A large scale conversion facility; located at the Esfahan (Isfahan) Nuclear Technology Center (ENTC); overseen by the Atomic Energy Organization of Iran (AEOI); construction began in 1999; first declared to the International Atomic Energy Agency (IAEA) in 2000; Iran provided preliminary design information to the IAEA on July 31, 2000, and updated design information on April 9, 2003; according to Iranian officials, based on a design provided by a foreign supplier in the mid-1990s; contract between the AEOI and the China National Nuclear Corporation (CNNC) reportedly signed in January 1991; foreign supplier provided facility blueprint, equipment test reports and design information for equipment; according to Iran, detailed design and manufacturing of the equipment was completed domestically.

IAEA inspectors discovered underground tunneling work at the facility during a visit on December 15, 2004; under its inspection agreement with the IAEA, Iran should have declared plans for such activity when the decision was made to dig the tunnels; according to Iran, excavation work began in September 2004 and is intended to create a storage area "to increase capacity, safety and security" of nuclear material.

According to Iran, conversion process lines include uranium ore concentrate into UF6 (yielding 200 t annually of UF6 ); low enriched UF6 into UO2 (yielding 30 t annually of UO2 enriched to 5% U-235); depleted UF6 into UF4 (yielding 170 t annually of depleted UF4); low enriched UF6 into low enriched uranium metal (yielding 30 kg annually of uranium metal enriched to 19.7% U-235); and depleted UF4 into depleted uranium metal (yielding 50 t annually of depleted uranium metal); additional conversion lines to produce natural UO2 and natural uranium metal declared in April 2003; according to Iran, uranium metal could be used in the production of shielding material and in the laser enrichment program, natural UO2 could be used in the heavy water reactor under construction at Arak, and UF6 would be enriched up to 5% U-235 in domestic uranium enrichment activities at Natanz.

After visiting the facility between April 24 and May 5, 2004, the IAEA confirmed that construction was based on foreign drawings and technical reports, except for the UOC purification process, which was modified from mixer settlers to pulse columns, and the uranium metal production process, in which Iran chose a more simplified method based on tests at the Tehran Nuclear Research Center (TNRC).

Iran informed the IAEA that hot tests of the UOC purification process (converting UOC into ammonium uranyl tricarbonate (AUTC)) began on March 15, 2004, that experiments converting AUTC into UO2 and then into UF4 would begin soon after, and that hot tests of the UF6 production line would follow; despite Iran's assertions that these experiments were tests, and not carried out for the purpose of UF6 production, the IAEA held that due to the amount of nuclear material being used, the hot testing would technically result in the production of feed material for the enrichment process, and would be "at variance" with the IAEA's understanding of Iran's October 2003 pledge to suspend enrichment activities; nevertheless, Iran began process tests for the production of UO2, UF4 and UF6 in March 2004, and by June 2004 had produced 40-45 kg of UF6 using domestically produced UF4.

On November 22, 2004, in order to verify Iran's new pledge to freeze all uranium enrichment related activities, the IAEA placed seals on key points at the facility; by that date, Iran had already introduced 37 tons of yellowcake into the facility; all this material was converted into UF4, and some of the UF4 was converted to UF6, by February 18, 2005; all material was then verified and sealed by the IAEA; during an IAEA visit in October 2004, a UCF operator stated that 22.5 tons of yellowcake had been processed by then, yielding about two tons of UF4; also in October, the IAEA visited the fluorine production building at the facility and found that five of ten fluorine production cells had been installed, one of which was ready for operation; the IAEA carried out a physical inventory verification at UCF in April 2005, during which the UF4, UF6, and scrap and waste generated by the conversion processes were verified, and the material unaccounted for (MUF) was calculated to be acceptable, at less than 1% of the total quantity of material used; conversion process lines and nuclear material remained under IAEA seal until August 2005.

On August 1, 2005, Iran notified the IAEA that it had decided to resume uranium conversion activities; the IAEA installed additional surveillance equipment at UCF between August 8 and 10; on August 8, Iran started to feed UOC into the first part of the process line, and on August 10 Iran removed seals from the remaining process lines and from the UF4.

In a resolution on August 11, the IAEA Board of Governors expressed "serious concern" at Iran's decision to resume uranium conversion and urged Iran to re-establish a suspension of all enrichment-related activities; as of August 29, Iran had introduced approximately 4,000 kg of UOC into the first part of the process, yielding about 600 kg of ammonium uranyl carbonate (AUC), of which approximately 110 kg was fed into the next process line; also as of August 29, Iran had produced about 6,800 kg of UF6 using approximately 8,500 kg of UF4 produced previously.

Iran informed the IAEA in October 2005 that the conversion campaign would end around November 1 and that another campaign with "150 drums" would begin following a one-week maintenance period; this campaign began on November 16; in January 2006, Iran presented information about and allowed the IAEA to take samples from corrosion resistant steel, valves and filters procured for UCF.

A company involved in procurement for UCF has been linked to the "Green Salt Project," allegedly a series of interconnected studies involving the production of UF4, tests related to high explosives, and missile re-entry vehicle design; on February 12, 2006, the IAEA modified the containment and surveillance measures to comply with Iran's request that such measures be limited to those of the standard inspection agreement; under this agreement, UF6 filling stations, UF6 cylinders and all UF6 produced remain under IAEA surveillance; from March 2004 to May 2008, 320 tons of UF6 were produced at UCF.

Key officials include Abdollah Solat Sana (managing director), Hamid-Reza Mohajerani (involved in production management and the planning, building and installation of the UF6 unit at UCF), and Mohammad Qannadi Maragheh (Mohammad Qannadi), reportedly the head of the UCF project.