The Chernobyl Disaster was a nuclear accident of catastrophic proportions that occurred on April 26th, 1986, at approximately 1:23 A.M. at the Chernobyl Nuclear Power Plant in the Ukraine and is considered the worst nuclear power plant accident in history (although the Fukushima Disaster is gaining ground). A sudden power output surge took place at Chernobyl reactor number 4 which led to the rupture of the reactor vessel as well as a series of explosions. One person was killed immediately and a second died in the hospital soon after as a result of injuries. 30 operators and firemen were dead within three months and several others died later as a result of radiation exposure from the Chernobyl accident. During the explosion, a plume of radioactive fallout was released into the atmosphere and covered an extensive area, including Pripyat. It then drifted over the populations of western Russia and Europe.
A timeline of the events at Chernobyl is thought to be as follows:
1:26 A.M. – fire alarm activated
1:28 A.M. – arrival of local firefighters, Pravik’s guard
1:35 A.M. – arrival of firefighters from Pripyat, Kibenok’s guard
1:40 A.M. – arrival of Telyatnikov
2:10 A.M. – turbine hall roof fire extinguished
2:30 A.M. – main reactor hall roof fires suppressed
3:30 A.M. – arrival of Kiev firefighters
4:50 A.M. – fires mostly localized
6:35 A.M. – all fires extinguished
Radiation at Chernobyl
A 2006 report by the World Health Organization (WHO) reported that among the 134 emergency workers involved in the immediate mitigation of the Chernobyl accident (severely exposed workers and firemen during the first days) 28 people died in 1986 due to ARS (Acute Radiation Syndrome), and 19 more people died from 1987 to 2004 from different causes. Among the general population affected by Chernobyl radioactive fallout, the much lower exposures meant that ARS cases did not occur.
Four hundred times more radioactive material was released during the Chernobyl accident than had been released on the population of Hiroshima during World War II. The radiation levels in the worst hit areas of the Chernobyl reactor building have been estimated to be 5.6 roentgens per second (R/s) (1.4 milliamperes per kilogram), which is equivalent to more than 20,000 roentgens per hour (see table below). A lethal dose is around 500 roentgens (0.13 coulombs per kilogram) over 5 hours, So in some areas of the Chernobyl reactor building, unprotected workers received fatal doses within several minutes.
Radiation levels at different locations in the Chernobyl reactor building shortly after the explosion:
Location / Radiation (roentgens per hour)
vicinity of the reactor core / 30,000
fuel fragments / 15,000–20,000
debris near the electrolyzers / 5,000–15,000
debris heap at circulation pumps / 10,000
water in the Level +25 feedwater room / 5,000
level 0 of the turbine hall / 500–15,000
area of the affected unit / 1,000–1,500
water in Room 712 / 1,000
Gidroelektromontazh depot / 30
nearby concrete mixing unit /10–15
control room, shortly after explosion / 3–5
Following the accident, Ukraine continued to operate the remaining reactors at Chernobyl for many years.
Scale of the Chernobyl Disaster
The Chernobyl Disaster (along with possibly Fukushima) is the worst nuclear power plant accident in history. On the International Nuclear Event Scale, Chernobyl and Fukushima are the only level 7 events. Below is the color coded International Nuclear Event Scale.
Color Coded International Nuclear and Radiological Event Scale (INES):
Impact on People and Environment
Level 7: Major release of radio active material with widespread health and environmental effects requiring implementation of planned and extended countermeasures. Color code : #FF66CC
Level 6: Significant release of radioactive material likely to require implementation of planned countermeasures. Color code : #FF6600
Level 5: Limited release of radioactive material likely to require implementation of some planned ountermeasures. Several deaths from radiation. Color code : #FF9900
Level 4: Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls. At least one death from radiation. Color code : #FFCC33
Level 3: Exposure in excess of ten times the statutory annual limit for workers. Non-lethal deterministic health effect (e.g., burns) from radiation. Color code : #FFFF00
Level 2: Exposure of a member of the public in excess of 10 mSv. Exposure of a worker in excess of the statutory annual limits. Color code : #99CC66
Level 1: Overexposure of a member of the public in excess of statutory ¬annual limits. Minor problems with safety components with significant defence-in-depth remaining. Low activity lost or stolen radioactive source, device or transport package. Color code : #009900
Level 0: No safety significance. Color code : #999999
Modern ChernobylToday, Chernobyl reactor #4 is enclosed in a large concrete shelter which was erected quickly to allow continuing operation of the other reactors at the plant. The International Shelter Implementation Plan in the 1990s raised money for remedial work including removal of the fuel-containing materials at the Chernobyl plant. There was also major work on the shelter in 1998 and 1999. Some 200 tonnes of highly radioactive material still remain within Chernobyl reactor #4 and will continue to pose an environmental hazard until better contained.
There is a plan in place to build a new safe confinement structure at Chernobyl sometime in the near future. The structure is purposed to be an 18,000-ton metal arch, 105 meters high, 200 meters long, and spanning 257 meters. This structure is planned to cover both Chernobyl reactor #4 as well as the quickly-built 1986 structure. The Chernobyl Shelter Fund (which was set up in 1997) has received funding from international donors towards this project and previous work and along with the Nuclear Safety Account, also applied to Chernobyl decommissioning.
The Chernobyl Disaster obviously raised concerns about the safety of the nuclear power industry and nuclear power in general. Since the Chernobyl accident, safety of nuclear reactors has improved vastly. Many international programs were initiated following the Chernobyl Disaster. The International Atomic Energy Agency (IAEA) safety review brings together operators and Western engineers to focus on these safety improvements. The Nuclear Safety Assistance Coordination Center database lists Western aid totalling almost 1 billion US dollars for more than 700 safety-related projects in former Eastern Bloc countries. The Convention on Nuclear Safety adopted in Vienna in June 1994 is another such program.