Source: Appendix A of the PEIS (DOE/EIS-0269)
Triuranium octaoxide (U3O8) occurs naturally as the olive-green-colored mineral pitchblende. U3O8 is readily produced from UF6 and has potential long-term stability in a geologic environment. In the presence of oxygen (O2), uranium dioxide (UO2) and uranium trioxide (UO3) are oxidized to U3O8. U3O8 can be made by three primary chemical conversion processes, involving either UF4 or UO2F2 as intermediates. It is generally considered to be the more attractive form for disposal purposes because, under normal environmental conditions, U3O8 is one of the most kinetically and thermodynamically stable forms of uranium and also because it is the form of uranium found in nature. It is insoluble in water and it has a bulk density in the range of 1.5 - 4.0 g/cm3 depending on the process used for production. Its particle density is 8.3 g/cm3.
Triuranium octaoxide (U3O8) has no hazardous chemical properties that are significant.