Simulation Of Neutron Irradiation-induced Defects And Recrystallization In Tungsten

Magnetic confinement fusion is one of the approaches to achieving fusion energy for peaceful use.And currently,the mainstream magnetic confinement fusion device is the Tokamak.During the operation of future Tokamak-type reactors,plasma-facing materials(PFM)will serve in a harsh environment with high neutron irradiation(peak energy of about 14 MeV)and high heat flux(greater than 10 MW/m2).Thus,tungsten is chosen to be the primary candidate material for PFM in fusion reactors due to its high melting point,high sputtering threshold,low fuel retention,etc.However,neutroninduced irradiation damage and a high-temperature environment can cause changes in the microstructure of tungsten and induce recrystallization,resulting in intergranular embrittlement,which poses a threat to the safe operation of the reactor.Currently,there is no fusion device that can provide a fusion neutron source,so experimental and numerical simulation methods are commonly used to study the effects of neutron irradiation on tungsten.Compared with fission neutron experimental simulations,numerical simulations play an irreplaceable role in explaining the mechanisms of irradiation damage and have become an important means to simulate the effects of neutron irradiation in fusion.In this study,in order to investigate the evolution of defects and their influence on the recrystallization process in tungsten under neutron irradiation,a cluster dynamics(CD)method is used to simulate the longterm evolution of defects.Moreover,an irradiation-induced recrystallization(IIR)model that considers the effects of the irradiation-enhanced driving force and grain boundary migration is established.The work and corresponding results of this study mainly include two parts.Firstly,after establishing the mean-field CD model for the evolution of defects in tungsten under neutron irradiation,the effects of different parameters on the results of defect evolution(without the effect of transmutation elements)were systematically analyzed and discussed,including dislocation density,grain size,neutron spectrum,irradiation temperature,and irradiation duration.Among them,the variation of dislocation density and neutron spectrum have a minor influence on the evolution of defects.But grain size,irradiation temperature,and irradiation duration can affect the evolution of irradiation defects,especially irradiation temperature and irradiation duration determine the size distribution of irradiation defects.Secondly,after establishing the IIR model that includes the irradiation-enhanced grain boundary migration factor(R),a comparison with recent neutron irradiation experiments on tungsten in the HFIR reactor showed that the simulation results of the IIR model with the introduction of R are in good agreement with the experimental results.This result indicates that the irradiationinduced recrystallization process is not only influenced by the irradiation-enhanced recrystallization driving force but also by the irradiation-enhanced grain boundary migration effect.After verifying the reliability of the model,the IIR model was used to predict the neutron irradiation-induced recrystallization process of tungsten in the EUDEMO.The results indicate that in order to ensure tungsten does not reach half recrystallization fraction within two years of service,the long-term operating temperature of the first wall tungsten should be kept below 700℃.