Enrichment Feedstocks Production

A country choosing to join the nuclear weapons community must acquire the necessary weapons (fissile) materials (U-235 or Pu-239). A state selecting uranium for its weapons must obtain a supply of uranium ore and construct an enrichment plant because the U-235 content in natural uranium is over two orders of magnitude lower than in weapons grade uranium (>90 percent of U-235). Almost all uranium enrichment plants utilize uranium hexafluoride (UF6) as their feed. A country may select the electromagnetic isotope separation (EMIS) process, which uses uranium tetrachloride (UCl4) as its feed material, for enriching uranium.

Below follows description of technologies mainly adopted here and utilized in the conversion of uranium ore concentrates to highly purified UF6 and UCl4 for subsequent use as feedstock in a uranium-enrichment process. Gaseous UF6 is used as the feed in the gas centrifuge and gaseous diffusion processes, and UCl4 is used as feed in the EMIS process. Uranium ore concentrates, also known as yellowcake, typically contain (60 - 80) % uranium and up to 20 % extraneous impurities. There are two commercial processes used to produce purified UF6 from yellowcake. The primary difference between the two processes - solvent extraction/fluorination ("wet process") and fluorination/fractionation ("dry process") - is whether the uranium is purified by solvent extraction before conversion to UF6 or by fractional distillation of the UF6 after conversion. In the wet process, yellowcake is dissolved in nitric acid (HNO3), and the insoluble residue is removed by filtration or centrifugation. Uranium is separated from the acid solution with liquid-liquid extraction, the uranyl nitrate product is decom- posed to uranium trioxide (UO3) via thermal denitration, and the trioxide is reduced to uranium dioxide (UO2) with hydrogen or cracked ammonia (NH3). In most cases, the standard Purex process, using tri-n-butyl phosphate (TBP) in a hydrocarbon diluent, separates uranium from its impurities in the extraction step. In the dry process, the conversion and purification steps occur throughout the process. If the yellowcake was produced by the alkali-leach process (yields (Na2U2O7), the sodium must be removed from the material by partial digestion in sulfuric acid followed by ammonia precipitation of ammonium diuranate [(NH4)2U2O7). The ammonium-containing uranium salt is decomposed to UO3 by heating, and this oxide is reduced to UO2 with hydrogen or cracked NH3. The remaining steps used to produce UF6 for both processes are similar in that the UO2 is converted to UF4 by hydrofluorination (using hydrogen fluoride gas - HF). The UF4 (impure in the dry process) is converted to UF6 using electrolytically generated fluorine gas (F2). In the dry process, the UF6 is purified in a two-stage distillation step. Direct fluorination of UO3 to UF6 has been used, but this procedure is more amenable to relatively small capacity plants.

The EMIS uranium-enrichment process uses UCl4 for its feed material. Uranium tetrachloride is produced by the reaction of carbon tetrachloride (CCl4) with pure UO2 at 700 degrees Fahrenheit.

Conclusion

UF6 and UCl4 are the principal compounds used as inputs to uranium enrichment process Manufacture of these feedstocks is straightforward industrial chemistry process These processes are unclassified and widely known