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The Chernobyl disaster occurred at 01:23 a.m. on April 26, 1986 at the Chernobyl nuclear power plant in Pripyat, Ukraine. It is regarded as the worst accident in the history of nuclear power. A plume of radioactive fallout drifted over parts of the western Soviet Union, Eastern and Western Europe, Scandinavia, the British Isles, and eastern North America. Large areas of Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. About 60% of the radioactive fallout landed in Belarus according to official post-Soviet data . According to the 2006 TORCH report, half of the radioactive fallout landed outside those three Soviet republics . The disaster released as much as 300 times more radioactive fallout than the atomic bomb of Hiroshima.

The accident raised concerns about the safety of the Soviet nuclear power industry, slowing its expansion for a number of years, while forcing the Soviet government to become less secretive. The now-independent countries of Russia, Ukraine, and Belarus have been burdened with continuing and substantial decontamination and health care costs of the Chernobyl accident. It is difficult to tally accurately the number of deaths caused by the events at Chernobyl, as Soviet-era cover-up made it difficult to track down victims. Lists were incomplete, and Soviet authorities later forbade doctors to cite "radiation" on death certificates. Most of the expected long-term fatalities, especially those from cancer, have not yet actually occurred, and will be difficult to attribute specifically to the accident. Estimates and figures vary widely. A 2005 report prepared by the Chernobyl Forum, led by the International Atomic Energy Agency (IAEA) and World Health Organization (WHO), attributed 56 direct deaths (47 accident workers, and nine children with thyroid cancer), and estimated that as many as 9,000 people, among the approximately 6.6 million most highly exposed, will die from some form of cancer (one of the induced diseases). For its part, Greenpeace estimates a total death toll of 93,000 but cites in their report “The most recently published figures indicate that in Belarus, Russia and the Ukraine alone the accident could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004.” .

The plant

The Chernobyl station (Чернобыльская АЭС им. В.И.Ленина – V.I. Lenin Memorial Chernobyl Nuclear Power Station) (51°23′14″N 30°06′41″E / 51.38722°N 30.11139°E / 51.38722; 30.11139) is in the town of Pripyat, Ukraine, 18 km northwest of the city of Chernobyl, 16 km from the border of Ukraine and Belarus, and about 110 km north of Kiev. The station consisted of four reactors, each capable of producing 1 GW of electric power (3.2 GW of thermal power), and the four together produced about 10% of Ukraine's electricity at the time of the accident. Construction of the plant began in the 1970s, with reactor no. 1 commissioned in 1977, followed by no. 2 (1978), no. 3 (1981), and no. 4 (1983). Two more reactors (nos. 5 and 6, capable of producing 1 GW each) were under construction at the time of the accident. The four power plants were using reactor type RBMK-1000.

The accident

On Saturday April 26, 1986, at 1:23:58 a.m. reactor 4 suffered a catastrophic steam explosion that resulted in a fire, a series of additional explosions, and a nuclear meltdown.

Causes

There are two conflicting official theories about the cause of the accident. The first was published in August 1986 and effectively placed the blame solely on the power plant operators. The second theory, proposed by Valeri Legasov and published in 1991, attributed the accident to flaws in the RBMK reactor design, specifically the control rods. Both commissions were heavily lobbied by different groups, including the reactor's designers, Chernobyl power plant personnel, and the government. Some independent experts now believe that neither theory is completely correct.

Another important factor contributing to the accident was that the operators were not informed about problems with the reactor. According to one of them, Anatoliy Dyatlov, the designers knew that the reactor was dangerous in some conditions but intentionally concealed this information. Contributing to this was that the plant's management was largely composed of non-RBMK-qualified personnel: the director, V.P. Bryukhanov, had experience and training in a coal-fired power plant. His chief engineer, Nikolai Fomin, also came from a conventional power plant. Anatoliy Dyatlov himself, deputy chief engineer of reactors 3 and 4, had only "some experience with small nuclear reactors", namely smaller versions of the VVER nuclear reactors that were designed for the Soviet Navy's nuclear submarines.

