Phase Field Simulation Of Fracture Behavior Of Plate Dispersed Nuclear Fuel

Compared with fossil fuels,nuclear energy has the advantages of high energy density and abundant fuel reserves,and its energy conversion process has less environmental pollution.As an important part of the fourth generation nuclear power technology,dispersed nuclear fuel can achieve higher fuel consumption due to its uniform reaction and small temperature gradient.With the extension of design service life of nuclear power plant,in order to ensure the safe and stable operation of nuclear power plant in service and prevent catastrophic accidents,it is necessary to predict the fracture behavior and failure of dispersed nuclear fuel.The equivalent elastic properties,radiation swelling,creep and other mechanical properties of dispersed nuclear fuel have been widely concerned and studied by experts and scholars at home and abroad.However,the research on fracture mechanics is less and needs further development.In this paper,the fuel core of uranium dioxide（UO₂）reinforced Zr-4 alloy（Zr-4）is studied.The fracture phase field method is used to simulate the UO₂ fuel particles dispersed in the fuel core and the whole fuel core.The whole process of crack initiation,propagation and connection inside the fuel particle and fuel core,as well as the threshold of internal pressure and critical fuel consumption of core cracking are obtained.（1）The characteristics and advantages of plate dispersed nuclear fuel and the significance of its fracture behavior in service are summarized.The core of plate dispersed nuclear fuel is essentially ceramic fuel particle reinforced metal matrix composites.Combined with the development status of fracture mechanics research methods at home and abroad,the fracture phase field method suitable for plate dispersed nuclear fuel is proposed,and the crack initiation,propagation and fracture behavior in service are simulated.（2）Considering the stress of fuel particles in service environment,the phase field theory of fracture of porous materials is established.The classical fracture phase field theory introduces the length scale scalar7)₀ and phase field variables(9,so that the discrete crack surface is transformed into a dispersed crack region.The governing equation and evolution equation of the phase field are obtained by solving the variational energy functional of the elastic body.Based on the classical phase field theory,considering the complex pore distribution,high pore pressure and thermal strain caused by high temperature of fuel particles due to fission reaction,the phase field theory of fracture of porous materials is deduced,and the corresponding finite element discrete form is given.（3）Based on the phase field theory of porous material fracture,the phase field of uranium dioxide（UO₂）fuel particles was simulated at meso scale.Different pore distribution patterns（different density,different diameter,different air pressure and uniform distribution or not）were taken as the influencing factors to study the internal crack initiation and propagation stages of fuel particles with the change of pore pressure,so as to obtain the internal pressure threshold of UO₂ fuel particles with different pore distribution patterns in service.Fracture parameters such as crack propagation morphology and crack propagation path are also obtained.（4）Based on the phase field theory of porous material fracture,the phase field simulation of the fuel core of uranium dioxide（UO₂）reinforced Zr-4 alloy（Zr-4）was carried out on the macro scale.Taking different particle distribution patterns（different density,uniform distribution and agglomeration degree）as influencing factors,and considering the total thermal strain,that is,the thermal expansion strain caused by high temperature and the radiation swelling strain under high burnup,the crack propagation stage of ceramic fuel particles penetrating into the metal matrix was studied.The critical burnup,crack propagation morphology and crack propagation path of the fuel core at different stages of crack propagation under different fuel particle distribution modes are also obtained.