# History of Nuclear Energy

> 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.

- Interactive version: https://timelinegraph.app/examples/nuclear-energy
- Published on [Timeline Graph](https://timelinegraph.app/), a free diagonal timeline maker
- Sources: [Compiled from public sources; summaries for illustration](https://en.wikipedia.org/wiki/History_of_nuclear_power)

## Eras

- **Discovery (1896–1938)** (13 Mar 1896 to 20 Dec 1938): 12 items
- **Atomic Age (1939–1953)** (19 Apr 1939 to 5 Dec 1953): 10 items
- **Commercial Build-out (1954–1978)** (19 Jan 1954 to 19 Apr 1977): 12 items
- **Accidents & Stagnation (1979–1999)** (28 Mar 1979 to 20 Dec 1987): 5 items
- **Renaissance & Fusion (2000–present)** (7 Aug 2005 to 13 Sep 2024): 12 items

## Kinds of connection

- Builds on
- Prompts reaction

## 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.

Topics: Physics, radioactivity, uranium

Further reading: [Read more](https://en.wikipedia.org/wiki/Henri_Becquerel)

- Becquerel showed that uranium salts emit penetrating rays without any external energy source, fogging wrapped photographic plates.
- He shared the 1903 Nobel Prize in Physics with Pierre and Marie Curie for the discovery of spontaneous radioactivity.

Later built on by: The Curies isolate polonium and radium, Rutherford and Soddy: transmutation

### 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.

Topics: Physics, polonium, radium

Further reading: [Read more](https://en.wikipedia.org/wiki/Marie_Curie)

- Marie Curie proposed that radiation is an atomic property of the element itself and coined the word "radioactivity".
- In July and December 1898 the Curies announced polonium and radium, isolated by laboriously processing tonnes of pitchblende.
- Marie Curie received the 1911 Nobel Prize in Chemistry for isolating radium, her second Nobel Prize.

Later built on by: Rutherford and Soddy: transmutation, Einstein: E = mc²
Builds on: Becquerel discovers radioactivity

### 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.

Topics: Physics, alpha, beta, half-life

Further reading: [Read more](https://en.wikipedia.org/wiki/Ernest_Rutherford)

- In 1899 Rutherford distinguished two kinds of uranium radiation by penetrating power, naming them alpha and beta rays.
- Studying thorium emanation in 1900, Rutherford found activity decays exponentially, introducing the concept of half-life.
- In 1902 Rutherford and Soddy proposed that radioactive atoms transmute into other elements, a heresy to chemists of the day.
- Soddy introduced the concept of isotopes in 1913: atoms of one element with differing masses, earning the 1921 Chemistry Nobel.

Builds on: The Curies isolate polonium and radium, Becquerel discovers radioactivity
Later built on by: The atomic nucleus, Fusion powers the stars, Neutron multiplication confirmed, US abandons reprocessing

### 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.

Topics: Physics, mass–energy

Further reading: [Read more](https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence)

- The paper "Does the Inertia of a Body Depend Upon Its Energy Content?" established that mass and energy are equivalent.
- Einstein suggested his relation might be tested with radium salts, whose energy output seemed inexhaustible.
- The equation explains nuclear binding energy: a tiny mass defect in fission or fusion corresponds to millions of electronvolts.

Builds on: The Curies isolate polonium and radium
Later built on by: Fusion powers the stars, Cockcroft and Walton split the atom, Discovery of nuclear fission

### 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.

Topics: Physics, nucleus, proton

Further reading: [Read more](https://en.wikipedia.org/wiki/Rutherford_model)

- Geiger and Marsden found in 1909 that a few alpha particles bounce back from gold foil, implying a dense concentrated charge.
- Rutherford proposed in 1911 that nearly all an atom's mass sits in a tiny positively charged nucleus.
- By bombarding nitrogen with alpha particles, Rutherford knocked out hydrogen nuclei: the first deliberate nuclear transmutation (1919).

Builds on: Rutherford and Soddy: transmutation
Later built on by: Chadwick discovers the neutron, Cockcroft and Walton split the atom, Artificial radioactivity

### 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.

Topics: Fusion, Physics, stellar energy

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_fusion)

- Aston's mass spectrograph showed helium-4 is about 0.8% lighter than four hydrogen atoms, a measurable mass defect.
- In a 1920 address Eddington proposed that stars are powered by converting hydrogen into helium.
- Hans Bethe's 1939 paper described the proton–proton chain and CNO cycle, later earning the 1967 Nobel Prize.

