The Fuel Enrichment Plant (FEP) is an underground uranium centrifuge enrichment plant, and the primary facility in Iran's centrifuge program. Construction started in the early 2000s, and the plant has been partially operating since February 2007. According to ISIS, the facility "consists of three large underground buildings, two of which are designed to be cascade halls to hold 50,000 centrifuges."[1] The exile group The National Council of Resistance of Iran revealed the existence of the facility to the public in 2002 and the IAEA first visited the complex in 2003.[2]

According to some estimates, when fully operational the plant would be able to produce 500kg of weapons grade uranium annually.[3] However, Iran has not enriched uranium at the FEP to levels higher than 5%, nor has it concluded the construction and installation of centrifuges in both of the production halls.

The installation of additional centrifuges is ongoing. As of the most recent November 2012 IAEA safeguards report, Iran had fully installed 61 cascades and partially installed one additional cascade with a total of 10,414 IR-1 centrifuges.[4] Consistent with the previous reporting period, 9,156 centrifuges within 54 fully installed cascades are currently fed with UF6 produced in the conversion facility at Isfahan (Esfahan).[5] In its August 2012 report, the IAEA noted that, "not all of the centrifuges in the cascades being fed with UF6 may have been working" at the time of reporting.[6] This qualification was not included in the Agency’s November 2012 report. Since enrichment began in 2007, Iran has produced approximately 7,611kg of LEU with a maximum enrichment level of 5%.[7] As of the November 2012 IAEA report, preparatory centrifuge installation work was completed for an additional 28 cascades, and was ongoing in 54 others.[8]

Between February 2010 and November 2012, Iran fed 1,177 kg of UF6 enriched to 5% at the FEP into cascades in the production area of the above-ground Pilot Fuel Enrichment Plant, also located at the Natanz complex, for further enrichment up to 19.75% U-235.[9] Due to the potential military applications of uranium enrichment, the IAEA closely monitors activities at the facility.

Sources:
[1] "Nuclear Sites, Facilities, Natanz," Institute for Science and International Security, www.isisnucleariran.org.
[2] Yonah Alexander and Milton M. Hoenig, The New Iranian Leadership (London: Praeger Security International, 2008), p. 119.
[3] Anthony H. Cordesman and Adam C. Seitz, Iranian Weapons of Mass Destruction: The Birth of a Regional Arms Race (Washington, DC: Center for Strategic and International Studies, 2009), p. 217.
[4] International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 16 November 2012, www.iaea.org.
[5] International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 16 November 2012, www.iaea.org.
[6] " International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 30 August 2012, www.iaea.org.
[7] International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 16 November 2012, www.iaea.org.
[8] International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 16 November 2012, www.iaea.org.
[9] International Atomic Energy Agency, "Implementation of the NPT Safeguards Agreement and relevant provisions of Security Council Resolutions in the Islamic Republic of Iran," Report by the Director General, 16 November 2012, www.iaea.org.