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  1. Britannica Money. Discover all you need to know about retirement, investing, and household finance, without the jargon or agenda. Get reliable guidance, insight, and easy-to-understand explanations, written, edited, and verified to Britannica’s exacting standards. Advocacy for Animals.

    • Overview
    • The explosion at Unit 4 and initial containment efforts
    • Deaths, radioactivity, and the creation of the Chernobyl Exclusion Zone

    The Chernobyl disaster occurred on April 25 and 26, 1986, at the Chernobyl nuclear power station in the Soviet Union. It is one of the worst disasters in the history of nuclear power generation.

    What happened in the Chernobyl disaster?

    The Chernobyl disaster occurred when technicians at nuclear reactor Unit 4 attempted a poorly designed experiment. They shut down the reactor’s power-regulating system and its emergency safety systems, and they removed control rods from its core while allowing the reactor to run at 7 percent power. These mistakes, compounded by others, led to an uncontrolled chain reaction that resulted in several massive explosions.

    How many people died as a result of the Chernobyl disaster?

    Some sources state that two people were killed in the initial explosions of the Chernobyl disaster, whereas others report that the figure was closer to 50. Dozens more contracted serious radiation sickness; some of these people later died. In addition, thousands of deaths from radiation-induced illnesses and cancer were expected years later.

    How big was the exclusion zone created after the Chernobyl disaster?

    The disaster occurred on April 25–26, 1986, when technicians at reactor Unit 4 attempted a poorly designed experiment. Workers shut down the reactor’s power-regulating system and its emergency safety systems, and they withdrew most of the control rods from its core while allowing the reactor to continue running at 7 percent power. These mistakes were compounded by others, and at 1:23 am on April 26 the chain reaction in the core went out of control. Several explosions triggered a large fireball and blew off the heavy steel and concrete lid of the reactor. This and the ensuing fire in the graphite reactor core released large amounts of radioactive material into the atmosphere, where it was carried great distances by air currents. A partial meltdown of the core also occurred.

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    On April 27 the 30,000 inhabitants of Pryp’yat began to be evacuated. A cover-up was attempted, but on April 28 Swedish monitoring stations reported abnormally high levels of wind-transported radioactivity and pressed for an explanation. The Soviet government admitted there had been an accident at Chernobyl, thus setting off an international outcry over the dangers posed by the radioactive emissions. By May 4 both the heat and the radioactivity leaking from the reactor core were being contained, albeit at great risk to workers. Radioactive debris was buried at some 800 temporary sites, and later in the year the highly radioactive reactor core was enclosed in a concrete-and-steel sarcophagus (which was later deemed structurally unsound).

    Some sources state that two people were killed in the initial explosions, whereas others report that the figure was closer to 50. Dozens more people contracted serious radiation sickness; some of them later died. Between 50 and 185 million curies of radionuclides (radioactive forms of chemical elements) escaped into the atmosphere—several times more radioactivity than that created by the atomic bombs dropped on Hiroshima and Nagasaki, Japan. This radioactivity was spread by the wind over Belarus, Russia, and Ukraine and soon reached as far west as France and Italy. Millions of acres of forest and farmland were contaminated, and, although many thousands of people were evacuated, hundreds of thousands more remained in contaminated areas. In addition, in subsequent years many livestock were born deformed, and among humans several thousand radiation-induced illnesses and cancer deaths were expected in the long term. The Chernobyl disaster sparked criticism of unsafe procedures and design flaws in Soviet reactors, and it heightened resistance to the building of more such plants. Chernobyl Unit 2 was shut down after a 1991 fire, and Unit 1 remained on-line until 1996. Chernobyl Unit 3 continued to operate until 2000, when the nuclear power station was officially decommissioned.

    Following the disaster, the Soviet Union created a circle-shaped exclusion zone with a radius of about 18.6 miles (30 km) centred on the nuclear power plant. The exclusion zone covered an area of about 1,017 square miles (2,634 square km) around the plant. However, it was later expanded to 1,600 square miles (4,143 square km) to include heavily radiated areas outside the initial zone. Although no people actually live in the exclusion zone, scientists, scavengers, and others may file for permits that allow them to enter for limited amounts of time. With the dissolution of the Soviet Union in 1991, control of the site passed to Ukraine. In 2011 the Ukrainian government opened parts of the exclusion zone to organized tour groups, and Chernobyl and the abandoned city of Pryp’yat became popular destinations for so-called “dark tourists.” During the Russian invasion of Ukraine in 2022, Russian forces attacking from Belarus captured Chernobyl after a brief but pitched battle. Combat at the site of the world’s worst nuclear disaster led to concerns about damage to the containment structure and the possibility of widespread radioactive contamination.

    • The Editors of Encyclopaedia Britannica
  2. 2024年4月16日 · cellular respiration, the process by which organisms combine oxygen with foodstuff molecules, diverting the chemical energy in these substances into life-sustaining activities and discarding, as waste products, carbon dioxide and water. Organisms that do not depend on oxygen degrade foodstuffs in a process called fermentation.

  3. In the United States, commonwealth has continued to be the official description of four states (Kentucky, Massachusetts, Pennsylvania, and Virginia). It confers no distinction, other than in name, from the other states. The same term also was applied to Puerto Rico after an act of Congress of 1950 and adoption of the constitution of 1952.

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  5. 2024年5月8日 · Ed Ward. Rock and roll, style of popular music that originated in the United States in the mid-1950s and that evolved by the mid-1960s into the more encompassing international style known as rock music, though the latter also continued to be known as rock and roll. Learn more about the history of rock and roll in this article.

  6. 1999年5月28日 · Titanic, British luxury passenger liner that sank on April 14–15, 1912, during its maiden voyage, en route to New York City from Southampton, England, killing about 1,500 people. One of the most famous tragedies in modern history, it inspired numerous works of art and has been the subject of much scholarship.

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