The highly enriched nuclear fuel assemblies were originally supplied to Bulgaria by the Soviet Union for the Russian-designed two-megawatt research reactor, located in Sofia. The reactor was shut down in 1989 and is going to be reconstructed as a low-power, LEU research reactor.
The nuclear fuel was loaded into four transportation canisters provided by the Russian Federation. International Atomic Energy Agency (IAEA) safeguards inspectors and technical experts from the U.S. Department of Energy monitored the process.
The shipment of HEU from Bulgaria is the second shipment conducted under a tripartite initiative, comprised of the United States, Russian Federation, and IAEA, to return Russian-supplied HEU research reactor fuel for long-term management and disposition. The first shipment of fresh Russian-origin HEU fuel, from Romania to the Russian Federation, was carried out Sept. 21, 2003. (See ACT, October 2003.)