In particular,

• The reactor had a dangerously large positive void coefficient. The RBMK reactor design used liquid as its coolant. Coolant gives the operators some control over the speed of the reactions, controlling the reactors energy output. If the coolant has bubbles in it (voids), from steam, these voids increase the amount of energy the reactor produces (i.e. no liquid to absorb neutrons). Without intervention, the reactor produces more energy, creating more voids, becoming harder to control. That the RBMK reactor design was dangerous at low power levels was counter-intuitive and unknown to the crew.
• A more significant flaw of the reactor was in the design of the control rods. In a nuclear reactor, control rods are inserted into the reactor to slow down the reaction. However, in the RBMK reactor design, the control rod end tips were made of graphite, the extenders (the end areas of the control rods above the end tips, measuring 1 m in length) were hollow and filled with water, while the balance of the control rod—the truly functional area, absorbing the neutrons and thereby halting the reaction—were made of boron carbide. For the initial few moments when control rods of this design are inserted into the reactor, coolant was displaced by the graphite ends of the rods. The coolant (water), a neutron absorber, was therefore replaced by graphite, a neutron moderator – that is, a material that enables the nuclear reaction rather than slow the reaction down. For the first few seconds of control rod activation the rods increased the reactor's speed, rather than the desired effect of decreasing the reaction. This behavior is rather counter-intuitive and was not known to the reactor operators.
• The operators were careless and violated plant procedures, partly due to their lack of knowledge of the reactor's design flaws. Also, several procedural irregularities contributed to the cause of the accident. One was insufficient communication between the safety officers and the operators in charge of an experiment being run that night.

The operators switched off many of the reactor's safety systems, which was generally prohibited by the plant's published technical guidelines.

According to a Government Commission report published in August 1986, operators removed at least 204 control rods from the reactor core out of a total of 211, leaving seven (see Boris Gorbachev's article in Russian about the causes). The same guidelines (noted above) prohibit operation of the RBMK-1000 with fewer than 15 rods inside the core zone.

Events

On April 25, 1986, the reactor 4 was scheduled to be shut down for a test. It had been decided to use this occasion as an opportunity to test the ability of the reactor's turbine generator to generate sufficient electricity to power the reactor's safety systems (in particular, the water pumps) in the event of a loss of external electric power. Reactors such as Chernobyl have a pair of diesel generators available as standby, but these do not activate instantaneously—the reactor was, therefore, to be used to spin up the turbine, at which point the turbine would be disconnected from the reactor and allowed to spin under its own rotational momentum, and the aim of the test was to determine whether the turbines in the rundown phase could sufficiently power the pumps while the generators were starting up. The test was successfully carried out previously on another unit (with all safety provisions active) and the outcome was negative (that is, the turbines generated insufficient power in the rundown phase to power the pumps), but additional improvements were made to the turbines which prompted the need for another test.

The power output of the reactor 4 was to be reduced from its normal 3.2 GW thermal to 1 GW thermal in order to conduct the test at a safer, lower level of power. However, due to a delay in beginning the experiment the reactor operators reduced the power level too rapidly, and the actual power output fell to 30 MW thermal. As a result, the concentration of the nuclear poison product xenon-135 increased (this product is typically consumed in a reactor under higher power conditions). Though the scale of the power drop was close to the maximum allowed by safety regulations, the crew's management chose not to shut down the reactor and to continue the experiment. Further, it was decided to 'shortcut' the experiment and raise power output to only 200 MW. In order to overcome the neutron absorption of the excess xenon-135, the control rods were pulled out of the reactor somewhat farther than normally allowed under safety regulations. As part of the experiment, at 1:05 a.m. on April 26, the water pumps which were to be driven by the turbine generator were turned on; the water flow generated by this action exceeded that specified by safety regulations. The water flow increased at 1:19 — since water also absorbs neutrons, this further increase in the water flow necessitated the removal of the manual control rods, producing a very unstable and dangerous operating condition.

