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Uranium dioxide or uranium(IV) oxide (UO 2), also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used as MOX fuel.
Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel. [3] At ambient temperatures, UO 2 will gradually convert to U 3 O 8. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal. [3]
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays, usually by emitting an alpha particle.
The metal uranium forms several oxides: Uranium dioxide or uranium(IV) oxide (UO 2, the mineral uraninite or pitchblende) Diuranium pentoxide or uranium(V) oxide (U 2 O 5) Uranium trioxide or uranium(VI) oxide (UO 3) Triuranium octoxide (U 3 O 8), the most stable uranium oxide; yellowcake typically contains 70 to 90 percent triuranium octoxide)
Ammonium uranyl carbonate (UO 2 CO 3 ·2(NH 4) 2 CO 3) is known in the uranium processing industry as AUC [2] and is also called uranyl ammonium carbonate.This compound is important as a component in the conversion process of uranium hexafluoride (UF 6) to uranium dioxide (UO 2). [3]
According to the International Nuclear Safety Center [22] the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations. The bulk density of the fuel can be related to the thermal conductivity. Where ρ is the bulk density of the fuel and ρ td is the theoretical density of the uranium dioxide.
The compounds identified in yellowcakes include uranyl hydroxide, uranyl sulfate, sodium para-uranate, and uranyl peroxide, along with various uranium oxides. Modern yellowcake typically contains 70% to 90% triuranium octoxide (U 3 O 8) by weight. Other oxides such as uranium dioxide (UO 2) and uranium trioxide (UO 3) exist. [4]
The uranium to zirconium ratio in different parts of the solid differs a lot, in the brown lava a uranium-rich phase with a U:Zr ratio of 19:3 to about 19:5 is found. The uranium-poor phase in the brown lava has a U:Zr ratio of about 1:10. [37] It is possible from the examination of the Zr/U phases to determine the thermal history of the mixture.