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Black crystals. Insoluble inwater; soluble in nitric acid and concentrated sulfuric acid.

A crystalline (or pellet) form is used to pack nuclear fuel rods.

High radiation risk. Ignites spontaneously in finely divided form.

Uranium dioxide, also known as yellow cake, has a molecular formula of UO2. It is a black crystal that is insoluble in water. It is a high radiation risk and ignites spontaneously in finely divided form. It is used to pack nuclear fuel rods for nuclear reactors.

Brown to black powder or cubic crystals; density 10.97 g/cm³; Mohs hardness 5.5; melts at 2,827°C; insoluble in water and dilute acids; soluble in concentrated acids.

Uranium dioxide occurs in mineral uraninite. Purified oxide may be obtained from uraninite after purification. The commercial material, however, also is recovered from other uranium sources. Uranium dioxide is obtained as an intermediate during production of uranium metal (See Uranium). Uranyl nitrate, UO₂(NO₃)₂, obtained from digesting the mineral uraninite or pitchblende with concentrated nitric acid and separated by solvent extraction, is reduced with hydrogen at high temperatures to yield the dioxide.