Later built on by: Early fusion programmes
Builds on: Rutherford and Soddy: transmutation, Einstein: E = mc²

### 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.

Topics: Physics, neutron

Further reading: [Read more](https://en.wikipedia.org/wiki/Discovery_of_the_neutron)

- Chadwick showed the "beryllium radiation" misread by Bothe and the Joliot-Curies as gamma rays was a neutral particle of proton mass.
- Uncharged neutrons are not repelled by the nucleus, making them ideal projectiles for inducing nuclear reactions.
- Chadwick received the 1935 Nobel Prize in Physics for the discovery.

Builds on: The atomic nucleus
Later built on by: Fermi and slow neutrons, Szilard conceives the chain reaction

### 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.

Topics: Physics, accelerator

Further reading: [Read more](https://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator)

- Protons accelerated to about 700 keV split lithium-7 into two alpha particles.
- The energy of the alpha particles matched the mass lost, an early experimental confirmation of E = mc².
- The pair shared the 1951 Nobel Prize in Physics; Cockcroft later directed Britain's Harwell atomic research establishment.

Builds on: Einstein: E = mc², The atomic nucleus
Later prompted: Szilard conceives the chain reaction

### 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.

Topics: Physics, Weapons, chain reaction

Further reading: [Read more](https://en.wikipedia.org/wiki/Leo_Szilard)

- Waiting at a London traffic light in September 1933, Szilard conceived a self-sustaining neutron chain reaction.
- He filed a British patent on the neutron chain reaction in 1934, describing critical mass.
- In 1936 Szilard assigned the patent to the British Admiralty to keep it secret from Nazi Germany.

Builds on: Chadwick discovers the neutron
Reacts against: Cockcroft and Walton split the atom
Later built on by: Neutron multiplication confirmed, Chicago Pile-1, Einstein–Szilard letter

### 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.

Topics: Physics, induced radioactivity

Further reading: [Read more](https://en.wikipedia.org/wiki/Induced_radioactivity)

- Alpha bombardment turned aluminium into radioactive phosphorus-30, the first artificially created radioisotope.
- The couple received the 1935 Nobel Prize in Chemistry for synthesising new radioactive elements.

Builds on: The atomic nucleus
Later built on by: Fermi and slow neutrons

### 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.

Topics: Physics, slow neutrons, moderation

Further reading: [Read more](https://en.wikipedia.org/wiki/Enrico_Fermi)

- Fermi's "Via Panisperna boys" irradiated uranium with neutrons in 1934, unknowingly producing fission products.
- In October 1934 they found that passing neutrons through paraffin wax greatly increased induced activity: neutron moderation.
- Fermi won the 1938 Nobel Prize in Physics and used the trip to Stockholm to emigrate to the United States with his Jewish wife.

Later built on by: Chicago Pile-1, Discovery of nuclear fission, CANDU heavy-water reactors
Builds on: Chadwick discovers the neutron, Artificial radioactivity

### 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.

Topics: Physics, fission, uranium

Further reading: [Read more](https://en.wikipedia.org/wiki/Discovery_of_nuclear_fission)

- Hahn and Strassmann chemically identified barium in irradiated uranium in December 1938, a result Hahn could not explain.
- Meitner and Frisch interpreted the result with the liquid-drop model and named the process "fission".
- Using E = mc², they estimated each fission releases about 200 MeV, millions of times more than a chemical reaction.
- Hahn alone received the 1944 Nobel Prize in Chemistry; Meitner's exclusion is now widely regarded as an injustice.

Later built on by: Neutron multiplication confirmed, Einstein–Szilard letter
Builds on: Einstein: E = mc², Fermi and slow neutrons

## Atomic Age (1939–1953)

### 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.

Topics: Physics, U-235, secondary neutrons

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_chain_reaction)

- Joliot, von Halban and Kowarski measured more than two neutrons emitted per fission, confirming a chain reaction was feasible.
- Bohr argued that slow-neutron fission occurs in uranium-235, just 0.7% of natural uranium, implying enrichment or a moderator.
- Bohr and Wheeler's September 1939 paper gave the theoretical foundation of fission and predicted fissility of element 94.

