A timeline of the Chernobyl disaster.
Created by cqchoi on Feb 26, 2011
Last updated: 04/05/11 at 07:36 AM
The 25th anniversary of the disaster. Image: From the official site of the Chernobyl Nuclear Power Plant at http://new.chnpp.gov.ua/eng/photo/shelter_nord.jpg.
In response to the Chernobyl Forum's findings on the consequences of the disaster, the European Green Party commissioned a study dubbed "The Other Report on Chernobyl," or the TORCH report. It estimates the disaster will result in 30,000 to 60,000 extra cancer deaths, up to 15 times the Chernobyl Forum's estimate.
A comprehensive report on the consequences of the disaster comes out from the Chernobyl Forum, which is made up eight United Nations agencies and the governments of Belarus, the Russian Federation and Ukraine. The report, entitled "Chernobyl’s Legacy: Health, Environmental and Socio-Economic Impacts," was drafted by an international team of more than 100 scientists, and predicted that a total of up to 4,000 people could eventually die of exposure to radiation from the accident.
The sarcophagus was not meant to permanently entomb the destroyed reactor, and corrosion has taken a serious toll on it. Work begins on stabilizing the sarcophagus. Image credit: Charles Q. Choi.
Despite the disaster, the three remaining nuclear reactors at the power plant continued to run for years. On December 15, 2000, the last reactor in operation there was shut down.
Image: From Wikimedia Commons at http://commons.wikimedia.org/wiki/File:The_dangerous_view_-_Pripyat_-_Chernobyl.jpg.
The International Nuclear Safety Advisory Group updated the initial INSAG-1 report on the disaster, concluding that in addition to human error, a faulty reactor design was to blame as well.
Image: The cover of the INSAG-7 report from the International Nuclear Safety Advisory Group (http://www-pub.iaea.org/mtcd/publications/PubDetails.asp?pubId=3786)
The Soviet Union is formally dissolved. Image credit: Wikimedia Commons.
A fire breaks out in a turbine of Chernobyl's second reactor. This unit is ultimately shut down as well. Image: From Wikimedia Commons at http://commons.wikimedia.org/wiki/File:Fire02.jpg.
The Soviet government puts a stop to construction on Chernobyl's fifth and sixth units.
Image: From the official site of the Chernobyl Nuclear Power Plant at http://new.chnpp.gov.ua/eng/photo/chnpp_5.jpg.
Six officials, including the head of the Chernobyl nuclear power plant at the time of the accident, are tried and found guilty of charges related to the disaster.
Image credit: Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Scale_of_justice.png).
The first report of the International Nuclear Safety Advisory Group on the disaster largely concludes that the accident was due to human error.
Image: The logo of the International Atomic Energy Agency.
Work hastily begins on the sarcophagus for Unit 4, technically known as the "Shelter Object." This massive structure of more than 7,000 tons of metal and 400,000 cubic meters of concrete is meant to confine radioactive material from the destroyed reactor, keeping it from contaminating the rest of the world. Roughly 90,000 workers complete its construction in just 206 days.
Image: From the U.N. Development Program-managed site Chernobyl.info at http://www.chernobyl.info/index.php?userhash=941888&navID=13&lID=2.
The head of the Soviet Union, Mikhail Gorbachev, gives the first public statement on Chernobyl nuclear power plant disaster, acknowledging that a serious accident has occurred.
Image credit: White House Photo Office (http://www.reagan.utexas.edu/archives/photographs/large/c44007-9.jpg).
More than 30 military helicopters flew over the burning reactor, dropping 2,400 metric tons of lead and 1,800 metric tons of sand to try to smother the fire and absorb the radiation. In the final phase of firefighting, the core of the reactor was cooled with nitrogen. The fire was only controlled 10 days after the disaster.
Image: From the U.N. Development Program-managed site Chernobyl.info at http://www.chernobyl.info/index.php?userhash=941888&navID=11&lID=2.
The U.S. Task Force on the Soviet Nuclear Accident reports that radiation from the accident has reached the United States.
Image credit: Wikimedia Commons (http://commons.wikimedia.org/wiki/File:North_America_satellite.jpg).
Radiation from the accident reaches Japan.
Image credit: Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Satellite_image_of_Japan_in_May_2003.jpg).
Radiation from the accident reaches Poland, Germany, Austria and Romania.
