Key Issues
Chernobyl Accident and Its Consequences
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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 graphite moderator 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.
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 graphite moderator 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.