Builds on: Discovery of nuclear fission, Rutherford and Soddy: transmutation, Szilard conceives the chain reaction
Later built on by: Chicago Pile-1, Manhattan Project, Plutonium discovered

### 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.

Topics: Policy, Weapons, Roosevelt

Further reading: [Read more](https://en.wikipedia.org/wiki/Einstein%E2%80%93Szilard_letter)

- The letter dated 2 August 1939 urged the US to secure uranium supplies and fund chain-reaction research.
- After Alexander Sachs delivered it in October 1939, Roosevelt created the Advisory Committee on Uranium.

Later built on by: Manhattan Project
Builds on: Szilard conceives the chain reaction, Discovery of nuclear fission

### 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.

Topics: Physics, Fuel Cycle, plutonium, breeding

Further reading: [Read more](https://en.wikipedia.org/wiki/Plutonium)

- Seaborg, McMillan, Kennedy and Wahl identified plutonium in February 1941 using the Berkeley cyclotron.
- In March 1941 they showed plutonium-239 fissions with slow neutrons even more readily than uranium-235.
- Because U-238 absorbs neutrons to become Pu-239, reactors could convert non-fissile uranium into new fuel.

Builds on: Neutron multiplication confirmed
Later built on by: Manhattan Project, EBR-I generates electricity, France's Messmer plan

### 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.

Topics: Weapons, Industry, Fuel Cycle, Groves, Oak Ridge, Hanford

Further reading: [Read more](https://en.wikipedia.org/wiki/Manhattan_Project)

- Britain's 1941 MAUD Report concluded a uranium bomb was feasible, spurring the US to a full-scale programme.
- Oak Ridge built Y-12 electromagnetic and K-25 gaseous-diffusion plants, the first industrial uranium enrichment.
- The X-10 Graphite Reactor went critical in November 1943, the first continuously operating reactor.
- Hanford's B Reactor, critical in September 1944, was the first full-scale plutonium production reactor.
- Wartime reprocessing left Hanford with tens of millions of gallons of high-level waste, still being cleaned up today.

Builds on: Einstein–Szilard letter, Neutron multiplication confirmed, Plutonium discovered
Later built on by: Trinity, Hiroshima and Nagasaki, Calder Hall and Windscale, Kyshtym disaster
Later prompted: Yucca Mountain repository

### 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.

Topics: Reactor Design, Physics, first criticality

Further reading: [Read more](https://en.wikipedia.org/wiki/Chicago_Pile-1)

- At 3:25 pm on 2 December 1942 CP-1 went critical, producing about half a watt of power.
- The pile used about 400 tons of graphite as moderator with natural uranium metal and oxide, needing no enrichment.
- Cadmium-coated control rods, including an emergency "zip" rod, absorbed neutrons to regulate the reaction.
- Arthur Compton reported the success by phone in code: "The Italian navigator has landed in the new world."

Builds on: Fermi and slow neutrons, Szilard conceives the chain reaction, Neutron multiplication confirmed
Later built on by: Calder Hall and Windscale, Obninsk: first grid-connected plant, RBMK reactor enters service

### 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.

Topics: Weapons, atomic bomb

Further reading: [Read more](https://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki)

- The Trinity test of a plutonium implosion device in New Mexico on 16 July 1945 was the first nuclear detonation.
- Bombs dropped on Hiroshima (6 August) and Nagasaki (9 August) killed well over 100,000 people.
- Linking the atom to mass destruction left an enduring public dread of radiation that later shaped opposition to power plants.

Builds on: Manhattan Project
Later prompted: Atomic Energy Commission, Atoms for Peace, Non-Proliferation Treaty
Later built on by: Three Mile Island accident

### 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.

Topics: Policy, AEC, NRC

Further reading: [Read more](https://en.wikipedia.org/wiki/United_States_Atomic_Energy_Commission)

- The McMahon Act of August 1946 transferred control from the Army to a five-member civilian commission.
- The Act kept all fissile material and reactor know-how in government hands and restricted sharing even with Britain.
- The Energy Reorganization Act of 1974 abolished the AEC, creating the Nuclear Regulatory Commission and ERDA.
- The 1975 Rasmussen Report (WASH-1400) pioneered probabilistic risk assessment for reactor accidents.

