is in a compression process or a rebound process.