At 1:23:04 the experiment began. The unstable state of the reactor was not reflected in any way on the control panel, and it does not appear that anyone in the reactor crew was fully aware of danger. Electricity to the water pumps was shut off, and as they were driven by the inertia of the turbine generator the water flow rate decreased. The turbine was disconnected from the reactor, increasing the level of steam in the reactor core. As the coolant heated, pockets of steam formed in the coolant lines. The particular design of the RBMK graphite moderated reactor at Chernobyl has a large positive void coefficient, which means that the power of the reactor increases rapidly in the absence of the neutron-absorbing effect of water, and in this case, the reactor operation becomes progressively less stable and more dangerous. At 1:23:40 the operators pressed the AZ-5 ("Rapid Emergency Defense 5") button that ordered a "SCRAM" — a shutdown of the nuclear reactor, fully inserting all control rods, including the manual control rods that had been incautiously withdrawn earlier, into the reactor. It is unclear whether it was done as an emergency measure, or simply as a routine method of shutting down the reactor upon the completion of an experiment (the reactor was scheduled to be shut down for routine maintenance). It is usually suggested that the SCRAM was ordered as a response to the unexpected rapid power increase. On the other hand, Anatoly Dyatlov, chief engineer on Chernobyl nuclear station at the time of the accident, writes in his book:

"Prior to 01:23:40, systems of centralized control ... didn't register any parameter changes that could justify the SCRAM. Commission ... gathered and analyzed large amount of materials and, as stated in its report, failed to determine the reason why the SCRAM was ordered. There was no need to look for the reason. The reactor was simply being shut down upon the completion of the experiment."

Due to the slow speed of the control rod insertion mechanism (18–20 seconds to complete), the hollow tips of the rods and the temporary displacement of coolant, the SCRAM caused the reaction rate to increase. Increased energy output caused the deformation of control rod channels. The rods became stuck after being inserted only one-third of the way, and were therefore unable to stop the reaction. By 1:23:47 the reactor jumped to around 30 GW, ten times the normal operational output. The fuel rods began to melt and the steam pressure rapidly increased causing a large steam explosion. Generated steam traveled vertically along the rod channels in the reactor, displacing and destroying the reactor lid, rupturing the coolant tubes and then blowing a hole in the roof.

To reduce costs, and because of its large size, the reactor had been constructed with only partial containment. This allowed the radioactive contaminants to escape into the atmosphere after the steam explosion burst the primary pressure vessel. After part of the roof blew off, the inrush of oxygen—combined with the extremely high temperature of the reactor fuel and graphite moderator—sparked a graphite fire. This fire greatly contributed to the spread of radioactive material and the ultimate contamination of outlying areas.

There is some controversy surrounding the exact sequence of events after 1:22:30 due to the inconsistencies between eyewitness accounts and station records. The version that is most commonly agreed upon is described above. According to this theory, the first explosion happened at approximately 1:23:47, seven seconds after the operators ordered the "SCRAM". It is sometimes claimed that the explosion happened 'before' or immediately following the SCRAM (this was the working version of the Soviet committee studying the accident). This distinction is important, because, if the reactor went critical several seconds after the SCRAM, its failure would have to be attributed to the design of the control rods, whereas the explosion at the time of the SCRAM would place the blame on the operators. Indeed, a weak seismic event, similar to a magnitude-2.5 earthquake, was registered at 1:23:39 in the Chernobyl area.

In January 1993, the IAEA issued a revised analysis of the Chernobyl accident, attributing the main root cause to the reactor's design and not to operator error. The IAEA's 1986 analysis had cited the operators' actions as the principal cause of the accident.

Radioactive release (source term)

A short report on the release of radioisotopes from the site can be read at the OSTI web site. A more detailed report can be downloaded from the OECD web site's public library as a 1.85MB PDF file.

At different times after the accident, different isotopes were responsible for the majority of the external dose. The dose which has been calculated is from external gamma irradiation, for a person standing in the open. The gamma dose to a person in a shelter or the internal dose is harder to estimate.

Because the fission products page has a detailed discussion of the properties of those fission products which are most dangerous, only a short description of the radioisotopes released will be given here.

The release of the radioisotopes from the nuclear fuel was largely controlled by their boiling points, and the majority of the radioactivity present in the core was retained in the reactor.

• All of the noble gases, including (Kr and Xe) contained within the reactor were released immediately into the atmosphere by the first steam explosion.
• About 55% of the radioactive iodine in the reactor was released, as a mixture of vapour, solid particles and also in the form of organic iodine compounds.
• Caesium and tellurium were released in aerosol form.

