The Experimental Breeder Reactor-II (EBR-II) operated at Argonne-West in Idaho from 1964 to 1994. In 1995, the American Nuclear Society declared EBR-II a Nuclear Historic Landmark, calling EBR-II "… arguably the most successful test reactor ever."
From 1964 to 1969, EBR-II demonstrated a complete breeder-reactor power plant with on-site reprocessing of metallic fuel, processing 35,000 fuel elements, producing 366 subassemblies and assembling 66 control and safety rods.
From 1964 to 1994, EBR-II was the backbone of the U.S. breeder reactor effort, when research was terminated.
The EBR-II accommodated as many as 65 experimental subassemblies at one time for irradiation and operational reliability tests. EBR-II also performed over 30,000 irradiation tests.
Most recently, EBR-II was the prototype for the Integral Fast Reactor (IFR), a reactor fueled by metal alloy and cooled by liquid sodium.
On April 3, 1986, two tests at EBR-II demonstrated the inherent safety of the IFR concept. These tests simulated accidents involving loss of coolant flow. Even with its normal shutdown devices disabled, the reactor shut itself down safely without overheating anywhere in the system.