Study On Solute Atomic Clusters After Proton Irradiation In RPV Steel

The nuclear power reactor pressure vessel（RPV）is the only non-replaceable first-class safety equipment in the nuclear power plant.Its performance and life directly determine the service life of the entire reactor.RPV steel will be hardened and embrittled by high temperature,high pressure and high energy particle irradiation during long-term service,that is,radiation damage.Solute clusters are one of the main mechanisms of radiation damage,which are mainly Cu-rich and Mn-Ni-Si-rich.With the decrease of copper content in RPV steel,the solute atomic clusters formed in commercial RPV steel after irradiation are mainly Mn-Ni-Si rich.However,due to safety and experimental conditions,study on this type of solute atomic cluster is not yet systematic.Therefore,studying the structure,distribution,and formation mechanism of Mn-Ni-Si clusters is helpful for further understanding of irradiation damage,and has important academic significance and application value for the development of RPV steel and nuclear power safety.In this paper,the domestic A508-3 RPV steel is taken as the research object.Referring to the RPV service conditions,proton irradiation at 292℃with proton energy of 250ke V was conducted on the RPV steel samples with cumulative fluence to 0.273dpa,which is equivalent to service life of 100years.Kinetics software were used to simulate the vacancy/vacancy cluster distribution of irradiation damage,The first-principles were used to calculate the interaction between the elements in the cluster,and the distribution and atomic composition of the Mn-Ni-Si atomic clusters after proton irradiation was studied by three-dimensional atom probe technology.Based on the above work,the formation and evolution model of Mn-Ni-Si-rich clusters in RPV steel under proton irradiation was established.The results show:the damage distribution caused by 250ke V proton irradiation simulated by SRIM and IM3D is within 1300nm of the sample depth.Among them,the damage is larger in the range of 900～1200nm,and the irradiation damage reaches the peak at 1100nm.Annealing simulation results show that in the 900～1200nm region,during the recovery of the primary dislocation defects,most of the vacancies are combined with interstitial atoms or clustered with vacancies to form vacancy clusters,which eventually leave"alive"vacancy-type defects.Type defects will serve as effective locations for solute atom cluster segregation.In RPV steel irradiated by 0.273dpa protons,solute atom clusters were observed.The clusters in the crystal were spherical,while the clusters at the dislocations were rod-shaped.The number density of solute atom clusters is 2.27×10²³/m³,and the average size of spherical clusters is 1.36nm.Based on the calculation and experimental results,a cluster formation process model is established:after proton irradiation,a large number of vacancy-type defects are generated in the RPV steel,and the Mn and Ni atoms are combined with the vacancy-type defects to form a vacancy-Mn/Ni atomic complex;Subsequently,due to the strong binding force between Ni and Si,more Si atoms are attracted around the Ni-rich core to form a Ni-Si-rich cluster sub-layer;due to the strong diffusion ability of Mn atoms and the weak binding ability with Ni,the Mn-rich atoms region immediately disperses to the outside of the cluster,and finally forms a Mn-（Ni-Si）-Ni solute cluster structure.