Two sizes of particles were released, the small particles were 0.3 to 1.5 micrometers (aerodynamic diameter) while the large were 10 micrometers in size. The larger particles contained about 80 to 90% of the released nonvolatile radioisotopes (

Immediate crisis management

The scale of the tragedy was exacerbated by both the unpreparedness of local administrators and the lack of proper equipment. All but two dosimeters present in the fourth reactor building had limits of 1 milliröntgen per second. The remaining two had limits of 1000 R/s; access to one of them was blocked by the explosion, and the other one broke when turned on. Thus the reactor crew could only ascertain that the radiation levels in much of the reactor building were above 4 R/h (true levels were up to 20,000 R/h in some areas; lethal dose is around 500 R over 5 hours).

This allowed the chief of reactor crew, Alexander Akimov, to assume that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 4:30 a.m. were dismissed under the assumption that the new dosimeter must have been defective. Akimov stayed with his crew in the reactor building until morning, trying to pump water into the reactor. None of them wore any protective gear. Most of them, including Akimov himself, died from radiation exposure during the three weeks following the accident.

Shortly after the accident, firefighters arrived to try to extinguish the fires. The first one to the scene was a Chernobyl Power Station firefighter brigade under the command of Lieutenant Vladimir Pravik (Pravik died on May 9, 1986). They were not told how dangerously radioactive the smoke and the debris were. The fire was extinguished by 5 a.m., but many firefighters received high doses of radiation.

The explosion and fire threw into the air not just the particles of the nuclear fuel, but also far more dangerous radioactive elements like caesium-137, iodine-135, strontium-90 and other radionuclides. The residents of the surrounding area observed the radioactive cloud on the night of the explosion. The cloud was noticeably glowing.

The government committee, led by Valeri Legasov, formed to investigate the accident arrived at Chernobyl in the evening of April 26. By that time two people were dead and fifty-two were hospitalized. During the night of April 26–April 27—more than 24 hours after the explosion—the committee, faced with ample evidence of extremely high levels of radiation and a number of cases of radiation exposure, had to acknowledge the destruction of the reactor and order the evacuation of the nearby city of Pripyat. In order to reduce baggage, the residents were told that the evacuation would be temporary, lasting approximately three days. As a result, Pripyat still contains personal belongings that can never be moved due to radiation. From eyewitness accounts of the firefighters involved before they died (as reported on the BBC television series Witness), one described his experience of the radiation as "tasting like metal", and feeling a sensation similar to that of pins and needles all over his face.

The water that had hurriedly been pumped into the reactor building in a futile attempt to extinguish the fire had run down underneath the reactor floor to the space underneath. The problem presented by this was the fact that the smouldering fuel and other material on the reactor floor was starting to burn its way through this floor, and was being made worse by materials being dropped from helicopters, which simply acted as a furnace to increase the temperatures further. If this material came into contact with the water, it would have generated a thermal explosion which would have arguably been worse than the initial reactor explosion itself, and would have, by many estimates, rendered land in a radius of hundreds of miles from the plant uninhabitable for at least 100 years.

In order to prevent this, soldiers and workers (called "liquidators") were sent in as cleanup staff by the Soviet government. Two of these were sent in wet suits to open the sluice gates to vent the radioactive water, and thus prevent a thermal explosion. These men, just like the other liquidators and firefighters that helped with the cleanup, were not told of the danger they faced. They very likely prevented an incident of greater magnitude than that of the initial explosion.

The worst of the radioactive debris was collected inside what was left of the reactor. The reactor itself was covered with bags with sand, lead and boric acid thrown off helicopters (some 5,000 tons during the week following the accident). By December 1986 a large concrete sarcophagus had been erected, to seal off the reactor and its contents.

Many of the vehicles used by the "liquidators" remain scattered around the Chernobyl area to this day.

The effects of the disaster

See main article: The effects of the Chernobyl disaster

Immediate results

The nuclear meltdown produced a radioactive cloud which flew over Russia, Belarus and Ukraine, but also the European part of Turkey, Greece, Moldova, Romania, Lithuania, Finland, Denmark, Norway, Sweden, Austria, Hungary, the Czech Republic and the Slovak Republic, Slovenia, Poland, Switzerland, Germany, Italy, Ireland, France (including Corsica ) and the United Kingdom (UK) . The initial evidence that a major exhaust of radioactive material was affecting other countries came not from Soviet sources, but from Sweden, where on April 27 workers at the Forsmark Nuclear Power Plant (approximately 1100 km from the Chernobyl site) were found to have radioactive particles on their clothes. It was Sweden's search for the source of radioactivity, after they had determined there was no leak at the Swedish plant, that led to the first hint of a serious nuclear problem in the western Soviet Union.

