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. 1. Introduction 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]. CANada Deuterium Uranium (CANDU) and almost all other nuclear reactors have structural elements made of zirconium alloys [2] making zirconium alloys the perfect choice for fuel cladding and pressure tubes in nuclear fuel channels. 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]. Zirconium can dissolve up to 450？wtppm of hydrogen at a temperature of 500°C, but the solubility drastically decreases to 65？wtppm at 300°C and it further decreases to 0.05？wtppm at room temperature. The low solubility of the hydrogen with temperature leads to formation of brittle hydride platelets [4]. These hydrides are brittle and crack on application of stress, which reduces life expectancy of nuclear components thereby increasing the cost of nuclear power. Hydride precipitates play an important role in the hydrogen embrittlement of various zirconium alloys [1–10]. Fracture toughness tests under tension
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