Stress Analysis Of Heat Transfer Helical Tube For PWR Steam Generator

In nuclear power plants,the heat transfer tube of the steam generator is the weakest part of the primary circuit pressure boundary,the wall thickness of the steam generator tubes generally are 1?1.2mm,and the steam generator tube rupture has always been a very important safety issue in running a nuclear power plant.This is due to the steam generator tube rupture will lead to the release of radioactive fission products as well as accident of loss of coolant.Stress corrosion and micro vibration wear is a main factor of the pipe damage.In this paper,ANSYS finite element software was used to carry out the modal analysis and the fluid-solid-thermal coupling analysis for steam generator helical tube of the SMART nuclear power plant,and the software was also used to carry out fluid-solid-thermal coupling analysis for the steam generator helical tube of the 10MW high temperature gas cooled reactor which was made by Tsinghua university,using the finite element software analyze the micro-vibration and the Stress corrosion properties of the helical tube in the steam generator.SMART steam generator spiral heat transfer tube wall thickness is 1.5 mm,the vibration of the heat transfer tube will be caused by the excitation of the fluid in the SG's secondary side.Therefore,in order to ensure the safety of nuclear plant,the induced vibration analysis of a heat transfer tube is very necessary.And the analysis is the basis to find out the natural frequency and vibration mode of the helical tube.The support of a helical tube played a great role to the stability of the helical tube in SMART reactor cassette steam generator.ANSYS finite element software Mechanical APDL is used to carry out modal analysis for the SMART helical tube.It is found that the simple support method can be also efficiently applied to the modal analysis for the tube.From our numerical results it is concluded that eight supports for the helical tube are enough to avoid the fluid-elastic instability by producing high natural frequencies.It is also found that a smaller coil diameter helical tube produce a larger natural frequency and is benefit to prevent from the instability by flow induced vibration.Compared with the height of the helical tube,the coil diameter influences the natural frequency of the first mode more significantly.For smaller coil diameter a new vibration characteristics is found.The fluid analysis module,the steady state thermal analysis module and the static structure analysis module of ANSYS workbench are used for the fluid-solid-thermal coupling analysis of helical tube in SMART and 10MW high temperature gas cooled reactor.Then through the observe of the stress distribution,we can find the distribution of the complex stress of the helical tube at work and the location of the maximum equivalent stress of the tubes,which can provide help and reference for the maintenance and design of the helical heat transfer tube in steam generator.