ESTIMATION OF THE EVOLUTION OF PORES IN α - IRON UNDER NEUTRON IRRADIATION

Abstract

Changes in the mechanical properties of the reactor body of nuclear power plants are due to a number of physical processes at nano-, micro-, meso- and macro-levels both in time and space. The molecular dynamics method, the Monte Carlo method and the quantum mechanical method (ab-initio method) are used to study the cascade stage of interaction of irradiation (electrons, neutrons and ions) with reactor materials, which lasts from 10-15 to 1012 seconds in the size range up to 10 nm. The cluster dynamics method allows to study the longterm kinetics of point defect clusters (vacancies and internodes), as well as clusters and precipitates, which include point defects and alloying elements of reactor alloys. Based on the results of cluster dynamics such as concentration, average size, and numerical density of clusters and precipitates, it is possible to calculate the change in yield stress caused by irradiation. But so far, the urgent task of reactor materials science is to take into account the effects of irradiation on the physical mechanism of their plastic deformation and destruction. This article is devoted to one of the aspects of destruction of irradiated materials, which is based on taking into account the origin and evolution of pores during loading. A physical and mechanical model of intergranular fracture, which is caused by the evolution of pores, is proposed to evaluate the mechanical stability of reactor steels. The time dependence of the increase of the yield strength for the irradiation regime in the BR-2 research reactor (Mol, Belgium) was determined from the results of cluster dynamics for the evolution of the average size and numerical density of clusters for a constant temperature of 300 oC of the reactor vessel and its decrease from 300 oC to 123 oC. The evolution of the pore size and the magnitude of the relative plane of pores are calculated from the kinetic equations.