Modelling And Simulation In Radiation Induced Defects In Reactor Pressure Vessel Steels

Reactor pressure vessel(RPV)steel undergoes neutron irradiation and results in a large number of matrix defects.Not only will these defects evolve during irradiation,but they will also change the diffusion kinetics and thermodynamic conditions of the solute atoms in the RPV steel,therefore,forming solute atoms segregation and clustering.Microstructure changes lead to changes in its mechanical properties,such as hardening,embrittlement,lower ductile-brittle transition temperatures,and lower toughness,making it more possibility to brittle fractures and dangerous.In this paper,the thermodynamic conditions for nucleation of RPV model steels in different systems and the generation of point defects under ion irradiation and neutron radiation conditions have been calculated by combining the phase field model,the rate theory,and the constrained string method.The defects evolution and precipitation of solute atoms are investigated.The main contents are as follows:By combining the constrained string method and phase field model,we simulated the non-classical nucleation behavior of each solute element in RPV model steels of FeCu,Fe-Cu-Mn and Fe-Cu-Ni systems.The energy barrier,critical nucleus,the minimum energy path of clustering and properties of stable cluster are investigated.The results showed that lower temperature and higher copper concentration promote the non-classical nucleation and reduce the energy barrier.The "Core-Shell" structures of Cu-Mn and CuNi clusters were observed,and its stability was proved from the thermodynamic energy point of view.According to the minimum nucleation energy path,the formation process of the core-shell structure of the composite cluster was described.It was proved that the addition Ni and Mn can effectively reduce the nucleation energy barrier and promote the formation of Cu clusters in RPV steel.The reaction rate theory model was applied to simulate the evolution of defects and solute atoms segregation caused by ion irradiation in the RPV model steel of Fe-Mn-Ni and Fe-Cr-Ni systems.The results showed that a large number of defects are formed along the ion injected path,affecting the diffusion kinetic conditions of the solute atoms,leading to segregation of solute elements.The simulation results explained the ion irradiation hardening observed in the experiments.A phase field approach and reaction rate theory combined model was established and applied to simulate the RPV model steel under the condition of neutron radiation.The neutron radiation induced defects,segregation of solute atoms,and the evolution of these defects were simulated.In the combined model,the dynamics and thermodynamic driving force are taken into account simultaneously.In this thesis,a series of models are established to simulate the microstructure changes in RPV model steels.The thermodynamic properties of solute clusters are obtained,which is basic for the simulation of ion irradiation and neutron radiation models.On the other hand,the combined rate theory with phase field model describe the process of generation and evolution of point defects during ion irradiation or neutron radiation.The radiation induced segregation and precipitation of solute elements are investigated.All the simulation results are in good agreement with experimental results.