Study On The Quality Control Of End-cap Welding Of CANDU-6 Nuclear Fuel Element

“End-cap welding” is the most important manufacture process in influencing the CANDU-6 product quality.According to the underwater inspection report of Qinshan No.3 Nuclear Power Co.,Ltd.on the damaged fuel bundle after 2006,the main reason for bundle damaging is the end cap welding defect.In order to realize zero damage of fuel bundle in heavy water reactor operation,a series of technical exchanges on how to improve the welding quality of end cap are conducted between TQNPC and CNNFC and some corresponding action items are listed.Based on the situation that our company and other related sector outside our company put forward new requirements for assuring the product quality in the end cap welding process,this topic has been set up.This topic aims at solving some technical problems,i.e.The solution of potential quality hazard caused by process and equipment and the optimization and standardization of process parameters,so that the quality of end cap welding can reach a higher level.Firstly,this thesis makes improvement research on the requirements put forward by users and the hidden dangers existing in the end cap welder itself,includes the quality control of reverse end cap 、improvement of groove quality of element to be welded,and improvement of locking quality of element to be welded.Then four kinds of adjustable weld parameters(the percent of heat,squeezing force,pre-press time and maintain time)are confirmed and optimized with single factor alternative method and by monitoring weld upset,visual inspect and metallurgical inspection.In the end,based on the single factor alternatively method,orthogonal experiment is used.In conclu sion,the percent of heat is the most important influence factor on welded joint,then squeezing force,pre-press time and maintaining time.Maintaining time has the least function on welded joint plastic deformation and joint quality.On the base of above experiments,the optimizing parameter match is the following: the percent of the main heat being 80%,squeezing force being200 lb,pre-press time being 60 cycles,main-heat powering time being 4 cycles,maintain time being 25 cycles and overhang length being0.39 mm.Through the research of quality control,the quality of end cap welding products can be effectively improved.