| The energy produced by nuclear reactions is a high-profile clean energy source,and nuclear fuels as the nuclear power source is the core part of nuclear reactors.Its safety and reliability are the key to nuclear energy utilization.Irradiation of nuclear fuels during using can result in various complex phase transitions,which not only poses a safety hazard to the entire reactor,but also increases the difficulty of handling spent fuel.At present,due to the particularity of nuclear fuels,the experimental research conditions are strict and the costly.Therefore,the study of phase and microstructure stability of nuclear fuels under irradiation based on thermodynamics and phase field method is of great significance for the development of nuclear fuels.In this work,based on the effective free energy model under irradiation conditions and general thermodynamic free energy model,the phase diagrams of pure Pu,Pu-X(X:Ga,U)and U-X(X:Ti,V)binary alloys were calculated,and the Phase-field method was used to study the microstructure evolution of the U-Nb alloys under irradiation.The main research results are as follows:(1)For the pure Pu and Pu-X(X:Ga,U)alloys,based on the thermodynamic and kinetic parameters which from the references,the model of final free energy was built and used to study the effects of different irradiation conditions on the total free energy of phases,and phase diagram of pure Pu and Pu-X(X:Ga,U)binary alloys under irradiation was calculated.The results show that the a-Pu phase of pure plutonium has a stable tendency at low temperature under irradiation,and the temperature range of y-Pu phase which appears at lower temperature increases with the irradiation time;the ? phase in Pu-Ga alloy appears at lower temperature without irradiation,the difference between the two experimental phase diagrams is theoretically discussed.For the Pu-U alloy,the high temperature phase boundary of the ?-Pu+? region increases with the K0 and ?repl,the range of the ?+?-U phasc region decreases as the irradiation intensity increases.(2)For U-X(X:Ti,V)binary systems,based on the thermodynamic and kinetic parameters which from the references,the model of final free energy was built and was used to study the effects of different irradiation conditions on the total free energy of phases.For the phase diagrams of U-X(X:Ti,V)binary alloys,the results show that,under irradiation,the high temperature part of phase diagram is basically consistent with the thermodynamic equilibrium phase diagram.However,the continuous solid solution(|3Ti,yU)phase appears in the lower temperature region of the U-Ti alloy phase diagram.A continuous solid solution(?U,V)phase appears in the low temperature region of the U-V alloy phase diagram.In addition,the(?Ti,?U)phase and(?U,V)phase region expand with the increase of irradiation intensity.(3)For the spinodal decomposition in U-Nb alloys,the spinodal decomposition were studied based on the related thermodynamic parameters reported in the literature and the Phase-field method.By considering the irradiation term in the governing equation,the effects of different irradiation conditions on the spinodal decomposition process and the two-phase microstructure were studied.The simulation results show that the irradiation in the process of spinodal decomposition can effectively inhibit phase separation and reduce the formation of Nb-rich phase,and the inhibition effect is more obvious with the increase of irradiation intensity.For the two-phase microstructure produced by the spinodal decomposition,the irradiation can also promote its decomposition and reduce the volume fraction of the Nb-rich phase.In this study,the calculation of phase stability and microstructure evolution of spinodal decomposition under irradiation were carried out for partial Pu-based and U-based alloys.These research results will provide important theoretical basis for the design of new nuclear fuels and the treatment of spent fuels. |
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