Research Of Numerical Analysis And Relief Of Welding Residual Stress Of Nuclear Power Containment Vessel

As an important safety barrier for nuclear power plant reactor,steel containment vessel contains radiation from the reactor core in case of coolant loss accident.Compared with CAP1000 nuclear power unit,the thickness of steel containment vessel of CAP1400 passive nuclear power plant increased from 45 mm to 55 mm,resulting in the greater welding residual stress.The existence of welding residual stress will affect the quality and life of containment,and then bring potential risks to the safe operation of nuclear power plants.According to the design requirements,the welding stress relief of the whole containment cylinder needs to be carried out by post weld heat treatment(PWHT).Because of the difficulty of on-site power load,deformation control and temperature uniformity,post weld heat treatment of CAP1400 containment vessel is facing a series of challenges,which increases the difficulty of engineering implementation.Therefore,it is necessary to study the distribution of welding residual stress and its elimination technology in nuclear power plant containment vessel.Firstly,ABAQUS software is used to simulate the temperature field of the containment joint.The results show that the temperature field of different weld layers is inconsistent due to the difference of welding parameters and heat source model.The larger the linear energy,the longer the cooling time,and the subsequent peak temperature of the weld increases step by step.The heating rate of each layer is faster than that of cooling.The highest peak temperature occurs in the molten pool,while the temperature field near the heat affected zone of the weld seam changes sharply.Secondly,ABAQUS software is used to simulate the welding stress field of the containment joint.The results show that the residual stress basically distributes symmetrically,and the peak value appears in the groove of the weld bead of the cover layer and near the fusion line,which is far away from the fusion line,and the stress value decreases rapidly.Longitudinal and transverse stresses are much higher than normal stresses,while normal stresses remain low and change little.Then the welding temperature field,stress field and fusion line morphology obtained,which verifies the reliability of the heat source model and numerical simulation results.Through the numerical simulation results,the stress peak value and distribution trend of weld in different paths are analyzed and grasped,which provides a direction for the regulation and reduction of residual stress.Finally,according to the stress distribution simulated by finite element method,the stress relief technology is studied from two aspects of optimizing welding process and ultrasonic impact treatment(UIT).It is found that the residual stress of the joint can be reduced to a certain extent by adjusting the preheating temperature,reducing the welding line energy and adopting alternately symmetrical welding sequence.With the increase of current and time,the stress relief rate increases with the increase of ultrasonic shock treatment,especially when the impact time is more than 240 s and the impact current is more than 2.1A,the critical saturation is reached,the stress relief rate is as high as 145%,and the surface residual is increased.The residual tensile stress is transformed into compressive stress.