Metal hydride formation in an Lm - Ni-5 storage tank is numerically studied with a continuum mathematical model. The model considers complex heat, and mass transfer and chemical reaction in the reaction bed. It is found that hydride formation enhances at regions with lower equilibrium pressure. The adsorbed hydrogen mass increases faster at the initial times of the hydriding process and slows down after the temperature of reaction bed increases due to the heat of the reaction. Numerical results agree satisfactorily with the experimental data in the literature.