History of Nuclear Energy51 milestones · 177 developments

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An interactive timeline of the history of nuclear energy: 51 milestones · 177 developments, from Discovery (1896–1938) to Renaissance & Fusion (2000–present), with the connections between them.

Discovery (1896–1938)

Becquerel discovers radioactivity (February–March 1896)

Henri Becquerel found that uranium salts fogged photographic plates even in darkness, revealing a spontaneous radiation unrelated to sunlight. The discovery opened the study of atomic nuclei.

The Curies isolate polonium and radium (1898–1911)

Marie and Pierre Curie traced the activity of pitchblende to two new elements, polonium and radium. Marie Curie coined the term "radioactivity" and became the first person to win two Nobel Prizes.

Rutherford and Soddy: transmutation (1899–1913)

Working at McGill University, Ernest Rutherford and Frederick Soddy showed that radioactivity is the spontaneous transformation of one element into another. Rutherford also classified alpha and beta rays and introduced the half-life.

Einstein: E = mc² (September 1905)

In a short follow-up to special relativity, Albert Einstein argued that a body losing energy E loses mass E/c². Mass–energy equivalence later explained the enormous energy released by nuclear reactions.

The atomic nucleus (1909–1919)

Alpha-scattering experiments by Geiger and Marsden led Rutherford to the nuclear model of the atom. In 1917–1919 he achieved the first artificial nuclear transmutation, identifying the proton.

Fusion powers the stars (1920–1939)

Francis Aston's precise mass measurements showed a helium atom weighs less than four hydrogen atoms. Arthur Eddington inferred that the Sun shines by fusing hydrogen, and Hans Bethe worked out the reaction cycles in 1939.

Chadwick discovers the neutron (February 1932)

James Chadwick identified the neutral radiation from beryllium bombarded with alpha particles as a new particle, the neutron. With no charge, neutrons could penetrate nuclei, becoming the key tool of nuclear physics.

Cockcroft and Walton split the atom (April 1932)

At Cambridge's Cavendish Laboratory, John Cockcroft and Ernest Walton used a high-voltage accelerator to split lithium nuclei with protons. It was the first nuclear reaction driven by artificially accelerated particles.

Szilard conceives the chain reaction (September 1933)

Irritated by Rutherford's dismissal of atomic power as "moonshine", Leo Szilard realised that a neutron-induced reaction releasing two neutrons could sustain itself. He patented the idea and later kept it secret for fear of weapons.

Artificial radioactivity (January 1934)

Irène Joliot-Curie and Frédéric Joliot made stable elements radioactive by bombarding them with alpha particles. Their work showed radioisotopes could be manufactured, with wide uses in medicine and research.

Fermi and slow neutrons (1934–1938)

Enrico Fermi's group in Rome bombarded element after element with neutrons, creating many new radioisotopes. Their discovery that slowed neutrons react far more readily underpins every thermal reactor.

Discovery of nuclear fission (December 1938 – February 1939)

Otto Hahn and Fritz Strassmann found barium among the products of neutron-irradiated uranium. Lise Meitner and Otto Frisch explained that the nucleus had split in two, releasing about 200 MeV per event.

Neutron multiplication confirmed (February–September 1939)

Within months of fission's discovery, groups in Paris and New York showed that each fission emits extra neutrons, making a chain reaction possible. Niels Bohr and John Wheeler identified rare uranium-235 as the isotope that fissions with slow neutrons.

Einstein–Szilard letter (August–October 1939)

Drafted by Szilard and signed by Einstein, the letter warned President Roosevelt that uranium chain reactions could yield extremely powerful bombs and that Germany might pursue them. It led to the first US government uranium research.

Plutonium discovered (February–March 1941)

Glenn Seaborg's team at Berkeley produced and identified element 94, plutonium. Plutonium-239 proved fissile and could be bred from abundant uranium-238 inside a reactor.

Manhattan Project (1942–1946)

The US Army's Manhattan Project, led by General Leslie Groves, built the industrial base for enrichment, reactors and reprocessing. Its sites and expertise became the foundation of the post-war nuclear industry.

