Atomistic simulations of the mechanism of hydrogen pileup around a vacancy and its effect on the vacancy mobility are performed to investigate possible mechanisms for hydrogen embrittlement in nickel.We show that the vacancy is capable of trapping 12 hydrogen atoms.The trapping energy is found to be approximately equal to -0.14 eV.We find that the interstitial hydrogen in the bulk lattice prefers to be located at octahedral interstitial positions which is in agreement with previous works.The influence of the vacancy defect is not limited to its volume but also extends to the octahedral sites of its first-nearest-neighbours.The hydrogen atoms prefer to cluster around the single vacancy.We also look at the effect of pressure on the trapping and migration energies of the hydrogen-vacancy complex.We find that the magnitude of the energy is influenced by stress.The hydrogen atom cloud around the vacancy defect also exerts some resistance towards the migration of the defect.