Contamination from the Chernobyl accident was not evenly spread across the surrounding countryside, but scattered irregularly depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. However, the TORCH 2006 report stated that half of the volatile particles had landed outside Ukraine, Belarus and Russia. A large area in the Russian Federation south of Bryansk was also contaminated, as were parts of northwestern Ukraine.

In western Europe, measures were taken including seemingly arbitrary regulations pertaining to the legality of importation of certain foods but not others. One commonly ridiculed contention was in France where local protectionists stated that the radioactive cloud had stopped at the German and Italian borders.

Two-hundred people were hospitalized immediately, of whom 31 died (28 of them died from acute radiation exposure) . Most of these were fire and rescue workers trying to bring the accident under control, who were not fully aware of how dangerous the radiation exposure (from the smoke) was (for a discussion of the more important isotopes in fallout see fission products). 135.000 people were evacuated from the area, including 50,000 from the nearby town of Pripyat, Ukraine. Health officials have predicted that over the next 70 years there will be a 2% increase in cancer rates in much of the population which was exposed to the 5–12 (depending on source) EBq of radioactive contamination released from the reactor. An additional ten people have already died of cancer as a result of the accident.

Soviet scientists reported that the Chernobyl Unit 4 reactor contained about 180–190 t of uranium dioxide fuel and fission products. Estimates of the amount of this material that escaped range from 5 to 30%, but some liquidators, who have actually been inside the sarcophagus and the reactor shell itself — e.g. Mr. Usatenko and Dr. Karpan — state that not more than 5–10% of the fuel remains inside; indeed, photographs of the reactor shell show that it is completely empty. Because of the intense heat of the fire, much of the ejected fuel was lofted high into the atmosphere (with no containment building to stop it), where it spread.

The workers involved in the recovery and cleanup after the accident, known as "liquidators", received high doses of radiation. According to Soviet estimates, between 300,000 and 600,000 liquidators were involved in the cleanup of the 30-km evacuation zone around the reactor, but many of them entered the zone two years after the accident.

Some children in the contaminated areas were exposed to high radiation doses of up to 50 grays (Gy) because of an intake of radioactive iodine-131, a relatively short-lived isotope with a half-life of eight days, from contaminated milk produced locally. Several studies have found that the incidence of thyroid cancer among children in Belarus, Ukraine and Russia has risen sharply. So far, no increase in leukemia is discernible, but this is expected to be evident in the next few years along with a greater, though not statistically discernible, incidence of other cancers. There has been a substantiated increase attributable to Chernobyl in congenital abnormalities, adverse pregnancy outcomes or any other radiation-induced disease in the general population, both in the contaminated areas or further afield

Long-term health effects

Right after the accident, the main health concern involved radioactive iodine, with a half-life of eight days. Today, there is concern about contamination of the soil with strontium-90 and caesium-137, which have half-lives of about 30 years. The highest levels of caesium-137 are found in the surface layers of the soil where they are absorbed by plants, insects and mushrooms, entering the local food supply. Some scientists fear that radioactivity will affect the local population for the next several generations.

Soviet authorities started evacuating people from the area around the Chernobyl reactor 36 hours after the accident. By May 1986, about a month later, all those living within a 30-kilometre (18 mile) radius of the plant—about 116,000 people—had been relocated. This region is often referred to as the Zone of alienation. However, radiation affected the area in a much wider scale than this 30 km radius.

The issue of long-term effects of Chernobyl disaster on civilians is controversial. Over 300,000 people were resettled because of the accident; millions lived and continue to live in the contaminated area. On the other hand, most of those affected received relatively low doses of radiation; there is little evidence of increased mortality, cancers or birth defects among them; and when such evidence is present, existence of a causal link to radioactive contamination is uncertain.

