A uranium enrichment process used to prepare uranium for use in fabricating fuel for nuclear reactors by separating its isotopes (as gases) based on their slight difference in mass. This process uses a large number of interconnected centrifuge machines (rapidly spinning cylinders). No commercial gas centrifuge plants are operating in the United States; however, both Louisiana Energy Services (LES) and United States Enrichment Corporation (USEC) have received licences to construct and operate such facilities, and both facilities are under construction. For additional information, see Gas Centrifuge Enrichment Facility licencing and the Fact Sheet on Uranium Enrichment.