During a severe loss of coolant accident in a nuclear reactor, steam and hydrogen are produced by the oxidation of reactor core and get distributed in the containment. A water spray system is employed to cool the mixture as well as to enhance the mixing of the gases to avoid hydrogen accumulation. This paper presents two-phase numerical simulations of transient vaporization of a moving spherical water droplet. The numerical model considers the variation of thermo-physical properties in both liquid- and vapor-phases, as functions of temperature and species concentrations. Multi-component diffusion and surface tension effects are also considered. The model has been validated using experimental results available in literature for hydrocarbon fuel droplet evaporation. Validated model is used to study the evaporation characteristics of moving water droplets under conditions typically observed in nuclear reactor during a loss of coolant accident. The effects of ambient temperature and hydrogen concentration on the vaporization characteristics are studied thoroughly. (C) 2013 Elsevier Ltd. All rights reserved.