Aside from obstacles posed by Soviet policies during and after the catastrophe, scientific studies may still be limited by a lack of democratic transparency. In Belarus, Yuri Bandazhevsky, a scientist who questioned the official estimates of Chernobyl's consequences and the relevance of the official maximum limit of 1000 Bq/kg, has allegedly been a victim of political repression. He was imprisoned from 2001 to 2005 on a bribery conviction, after his 1999 publication of reports critical of the official research being conducted into the Chernobyl incident.

Food restrictions

In April 1986, several European countries, excluding France, had enforced food restrictions, most notably on mushrooms and milk. Twenty years after the catastrophe, restriction orders remain in place in the production, transportation and consumption of food contaminated by Chernobyl fallout, in particular caesium-137, in order to prevent them from entering the human food chain. In parts of Sweden and Finland, restrictions are in place on stock animals, including reindeer, in natural and near-natural environments. "In certain regions of Germany, Austria, Italy, Sweden, Finland, Lithuania and Poland, wild game, including boar and deer, wild mushrooms, berries and carnivore fish from lakes reach levels of several thousand Bq per kg of caesium-137", while "in Germany, caesium-137 levels in wild boar muscle reached 40,000 Bq/kg. The average level is 6800 Bq/kg, more than ten times the EU limit of 600 Bq/kg", according to the TORCH 2006 report. The European Commission has stated that "The restrictions on certain foodstuffs from certain Member States must therefore continue to be maintained for many years to come".

In the United Kingdom, under powers provided in the 1985 Food and Environment Protection Act (FEPA), Emergency Orders have been used since 1986 to impose restrictions on the movement and sale of sheep exceeding the limit of 1000 becquerels per kilogramme (Bq/kg). This safety limit was introduced in the UK in 1986 based on advice from the European Commission's Article 31 group of experts. However, the area covered by these restrictions has decreased by 95% since 1986: while it covered at first almost 9000 farms and over 4 million sheep, as of 2006 it covers 374 farms covering 750 km and 200 000 sheep. Only limited areas of Cumbria, South Western Scotland and Northern Wales are still covered by restrictions.

In Norway, the Sami people were affected by contaminated food. Their reindeer had been contaminated by eating lichens, which extract radioactive particles from the atmsophere along with their nutrients.

Fauna and vegetation

After the disaster, four square kilometres of pine forest in the immediate vicinity of the reactor went ginger brown and died, earning the name of the Red Forest, according to the BBC. Some animals in the worst-hit areas also died or stopped reproducing. Mice embryos simply dissolved, while horses left on an island 6km from the power plant died when their thyroid glands disintegrated. Cattle on the same island were stunted due to thyroid damage, but the next generation were found to be surprisingly normal. In the years since the disaster, the exclusion zone abandoned by humans has become a haven for wildlife, with nature reserves declared (Belarus) or proposed (Ukraine) for the area.

Controversy over fatality estimates

The Chernobyl Forum report

In September 2005, a draft summary report by the Chernobyl Forum, comprising a number of UN agencies including the International Atomic Energy Agency (IAEA), the World Health Organization (WHO), the United Nations Development Programme (UNDP), other UN bodies and the Governments of Belarus, the Russian Federation and Ukraine, put the total predicted number of deaths due to the accident at 4000 . This death toll predicted by the WHO included the 47 workers who died of acute radiation syndrome as a direct result of radiation from the disaster and nine children who died from thyroid cancer, in the estimated 4000 excess cancer deaths expected among the 600,000 with the highest levels of exposure. The full version of the WHO health effects report adopted by the UN, published in April 2006, included the prediction of 5000 additional fatalities from significantly contaminated areas in Belarus, Russia and Ukraine and predicted that, in total, 9000 will die from cancer among the 6.8 million most exposed Soviet citizens .

The TORCH 2006 report

German Green MEP (member of the European Parliament) Rebecca Harms, commissioned a report (TORCH ,The Other Report on Chernobyl) in 2006 in response to the UN report; it stated that:

"In terms of their surface areas, Belarus (22% of its land area) and Austria (13%) were most affected by higher levels of contamination. Other countries were seriously affected; for example, more than 5% of Ukraine, Finland and Sweden were contaminated to high levels (> 40,000 Bq/m caesium-137). More than 80% of Moldova, the European part of Turkey, Slovenia, Switzerland, Austria and the Slovak Republic were contaminated to lower levels (> 4000 Bq/m caesium-137). And 44% of Germany and 34% of the UK were similarly affected." (See map of radioactive distribution of Caesium-137 in Europe)

The IAEA/WHO and UNSCEAR considered areas with exposure greater than 40,000 Bq/m; the TORCH report also included areas contaminated with more than 4000 Bq/m of Cs-137.

