impacts of Chernobyl
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The 1986 accident at the Chernobyl nuclear power plant in Ukraine, then part of the former Soviet Union, is the only accident in the history of commercial nuclear power to cause fatalities from radiation. It was the product of a severely flawed Soviet-era reactor design combined with human error. Key differences in U.S. reactor design, regulation and emergency preparedness make it highly unlikely that a Chernobyl-type accident could occur in the United States.Twenty-eight highly exposed reactor staff and emergency workers died from radiation and thermal burns within four months of the accident. Officials believe the accident also was responsible for nearly 7,000 cases of thyroid cancer among individuals who were under 18 years of age at the time of the accident. As of 2005, 15 children had died of thyroid cancer. Improved monitoring has been implemented to help ensure that thyroid cancer is detected early, when it is highly treatable.Most emergency workers and people living in contaminated areas received relatively low whole-body radiation doses, according to a United Nations study published in 2011. The study found no evidence of increases in solid cancers, decreased fertility or congenital malformations. However, there is “some evidence of a detectable increase” in leukemia and cataract risk among workers who received higher radiation doses when engaged in recovery at the site. Long-term health monitoring of these workers is ongoing.
What Happened
The accident, which occurred in the early morning of April 26, 1986, resulted when operators took actions in violation of the plant’s technical specifications. Operators ran the plant at very low power, without adequate safety precautions and without properly coordinating or communicating the procedure with safety personnel.
The four Chernobyl reactors were pressurized water reactors of the Soviet RBMK design, or Reactor BolshoMoshchnosty Kanalny, meaning “high-power channel reactor.” Designed to produce both plutonium and electric power, they were very different from standard commercial designs, employing a unique combination of a graphite moderator and water coolant.
The reactors also were highly unstable at low power, primarily owing to control rod design and “positive void coefficient,” factors that accelerated nuclear chain reaction and power output if the reactors lost cooling water.
These factors all contributed to an uncontrollable power surge that led to Chernobyl 4’s destruction. The power surge caused a sudden increase in heat, which ruptured some of the pressure tubes containing fuel.
The hot fuel particles reacted with water and caused a steam explosion, which lifted the 1,000-metric-ton cover off the top of the reactor, rupturing the rest of the 1,660 pressure tubes, causing a second explosion and exposing the reactor core to the environment. The fire burned for 10 days, releasing a large amount of radiation into the atmosphere.
The Chernobyl plant did not have the massive containment structure common to most nuclear power plants elsewhere in the world. Without this protection, radioactive material escaped into the environment.
The crippled Chernobyl 4 reactor now is enclosed in a concrete structure that is growing weaker over time. Ukraine and the Group of Eight industrialized nations have agreed on a plan to stabilize the existing structure by constructing an enormous new sarcophagus around it, which is expected to last more than 100 years.
Officials shut down reactor 2 after a building fire in 1991 and closed Chernobyl 1 and 3 in 1996 and 2000, respectively.
Dealing With the Consequence
Soviet scientists reported that the Chernobyl 4 reactor contained about 190 metric tons of uranium dioxide fuel and fission products. An estimated 13 percent to 30 percent of this escaped into the atmosphere. Contamination from the accident scattered irregularly, depending on weather conditions. Reports from Soviet and western scientists indicate that Belarus received about 60 percent of the contamination that fell on the former Soviet Union. A large area in the Russian Federation south of Bryansk also was contaminated, as were parts of northwestern Ukraine.
The 1986 accident at the Chernobyl nuclear power plant in Ukraine, then part of the former Soviet Union, is the only accident in the history of commercial nuclear power to cause fatalities from radiation. It was the product of a severely flawed Soviet-era reactor design combined with human error. Key differences in U.S. reactor design, regulation and emergency preparedness make it highly unlikely that a Chernobyl-type accident could occur in the United States.Twenty-eight highly exposed reactor staff and emergency workers died from radiation and thermal burns within four months of the accident. Officials believe the accident also was responsible for nearly 7,000 cases of thyroid cancer among individuals who were under 18 years of age at the time of the accident. As of 2005, 15 children had died of thyroid cancer. Improved monitoring has been implemented to help ensure that thyroid cancer is detected early, when it is highly treatable.Most emergency workers and people living in contaminated areas received relatively low whole-body radiation doses, according to a United Nations study published in 2011. The study found no evidence of increases in solid cancers, decreased fertility or congenital malformations. However, there is “some evidence of a detectable increase” in leukemia and cataract risk among workers who received higher radiation doses when engaged in recovery at the site. Long-term health monitoring of these workers is ongoing.
What Happened
The accident, which occurred in the early morning of April 26, 1986, resulted when operators took actions in violation of the plant’s technical specifications. Operators ran the plant at very low power, without adequate safety precautions and without properly coordinating or communicating the procedure with safety personnel.
The four Chernobyl reactors were pressurized water reactors of the Soviet RBMK design, or Reactor BolshoMoshchnosty Kanalny, meaning “high-power channel reactor.” Designed to produce both plutonium and electric power, they were very different from standard commercial designs, employing a unique combination of a graphite moderator and water coolant.
The reactors also were highly unstable at low power, primarily owing to control rod design and “positive void coefficient,” factors that accelerated nuclear chain reaction and power output if the reactors lost cooling water.
These factors all contributed to an uncontrollable power surge that led to Chernobyl 4’s destruction. The power surge caused a sudden increase in heat, which ruptured some of the pressure tubes containing fuel.
The hot fuel particles reacted with water and caused a steam explosion, which lifted the 1,000-metric-ton cover off the top of the reactor, rupturing the rest of the 1,660 pressure tubes, causing a second explosion and exposing the reactor core to the environment. The fire burned for 10 days, releasing a large amount of radiation into the atmosphere.
The Chernobyl plant did not have the massive containment structure common to most nuclear power plants elsewhere in the world. Without this protection, radioactive material escaped into the environment.
The crippled Chernobyl 4 reactor now is enclosed in a concrete structure that is growing weaker over time. Ukraine and the Group of Eight industrialized nations have agreed on a plan to stabilize the existing structure by constructing an enormous new sarcophagus around it, which is expected to last more than 100 years.
Officials shut down reactor 2 after a building fire in 1991 and closed Chernobyl 1 and 3 in 1996 and 2000, respectively.
Dealing With the Consequence
Soviet scientists reported that the Chernobyl 4 reactor contained about 190 metric tons of uranium dioxide fuel and fission products. An estimated 13 percent to 30 percent of this escaped into the atmosphere. Contamination from the accident scattered irregularly, depending on weather conditions. Reports from Soviet and western scientists indicate that Belarus received about 60 percent of the contamination that fell on the former Soviet Union. A large area in the Russian Federation south of Bryansk also was contaminated, as were parts of northwestern Ukraine.
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