On April 26, 1986, at 1:23 a.m. local time, reactor number four at the Chernobyl Nuclear Power Plant in the Soviet Union exploded. Additional
explosions and the resulting fire sent a plume of radioactive fallout into the atmosphere. The fallout released was four hundred times more than had
been released by the atomic bombing of Hiroshima.
The plume drifted over extensive parts of:
- Western Soviet Union
- Western Europe
- Eastern Europe
- Northern Europe
- Eastern North America
Large areas of Russia, Belarus, and the Ukraine were badly contaminated. The contamination resulted in the evacuation of over 300,000 people. About
60% of the radioactive fallout landed in Belarus.
It was the worst nuclear power plant disaster ever, resulting in a severe release of radioactivity into the environment. Two people died in the
initial steam explosion, but most deaths from the accident were attributed to radiation.
Russia, the Ukraine, and Belarus are still dealing with the continuing decontamination and health care costs of the Chernobyl accident.
The cost of the disaster is estimated to be around $200 billion USD, making Chernobyl the costliest disaster in modern history.
According to the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO), 56 direct deaths and an estimated 4,000 extra
cancer deaths have been attributed to the disaster.
The Chernobyl Exclusion Zone and other limited areas remain off limits. The majority of affected areas are now considered safe for economic activity
The accident occurred on April 26, 1986, when reactor four suffered a massive, catastrophic power excursion. This resulted in a steam explosion,
tearing the top from the reactor, exposing the core, and dispersing large amounts of radioactive particulate and gaseous debris (mostly Strontium-90
and Cesium-137). This allowed oxygen to contact the hot core, which contained 1,700 tons of combustible graphite moderator. The burning graphite
moderator increased the emission of the radioactive particles.
The radioactivity was not contained by any type of containment vessel, and radioactive particles were carried by the wind across international
The radiation levels in the worst-hit areas of the reactor building are estimated to have been 5.6 rontgen per second (R/s), or 20,000 R/hr. A lethal
dose is around 500 rontgen over 5 hours; some workers received fatal doses within several minutes.
Due to faulty dosimeters (equipment to measure rontgens) or dosimeters which only read low levels of rontogens, the reactor crew chief assumed that
the reactor was intact. Operating under this assumption, the chief and his crew stayed in the reactor building until morning trying to pump water into
None wore protective gear, and most died from radiation exposure within three weeks.
Shortly after the accident, firefighters arrived to try to extinguish the fire. They were not told how dangerous the smoke and debris were. They were
not told that the fire involved the reactor.
The fires were extinguished by 5 a.m., but many firefighters received high doses of radiation. The fire inside reactor no. 4 continued to burn until
May 10, 1986. It was finally extinguished by dropping tons of sand, lead, and clay onto the burning reactor and injecting liquid nitrogen.
Causes of the Disaster
There were two official explanations of the accident:
Effects of the Disaster
- Flawed operators explanation
Placed the blame on the power plant operators
- Flawed design explanation
Placed the blame on flaws in the reactor design, especially the control rods
Chernobyl After the Disaster
- International spread of radioactivity
- Radioactive release
- Human cost
237 people suffered from acute radiation sickness
31 died within the first 3 months after the disaster
135,000 evacuated from the area
- Environmental costs
Radioactive contamination of aquatic systems
Four square kilometers of pine forest in the immediate vicinity of the reactor turned brown and died
Some animals in the worst-hit areas died or stopped reproducing
All work on the unfinished reactors at Chernobyl halted in 1989. A fire broke out in reactor 2 in 1991, resulting in it being taken off-line. Reactor
1 was decommissioned in 1996. Reactor 3 was turned off in 2000, effectively shutting down the entire plant.
Disaster's Effect on Human Health
57 direct deaths in the accident itself
4,000 additional cancer cases due to the accident
Primarily thyroid cancer
No increase in the rate of birth defects or abnormalities
No increase in solid cancers
Possibility of tens of thousands of cases of thyroid cancer in the future
Chernobyl: A Nuclear Disaster
Relevant discussion threads on AboveTopSecret.com
Chernobyl, Radiation, Strange Long-Term Effects
Wildlife Defies Chernobyl Radiation
20th Anniversary of Chernobyl Accident