Experimental Breeder Reactor-II (EBR-II) was arguably the most successful of the U. S. fast reactors. See figure 7.2. It was a 62.5 MWt, 20 megawatt electric (MWe), sodium-cooled, "pool-type" reactor, i. e. the heat exchangers for transferring heat to a secondary loop of liquid sodium were submerged in the reactor vessel. It was designed by ANL and constructed, beginning in June 1958, at the National Reactor Testing Station (today the Materials and Fuels Complex in the Idaho National Laboratory). Criticality at low power without sodium coolant was achieved on September 30, 1961; criticality with sodium coolant on November 11, 1963; and design power on September 25, 1969.

EBR-II demonstrated the feasibility of a sodium-cooled fast breeder reactor operating as a power plant. It operated initially with metallic HEU fuel. A hallmark feature was that it had an adjoining Fuel Cycle Facility (FCF) (now called the Fuel Conditioning Facility) that permitted continuous reprocessing and recycling of fuel to keep the working inventory down.25 EBR-II spent fuel was processed and fresh fuel fabricated at the FCF from 1964 to 1969.26 In 1967, the EBR-II was reoriented from a demonstration plant to an irradiation facility.

After cancellation of the Clinch River Breeder Reactor (CRBR) in 1983, the EBR-II reactor and the FCF became the research and demonstration facilities for the Integral Fast Reactor (IFR) concept promoted by ANL. The IFR program was terminated and EBR-II began shutdown operations in September 1994, after 30 years of operation.

The EBR-II shutdown activities included defueling and draining the primary and secondary sodium loops. The FCF has been converted to a Fuel Conditioning Facility whose mission is to electrochemically treat spent EBR-II fuel to create radioactive waste forms that are acceptable for disposal in a national geological repository. The fuel is not considered suitable for direct disposal in a geological repository because it contains sodium to provide a good thermal link between the fuel pellets and the fuel cladding. Sodium would react with any water that penetrated the cladding to generate hydrogen. The laboratory has signed an agreement with the state of Idaho that the fuel conditioning work will be completed by 2035.