A simplified model is developed for assessment of a continuous-feed solar reactor for metal production. The main issue here is the transient pellet external surface motion due to the solid-to-gas reaction, its coupling with reaction kinetics, the radiative and the conductive heat transfer. The underlying model assumptions and the numerical approach are described. The model validation is presented, followed by the approximate solution for the shrinking pellet problem. (C) 2015 Elsevier Ltd. All rights reserved.