Uranium dioxide

Uranium dioxide or uranium(IV) oxide (UO₂), 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. Prior to 1960, it was used as yellow and black color in ceramic glazes and glass.

Production

Uranium dioxide is produced by reducing uranium trioxide with hydrogen.

This reaction plays an important part in the creation of nuclear fuel through nuclear reprocessing and uranium enrichment.

Chemistry

Structure

The solid is isostructural with (has the same structure as) fluorite (calcium fluoride), where each U is surrounded by eight O nearest neighbors in a cubic arrangement. In addition, the dioxides of cerium, plutonium and neptunium have the same structures. No other elemental dioxides have the fluorite structure. Upon melting, the measured average U-O coordination reduces from 8 in the crystalline solid (UO₈ cubes), down to 6.7±0.5 (at 3270 K) in the melt. Models consistent with these measurements show the melt to consist mainly of UO₆ and UO₇ polyhedral units, where roughly 2/3 of the connections between polyhedra are corner sharing and 1/3 are edge sharing.