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  • Wilhelm Roentgen, a German physicist, discovered X-rays.
  • J. J. Thomson (England) discovered the electron. In 1906, he received the Nobel Prize in Physics for this discovery.
  • Marie Curie (France), a two-time Nobel Prize winner in Chemistry and Physics, discovered the radioactive elements radium and polonium.  
  • Ernest Rutherford (Canada) discovered two kinds of rays emitting from radium. He called the first rays, alpha rays; and the more penetrating rays, beta rays. 
  • Frederick Soddy (England) observed spontaneous disintegration of radioactive elements into variants.  He called these isotopes. 
  • Rutherford and Soddy published the theory of radioactive decay.
  • Albert Einstein (U.S. immigrant from Germany) wrote the special theory of relativity.  He created a new era of physics when he unified mass, energy, magnetism, electricity, and light. One of the most significant events of the 20th century was Einstein's developing the formula of E=mc2 (that is, energy equals mass times the square of the speed of light).
  • Rutherford (United Kingdom) discovered the nucleus of the atom.
  • Niels Bohr (Denmark) published the theory of atomic structure, combining nuclear theory with quantum theory.
  • The general theory of relativity was published by Albert Einstein (U.S. immigrant from Germany). He proposed that gravity, as well as motion, could affect the intervals of time and space.
  • Rutherford (United Kingdom) bombarded nitrogen gas with alpha.  The transmutation of nitrogen into oxygen was the first artificially induced nuclear reaction.
  • Werner Heisenberg, Max Born (Germany) and later Erwin Schrödinger (Austria) formulated quantum mechanics.
  • Herman Blumgart (United States), a Boston physician, used radioactive tracers to diagnose heart disease.
  • Ernest O. Lawrence (United States) conceived the idea for the first cyclotron, a device used to produce high-energy beams for use in nuclear physics experiments. He was awarded the 1939 Nobel Prize in Physics for this invention and for results obtained with it.
  • John Crockcroft and E. T. S. Walton (United Kingdom) developed a high-voltage apparatus for accelerating protons, called a linear accelerator.
  • James Chadwick (United Kingdom) discovered the neutron as well as studied the deuterium, known as heavy hydrogen and used in nuclear reactors.
  • Crockcroft and Walton (United Kingdom) split the atom with protons accelerated with their “linear accelerator.”
  • Werner Heisenberg (Germany) was awarded the Nobel Prize in Physics for the creation of quantum mechanics.
  • Enrico Fermi (U.S. immigrant from Italy) irradiated uranium with neutrons. He believed he had produced elements beyond uranium, not realizing that he had split the atom, thus achieving the world's first nuclear fission. He won the Nobel Prize in Physics for this discovery in 1938.
  • The process of splitting uranium atoms, called nuclear fission, was demonstrated by scientists Otto Hahn and Fritz Strassman (Germany).
  • President Roosevelt received a letter from Albert Einstein on the possibility of a uranium weapon.
  • German troops occupied Norway, and seized what was then the world's only heavy-water production plant at Vemork.
  • Philip Abelson and Edwin McMillan (United States) demonstrated that neutrons captured by uranium-238 lead to the creation of elements 93 and 94, neptunium and plutonium.
  • A new element (atomic number 94), was found and named plutonium. American physicists confirmed that plutonium was fissionable, thus usable for a bomb.
  • British scientists reported that a weapon could be made with 22 pounds of pure uranium 235.
  • The Manhattan Project was formed in the United States to secretly build the atomic bomb for use in World War II.
  • The first self-sustaining, controlled nuclear chain reaction led by Enrico Fermi (U.S. immigrant from Italy) and other scientists at the University of Chicago.
  • The first test of a nuclear weapon, code-named Trinity,occurred at Alamogordo, New Mexico.
  • The United States dropped an atomic bomb on Hiroshima, Japan, and three days later dropped another one on Nagasaki, Japan. Japan surrendered less than two weeks later, ending World War II.
  • The Atomic Energy Act (AEA) of 1946 was passed, establishing the United States Atomic Energy Commission (AEC) to control nuclear energy development and to explore peaceful uses of nuclear energy.
  • First demonstrations against nuclear testing were held in Times Square, New York.
  • The Joint Congressional Committee on Atomic Energy was established to oversee all civilian and military nuclear affairs.
  • The Soviet Union achieved its first nuclear chain reaction.
  • The Soviet Union detonated its first atomic device.
  • President Truman announced the decision to proceed with the development of the hydrogen bomb.
  • Klaus Fuchs (U.S. immigrant from Germany) confessed to giving atomic secrets to the Soviets while working on the Manhattan Project.
  • An experimental breeder reactor (EBR Reactor I, or EBR-I) in Idaho produced the first usable electric power from the atom, lighting four light bulbs.
  • Scientists had already known that nuclear power could produce electricity. The purpose of the experimental EBR was to prove that a breeder reactor could produce more fuel than it used.
  • The first nuclear-powered submarine, the U.S.S. Nautilus, was launched.
  • Eisenhower's Atoms for Peace Program proposed an international agency to develop peaceful nuclear technologies.