Chicago Pile-1 (2 December 1942)

Under the stands of Stagg Field at the University of Chicago, Fermi's team achieved the first self-sustaining nuclear chain reaction. The crude pile of graphite and uranium proved controlled fission was possible.

Trinity, Hiroshima and Nagasaki (July–August 1945)

The first nuclear explosion at Trinity was followed weeks later by the bombing of Hiroshima and Nagasaki. The weapons' origin shaped public perceptions of nuclear energy and the secrecy around it for decades.

Atomic Energy Commission (1946–1974)

The Atomic Energy Act of 1946 placed US nuclear technology under a civilian Atomic Energy Commission with a government monopoly on fissile material. Criticism that it both promoted and regulated the industry led to its split in 1974.

Early fusion programmes (1951–1958)

In 1951 Lyman Spitzer proposed the stellarator and the US launched the secret Project Sherwood, while Soviet physicists Tamm and Sakharov conceived the tokamak. Early optimism faded as plasmas proved unstable.

EBR-I generates electricity (20 December 1951)

Experimental Breeder Reactor I in Idaho produced the first usable electricity from nuclear fission, lighting four light bulbs. A sodium-potassium cooled fast reactor, it also demonstrated breeding of new fuel.

Atoms for Peace (1953–1957)

President Eisenhower's speech to the UN General Assembly proposed sharing peaceful nuclear technology under international oversight. It led to new US law allowing private reactors, the 1955 Geneva conference and the IAEA.

USS Nautilus (1954–1958)

The world's first nuclear-powered submarine, driven by Hyman Rickover's Naval Reactors programme, ran on a Westinghouse pressurised water reactor. Its compact PWR design became the template for most of the world's power reactors.

Obninsk: first grid-connected plant (June 1954)

The Soviet AM-1 reactor at Obninsk became the first nuclear power plant to supply an electrical grid. Its small graphite-moderated, water-cooled design was a forerunner of the RBMK.

Calder Hall and Windscale (1956–1957)

Opened by Queen Elizabeth II, Calder Hall was the first nuclear power station to deliver electricity on an industrial scale, while also making plutonium. A year later a fire in the neighbouring Windscale pile caused Britain's worst nuclear accident.

Kyshtym disaster (29 September 1957)

A failed cooling system caused a high-level waste tank to explode at the Soviet Mayak reprocessing complex. Rated INES level 6, it contaminated a vast area and was kept secret for decades.

Shippingport Atomic Power Station (1957–1982)

Built by Westinghouse under Rickover's Naval Reactors office for Duquesne Light, Shippingport was the first full-scale US nuclear power plant devoted to electricity. It adapted naval PWR technology for civilian use.

Dresden 1 and the BWR (1960–1967)

General Electric's Dresden 1 near Chicago was the first privately financed full-scale US nuclear plant and established the boiling water reactor. GE and Westinghouse turnkey offers then sparked the "great bandwagon market" of the mid-1960s.

CANDU heavy-water reactors (1962–1971)

Canada developed the CANDU reactor, which uses heavy water as moderator so it can burn natural uranium without enrichment. Pressure tubes allow refuelling while the reactor runs at full power.

Non-Proliferation Treaty (1968–1975)

The Treaty on the Non-Proliferation of Nuclear Weapons traded access to peaceful nuclear energy for renunciation of weapons by non-nuclear states. IAEA safeguards verify that civilian material is not diverted.

Soviet T-3 tokamak breakthrough (1968–1969)

Lev Artsimovich's team at the Kurchatov Institute reported electron temperatures of about 10 million degrees in the T-3 tokamak. Confirmation by a British team set off a worldwide shift to tokamak research.

RBMK reactor enters service (1973)

The RBMK-1000, a large graphite-moderated, light-water-cooled channel reactor, first entered service at Leningrad in 1973. Cheap to build from standard parts, it had design flaws that would prove catastrophic at Chernobyl.

France's Messmer plan (1974–1999)

Responding to the 1973 oil shock, Prime Minister Pierre Messmer launched a crash programme of standardised pressurised water reactors. France became the world's most nuclear-dependent country, with a closed fuel cycle at La Hague.

