2018 | AFC ACCOMPLISHMENTS 58 Oxidation Behavior and Thermophysical Properties of UN/UO2 Fissile Composite Principal Investigator: Nicholas R.Wozniak Collaborator: Joshua T.White Figure 1. Thermograms comparing the mass gain of the composite materials and the monolithic UN and UO2 during ramped heating to 1000°C under 62% to 83% H2O (g) atmosphere. Composite uranium materials could be used as a fuel alter- native that would combine advantages of phase pure fuel forms. Traditionally used UO2, while ther- modynamically stable, has a less than desirable thermal conductivity. Uranium nitride fuels would have a higher uranium atom density, a higher melting temperature, and a higher thermal conductivity, albeit with poor oxidation resistance. A composite fuel consisting of uranium nitride (UN) in a UO2 matrix, could exhibit the strong oxidation resistance of UO2, while increasing the uranium atom density and thermal conductivity. Project Description: Composite fuels consisting of UN in a uranium oxide matrix could have significant safety advantages over either material in a monolithic form. The increased thermal conduc- tivity, compared to tradition UO2 fuels, would result in a decreased temperature gradient across the fuel and subsequently less cracking of the