Uranium dioxide is oxidized in contact with oxygen to the triuranium octaoxide.
:3 UO + O → UO at 700 °C (970 K)
The electrochemistry of uranium dioxide has been investigated in detail as the galvanic corrosion of uranium dioxide controls the rate at which used nuclear fuel dissolves. See spent nuclear fuel for further details. Water increases the oxidation rate of plutonium and uranium metals.