Built with Chinese assistance and opened in 1984, the Isfahan (Esfahan) Nuclear Technology Center (INTC) today is Iran's largest nuclear research complex and employs approximately 3,000 scientists. [1] Isfahan is a multi-purpose research center suspected of being the center of a secret Iranian nuclear weapons program. [2] It operates three small Chinese-supplied research reactors. [3] It also operates a conversion facility, a fuel production plant, a zirconium cladding plant, and other facilities and laboratories. The INTC is the target of both U.S. and UN sanctions. [4] Additionally, UNSCR 1747 imposed an international travel ban and assets freeze on Javad Rahiqi, head of the INTC. [5]

Sources:
[1] Hussein D. Hassan, "Iranian nuclear sites,"Congressional Research Service Report for Congress, 9 August 2007.
[2] Hussein D. Hassan, "Iranian nuclear sites," Congressional Research Service Report for Congress, 9 August 2007.
[3] "Nuclear Sites, Esfahan Nuclear Technology Center," Institute for Science and International Security, www.isisnucleariran.org.
[4] "New UN Iran Steps Target Isfahan Atomic Site Chief," Reuters, 8 June 2010.
[5] Kenneth Katzman, "Iran Sanctions," Congressional Research Service Report for Congress, 23 June 2010.