Reacts against: Trinity, Hiroshima and Nagasaki
Later prompted: Atoms for Peace, Three Mile Island accident
Later built on by: EBR-I generates electricity, Three Mile Island accident

### 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.

Topics: Fusion, stellarator, ZETA

Further reading: [Read more](https://en.wikipedia.org/wiki/History_of_nuclear_fusion)

- Spitzer's figure-eight stellarator at Princeton aimed to confine hot plasma in a twisted magnetic field.
- Tamm and Sakharov proposed a toroidal magnetic trap with plasma current in 1950–51, the concept behind the tokamak.
- Britain's ZETA announced fusion neutrons in January 1958, but the claim was retracted months later.
- Fusion research was declassified at the 1958 Geneva Atoms for Peace conference, opening international collaboration.

Builds on: Fusion powers the stars
Later built on by: Soviet T-3 tokamak breakthrough
Later prompted: Soviet T-3 tokamak breakthrough

### 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.

Topics: Reactor Design, Fuel Cycle, fast breeder, Idaho

Further reading: [Read more](https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_I)

- On 20 December 1951 EBR-I lit four 200-watt bulbs, the first electricity generated by nuclear power.
- In 1953 EBR-I showed it could produce more fissile material than it consumed, validating the breeder concept.
- During an experiment in November 1955 part of its core melted, one of the earliest reactor accidents.

Builds on: Plutonium discovered, Atomic Energy Commission
Later built on by: Obninsk: first grid-connected plant, US abandons reprocessing
Later prompted: Atoms for Peace

### 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.

Topics: Policy, Eisenhower, IAEA

Further reading: [Read more](https://en.wikipedia.org/wiki/Atoms_for_Peace)

- On 8 December 1953 Eisenhower proposed an international agency to pool fissile material for peaceful uses.
- The Atomic Energy Act of 1954 allowed private companies to own and operate reactors under AEC licence.
- The August 1955 Geneva conference declassified much reactor science; chair Homi Bhabha forecast fusion power within two decades.
- The 1957 Price–Anderson Act capped operator liability for accidents, making private investment insurable.
- The International Atomic Energy Agency was established in July 1957 to promote and safeguard nuclear technology.

Later built on by: Dresden 1 and the BWR, Shippingport Atomic Power Station, Non-Proliferation Treaty
Reacts against: Trinity, Hiroshima and Nagasaki, Atomic Energy Commission, EBR-I generates electricity

## Commercial Build-out (1954–1978)

### 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.

Topics: Reactor Design, Industry, naval reactors, Rickover

Further reading: [Read more](https://en.wikipedia.org/wiki/USS_Nautilus_(SSN-571))

- The S1W land-based prototype in Idaho reached full power in 1953, proving the naval pressurised water reactor.
- Nautilus was launched in January 1954 and signalled "Underway on nuclear power" on 17 January 1955.
- In August 1958 Nautilus made the first submerged transit beneath the North Pole.
- The PWR's water-cooled, water-moderated design was adopted by industry largely because the Navy had already proven it.

Later built on by: Shippingport Atomic Power Station, France's Messmer plan

### 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.

Topics: Reactor Design, Industry, USSR, AM-1

Further reading: [Read more](https://en.wikipedia.org/wiki/Obninsk_Nuclear_Power_Plant)

- On 27 June 1954 the 5 MWe AM-1 ("Peaceful Atom") reactor began supplying the Mosenergo grid.
- Its graphite-moderated, water-cooled channel design was scaled up into the RBMK reactors.
- The reactor operated for almost 48 years until its shutdown in 2002 and is now a museum.

Builds on: Chicago Pile-1, EBR-I generates electricity
Later built on by: RBMK reactor enters service

### 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.

Topics: Reactor Design, Industry, Magnox, UK

Further reading: [Read more](https://en.wikipedia.org/wiki/Calder_Hall_nuclear_power_station)

- Calder Hall was opened on 17 October 1956, the world's first commercial-scale nuclear power station.
- Its Magnox reactors used natural uranium in magnesium-alloy cladding, moderated by graphite and cooled by CO₂.
- The station also produced weapons plutonium, typical of early dual-purpose programmes.
- On 10 October 1957 Windscale Pile 1 caught fire, releasing iodine-131; milk was banned over 500 km² (INES level 5).