Image credit: Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Europe.jpg).
Workers at the Forsmark Nuclear Power Plant in Sweden detect high levels of radiation coming from outside their plant. The Soviet Union admits that an accident occurred, but gives no details.
Image credit: Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Forsmark.jpg).
The evacuation of the nearby town of Pripyat is announced at 11 a.m. local time, begins at 2 p.m., and is completed about two-and-a-half hours later. Roughly 115,000 people are ultimately cleared from settlements in the 30 kilometers around the disaster, an area later known as the Exclusion Zone.
Image: From the U.N. Development Program-managed site Chernobyl.info at http://www.chernobyl.info/index.php?userhash=&navID=12&lID=2.
At 1:23:40 local time, the emergency shutdown fails.
At 1:23:44, the reactor in Unit 4 runs out of control. Two explosions destroy the core of Unit 4 and the roof of the reactor's building. The intense fire that results disperses radioactive material high into the atmosphere. Most of the radiation is released in the first ten days. At first, northerly and northwesterly winds predominate, but later in the month the wind switches to the south and southeast, and there are frequent but local showers, resulting in a highly varied regional and local distribution of the radiation.
At 1:28 a.m., the first group of 14 firemen arrive on the scene to try and put out the fires. These and other firefighters received the highest exposures of radiation and suffered the greatest losses in personnel.
Image: From the official site of the Chernobyl Nuclear Power Plant at http://new.chnpp.gov.ua/eng/photo/Helicopt03_05_86_1.jpg.
Reactor number four was supposed to be shut down for routine maintenance on April 25, 1986. During this time, an experiment was scheduled to test whether cooling of the core could continue in the event of a loss of power. Unfortunately, this test was postponed until 11 p.m., when there was less consumer demand for the electricity the power plant generated. As such, the day shift that had prepared for the test had left.
The head of the plant called to shut down the reactor's emergency core cooling system during the test. This important failsafe was designed to send water to cool the reactor core in an emergency, and disabling it reflected a lax attitude towards safety procedures.
The power level of the reactor was supposed to be lowered to about 1,000 megawatts for the test, but due to operator error, power fell to roughly 30 megawatts. They managed to stabilize the reactor at approximately 200 megawatts, but this reactor was unstable below about 700 megawatts and prone to sudden power surges.
Normally a minimum of 30 control rods were fully inserted in the reactor at all times. These neutron-absorbing rods can slow or even stop nuclear fission reactions in the reactor. Right before the disaster, only six to eight rods were used. This helped bring power levels back up from the dangerously low point they reached, but diminished operator ability to control the reactor.
Image: Decommissioned equipment at Chernobyl. Credit: From the official site of the Chernobyl Nuclear Power Plant at http://new.chnpp.gov.ua/eng/photo/sniatie1.jpg.
The Chernobyl Nuclear Power Plant has generated 100 billion kilowatt-hours, about twice as much energy as the Earth receives from the sun per second.
Image: From Fotopedia at http://www.fotopedia.com/items/flickr-3157251517.
The first fuel assembly is loaded into Unit 4. This is the last reactor that gets completed at Chernobyl, and the one that ended in tragedy.
Image: From the U.N. Development Program-managed site Chernobyl.info at http://www.chernobyl.info/index.php?userhash=&navID=642&lID=2
At the Three Mile Island nuclear power plant near Middletown, Pa.. the unit 2 reactor suffered a partial core meltdown. This is the most serious accident in the history of U.S. commercial nuclear power.
Image: A schematic of the Three Mile Island unit 2 reactor. Credit: U.S. Nuclear Regulatory Commission.
Production of the first reactor, Unit 1, begins. This and the other RBMK-1000 reactors at Chernobyl can each generate 1,000 megawatts of electricity, which is often said to be enough to serve 1 million typical American homes.
Image: From the U.N. Development Program-managed site Chernobyl.info at http://chernobyl.info/index.php?userhash=941888&navID=9&lID=2
Construction on the Chernobyl Nuclear Power Plant in Ukraine starts about 18 kilometers northwest of the town of Chornobyl, which is Ukrainian for wormwood. (Chernobyl, as it is most often known in the West, is the Russian name, while Ukrainians know it as Chornobyl.)
Image: From the official site of the Chernobyl Nuclear Power Plant at http://www.chnpp.gov.ua/photogallery/construction/const9.jpg.