Title: Nuclear power plant
Content:  Electricity was generated by a nuclear reactor for the first time ever on September 3, 1948, at the X-10 Graphite Reactor in Oak Ridge, Tennessee, United States which was the first nuclear power station to power a light bulb. The second, rather larger experiment occurred on December 20, 1951, at the EBR-I experimental station near Arco, Idaho. On June 27, 1954, the world's first nuclear power station to generate electricity for a power grid, the Obninsk Nuclear Power Plant, commenced operations in Obninsk, in the Soviet Union. The world's first full scale power station, Calder Hall in the United Kingdom, opened on October 17, 1956. The world's first full scale power station solely devoted to electricity production—Calder Hall was also meant to produce plutonium—the Shippingport Atomic Power Station in Pennsylvania, United States—was connected to the grid on December 18, 1957.
Title: Nuclear power in the United States
Content:  From the successful naval reactor program, plans were quickly developed for the use of reactors to generate steam to drive turbines turning generators. In April 1957, the SM-1 Nuclear Reactor in Fort Belvoir, Virginia was the first atomic power generator to go online and produce electrical energy to the U.S. power grid. On May 26, 1958 the first commercial nuclear power plant in the United States, Shippingport Atomic Power Station, was opened by President Dwight D. Eisenhower as part of his Atoms for Peace program. As nuclear power continued to grow throughout the 1960s, the Atomic Energy Commission anticipated that more than 1,000 reactors would be operating in the United States by 2000. As the industry continued to expand, the Atomic Energy Commission's development and regulatory functions were separated in 1974; the Department of Energy absorbed research and development, while the regulatory branch was spun off and turned into an independent commission known as the U.S. Nuclear Regulatory Commission (USNRC or simply NRC).
Title: History of nuclear power
Content:  The United States Navy Nuclear Propulsion design and operation community, under Rickover's style On June 27, 1954, the Obninsk Nuclear Power Plant in the USSR became the world's first nuclear power plant to generate electricity for a power grid, producing around 5 megawatts of electric power. The world's first commercial nuclear power station, Calder Hall at Windscale, England was connected to the national power grid on 27 August 1956. In common with a number of other generation I reactors, the plant had the dual purpose of producing electricity and plutonium-239, the latter for the nascent nuclear weapons program in Britain. It 
Title: Uranium
Content:  Arco became the first in the world to have all its electricity come from nuclear power generated by BORAX-III, another reactor designed and operated by Argonne National Laboratory). The world's first commercial scale nuclear power station, Obninsk in the Soviet Union, began generation with its reactor AM-1 on 27 June 1954. Other early nuclear power plants were Calder Hall in England, which began generation on 17 October 1956, and the Shippingport Atomic Power Station in Pennsylvania, which began on 26 May 1958. Nuclear power was used for the first time for propulsion by a submarine, the USS Nautilus, in 1954.
Title: Nuclear reactor
Content:  War II, the U.S. military sought other uses for nuclear reactor technology. Research by the Army led to the power stations for Camp Century, Greenland and McMurdo Station, Antarctica Army Nuclear Power Program. The Air Force Nuclear Bomber project resulted in the Molten-Salt Reactor Experiment. The U.S. Navy succeeded when they steamed the USS Nautilus (SSN-571) on nuclear power 17 January 1955. The first commercial nuclear power station, Calder Hall in Sellafield, England was opened in 1956 with an initial capacity of 50 MW (later 200 MW). The first portable nuclear reactor "Alco PM-2A" was used to generate electrical power (2 MW) for Camp Century from 1960 to 1963. 
Title: Nuclear power
Content:  1950s were characterized by strong optimism for the potential of nuclear power to provide cheap and endless energy. Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW. In 1953, American President Dwight Eisenhower gave his "Atoms for Peace" speech at the United Nations, emphasizing the need to develop "peaceful" uses of nuclear power quickly. This was followed by the Atomic Energy Act of 1954 which allowed rapid declassification of U.S. reactor technology and encouraged development by the private sector.
Title: Yankee Rowe Nuclear Power Station
Content:  The first power plant in this area was W.T. Turner's Hydro-electric production service to the town of Charlemont. Yankee atomic is the distant second as far as local heritage and historical significance. Yankee Nuclear Power Station (YNPS) was the third commercial nuclear power plant built in the United States and the first built in New England. According to several sources Yankee Rowe was the first commercial pressurized water reactor operating in the United States. This view discounts the government-sponsored Shippingport Atomic Power Station, which was not built on a commercial basis and relied on several technologies that would not be embraced by the commercial operators. The Dresden Generating Station, a commercial boiling water reactor (BWR), slightly preceded the opening of Yankee Rowe in 1960. US government sources place the first self-sustaining nuclear reaction at Dresden-1 on 15 October 1959 and the first one at Yankee Rowe on 19 August 1960. Yankee Rowe began commercial operation in 1961. It has also been named as the first large-scale nuclear unit in the United States.
Title: October 1956
Content: The world's first industrial-scale commercial nuclear power plant is opened by Queen Elizabeth II at Calder Hall in the UK. ; In chess's so-called "Game of the Century", 13-year-old Bobby Fischer defeats grandmaster Donald Byrne at the Rosenwald Memorial Tournament in New York City. 
Title: Nuclear power
Content:  The first organization to develop practical nuclear power was the U.S. Navy, with the S1W reactor for the purpose of propelling submarines and aircraft carriers. The first nuclear-powered submarine, USS Nautilus (SSN-571), was put to sea in January 1954. The S1W reactor was a Pressurized Water Reactor. This design was chosen because it was simpler, more compact, and easier to operate compared to alternative designs, thus more suitable to be used in submarines. This decision would result in the PWR being the reactor of choice also for power generation, thus having a lasting impact on the civilian electricity market in the years to come. On June 27, 1954, the Obninsk Nuclear Power Plant in the USSR became the world's first nuclear power plant to generate electricity for a power grid, producing around 5 megawatts of electric power. The world's first commercial nuclear power station, Calder Hall at Windscale, England was connected to the national power grid on 27 August 1956. In common with a number of other generation I reactors, the plant had the dual purpose of producing electricity and plutonium-239, the latter for the nascent nuclear weapons program in Britain.
Title: SM-1
Content:  Construction was completed in 18-months, the SM-1 reactor achieved first criticality on 8 April 1957, and the plant was formally opened in a public ceremony on 29 April 1957. Designed as a small-scale, pressurized-water, commercial nuclear power plant the power output from the SM-1 was connected to the local electrical grid. Thus, the SM-1 and Fort Belvoir hold the distinction of delivering the first nuclear generated electricity for public use in America, coming online several months before the (much larger, $55 million) Shippingport Reactor (in December 1957.) According to a June 1957 report in the industry magazine POWER, "Normal operation (of the SM-1) will need a total of 29 men. Operators will be high-school graduates with 1-year training, led by engineers." The location of the Army's nuclear reactor training facility alongside Gunston Cove explains why the floating MH-1A came to be tested at Fort Belvoir in April 1966.

Question: when was the first nuclear power plant opened?
Answer: December 20, 1951.
June 27, 1954.
On June 27, 1954.
the USSR.
December 2, 1942.