  • The first Boiling Reactor Experiment reactor was built in Idaho. It demonstrated that steam bubbles in the reactor core did not cause an instability problem. It was, instead, a rapid, reliable, and effective mechanism for limiting power. This could protect a reactor against “runaway” events.
  • The Atomic Energy Act of 1954 was passed. It was the first major amendment of the original Energy Act, which gave the civilian nuclear energy program further access to nuclear technology.
  • The AEC announced the beginning of a cooperative program between government and industry to develop nuclear power plants.
  • Arco, Idaho, (population 1,000) became the first U.S. town powered by nuclear energy. The power was provided by an experimental reactor, BORAX III, at the Idaho National Energy Laboratory.
  • The United Kingdom announced the decision to develop thermonuclear weapons.
  • The United Nations sponsored the first international conference on the peaceful uses of nuclear energy, held in Geneva, Switzerland.
  • The first time that power was generated from a commercial nuclear plant, at Santa Susana, California.
  • The Price-Anderson Act enacted. This legislation was designed to limit the financial risk of nuclear plant owners in the event of an accident.
  • The first full-scale nuclear power plant (Shippingport, Pennsylvania) began service.
  • The International Atomic Energy Agency (IAEA) was formed with 18 member countries to promote peaceful uses of nuclear energy and to prevent the spread of nuclear weapons.
  • The Soviet Union launched the first nuclear-powered surface ship, the Lenin.
  • President Eisenhower signed amendments to the 1954 Atomic Energy Act, which led to a bilateral agreement between the United Kingdom and the United States on nuclear weapon design information.
  • From November 1958 to September 1961, the United States, the United Kingdom, and the former Union of Soviet Socialist Republics (USSR) observed an informal moratorium on nuclear tests.
  • The United States deployed the first operational intercontinental ballistic missile (ICBM), the Atlas D.
  • The AEC published its 10-year plan for nuclear energy.
  • Small nuclear power generators were first used in remote areas to power weather stations and to light buoys for sea navigation.
  • The first nuclear-powered merchant ship, the N.S. Savannah, was put to sea. Developed as part of President Eisenhower's Atoms for Peace Program, the Savannah was christened by Mrs. Dwight D. Eisenhower in 1959.
  • President Lyndon Johnson signed the Private Ownership of Special Nuclear Materials Act of 1964, which allowed the nuclear energy industry to own the fuel for its units. After June 30, 1973, private ownership of the uranium fuel became mandatory.
  • The U.S. Navy sent three nuclear-powered surface ships (Enterprise, Long Beach and Bainbridge) on an around-the-world cruise to show their ability to operate away from land bases.
  • The AEC issued a construction permit for Oyster Creek nuclear power plant.
  • The first nuclear reactor, a 500-watt system, operated in space. It operated for 43 days and remains in orbit.
  • The AEC gave the liquid metal fast breeder reactor highest priority and decided to build the Fast Flux Test Facility.
  • The first major electrical blackout occurred in the northeastern United States.
  • The Treaty on the Non-Proliferation of Nuclear Weapons, also known as the Nuclear Non-Proliferation Treaty (NPT), was adopted. The treaty called for halting the spread of nuclear weapon capabilities.
  • The First Earth Day was celebrated.
  • Electricity "brownouts" hit the Northeast during a heat wave. A "brownout" is a reduction or cutback in electric power, especially as a result of a shortage, mechanical failure, or overuse by consumers.
  • President Nixon announced a national goal of completing the liquid metal fast breeder reactor by 1980.
  • President Nixon proposed replacing the Atomic Energy Commission with the Energy Research and Development Administration and the Nuclear Regulatory Commission.
  • The Arab Oil Embargo occurred, in which several Arab nations in the Organization of Petroleum Exporting Countries (OPEC) embargoed, or stopped selling, oil to the United States and Holland to protest their support of Israel in the Arab-Israeli “Yom Kippur” War. Arab OPEC production was cut by 25%, which caused some temporary shortages and helped oil prices to triple. This contributed to an increased interest in alternatives to petroleum, including nuclear power.
  • U.S. utilities ordered 41 nuclear power plants, a one-year record.
  • The first 1,000-megawatt nuclear plant went into service (Commonwealth Edison's Zion Nuclear Power Plant, Unit 1).
  • The Atomic Energy Commission was abolished, and the Nuclear Regulatory Commission (NRC) was created to regulate the nuclear industry. The Joint Congressional Committee on Atomic Energy was also abolished.
  • The Energy Research and Development Administration began operating.
  • President Carter combined the Energy Research and Development Administration with the Federal Energy Administration, creating the Department of Energy.
  • The Voyager 2 spacecraft was launched into space. The spacecraft's electricity was generated by the decay of plutonium pellets.
  • The accident at the Three Mile Island Unit 2 (TMI-2) nuclear power plant near Middletown, Pennsylvania, on March 28, 1979, was the most serious in the U.S. nuclear power plant industry's operating history. Equipment malfunctions, design-related problems, and human error led to led to a partial meltdown of the TMI-2 reactor core but only very minute releases of radioactivity. Although no deaths or injuries resulted, the accident brought about sweeping changes in emergency response planning, reactor operator training, human factors engineering, radiation protection, and many other areas of nuclear power plant operations. These changes enhanced the safety of the industry.
