[3] At 1:50 p.m. on December 20, 1951, it became one of the world's first electricity-generating nuclear power plants when it produced sufficient electricity to illuminate four 200-watt light bulbs.

[4][5] EBR-I soon generated sufficient electricity to power its building, and the town of Arco and continued to be used for experimental research until it was decommissioned in 1964.

The EBR-I produced 200 kW of electricity out of 1.4 MW of heat generated by the reactor.

A small steam turbine allowed that reactor to power a single light bulb.

[9] Later in 1955, another nuclear milestone was reached when an experimental boiling water reactor plant called BORAX-III (also designed, built, and operated by Argonne National Laboratory) was connected to external loads, powering the nearby city of Arco, Idaho, the first time a city had been powered solely by nuclear power.

[10] The design purpose of EBR-I was not to produce electricity but instead to validate nuclear physics theory that suggested that a breeder reactor should be possible.

[11] The EBR-I design aimed to increase this by limiting neutron loss and maintaining a fast spectrum, achieving a ratio above one.

[12][13] On November 29, 1955, the reactor at EBR-I suffered a partial meltdown during a coolant flow test.

[14] Besides being one of the world's first to generate plant electricity from atomic energy, EBR-I was also the world's first breeder reactor and the first to use plutonium fuel to generate electricity (see also the Clementine nuclear reactor).

This structure was surrounded by the double-walled tank containing the NaK primary coolant.

This tank was surrounded by the air-cooled outer blanket of natural uranium, used for its effective neutron reflecting properties, and which also contained the control rods.

The outer blanket was the movable component, as technique for moving parts within liquid metal were in early stages.

However the air-cooling greatly limited the maximum operating power, which was reached at 1.4 MWth.

[13][16] The primary liquid metal coolant flows by gravity from the supply tank through the reactor core, where it absorbs heat.

The secondary coolant is pumped to the boiler, where it gives up its heat to water, generating steam.

It was declared a National Historic Landmark in 1965[2][18] with its dedication ceremony held on August 25, 1966, led by President Lyndon Johnson and Glenn T.