Fasa is the suspected location of a Uranium Conversion Facility.[1] China reportedly constructed the small-scale pilot plant in the 1990s, following a secret 1991 nuclear cooperation agreement with Iran.[2] Iran allegedly received equipment for the plant from China in 1994.[3] According to John Garver, "the designed capacity of this hex plant was two hundred tons of UF6 per year."[4] Iran has neither declared this facility to the IAEA, nor has the Agency referred to it in its safeguards reports.

Sources:
[1] 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. 215.
[2] John W. Garver, China and Iran: Ancient Partners in a Post-Imperial World (Seattle: University of Washington Press, 2006), p. 152.
[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. 215.
[4] John W. Garver, China and Iran: Ancient Partners in a Post-Imperial World (Seattle: University of Washington Press, 2006), p. 152.