Builds on: Chicago Pile-1, Manhattan Project
Later built on by: CANDU heavy-water reactors

### 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.

Topics: Waste, Safety & Accidents, Mayak, secrecy

Further reading: [Read more](https://en.wikipedia.org/wiki/Kyshtym_disaster)

- A tank of liquid reprocessing waste overheated and exploded, contaminating the East Urals Radioactive Trace.
- The USSR acknowledged the accident only in 1989, after Zhores Medvedev publicised it in the West in 1976.

Builds on: Manhattan Project
Later prompted: Yucca Mountain repository

### 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.

Topics: Reactor Design, Industry, first US plant, PWR

Further reading: [Read more](https://en.wikipedia.org/wiki/Shippingport_Atomic_Power_Station)

- Shippingport reached criticality on 2 December 1957 and began supplying 60 MWe to the Pittsburgh grid that month.
- Its pressurised water reactor descended from a cancelled aircraft-carrier design developed under Rickover.
- From 1977 to 1982 it ran a thorium light-water breeder core that ended with more fissile material than it started with.

Builds on: Atoms for Peace, USS Nautilus
Later built on by: France's Messmer plan, Kairos Power and advanced reactors

### 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.

Topics: Reactor Design, Industry, BWR, General Electric

Further reading: [Read more](https://en.wikipedia.org/wiki/Boiling_water_reactor)

- In a BWR water boils in the core and drives the turbine directly, eliminating steam generators.
- Dresden 1 entered commercial service in 1960 at about 200 MWe, built without government subsidy.
- GE's fixed-price turnkey sale of Oyster Creek in 1963 triggered a rush of US utility orders, many at a loss to vendors.

Builds on: Atoms for Peace
Later built on by: Fukushima Daiichi accident, Three Mile Island accident

### 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.

Topics: Reactor Design, Fuel Cycle, Canada, heavy water

Further reading: [Read more](https://en.wikipedia.org/wiki/CANDU_reactor)

- The 22 MWe Nuclear Power Demonstration at Rolphton, Ontario began supplying power in 1962.
- Heavy water's low neutron absorption lets CANDU run on natural uranium, freeing Canada from enrichment plants.
- Horizontal pressure tubes allow on-power refuelling; Pickering A (1971) became a world capacity-factor leader.
- India used plutonium from the Canadian-supplied CIRUS research reactor for its 1974 test, prompting tighter export rules.

Builds on: Fermi and slow neutrons, Calder Hall and Windscale
Later prompted: Non-Proliferation Treaty, US abandons reprocessing

### 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.

Topics: Policy, Weapons, NPT, safeguards

Further reading: [Read more](https://en.wikipedia.org/wiki/Treaty_on_the_Non-Proliferation_of_Nuclear_Weapons)

- The NPT opened for signature on 1 July 1968 and entered into force in March 1970.
- Its three pillars are non-proliferation, disarmament and the right to peaceful use of nuclear energy.
- After India's 1974 test, supplier states formed the Nuclear Suppliers Group in 1975 to control sensitive exports.

Reacts against: Trinity, Hiroshima and Nagasaki, CANDU heavy-water reactors
Builds on: Atoms for Peace

### 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.

Topics: Fusion, tokamak, Kurchatov

Further reading: [Read more](https://en.wikipedia.org/wiki/T-3_(tokamak))

- At the 1968 IAEA conference in Novosibirsk, T-3 results showed far better confinement than any other device.
- In 1969 a Culham team used laser Thomson scattering on T-3 to confirm temperatures of about 1 keV.
- Princeton converted its Model C stellarator into a tokamak in 1970 as laboratories worldwide adopted the design.

Builds on: Early fusion programmes
Reacts against: Early fusion programmes
Later built on by: Joint European Torus, ITER

### 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.

Topics: Reactor Design, Safety & Accidents, RBMK, USSR

Further reading: [Read more](https://en.wikipedia.org/wiki/RBMK)

- Leningrad unit 1, the first RBMK-1000, was connected to the grid in December 1973.
- At low power the RBMK had a positive void coefficient: steam bubbles increased reactivity rather than reducing it.
- RBMKs lacked a full Western-style containment building around the reactor.

