First Principles Study Of Early Stage MnNiSi Solute Cluster Formation In Low-Cu Nuclear Reactor Pressure Vessel Steel

Improving the economy and safety of nuclear power is of great significance to the sustainable development of human being.The performance of nuclear reactor pressure vessel directly determines the service life of the reactor.Long-term high temperature and pressure and intense neutron irradiation environment makes the pressure vessel steel gradually degraded,of which irradiation embrittlement is the most important degradation effect.Once the mechanical properties of the material drop to the brittle fracture threshold,the reactor pressure vessel,the reactor pressure vessel in the state of high temperature and high pressure will burst instantly,which seriously threatens the safe operation of the reactor.Therefore,radiation embrittlement of pressure vessel materials has always been a major concern of researchers.Irradiation induced significant volume fractions of Mn-Ni-Si clusters have been characterized as severe cause for the matrix embrittlement in low Cu content reactor pressure vessel steels at high flux.The formation mechanism of these clusters is still unclear,especially when the RPV does not contain Cu.In this paper,the progress of first-principles calculations based on density generalization theory in this field will be presented,including solute/point defect interactions,diffusion patterns and irradiation-induced segregation trends of Mn,Ni,and Si,solute interactions with interstitial atomic clusters,and the nature of Mn-Ni-Si precipitated phases.Finally,this paper will focus on the results of our first principles calculations of quartet clusters of Mn-Ni-Si and defects in order to examine the mechanism of the role of specific element species in the local stability of clusters in Fe-Mn-Ni-Si system.We found that point defects are more likely to promote cluster formation,and when Mn is present near the dumbbell,it is favorable for the formation of cluster.Si also plays an important role by forming stable covalent bonds at 1nn to other solutes,but Si self-atoms cannot be close to each other because this would interfere with the magnetic properties of the surrounding Fe atoms to the extent of reducing the stability of the clusters.These results are helpful for a better understanding of the cluster formation mechanism and can provide fundamental parameters for the solute-cluster evolution with larger-scale simulations.