US abandons reprocessing (1977–1983)

Alarmed by proliferation risk after India's test, President Carter deferred commercial reprocessing and plutonium recycling indefinitely. The US committed to a once-through fuel cycle, putting pressure on direct disposal of spent fuel.

Three Mile Island accident (28 March 1979)

A stuck-open relief valve and operator confusion led to a partial meltdown of Unit 2 at Three Mile Island. Little radiation escaped, but the accident transformed US regulation and public opinion.

Joint European Torus (1983–2023)

JET at Culham was the world's largest operating tokamak for four decades and the first to produce controlled fusion power from deuterium–tritium fuel. Its results directly informed the design of ITER.

ITER (1985–present)

ITER grew out of a 1985 Reagan–Gorbachev summit proposal for an international fusion experiment. Under construction in southern France, it aims to produce 500 MW of fusion power from 50 MW of heating (Q = 10).

Chernobyl disaster (26 April 1986)

A safety test at Chernobyl Unit 4 triggered a power surge that destroyed the RBMK reactor and released massive radioactivity across Europe. It remains the worst accident in the history of nuclear power.

Yucca Mountain repository (1982–2010)

The Nuclear Waste Policy Act committed the US federal government to take spent fuel for deep geological disposal. Congress singled out Yucca Mountain in Nevada in 1987, but the project was defunded in 2010.

The "nuclear renaissance" (2005–2009)

Rising concern over climate change and gas prices revived interest in new reactors in the 2000s. The US Energy Policy Act of 2005 offered incentives, but cheap shale gas and Fukushima stalled most projects.

EPR: Europe's Gen III+ reactor (2005–2024)

The 1,600 MWe European Pressurised Reactor was developed by Framatome and Siemens with a core catcher and quadruple safety systems. Its first European builds suffered years of delay and cost overruns.

Fukushima Daiichi accident (11 March 2011)

The Tōhoku earthquake and tsunami knocked out power and cooling at Fukushima Daiichi, causing meltdowns in three reactors. It halted Japan's nuclear fleet and triggered policy reversals worldwide.

Germany's Atomausstieg (2000–2023)

Germany's Social Democrat–Green government agreed a nuclear phase-out with utilities in 2000. After a brief extension in 2010, Fukushima prompted an accelerated exit, completed in April 2023.

Onkalo deep geological repository (2004–present)

Finland's Posiva is building the world's first deep geological repository for spent nuclear fuel at Olkiluoto. Fuel will be sealed in copper canisters surrounded by bentonite clay some 400 metres down in granite bedrock.

AP1000 and passive safety (2006–2024)

Westinghouse's AP1000 uses gravity, natural circulation and stored water to cool the reactor without pumps or operator action. Builds in China succeeded first, while US projects drove Westinghouse into bankruptcy.

NuScale and small modular reactors (2020–2025)

NuScale's factory-built light-water module became the first small modular reactor design approved by the US NRC. SMRs promise lower up-front costs, but NuScale's first project was cancelled over rising prices.

High-temperature superconducting magnets (2021–present)

MIT and Commonwealth Fusion Systems demonstrated a 20-tesla magnet made of high-temperature superconductor tape. Such magnets allow far smaller tokamaks, spurring a wave of privately funded fusion companies.

NIF achieves fusion ignition (5 December 2022)

At Lawrence Livermore's National Ignition Facility, 192 lasers compressed a fuel capsule that released more fusion energy than the laser energy delivered to it. It was the first controlled fusion experiment to reach scientific ignition.

China's HTR-PM pebble-bed reactor (December 2023)

China's Shidaowan HTR-PM entered commercial operation as the world's first Generation IV pebble-bed high-temperature gas-cooled reactor plant. Helium-cooled TRISO pebbles give it inherent resistance to meltdown.

Kairos Power and advanced reactors (2023–present)

Kairos Power is developing a fluoride-salt-cooled high-temperature reactor using TRISO pebble fuel. Its Hermes test reactor received the first US permit for a non-light-water power-type reactor in decades.

AI data centres and the nuclear revival (2023–2025)

Surging electricity demand from AI data centres led tech companies to sign long-term deals for nuclear power, including restarting closed reactors. Governments set targets to expand nuclear capacity sharply by 2050.

Compiled from public sources; summaries for illustration