Later built on by: Chernobyl disaster
Builds on: Chicago Pile-1, Obninsk: first grid-connected plant

### 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.

Topics: Policy, Industry, France, oil crisis

Further reading: [Read more](https://en.wikipedia.org/wiki/Messmer_plan)

- Announced in March 1974, the plan aimed to free France from imported oil after the 1973 OPEC embargo.
- Framatome built series of near-identical PWRs under a Westinghouse licence, cutting costs through standardisation.
- France built 58 reactors in about 25 years, generating roughly 70–75% of its electricity.
- Spent fuel is reprocessed at La Hague and plutonium recycled as MOX fuel in French reactors.
- The 1,200 MWe Superphénix fast breeder connected in 1986 but was closed in 1997 after poor availability and protests.

Builds on: Plutonium discovered, USS Nautilus, Shippingport Atomic Power Station
Later prompted: US abandons reprocessing
Later built on by: EPR: Europe's Gen III+ reactor

### 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.

Topics: Fuel Cycle, Policy, Carter, once-through

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_reprocessing)

- In April 1977 Carter deferred commercial reprocessing indefinitely, stranding the Barnwell plant in South Carolina.
- Congress terminated the Clinch River Breeder Reactor in 1983 after years of cost growth.
- Without reprocessing, US spent fuel accumulated in pools and dry casks awaiting a permanent repository.

Builds on: Rutherford and Soddy: transmutation, EBR-I generates electricity
Reacts against: CANDU heavy-water reactors, France's Messmer plan
Later built on by: Yucca Mountain repository

## Accidents & Stagnation (1979–1999)

### 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.

Topics: Safety & Accidents, partial meltdown, Pennsylvania

Further reading: [Read more](https://en.wikipedia.org/wiki/Three_Mile_Island_accident)

- A pilot-operated relief valve stuck open while indicators suggested it was closed, draining coolant from the core.
- About half of the Unit 2 core melted; the containment held and off-site doses were very small.
- The Kemeny Commission faulted operator training and NRC complacency, leading to sweeping regulatory reforms.
- Utilities founded the Institute of Nuclear Power Operations in December 1979 to police operating standards.
- Sweden held a referendum in March 1980 and parliament voted to phase out nuclear power by 2010, a goal later dropped.
- Combined with high interest rates, the accident ended US reactor orders: over 100 were cancelled after 1974.

Builds on: Trinity, Hiroshima and Nagasaki, Dresden 1 and the BWR, Atomic Energy Commission
Reacts against: Atomic Energy Commission
Later prompted: The "nuclear renaissance", EPR: Europe's Gen III+ reactor, AP1000 and passive safety
Later built on by: Chernobyl disaster, AI data centres and the nuclear revival

### 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.

Topics: Fusion, JET, Culham

Further reading: [Read more](https://en.wikipedia.org/wiki/Joint_European_Torus)

- JET produced its first plasma on 25 June 1983.
- On 9 November 1991 JET achieved the first controlled release of fusion power using a deuterium–tritium mix.
- In 1997 JET produced 16 MW of peak fusion power, about two-thirds of the heating power (Q ≈ 0.67).
- Final D-T campaigns set energy records of 59 MJ (2021) and 69 MJ (2023) before JET shut down in December 2023.

Later built on by: ITER
Builds on: Soviet T-3 tokamak breakthrough

### 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).

Topics: Fusion, Policy, ITER, Cadarache

Further reading: [Read more](https://en.wikipedia.org/wiki/ITER)

- At the November 1985 Geneva summit Reagan and Gorbachev agreed to pursue fusion energy jointly.
- Seven members (EU, China, India, Japan, Korea, Russia, US) signed the ITER Agreement in November 2006.
- The tokamak is designed for Q = 10, ten times more fusion power than plasma heating power.
- A 2024 re-baseline moved the start of research operations to 2034 and D-T operation to 2039.

Builds on: Joint European Torus, Soviet T-3 tokamak breakthrough
Later prompted: High-temperature superconducting magnets

### 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.

Topics: Safety & Accidents, INES 7, Ukraine

Further reading: [Read more](https://en.wikipedia.org/wiki/Chernobyl_disaster)

- During a turbine run-down test at low power, operators disabled safety systems and withdrew most control rods.
- The positive void coefficient and graphite-tipped control rods caused a power excursion and steam explosion at 01:23.
- Two workers died in the explosion and 28 more from acute radiation syndrome; fallout spread across Europe.
- Pripyat's 49,000 residents were evacuated and a 30 km exclusion zone established; a New Safe Confinement was completed in 2016.
- Italy voted in a November 1987 referendum to abandon nuclear power and closed its last reactors by 1990.
- Operators worldwide formed the World Association of Nuclear Operators in 1989 to share safety lessons.

