ATOMISTIC MODELLING TO STUDY EFFECT OF RADIATION DAMAGE ON NUCLEAR MATERIALS

Abstract

Niobium (Nb), Zirconium (Zr) and Zr-Nb alloys are commonly used as the structural material in nuclear reactors. Niobium is a rare, soft, malleable, ductile, grey-white metal transition element. Due to superior creep properties and low neutron cross section, Zr-Nb are used for the manufacturing of pressure tubes and fuel cladding in nuclear reactors. Additionally, is used in alloys for nuclear reactors, jets, missiles, cutting tools, pipelines, welding rods and super magnets. On addition of Nb in Zr makes significant improvement in certain properties of Zr like corrosion and creep resistance. In this project molecular dynamics-based simulations were used to study the effect of the irradiation induced microstructural changes in these nuclear materials. Due to time and spatial scale involved in irradiation induced damage, experiments are not feasible, hence atomistic simulations are emerging as viable alternative. In this report, simulations were performed to study the effect of tilt grain boundaries on the point defect formation energies in a bi-crystal of Nb. In order to study the effect of grain boundary configuration on defect formation energies, tilt grain boundaries were generated in the simulation box containing either symmetrical or asymmetrical boundaries between the two crystals of Nb. All the tilt grain boundaries were generated along the [0001] as the tilt axis with different mis-orientation angles. Grain boundary energies were estimated for each mis-orientation angle and a relation is derived between the distance from the grain boundary and defect formation energy. The defect migration energy was also calculated for both symmetrical and asymmetrical tilt grain boundaries. It has been concluded from this part of research project that defect formation energies reduce significantly in vicinity of grain boundaries, which makes these configuration as sink for the radiation induced defects. The results obtained were validated with the help of data available in literature.