Radiative heat transfer within a chemical reacting system directly exposed to an external source of high-flux radiation is considered. The endothermic decomposition of CaCO3(s) into CaO(s) and CO2(g) is selected as the model heterogeneous reaction. Its interfacial kinetic parameters are determined by thermogravimetric measurements assuming a contracting geometry rate law and an Arrhenius temperature dependence law. Experimentation using an Argon arc as the radiation source was carried out in which powder samples were subjected to radiative power fluxes in the range 400-930 kW/m(2). Temperature distributions and reaction extent were recorded as a function of time. A 3D transient heat transfer model that links conduction-convection-radiation heat transfer to the chemical kinetics is formulated using wavelength and chemical composition dependent material properties and assuming the Rosseland diffusion approximation for the internal radiative transport. Monte-Carlo ray tracing is employed to obtain the radiative flux distribution at the boundaries. The unsteady energy equation is solved by finite volume technique. The model is validated by comparing the computed temperature and reaction extent variation with time to the values experimentally measured. (C) 2003 Elsevier Ltd. All rights reserved.