Builds on: RBMK reactor enters service, Three Mile Island accident
Later prompted: Germany's Atomausstieg, EPR: Europe's Gen III+ reactor
Later built on by: Fukushima Daiichi accident

### 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.

Topics: Waste, Policy, Nevada, repository

Further reading: [Read more](https://en.wikipedia.org/wiki/Yucca_Mountain_nuclear_waste_repository)

- The 1982 Nuclear Waste Policy Act obliged the DOE to begin accepting spent fuel in 1998.
- The 1987 amendments, dubbed the "Screw Nevada bill", designated Yucca Mountain as the only site to be studied.
- After approval in 2002 and a 2008 licence application, the Obama administration terminated funding in 2010.

Reacts against: Manhattan Project, Kyshtym disaster
Builds on: US abandons reprocessing

## Renaissance & Fusion (2000–present)

### 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.

Topics: Policy, Industry, loan guarantees, climate

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_renaissance)

- The Energy Policy Act of 2005 offered loan guarantees, a production tax credit and delay insurance for new reactors.
- Utilities filed combined licence applications for about 30 new US reactors between 2007 and 2009.
- The shale-gas boom collapsed power prices, and most of the planned US units were never built.

Reacts against: Three Mile Island accident
Later built on by: AP1000 and passive safety, NuScale and small modular reactors

### 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.

Topics: Reactor Design, Industry, EPR, Gen III+

Further reading: [Read more](https://en.wikipedia.org/wiki/EPR_(nuclear_reactor))

- The EPR has four independent safety trains, a double containment and a core catcher to hold molten fuel.
- Olkiluoto 3 in Finland began construction in 2005 and entered commercial operation in April 2023, 14 years late.
- China's Taishan 1 became the first EPR to operate commercially in December 2018.
- Flamanville 3 connected to the French grid in December 2024; Hinkley Point C in the UK is under construction.

Builds on: France's Messmer plan
Reacts against: Three Mile Island accident, Chernobyl disaster
Later built on by: Onkalo deep geological repository
Later prompted: NuScale and small modular reactors

### 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.

Topics: Safety & Accidents, tsunami, INES 7

Further reading: [Read more](https://en.wikipedia.org/wiki/Fukushima_nuclear_accident)

- A magnitude-9.0 earthquake and a tsunami about 14 m high flooded emergency diesel generators, causing station blackout.
- Units 1–3 suffered core meltdowns and hydrogen explosions wrecked reactor buildings 1, 3 and 4.
- More than 150,000 people were evacuated; the evacuation itself caused many more deaths than radiation.
- All of Japan's reactors were offline by 2012; a new Nuclear Regulation Authority set stricter restart standards.
- Discharge of treated, diluted cooling water into the Pacific began in August 2023.

Builds on: Dresden 1 and the BWR, Chernobyl disaster
Later prompted: Germany's Atomausstieg, NuScale and small modular reactors, China's HTR-PM pebble-bed reactor

### 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.

Topics: Policy, phase-out, Energiewende

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_power_in_Germany)

- The June 2000 "Atomkonsens" capped each plant's remaining output, implying closures by the early 2020s.
- Days after Fukushima the eight oldest reactors were shut, and a June 2011 law set final closure for 2022.
- Isar 2, Emsland and Neckarwestheim 2 were shut down on 15 April 2023, ending German nuclear power.

Reacts against: Chernobyl disaster, Fukushima Daiichi accident
Later prompted: AI data centres and the nuclear revival

### 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.

Topics: Waste, Finland, KBS-3

Further reading: [Read more](https://en.wikipedia.org/wiki/Onkalo_spent_nuclear_fuel_repository)

- After excavation began in 2004, Finland granted Posiva a construction licence in November 2015, a world first.
- The Swedish-designed KBS-3 method relies on copper canisters, bentonite buffer and stable bedrock for 100,000 years.
- Posiva began a trial run of disposal operations in 2024, ahead of routine operation.

