INVESTIGATION OF THE REACTION UO2+X+NPO2+C+N2 BY THERMOGRAVIMETRY

The kinetics of formation of uranium-neptunium mononitride by carbothermic reduction of uranium and neptunium oxides under flowing nitrogen has been investigated using thermogravimetric techniques in the temperature range 1670-1870 K. The starting blends were prepared from powder material and contained carbon in excess of the amount required to obtain the stoichiometric composition. The reaction investigated were: (a) carbothermic synthesis of a low-carbon carbonitride containing free carbon, and (b) decarburization of the carbonitride under nitrogen-8% hydrogen gas mixture. The carbothermic synthesis follows a first order rate equation and the value of the activation energy lies in the range 344 to 385 kJ/mol. A clear dependence of the activation energy on the neptunium or carbon content of the starting blends was not found. The removal of carbon impurity follows a phase boundary type rate equation with an activation energy of about 210 kJ/mol.