Conversion - Emissions

The U3O8 yellowcake is treated with a series of chemicals to convert the compound into UF6. The treatment begins with the removal of impurities in the U3O8, followed by the addition of nitric acid to the refined compound to produce uranyl nitrate (UO2(NO3)2) solution. Further impurities are removed by distillation and the water is evaporated. The leftover concentrated uranyl nitrate hexahydrate (UO2(NO3)2 x 6(H2O)) is thermally decomposed to uranium trioxide (UO3). The UO3 is ground into a fine powder, and reacted with hydrogen gas to form UO2 and H2O. After the water is removed, the uranium dioxide is reacted with hydrogen fluoride to form UF4 and liquid water. This mixture is calcinated to remove solvent, leaving the solute, UF4. The UF4 is reacted with fluorine gas to produce UF6 gas, which is then filtered, distilled and crystallized into a grayish-white crystalline solid.

Conversion is the least expensive step of uranium conversion, and represents only about 3% of the total cost of the development of nuclear fuel. Traditionally however, there have been problems with the conversion process, as many of the facilities at which it is conducted have problems with reliability. UF6 converters are located worldwide, with two in the United States, two in Europe, two in Russia and one in China.