as part of its efforts to safeguard potentially weapons-usable atomic material, the united nations nuclear watchdog assisted bulgaria with the removal of highly enriched uranium stored at the shut-down research reactor in sofia. the substance, which was 36% enriched and took the form of fresh fuel, was airlifted in december 2003 to russia, the original supplier, according to the international atomic energy agency (iaea). agency safeguards inspectors monitored and verified the packaging of the fuel, which moscow says it will re-fabricate into low-enriched uranium.