Ab initio calculations predict high positive binding energy (∼1 eV) between niobium atoms and self-interstitial configurations in hcp zirconium. It allows the expectation of increased niobium fraction in self-interstitials formed under neutron irradiation in atomic displacement cascades. In this paper, we report the results of molecular dynamics simulation of atomic displacement cascades in Zr-0.5%Nb binary alloy and pure Zr at the temperature of 300 K. Two sets of n-body interatomic potentials have been used for the Zr-Nb system. We consider a cascade energy range of 2–20 keV. Calculations show close estimations of the average number of produced Frenkel pairs in the alloy and pure Zr. A high fraction of Nb is observed in the self-interstitial configurations. Nb is mainly detected in single self-interstitial configurations, where its fraction reaches tens of percent, i.e. more than its tenfold concentration in the matrix. The basic mechanism of this phenomenon is the trapping of mobile self-interstitial configurations by niobium. The diffusion of pure zirconium and mixed zirconium-niobium self-interstitial configurations in the zirconium matrix at 300 K has been simulated. We observe a strong dependence of the estimated diffusion coefficients and fractions of Nb in self-interstitials produced in displacement cascades on the potential.

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The Zr–Nb alloys are widely used structural materials of modern nuclear power plants, where they undergo a significant neutron irradiation. In the present work, the cascades of atomic displacements in the Zr–n%Nb binary alloy (n = 0.5%, 1%, 1.5%, 2%, 2.5%, 3%) at temperatures 0 and 600 K are studied by means of the molecular dynamics simulation. The parameters of primary radiation damage are obtained. The results show that niobium atoms are actively involved in the formation of self-interstitial configurations: the fraction of niobium atoms in these structures is significantly higher than in the matrix, it ranges from 34% to 45% for considered alloys. Mostly, the niobium atoms form single interstitials: their fraction is no less than 82% depending on the niobium fraction in the matrix.