The precipitation behaviors of TaC in reduced activation steels are investigated by the means of experimental and theoretical model. A continuous model based on the Langer-Schwartz theory for nucleation, growth, and coarsening was developed for both homogeneous and heterogeneous precipitation. Applying this model, an extensive data set (the precipitation size and density) including experimental and reported results has been well described. The effects of the thermodynamics parameters on the microstructure were discussed. TaC showed a low coarsening rate during tempering as the solubility of tantalum in the ferrite matrix is quite small with a value of 10(-5) at 1023 K.