Abstract
Molecular dynamics approach is used to simulate hydrogen (H) diffusion in zirconium. Zirconium alloys are used in fuel channels of many nuclear reactors. Previously developed embedded atom method (EAM) and modified embedded atom method (MEAM) are tested and a good agreement with experimental data for lattice parameters, cohesive energy, and mechanical properties is obtained. Both EAM and MEAM are used to calculate hydrogen diffusion in zirconium. At higher temperatures and in the presence of hydrogen, MEAM calculation predicts an unstable zirconium structure and low diffusion coefficients. Mean square displacement (MSD) of hydrogen in bulk zirconium is calculated at a temperature range of 500–1200 K with diffusion coefficient at 500 K equals 1.92 * 10−7 cm2/sec and at 1200 K has a value 1.47 * 10−4 cm2/sec. Activation energy of hydrogen diffusion calculated using Arrhenius plot was found to be 11.3 kcal/mol which is in agreement with published experimental results. Hydrogen diffusion is the highest along basal planes of hexagonal close packed zirconium.
Highlights
The behavior of zirconium and its alloys under various operating conditions in nuclear reactors has been extensively studied
Calculations were carried out using molecular dynamics (MD) approach with the interactions between atoms represented by the embedded atom method (EAM) [12,13,14] and modified embedded atom method (MEAM) [15]
EAM used for zirconium structure and property calculation has shown a better agreement of lattice parameters and mechanical properties with available experimental data than MEAM method developed by Baskes [16]
Summary
The behavior of zirconium and its alloys under various operating conditions in nuclear reactors has been extensively studied. Zirconium (Zr) is a transition metal with strong anisotropic physical properties due to a hexagonal close packed (HCP) crystal structure. It is used in nuclear reactors because of low thermal neutron absorption and good corrosion resistance at high temperatures [1]. The hydrogen generated during reactor operation has deleterious influence on mechanical properties of zirconium. The hexagonal close packed structure of zirconium consists of both tetrahedral and octahedral sites, and hydrogen is expected to diffuse and occupy these sites [3]. The low solubility of the hydrogen with temperature leads to formation of brittle hydride platelets [4]
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