Using a rate theory model for a generic one-component material, we investigated interactions between grain size and recombination kinetics of radiation-induced defects. Specifically, by varying parametrically nondimensional kinetic barriers for defect diffusion and recombination, we determined the effect of these parameters on the shape of the dose to amorphization versus temperature curves. We found that whether grain refinement to the nanometer regime improves or deteriorates radiation resistance of a material depends on the barriers to defect migration and recombination, as well as on the temperature for the intended use of the material. We show that the effects of recombination barriers and of grain refinement can be coupled to each other to produce a phenomenon of interstitial starvation. In interstitial starvation, a significant number of interstitials annihilate at the grain boundary, leaving behind unrecombined vacancies, which in turn amorphize the material. The same rate theory model with material-specific parameters was used to predict the grain-size dependence of the critical amorphization temperature in SiC. Parameters for the SiC model were taken from ab initio calculations. We find that the fine-grained SiC has a lower radiation resistance when compared to the polycrystalline SiC due to the presence of high-energy barrier for recombination of carbon Frenkel pairs and due to the interstitial starvation phenomenon. © 2012 American Physical Society.