This study examined the processing parameters of a two-step carbothermal reduction-nitridation of ZrO 2 as a UO 2 /PuO 2 simulant to fabricate ZrN. Variables studied were the reaction time, reaction temperature and the starting powder composition Higher temperatures, longer reaction times and higher initial amounts of carbon in the starting material lead to increased nitridation similar to previous work with uranium oxide but that reaction rate decreases with time. SEM and TEM of the reacted powders reveal regions of ZrC with ledges indicative of crystal defects with small particles of ZrN growing on the ZrC bulk material suggesting a reaction that occurs via Zr transport to the reaction site either through mass diffusion or evaporation-condensation of Zr (g) and with N 2(g) forming the nitride. Annealing experiments on these mixed phases shows formation of a solid solution is rapid compared to the nitridation, where there is no formation of a mixed phase.