Study On Laser Shear Test Of Stainless Steel/Ceramic Composite Assembly

In order to realize the efficient and reliable laser cutting for the stainless steel/ceramic composite assembly of the spent fuel source item,it provides new technical reserve and support for the spent fuel reprocessing project.This paper adopts the method of numerical simulation combined with experimental research,the temperature distribution and change rule of the workpiece in the process of laser irradiation were obtained by ANSYS software,and then the laser process parameters were pre-optimized.Based on Fluent module,the distribution characteristics of the auxiliary gas flow field were explored,and the dynamic performance changes of the auxiliary gas were analyzed.The feasibility of fiber laser cutting off UO₂pellet-316Ti cladding was studied.The microstructure,element composition,phase composition and hard layer production of the cut surface of uranium pellets were observed and analyzed.The effect of thermal effect of laser cutting on the subsequent dissolution of nitric acid was studied by the nitric acid dissolution experiment of uranium pellets after laser cutting.The research results are as follows:(1)Based on the theory of heat transfer,a numerical simulation model of laser cutting temperature field was established.The thermal physical parameter,latent heat of phase transformation,thermal radiation,natural convection of air and other factors of 316Ti stainless steel and UO₂ceramic pellets were considered.Besides,the continuous moving loading of laser heat source was realized.The influence of laser power and scanning speed on the temperature distribution of workpiece is discussed by single factor analysis method.The results show that the maximum surface temperature,melting depth and melting width increase with the increase of laser power and the decrease of scanning speed,which provides a theoretical basis for determining the range of laser parameters in actual cutting process.(2)The simulation model of laser cutting auxiliary gas flow field was established.Based on the UDF function in Fluent module,the secondary development was carried out to build an adaptive heat source model with the depth changing with gas/liquid.Using the VOF multiphase flow model and turbulence model,the distribution characteristics of the auxiliary gas flow field were explored with reasonable consideration of the boundary conditions,and the changes of the velocity and pressure of the auxiliary gas after it flows out of the nozzle were analyzed.It is found that the influence of inlet pressure on the auxiliary gas flow field is decisive.In the actual cutting process,the appropriate inlet pressure should be selected to ensure the slag removal capacity of the auxiliary gas,so as to ensure the cutting quality.(3)Laser shearing experiments were carried out on Al₂O₃pellets and UO₂pellets simulation element rods.The experiments show that it is feasible to cut the single rod of 20 mm UO₂pellet-316Ti stainless steel cladding composite structure with the fiber laser cutting system with 4k W power.After laser cutting,the cutting surface of UO₂pellets is crisp and fragmented,and the cutting surface is fine,with tiny micropores and tiny cracks.EDS results show that the main elements of the cutting section are U element and O element.The XRD results show that the phase composition of UO₂pellets on the cutting surface is still UO₂without phase transformation after laser treatment at high temperature.The type of auxiliary gas has no influence on the change of microstructure and composition of the cutting section.(4)Nitric acid thermal dissolution experiments show that there is no uranium oxide phase insoluble in nitric acid produced by heat input during laser cutting of uranium pellets.The dissolution rate of UO₂pellets after laser cutting is basically the same as that of uncut UO₂pellets.The content of insoluble residue in the hard surface layer is far less than1%of the mass of the dissolved pellets.Three auxiliary gases,such as O₂,N₂and Ar,have no effect on the thermal dissolution of nitric acid after cutting UO₂ pellets.