Source: Appendix A of the PEIS (DOE/EIS-0269)
Uranium dioxide (UO2) is the form in which uranium is most commonly used as a nuclear reactor fuel. It is a stable ceramic that can be heated almost to its melting point, 5,212°F (2,878°C), without serious mechanical deterioration. It does not react with water to any significant level. At ambient temperatures, UO2 will gradually convert to U3O8. It has a bulk density of 2.0 - 5.0 g/cm3 depending on the process used for production. Its particle density is 10.96 g/cm3.
Uranium dioxide (UO2) will ignite spontaneously in heated air and burn brilliantly. It will slowly convert to U3O8 in air at ambient temperature. Its stability in air can be improved by sintering the powder in hydrogen.