The earliest U.S. nuclear power project had been started in 1946 at Oak Ridge, but the program was abandoned in 1948, with most of its personnel being transferred to the naval reactor program. In 1953 the first prototype submarine reactor was started up (leading to the launching the next year of the first nuclear-powered submarine, the Nautilus), and also in 1953 Pres. Dwight D. Eisenhower announced the Atoms for Peace program. Atoms for Peace established the groundwork for a formal U.S. nuclear power program and also expedited international cooperation on nuclear power. The U.S. nuclear power program was devoted to the development of several reactor types. Three of these types ultimately proved successful in the sense that they remain as commercial reactor types today or as systems scheduled for future commercial use. These are the fast breeder reactor (now called the liquid-metal reactor, or LMR), the pressurized-water reactor (PWR), and the boiling-water reactor (BWR).

The first LMR was the Experimental Breeder Reactor, EBR-I, which was designed at Argonne National Laboratory and constructed at what is now the Idaho National Laboratory near Idaho Falls, Idaho. EBR-I was an early experiment to demonstrate breeding, and in 1951 it produced the first electricity from nuclear heat. A much larger experimental breeder, EBR-II, was developed and put into service (with power generation) in 1963.

The principle of the BWR was first demonstrated in a research reactor in Oak Ridge, but development of this reactor type was also assigned to Argonne, which built a series of experimental systems designated BORAX in Idaho. In 1955 one of these, BORAX-III, became the first U.S. reactor to put power into a utility line on a continuous basis. A true prototype, the Experimental Boiling Water Reactor, was commissioned in 1957. The principle of the PWR, meanwhile, had already been demonstrated in naval reactors, and the Bettis Atomic Power Laboratory of the naval reactor program was assigned to build a civilian prototype at Shippingport, Pennsylvania. This reactor, the largest of the power-reactor prototypes, went online in 1957; it is often hailed as the first commercial-scale reactor in the United States.

In 1949 the Soviet Union’s nuclear efforts reached fruition with its first atomic bomb test. A decade later, the Soviets put their first nuclear-powered surface vessel, the icebreaker Lenin, into service, in conjunction with the United States’ launch of its first nuclear-powered surface warship, the cruiser Long Beach. Having established their presence among the nuclear powers, the Soviets directed considerable efforts toward the use of nuclear energy to generate electric power through a standard steam cycle. In 1954 a graphite-moderated plutonium production reactor was modified in Obninsk, Russia, to create the first nuclear-powered electricity generator in the world. In the mid-1960s the Soviet Union commissioned two graphite-moderated 100-megawatt BWRs. Immediately following, reactors began to be constructed throughout the Soviet Union, the nominal power ratings increasing steadily. In 1973 the first 1,000-megawatt Reaktor Bolshoy Moshchnosti Kanalny (RBMK; “high-power channel reactor”) went critical. The RBMK was an unusual pressurized-water design, originally intended to produce plutonium as well as generate electricity, in which the core was moderated by graphite. The Soviet nuclear power industry also built a more conventional PWR design, the Vodo-Vodyanoy Energetichesky Reaktor (VVER; “water-cooled water-moderated power reactor”), which, like U.S. PWR designs, developed from early work done on naval power plants.

In the United Kingdom, GLEEP was followed in the late 1940s and early 1950s by construction of the air-cooled Windscale No. 1 and No. 2 reactors, which produced plutonium for Britain’s nascent nuclear weapons program. (Britain’s first atomic bomb test took place in 1952.) Across the Calder River from Windscale, a new reactor, Calder Hall A, made history in 1956 by producing the world’s first electric power generation on a commercial scale (while also producing plutonium for weapons). The Calder Hall reactors were cooled by compressed carbon dioxide gas and used a fuel of natural uranium metal sheathed in a new magnesium-alloy cladding. Because of the cladding, Calder Hall-type reactors were also known as Magnox reactors. Continuing from this technology, Britain went on to develop the Advanced Gas-Cooled Reactor (AGR), which used a fuel of enriched uranium dioxide, thus allowing higher reaction temperatures and more efficient power generation. The prototype AGR was built at Windscale and went critical in 1963. Commercial AGRs were built in the United Kingdom through the 1980s.

France followed a modified British model with the G1, G2, and G3 graphite-moderated, gas-cooled reactors, which first went critical at Marcoule, on the Rhône River in southern France, in 1956–59. These reactors powered electric generators while also producing plutonium for France’s nuclear weapons program. (The first French atomic bomb test took place in 1960.) However, after initially focusing on gas reactors, France shifted to the development of light-water reactors. Ultimately, French commercial nuclear power plants were standardized on three basic PWR designs.

Canada embraced its abundant uranium ore reserves as well as its established ability to mass produce heavy water through the Canada Deuterium Uranium (CANDU) reactor design, which operates on natural or very slightly enriched uranium moderated by heavy water (deuterium oxide). The first CANDU reactor—producing about 20 megawatts of electricity—went critical in 1962 at Rolphton, Ontario, on the Ottawa River. Canada’s first commercial nuclear power plant, located at Pickering, Ontario, on the shore of Lake Ontario, went into operation in 1971. By the end of the century, more than 20 CANDU reactors had been built in Canada, and many more had been built abroad.

Up to the 1970’s, all commercial-scale nuclear power plants utilized thermal neutrons as their primary mechanism for fission. (For an explanation of neutron energies, see above Thermal, intermediate, and fast neutrons.) However, in 1973 the Soviet Union demonstrated the first commercial fast neutron reactor, built on the shore of the Caspian Sea near what is now Aqtau, Kazakhstan. The reactor, in addition to providing heat energy for a 120-megawatt electric power plant, also utilized its heat for desalination of water from the Caspian—a novel concept for alternative uses of nuclear energy that was subsequently adopted in other parts of the world. A number of fast neutron reactor prototypes had previously been developed in the United States, the United Kingdom, and elsewhere in the Soviet Union; however, no country had yet scaled this technology up to an economically useful level.