Study On Residual Stress Distribution Of J-bevel Weld In Pressure Vessel Head Of Nuclear Reactor

Reactor pressure vessel is one of the key equipment for pressurized water nuclear reactors,and its structural integrity has a prominent position for reactor safety of nuclear power plant.Control rod drive mechanism(CRDM)runs through the reactor pressure vessel(RPV)with weld,for the J-bevel welding process is complex and does not go through heat eradication,which may lead to high weld residual stress,and cause stress corrosion cracking(SCC)together with unanticipated coolant leakage.Therefore,weld residual stress distribution and influence factors must be carefully controlled and assessed to offer criterions for the quality examination of heterogeneous metal weld joint and life-cycle prediction.In this study,CRDM nozzle mock-up was investigated to complete several experiments:Firstly,by using the thermal-elastic-plastic finite element method of Simufact Welding software,the heating and cooling processes are simulated.Further mechanical and thermal stress analyses was taken into account,and also the analysis on the residual stress specific distribution.Then to validate the result of the finite element method,Hole-drilling strain-gage experiment was carried out to measure the axial and hoop stress of CRDM penetration mockup.Results showed that experimental data are in good agreement with calculation results,which proves the method could analyze the J-bevel welding stress distribution in multi-pass welding effectively.Secondly,different finite element models and varied welding parameters are compared and analyzed for the influence to stress distribution.The main conclusions obtained are as follow: When the other welding sequences stay the same,the welding residual stress shows positive relationship with welding interlayer cooling time length,and negative proportion to welding current.In the welding process of J-bevel weld,the deformation characteristics have also been taken into consideration,the penetration nozzles tend to have the opposite direction of angular distortion with the heat source.When the heat energy is loaded,the joint zone is heated and the angular will grow larger in this area.In most cases,the nozzles' distortion angular is with the same direction where heat source loaded.