  • The U.S. nuclear energy industry created the Institute of Nuclear Power Operations to address issues of safety and performance.
  • Completing a process begun by President Ford, President Carter banned the use of reprocessed uranium in nuclear fuel. The ban's purpose was to prevent the used fuels from falling into the wrong hands and being used for nuclear weapons.
  • For the first time, nuclear energy generated more electricity than oil in the United States.
  • President Ronald Reagan lifted the ban on reprocessing used nuclear fuel.
  • The Nuclear Waste Policy Act of 1982 was signed, approving the development of a high-level nuclear waste repository.
  • Nuclear energy generated more electricity than natural gas.
  • Nuclear replaced hydropower as the second-largest source of electricity in the United States, after coal.
  • The Perry power plant in Ohio became the 100th U.S. nuclear power plant in operation.
  • The world's worst nuclear power accident happened at the Chernobyl plant in the former USSR (now Ukraine).
  • Congress selected Yucca Mountain in Nevada for study as the first high-level nuclear waste repository site.
  • Nuclear power plants provided 19% of the electricity used in the United States; 46 units entered service during the 1980s.
  • The Energy Policy Act of 1992 reformed the licensing process for nuclear power plants.
  • Two decades after the first oil embargo, the 109 nuclear power plants operating in the United States provided about one-fifth of the nation's electricity.
  • The Nuclear Regulatory Commission (NRC) issued final design approval for the first two of four advanced nuclear power plant designs—General Electric's Advanced Boiling Water Reactor (ABWR) and ABB Combustion Engineering's System 80+.
  • The NRC granted the Tennessee Valley Authority (TVA) a full-power license for its Watts Bar 1 nuclear power plant. This was the last unit to be licensed in the United States in the 20th century.
  • Kashiwazaki-Kariwa 6, the world's first Advanced Boiling Water Reactor, began commercial service in Japan.
  • The NRC issued General Electric design certification for its Advanced Boiling Water Reactor.
  • Baltimore Gas and Electric Co. submitted an application to renew the license of its two-unit Calvert Cliffs nuclear power plant—the first U.S. company to apply for a 20-year extension of its 40-year license.
  • The NRC issued the first-ever license renewal to Constellation Energy's Calvert Cliffs Nuclear Power Plant, allowing an additional 20 years of operation.
  • The NRC approved a 20-year extension to the operating license of Duke Energy's three-unit Oconee Nuclear Station.
  • The National Energy Plan was published in May 2001. The Plan included a significant role for nuclear power in meeting energy demand and for reducing air pollution levels.
  • The Nuclear Power 2010 Program, developed in 2002, was a joint government/industry cost-shared effort to identify sites for new nuclear power plants, develop and bring to market advanced nuclear plant technologies, evaluate the business case for building new nuclear power plants, and demonstrate untested regulatory processes.
  • On April 30, the oldest nuclear power plant in the world, Obninsk (located in Russia), closed down its sole reactor.
  • Nuclear power provided about 16% of the world's electricity.
  • On August 14, the Nation's largest-ever power outage left much of the Northeast and parts of Canada without electricity for several days. A transmission line in Ohio strained the electrical system so much that plants all over the grid, including nine U.S. and eight Canadian commercial nuclear reactors, were shut down.
  • The British Nuclear Group announced the closing of the Chapelcross nuclear power plant, one of the world’s oldest plants.
  • On January 3, Lithuania, the world’s most nuclear-dependent nation, began the complete and final shutdown of one-half of its nuclear capacity. Lithuania's nuclear reactors are being shutdown owing to safety concerns. They have the same design as the reactors at Chernobyl, the site of the world's worst nuclear accident.
  • The Polish Government decided to build the Nation’s first nuclear power plant.
  • On August 8, President Bush signed the Energy Policy Act of 2005, which included measures to encourage the nuclear industry to build new nuclear power plants. (No construction of a nuclear plant has begun since 1971.)
  • A survey, in the United States, found a high level of support for nuclear energy among the public; with 68% favoring nuclear energy as one way to generate electricity and 49% stating a need to build more nuclear plants.
  • Browns Ferry Nuclear Power Plant Unit 1 was the first U.S. nuclear reactor to come online in the 21st century. Shut down in 1985, the Tennessee Valley Authority (TVA) decided in 2002 to restart the unit. It had the capacity to supply electricity to about 650,000 homes.

Last Revised: October 2008
Sources: Energy Information Administration, Unique Reactors, September 2008
National Academy of Engineering, Greatest Achievements, May 2008
National Science Digital Libraries,, Timelines of the Nuclear Age, May 2008
Nuclear Energy Institute, Nuclear Technology Milestones 1942 to Present, 2008
U.S. Department of Energy, Office of Nuclear Energy, Nuclear Power 2010, May 2008
The White House, Fact Sheet: Expanding the Safe Use of Nuclear Power, June 2007