Up to: Nuclear FAQ

2007 note: Here's a 1992 report by the International Atomic Energy Agency. Taking it properly into account would require modifying some of the details of the rest of this article.

2005 Sept 6: The World Health Organization (WHO) [] has just released a major study on the effects of the Chernobyl accident. The press release is Chernobyl: the true scale of the accident. The gist of the report is that the effects were much smaller than what the scientific community had expected. The present estimate is 50 direct deaths among workers and fire fighters. The Soviets gave 37 as the number. Also 9 children died from thyroid cancer among 4,000 who got the disease, and this compares with a ten-years-after estimate of 4. These estimates are far lower than those given by the Ukrainian government when it was soliciting money from Russia and Western Europe. How many more people will die of cancer from Chernobyl cannot be calculated, because it is such a tiny fraction of normal cancer deaths. A calculation also depends on what theory is adopted for the effects of very low radiation doses.

A further conclusion of the report is that encouraging people to classify themselves as victims has led to a culture of dependency. However, it was not possible to disentangle the effects of Chernobyl from the much larger harmful effects of the collapse of the Soviet Union.

The Chernobyl accident at Chernobyl, Ukraine, was the worst accident in the history of nuclear energy, worse than all others put together. The following factors made the accident worse than is likely to happen in other plants.

  1. The 16 RBMK reactors, of which the Chernobyl plant was one, are built without containment shells. In other reactors, the containment shell will keep almost all radioactive material from spreading in case of an accident.
  2. RBMK reactors were intended to produce power and also to produce plutonium for military use. This required that it be possible to remove fuel rods for reprocessing by means of a crane on top of the reactor at short intervals in order to get Pu-239 without substantial admixture of Pu-240. These facilities made the reactor too tall for a containment structure used in Western and other Soviet reactors.

  3. The reactor had several other features which were regarded as unsafe in the Soviet Union as well as by experts from other countries. The Soviet Union never exported RBMK reactors.
  4. Positive void coefficient under the conditions of the Chernobyl test. If the water in the reactor boils in some spot a bubble of steam is produced. In PWR and BWR reactors, this reduces reactivity, causing the nuclear reaction to slow down. In RBMK reactors it can cause the nuclear reaction to speed up.
  5. Carbon moderator This can catch fire in case of an accident and did at Chernobyl. Western power reactors and other Russian reactors use water as a moderator.
  6. Making an experiment with the reactor which involved disabling its safety features. This is the single main cause of the accident. The safety features would have safely shut down the reactor if they hadn't been disabled.
In order to prevent the reactor from shutting itself off from xenon poisoning, the operators pulled the control rods almost all the way out. This caused an enormous increase in the nuclear reaction to many times the reactor's normal power level. This caused a steam explosion that blew the top off the reactor, probably stopping the nuclear reaction. Then the carbon caught fire and burned for about nine days. This scattered the reactor contents and large amounts of radioactivity. 32 people died in the accident and in efforts to put out the fire. 38 more people died of acute radiation sickness in the following months. There were measurable health effects in Ukraine and Belarus.

The radioactivity spread over northern Europe caused some plants and wild animals to be more radioactive than was legal for human consumption. However, there were no identifiable illnesses outside the Soviet Union. There may be some increase in cancer but this is unlikely to be detectable, because of the large numbers of cancers from other causes.

The International Atomic Energy Agency (IAEA) had a tenth anniversary conference about the Chernobyl accident. Its conclusions and recommendations section is very comprehensive. I recommend reading it. Alas, the three above links are no longer valid. Maybe the pages are available somewhere else.

The following reports are earlier, and maybe I should delete the links.

Here's a report Abstract: Health Effects of the Chernobyl Accident by Vladimir G Bebeshko. It contains new information, but overall it is rather vague. The report was given at a symposium of the World Nuclear Association, London. These links are dead

Here's a report Chernobyl Nuclear Power Station: Past, Present, and Future. Anatolij Nosovsky. from the Deputy Director of the Chernobyl plant. This is also from the World Nuclear Association home page. This link is dead.

Chernobyl - Ten Years On is also from the World Nuclear Association. Also a dead link.

Science and Technology Review, the Lawrence Livermore National Laboratory, for 1999 September has an article by entitled "Researchers determine Chernobyl liquidators' exposure". The liquidators were the people, mostly soldiers, who cleaned up after the Chernobyl accident. 2003 July note: The article is now on-line as Researchers determine Chernobyl liquidators' exposure.

The article says,

"The Livermore team [led by Irene Jones] says its population of liquidators received on average a dose of about 15 centigrays, as determined by FISH [a way of estimating chromosome damage]. Such a radiation dose is roughly equivalent to aging about 10 years or to smoking cigarettes regularly. The expected health consequences to the population under study are small."

In a separate study led by biomedical scientist Joe Lucas, Livermore researchers applied FISH to a subset of Chernobyl liquidators suspected of receiving a large dose of ionizing radiation. They reconstructed doses for 27 Chernobyl liquidators from the frequency of translocation measured in their lymphocytes. Of the 27 individuals, 15 are being treated for radiation sickness. The remaining 12 show no medical symptoms.

The magazine is available on the web at Science and Technology Review. The html version of the article is extremely readable. For further information you can contact Irene Jones (925)423-3626 ( or Joe Lucas (925) 422-6283 (

The government of Ukraine gives much larger figures for the number of people who got sick or died because of Chernobyl. I don't believe these figures have been verified by outsiders. The large figures are presented in support of claims for compensation from Russia and donations from Western countries.

In 1999 at Tokaimura, Japan, workers at a plant preparing fuel for an experimental breeder reactor caused an accident by violating rules aimed at preventing the formation of a critical mass of uranium. To save time they used steel buckets to transfer the uranium rather than pouring into a device aimed at preventing a critical mass by not having room for too much uranium at one time. Three people got serious radiation sickness, two of whom died. 400 people were examined but found not to need treatment.

Unsupported large estimates of the casualties from Chernobyl are a staple of the anti-nuclear movement. It is interesting that the UN scientific committee on the effects of radiation has found it necessary to criticise the UN office on humanitarian affairs. The latter takes the common journalistic view of Chernobyl.

UNSCEAR Letter to Secretary General Kofi Annan [rtf file 21kb] 6 June 2000 "Sir, I write to you as Chairman of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which has just concluded its 49th session in Vienna. As you know, UNSCEAR is the body within the United Nations system with a mandate from the General Assembly to assess and report levels and health effects of exposure to ionizing radiation. The Committee has taken note of a publication by the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) entitled "Chernobyl - a continuing catastrophe" (OCHA/99/20, New York and Geneva, 2000). This report is full of unsubstantiated statements that have no support in scientific assessments. I should therefore like to draw your attention to the Committee's finding with regard to the radiological consequences of the Chernobyl accident..."

The Center for nuclear Technology and Society at Worcester Polytechnic Institute maintains an active site.

It is interesting that the press refers to the Tokaimura accident as the "worst nuclear accident since Chernobyl" 13 years earlier. An industry that kills only two people in 13 years is far safer than any other energy industry.

Wikipedia has a detailed article "Chernobyl disaster" which describes the accident in detail and also contains many references to estimates of the number who died and will die.

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