The Criticality Timeline

First human-made self-sustaining nuclear chain reaction (k = 1.0006, 3:25 p.m., Dec 2, 1942)

First continuously operated nuclear reactor and pilot plant for plutonium production

World's first heavy-water-moderated reactor

First industrial-scale nuclear reactor; produced plutonium for the Trinity test and the Nagasaki bomb

First reactor to go critical outside the United States; origin of Canada's heavy-water (CANDU) lineage

World's first fast-neutron reactor (full power reached March 1949)

First reactor to go critical in Europe; launched the Soviet nuclear program and ran until 2012

First reactor to go critical in Western Europe

France's first nuclear reactor, built under Frédéric Joliot-Curie

First reactor to generate usable electricity from nuclear energy (four lightbulbs, December 20, 1951) and first breeder

First nuclear power plant to deliver electricity to a civilian grid (June 26, 1954)

World's first commercial-scale nuclear power station (opened by Queen Elizabeth II, October 17, 1956)

First reactor in India and in Asia outside the USSR (rebuilt as Apsara-U in 2018)

Japan's first nuclear reactor

First full-scale civilian pressurized water reactor in the United States

First privately financed nuclear power plant in the United States and first commercial BWR

First CANDU prototype and first nuclear-generated electricity delivered to a Canadian grid

World's first molten-salt-fueled reactor; later became the first reactor to run on uranium-233

France's prototype fast breeder; first commercial-pilot-scale breeder connected to a national grid

World's first EPR to achieve criticality and grid connection

World's first Westinghouse AP1000 to achieve criticality

First of India's indigenous 700 MWe PHWR fleet to go critical

First nuclear power reactor in the Arab world

World's first modular pebble-bed high-temperature gas-cooled power reactor

First EPR in Europe and Western Europe's first new reactor in over 15 years

First AP1000 in the United States and first US reactor built from scratch in over three decades

France's first EPR and its first new reactor startup since Civaux-2 in 1999

First of six planned Hualong One units at Taipingling and the first Hualong One to enter operation in the Greater Bay Area

First of six planned Hualong One units at San'ao and the first Hualong One in operation in the Yangtze River Delta

India's first commercial-scale fast breeder reactor and the key step in stage two of its three-stage nuclear programme; criticality came roughly 15 years behind original schedule

Formerly Shin-Kori 5; operating licence issued December 2025, NSSC cleared initial criticality 10 April 2026 and it was achieved two days later. Commercial operation expected around August 2026.

First reactor to reach criticality under the DOE Reactor Pilot Program (EO 14301); zero-power fueled criticality — no power conversion or heat removal systems

First DOE-authorized reactor built outside a national laboratory; DOE-authorized zero-power fueled criticality June 18 (company reported an earlier non-DOE zero-power criticality in Nov 2025); power ascension to 10 kWt on June 22, 2026

Third DOE-authorized criticality under EO 14301; selected under the Nuclear Energy Launch Pad (successor/expansion of the Reactor Pilot Program), not among the original 11 pilot projects; ~150 days from project kick-off to zero-power fueled criticality (DOE announcement implies late June 30)

Fourth DOE-authorized reactor to reach criticality (zero-power fueled criticality at 12:20 a.m. MT, July 4, 2026), meeting the EO 14301 Independence Day goal