Experimental Breeder Reactor-II (EBR-II) was a sodium-cooled fast reactor designed, built and operated by Argonne National Laboratory at the National Reactor Testing Station in Idaho. It was shut down in 1994. Custody of the reactor was transferred to Idaho National Laboratory after its founding in 2005. Initial operations began in July 1964 and it achieved criticality in 1965 at a total cost of more than US$32 million ($ in dollars). The original emphasis in the design and operation of EBR-II was to demonstrate a complete breeder-reactor power plant with on-site reprocessing of solid metallic fuel. Fuel elements enriched to about 67% uranium-235 were sealed in stainless steel tubes and removed when they reached about 65% enrichment. The tubes were unsealed and reprocessed to remove neutron poisons, mixed with fresh U-235 to increase enrichment, and placed back in the reactor. Testing of the original breeder cycle ran until 1969, after which time the reactor was used to test concepts for the Integral Fast Reactor concept. In this role, the high-energy neutron environment of the EBR-II core was used for testing fuels and materials for future, larger, liquid metal reactors. As part of these experiments, in 1986 EBR-II underwent an experimental shutdown simulating complete cooling pump failure. It demonstrated its ability to self-cool its fuel through natural convection of the sodium coolant during the decay heat period following the shutdown. It was used in the IFR support role, and many other experiments, until it was decommissioned in September 1994. At full power operation, which it reached in September 1969, EBR-II produced about 62.5 megawatts of heat and 20 megawatts of electricity through a conventional three-loop steam turbine system and tertiary forced-air cooling tower. Over its lifetime it has generated over two billion kilowatt-hours of electricity, providing a majority of the electricity and also heat to the facilities of the Argonne National Laboratory-West. Design The fuel consists of uranium rods 5 millimeters in diameter and 33 cm (13 inches) long . Enriched to 67% uranium-235 when fresh, the concentration dropped to approximately 65% upon removal. The rods also contained 10% zirconium. Each fuel element is placed inside a thin-walled stainless steel tube along with a small amount of sodium metal. The tube is welded shut at the top to form a unit 73 cm (29 inches) long. The purpose of the sodium is to function as a heat-transfer agent. As more and more