Located at the Esfahan Nuclear Technology Center (ENTC); closed, according to Iran, in 1987; Iran commissioned a foreign supplier to construct the lab in 1981; first disclosed to the International Atomic Energy Agency (IAEA) in 1993; formally declared to the IAEA in 1998; between 1981 and 1993, conducted experiments involving 20 kg of depleted U3O8 imported in 1977 and exempted from safeguards until 1998; between 1982 and 1993, processed 85 kg of natural U3O8 concentrate imported in 1982; in 1998, Iranian officials claimed 5.2 kg of the depleted U3O8 and 45 kg of natural U3O8 concentrate as process losses; according to Iranian officials, produced 12.2 kg of natural UO2 between 1982 and 1987 using the natural U3O8 concentrate that had been declared as process loss; this UO2 was subsequently used for the production of UF4 at the Radiochemistry Laboratories of the Tehran Nuclear Research Center.