Mechanism and Kinetics for the Formation of Uranium Mononitride by the Reaction of Uranium Dioxide with Carbon and Nitrogen

The mechanism and kinetics of UN formation by reaction of a pellet of mixed UO₂ and C with N₂ were studied for temperatures of 1420° to 1750°C. The reaction followed the first-order rate equation; the activation energy was 83 kcal/mol. Only UN_1−xC _x was produced. The lattice parameter variation of UN_1−xC _x had a minimum and a maximum during reaction; at the maximum, UN_1−xC _x + C + N₂ were in equilibrium. The overall reaction was divided into four stages: (1) formation of UN_1−xC _x from UO₂, (2) decarburization of UN_1−xC _x , (3) formation of UN_1−xC _x with the equilibrium composition, and (4) pure UN formation. The lowest reaction rate was in stage (4).