A mathematical model for three-dimensional heat and mass transfer in metal-hydrogen reactor is presented. The model considers three-dimensional complex heat, and mass transfer and chemical reaction in the reactor. The main parameter in hydriding processes is found to be the equilibrium pressure, which strongly depends on temperature. Hydride formation enhanced at regions with lower equilibrium pressure. Hydriding processes are shown to be two dimensional for the system considered in this study. Effects of heat transfer rate and R/H (radius to height) ratio on hydride formation are investigated. Hydride formation increases significantly with larger heat transfer rate from the boundary walls, however after a certain heat transfer rate, the increase in formation rate is found to be not significant, due to the low thermal conductivity of the metal-hydride systems. The estimated results agree satisfactorily with the experimental data in the literature. Copyright (C) 2002 John Wiley Sons, Ltd.