In a nuclear reactor, the Zr-xNb alloy, which is used as a structural material in the core region, is irradiated by energetic particles that cause the atoms to be displaced from their lattice sites and giving rise to crystal defects. The local changes in the atomic arrangements lead to local deformations of the solid and thereby changes of its local mechanical properties. Understanding the mechanisms behind this evolution in the core region of a reactor, and its monitoring or controlling is a critical task in nuclear industry. In this work, using extensive molecular dynamics simulations, we have studied the effects of radiation damage on the local mechanical properties of Zr-xNb alloy. In the first step, the effect of Nb-concentration on the mechanical stability of homogeneous Zr-xNb alloy is investigated. In the second step, we have studied the local changes of the elastic constants due to local changes of the microstructure. These local changes include presence and accumulation of vacancies in the form of dislocation loops or voids, accumulation of Nb atoms in the form of clusters of different morphologies. This study covers both cases of T = 0 • K and finite temperatures up to T = 600 • K.

Nuclear-grade zirconium alloys' properties are very similar to those of pure zirconium (Zr) because in most cases they contain more than 95% of Zr atoms. They have extensive applications in the nuclear industry, especially in fuel cladding. In this work, for the atomic simulations, we have used an ADP model interatomic potential. The calculated lattice properties of Zr-1%Nb show a very good agreement with experiments. Investigation of the possibility of a di-vacancy formation showed that it is possible only for the first and second nearest neighbor positions. It shows that at zero pressure, the Nb atoms in the alloy tend to join and create Nb clusters. However, under external pressure, the Nb clusters become less stable, tending to decay into smaller ones.