A numerical model is developed to describe the process of transient dissolution of the interior surface of a reactor bottom head in a pool of molten aluminum resulting from a severe core meltdown accident. The model accounts for the transient heat conduction in the steel structure, the mass transfer due to dissolution, and the time variations of the bulk pool temperature and concentration. Results indicate that over the range of accident conditions considered in the study, the bulk pool always attains a saturated state while the interface temperature approaches an asymptotic value. Once this saturated state is achieved, no further dissolution would take place. For a given pool inventory, the critical time for achieving the saturated state is found to be a function of the Nusselt number and the dissolution coefficient. On the other hand, the fraction of the steel structure that is dissolved before reaching the saturated state is a function of the Nusselt number alone.