This timeline of nuclear power is an incomplete chronological summary of significant events in the study and use of nuclear power. This is primarily limited to sustained fission and decay processes, and does not include detailed timelines of nuclear weapons development or fusion experiments.
1920s
1925 On February 2, Patrick Blackett publishes experimental results of the first nuclear transmutation, by the bombardment of a nitrogen nucleus with an alpha particle, producing an oxygen-17 nucleus and a proton, at Cavendish Laboratory, Cambridge.
1930s
1931 On January 2, Ernest Lawrence and M. Stanley Livingston complete the first cyclotron, a type of circular particle accelerator. This early design is only 4.5 inches in diameter and yields a maximum proton energy of 80 keV. 1932 On January 1, Harold Urey, Ferdinand Brickwedde, and George M Murphy publish the discovery of deuterium. It is spectroscopically identified following separation from a sample of cryogenic liquid hydrogen at Columbia University, New York. Like all nuclei, preceding the discovery of the neutron, it is assumed to be composed entirely of protons and hypothetical "nuclear electrons". On February 27, James Chadwick publishes the discovery of the neutron, identified as the "beryllium radiation" emitted under alpha-particle bombardment, previously observed by Irène Joliot-Curie and Frédéric Joliot-Curie. On April 30, John Cockcroft and Ernest Walton publish the first disintegration of an atomic nucleus, popularly described as splitting the atom. They report the production of two alpha particles from the bombardment of lithium-7 nuclei by protons, using a Cockcroft–Walton generator at the University of Cambridge's Cavendish Laboratory. While in lithium this reaction is exothermic, nucleus disintegration is distinct from the undiscovered process of fission, which induces a radioactive decay. 1934 On June 24, Leo Szilard files the first patent for a nuclear reactor. The design, which predates the discovery of fission, resembles an accelerator-driven subcritical reactor, suggesting deuteron beam fusion interacting with indium, beryllium, bromine, or uranium as neutron-rich core materials.L. Szilárd, "Improvements in or relating to the transmutation of chemical elements," British patent number: GB630726 (filed: 28 June 1934; published: 30 March 1936). Mikhail Alekseevich Eremeev completes the first cyclotron in the Soviet Union and in Europe, at the Leningrad Physico-Technical Institute. It is a small design based a prototype by Lawrence, with a 28 cm diameter capable of achieving 530 keV proton energies. 1935 In January, Vemork hydroelectric plant in Norway operates the first large-scale heavy water production site, pioneered by Leif Tronstad. 1937 In March, V. N. Rukavishnikov, and Igor Kurchatov complete the first MeV cyclotron in the Soviet Union and in Europe, and outside the United States, at the V. G. Khlopin Radium Institute in Leningrad. It is a 100 cm (39 in) accelerator capable of achieving 3.2 MeV proton energies. On April 3, Yoshio Nishina, Tameichi Yasaki, and Sukeo Watanabe complete the first cyclotron in Japan and in Asia, at the Riken laboratory in Tokyo. It is a 26-inch accelerator capable of achieving 2.9 MeV deuteron energies. 1938 In August, Niels Bohr, George de Hevesy, and August Krogh complete the first cyclotron in Denmark, at the Institute for Theoretical Physics of the University of Copenhagen. 1939 On February 11, Lise Meitner and Otto Frisch publish the discovery of nuclear fission, collaborating with Otto Hahn and Fritz Strassmann who previously identified barium following neutron bombardment of uranium, at the Kaiser Wilhelm Institute for Chemistry, Berlin. Meitner and Frisch, both Jewish, had already fled Nazi Germany to Stockholm and Copenhagen respectively, and were barred from co-publishing with their German colleagues under Nazi anti-Jewish legislation. On March 8, Hans von Halban, Frédéric Joliot-Curie, Lew Kowarski, and Francis Perrin submit for publication the first net neutron production in an atomic pile. The experiment in Ivry-sur-Seine, Paris uses a 50-cm copper sphere filled with a uranyl nitrate water solution and a radium-beryllium neutron source. On March 16, Herbert L. Anderson, Enrico Fermi, and H B Hanstein submit for publication the first pile neutron production in the United States, from pile Columbia number 1 at Columbia University, New York. The pile submerges a 13-cm glass bulb filled with uranium oxide in water acting as a moderator and reflector. In March, Frédéric Joliot-Curie achieves a 7 MeV proton beam at the first cyclotron in France, at the Collège de France in Paris.