Builds on: EPR: Europe's Gen III+ reactor

### 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.

Topics: Reactor Design, Industry, Westinghouse, Vogtle

Further reading: [Read more](https://en.wikipedia.org/wiki/AP1000)

- Passive systems can cool the core for 72 hours after shutdown with no AC power or operator intervention.
- Sanmen 1 in China became the first AP1000 to connect to the grid in June 2018.
- Cost overruns pushed Westinghouse into Chapter 11 in 2017 and the V.C. Summer project was abandoned.
- Vogtle units 3 and 4 in Georgia entered service in 2023 and 2024, the first new US reactors built in decades.

Reacts against: Three Mile Island accident
Builds on: The "nuclear renaissance"
Later prompted: NuScale and small modular reactors
Later built on by: NuScale and small modular reactors, AI data centres and the nuclear revival

### 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.

Topics: Reactor Design, Industry, SMR, NuScale

Further reading: [Read more](https://en.wikipedia.org/wiki/NuScale_Power)

- The NRC completed its safety review in August 2020 and certified the 50 MWe module design in January 2023.
- Each module sits in a pool that can cool it indefinitely without power, pumps or operator action.
- The Carbon Free Power Project in Idaho was cancelled in November 2023 as projected power costs rose sharply.
- In May 2025 the NRC approved an uprated 77 MWe module design, the US460.

Builds on: The "nuclear renaissance", AP1000 and passive safety
Reacts against: EPR: Europe's Gen III+ reactor, AP1000 and passive safety, Fukushima Daiichi accident
Later built on by: Kairos Power and advanced reactors
Later prompted: AI data centres and the nuclear revival

### 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.

Topics: Fusion, Industry, CFS, SPARC

Further reading: [Read more](https://en.wikipedia.org/wiki/Commonwealth_Fusion_Systems)

- In September 2021 a large-bore HTS magnet reached 20 tesla, a record for its type.
- CFS is building SPARC, a compact tokamak in Massachusetts designed to reach Q > 1.
- Private fusion firms have raised billions of dollars, and CFS announced a planned ARC power plant in Virginia.

Reacts against: ITER

### 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.

Topics: Fusion, Physics, NIF, ignition

Further reading: [Read more](https://en.wikipedia.org/wiki/National_Ignition_Facility)

- A 2.05 MJ laser pulse produced 3.15 MJ of fusion energy, a target gain of about 1.5.
- The lasers drew roughly 300 MJ from the grid, so overall energy gain remains far from a power plant.
- Later shots, beginning in July 2023, repeated ignition with higher yields.

### 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.

Topics: Reactor Design, Gen IV, pebble bed

Further reading: [Read more](https://en.wikipedia.org/wiki/HTR-PM)

- The twin-reactor, 200 MWe HTR-PM began commercial operation at Shidaowan in December 2023.
- In 2024 tests, both reactors cooled naturally after all active cooling was cut, demonstrating inherent safety.

Reacts against: Fukushima Daiichi accident
Later built on by: Kairos Power and advanced reactors

### 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.

Topics: Reactor Design, Industry, molten salt, TRISO

Further reading: [Read more](https://en.wikipedia.org/wiki/Kairos_Power)

- The NRC issued a construction permit for Hermes in Oak Ridge in December 2023, its first non-LWR permit in over 50 years.
- Molten fluoride salt coolant works at low pressure, and TRISO fuel particles retain fission products at high temperature.
- In October 2024 Google agreed to buy power from a fleet of Kairos reactors totalling 500 MW by 2035.

Builds on: Shippingport Atomic Power Station, NuScale and small modular reactors, China's HTR-PM pebble-bed reactor
Later built on by: AI data centres and the nuclear revival

### 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.

Topics: Industry, Policy, AI, restarts

Further reading: [Read more](https://en.wikipedia.org/wiki/Nuclear_power_in_the_United_States)

- At COP28 in December 2023 more than 20 countries pledged to triple global nuclear capacity by 2050.
- In March 2024 Amazon bought a data-centre campus beside the Susquehanna plant; in October it invested in X-energy SMRs.
- Microsoft agreed in September 2024 to buy power from a restarted Three Mile Island Unit 1, renamed Crane Clean Energy Center.
- Meta signed a 20-year deal in June 2025 to support Constellation's Clinton nuclear plant in Illinois.
- US executive orders in May 2025 set a goal of 400 GW of nuclear capacity by 2050 and ordered faster NRC licensing.

Builds on: Three Mile Island accident, Kairos Power and advanced reactors, AP1000 and passive safety
Reacts against: Germany's Atomausstieg, NuScale and small modular reactors