1940s
1940 On May 27, Edwin McMillan and Philip Abelson publish the discovery of neptunium at the Berkeley Radiation Laboratory. They use the 60-inch cyclotron produce a small sample of neptunium-239 via neutron bombardment of uranium-238. They also correctly assume its beta decay to the alpha-emitting plutonium-239, but are unable to isolate it. On July 1, Georgy Flyorov and Konstantin Petrzhak publish the discovery of spontaneous fission, in uranium atoms insulated from cosmic rays 60 meters underground in the Dinamo station of the Moscow Metro. They also report no such reactions in protactinium or thorium. 1941 In January, Walther Bothe and Peter Jensen conduct an neutronics experiment with a 55-cm radius graphite sphere. They erroneously conclude, possibly due to unaccounted boron and cadmium impurities of a few ppm, a neutron capture cross-section value for carbon over twice its accepted value. This hinders development of the Nazi German nuclear program. On February 24, Glenn T. Seaborg, Edwin McMillan, Emilio Segrè, Joseph W. Kennedy, and Arthur Wahl make the discovery of plutonium at the Berkeley Radiation Laboratory. They identify plutonium-238 from oxidation of a sample of beta-decaying neptunium-238, produced via deuteron bombardment of uranium in the 60-inch cyclotron. A paper is submitted to Physical Review in March but publication is delayed until 1946 due to World War II. 1942 In May, the L-IV atomic pile at the University of Leipzig sees the first net neutron production of the Nazi German nuclear program. The design uses a uranium powder, a heavy water moderator and reflector, and a central radium-beryllium neutron source. On June 23, uranium powder in the L-IV atomic pile ignites on contact with air, causing a steam explosion and wider fire. This is the first nuclear-related accident, and leads the German program to use only solid uranium in future designs. On November 13, Alpha-I, the first calutron track, begins uranium enrichment operation at the Y-12 facility, the first electromagnetic separation plant. On December 2, Chicago Pile-1, the first artificial nuclear reactor, achieves criticality at the University of Chicago. The Manhattan Project's assembly uses blocks of natural uranium and graphite as a moderator to produce 0.5 watts of thermal power. 1943 On February 28, in the early hours of the morning, a Special Operations Executive-trained team of Norwegian commandos detonate explosive charges on the heavy-water electrolysis chambers at the Vemork hydroelectric plant during Operation Gunnerside. On March 20, Chicago Pile-2, the world's second reactor, achieves criticality at Site A, Illinois. It is a rebuilt and slightly enlarged version of CP-1. On March 22, Igor Kurchatov, director of Laboratory No. 2 writes a letter to Mikhail Pervukhin suggesting that "eka-osmium-239" (plutonium-239) produced in a theoretical "uranium boiler" (reactor) will undergo fission as an alternative to uranium-235 in bomb designs. In March, the US approves a Soviet request for over 0.3 tons of uranium compounds under the Lend-Lease program. General Leslie Groves hopes to hide the extent of the Manhattan Project, and reveal the location of Laboratory No. 2. On July 31, Igor Kurchatov learns via atomic spies of the successful criticality and graphite moderator choice of Chicago Pile-1 eight months prior. On November 4, the X-10 Graphite Reactor achieves criticality at Oak Ridge National Laboratory, Tennessee. It is the world's third reactor, the first built for continuous operation, the first reactor for the production of plutonium-239. 1944 On March 19, Takeuchi Masa of the Japanese nuclear weapons program's Riken laboratory constructs the country's first Clusius tube thermal diffusion design for uranium enrichment. In March, the 305 Test Pile begins operation at the Hanford Site, primarily to provide quality assurance of graphite for subsequent reactors. Via atomic spies, this design would be replicated as the USSR's first F-1 reactor. On May 9, LOPO (low-power), the first aqueous homogeneous reactor, the first reactor to use enriched uranium, and the first water-cooled and water-moderated reactor, achieves criticality at Los Alamos National Laboratory, using a solution of uranyl sulfate at 14.7% enrichment. On May 15, Chicago Pile-3, the first heavy-water reactor, achieves criticality at Site A, Illinois. It uses deuterium oxide i.e. heavy water as a moderator instead of graphite, as well as a coolant. In July, the X-10 Graphite Reactor becomes the first reactor to exceed 1 MWth power output, reading 4 MWth due to the addition of two large fans. On September 16, S-50, the first and only full-scale liquid thermal diffusion plant, begins operation at Clinton Engineer Works, Tennessee. On September 26, the B Reactor is started at Hanford Site, Washington. At 250 MWth, it is the first reactor to exceed 10 and 100 MWth and is considered the first large-scale reactor. The site is primarily built for weapons-grade plutonium production, but also produces weapons-usable tritium, polonium-210, and uranium-233, as well as non-military plutonium, thulium-170, and iridium-192. On September 27, the first instance of xenon poisoning occurs in the Hanford B reactor. Water contamination of graphite, boron impurities in the Columbia River water coolant, and nitrogen in the air are all suggested as the neutron poisoning cause. John Archibald Wheeler and Enrico Fermi calculate the cause and the problem is solved by loading additional fuel slugs into extra tubes. In December, HYPO (high-power), the second aqueous homogenous reactor, achieves criticality at Los Alamos National Laboratory, using a uranyl nitrate solution at 14.5% enrichment. In December, the D Reactor is started at Hanford Site, Washington. It is largely identical to the B Reactor with the same primary purpose of weapons-grade plutonium production. 1945 On January 20, a team led by Otto Robert Frisch achieves the first criticality burst in the Dragon Critical Assembly at Los Alamos National Laboratory, the first fast neutron reactor and first prompt criticality. The device uses a uranium hydride slug and hollow cylinder both enriched at 71-75%, with the former dropped through the latter. In February, the F Reactor is started at Hanford Site, Washington. It is largely identical to the B Reactor with the same primary purpose of weapons-grade plutonium production. On March 12, K-25, the first gaseous diffusion plant becomes fully operational at Oak Ridge National Laboratory, Tennessee. It is the world's largest building, and had an electrical consumption almost triple that of the entire city of Detroit. On March 15, 612 Boeing B-17 Flying Fortress bomb the Auergesellschaft plant of the Nazi German nuclear program, in Oranienburg. It is an attempt to deny its uranium to the advancing Soviet Army on the recommendation of General Leslie Groves. Over 100 tons are still ultimately recovered by Russian Alsos for the F-1 reactor. On April 23, the Allied Alsos Mission dismantles and recovers uranium and heavy water from the B-VIII atomic pile at Haigerloch, the final pile of the Nazi German nuclear program.