The TORCH 2006 report "estimated that more than half the iodine-131 from Chernobyl was deposited outside the former Soviet Union. Possible increases in thyroid cancer have been reported in the Czech Republic and the UK, but more research is needed to evaluate thyroid cancer incidences in Western Europe". It predicted about 30,000 to 60,000 excess cancer deaths and warned that predictions of excess cancer deaths strongly depend on the risk factor used; and predicted excess cases of thyroid cancer range between 18,000 and 66,000 in Belarus alone depending on the risk projection model Furthermore it pointed out that many diseases have latencies such that it is very difficult to generate accurate estimates as early as 2006, stating that "most solid cancers have long periods between exposure and appearance of between 20 and 60 years. Now, 20 years after the accident, an average 40% increased incidence in solid cancer has been observed in Belarus with the most pronounced increase in the most contaminated regions." It also quoted the 2005 Forum's report, which documented preliminary evidence of an increase in the incidence of pre-menopausal breast cancer among women exposed at ages lower than 45 years. The TORCH report also stated that "two non-cancer effects, cataract induction and cardiovascular diseases, are well documented with clear evidence of a Chernobyl connection." Quoting the report, Nature wrote that: "it is well known that radiation can damage genes and chromosomes"; "the relationship between genetic changes and the development of future disease is complex and the relevance of such damage to future risk is often unclear. On the other hand, a number of recent studies have examined genetic damage in those exposed to radiation from the Chernobyl accident. Studies in Belarus have suggested a twofold increase in the germline minisattelite mutation rate".

Greenpeace

Greenpeace claimed contradictions in the Chernobyl Forum reports, quoting a 1998 WHO study referenced in the 2005 report, which projected 212 dead from 72,000 liquidators . In its report, Greenpeace suggested there will be 270,000 cases of cancer attributable to Chernobyl fallout, and that 93,000 of these will probably be fatal, but state in their report that “The most recently published figures indicate that in Belarus, Russia and the Ukraine alone the accident could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004.” Blake Lee-Harwood, campaigns director at Greenpeace, believes that cancer was likely to be the cause of less than half of the final fatalities and that "intestinal problems, heart and circulation problems, respiratory problems, endocrine problems, and particularly effects on the immune system," will also cause fatalities. However concern has been expressed about the methods used in compiling the Greenpeace report.

The April 2006 IPPNW report

According to an April 2006 report by the German affiliate of the International Physicians for Prevention of Nuclear Warfare (IPPNW), entitled "Health Effects of Chernobyl", more than 10,000 people are today affected by thyroid cancer and 50,000 cases are expected. The report projected tens of thousands dead among the liquidators. In Europe, it alleges that 10,000 deformities have been observed in newborns because of Chernobyl's radioactive discharge, with 5,000 deaths among newborn children. They also claimed that several hundreds of thousands of the people who worked on the site after the accident are now sick because of radiation, and tens of thousands are dead .

Other studies and claims

• The Ukrainian Health Minister claimed in 2006 that more than 2.4 million Ukrainians, including 428,000 children, suffer from health problems related to the Chernobyl catastrophe . Psychological after-effects, as the 2006 UN report pointed out, have also had adverse effects on internally displaced persons.
• Another study alleged heightened mortality in Sweden .
• The UNSCEAR 2000 report on worldwide sources and effects of ionizing radiation, Volume II, Annex J is dedicated to exposures and effects of the Chernobyl Accident
• According to the Union Chernobyl, the main organization of liquidators, 10% of the 600,000 liquidators are now dead, and 165,000 disabled.
• The Abstract of the April 2006 International Agency for Research on Cancer report Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident stated "It is unlikely that the cancer burden from the largest radiological accident to date could be detected by monitoring national cancer statistics. Indeed, results of analyses of time trends in cancer incidence and mortality in Europe do not, at present, indicate any increase in cancer rates - other than of thyroid cancer in the most contaminated regions - that can be clearly attributed to radiation from the Chernobyl accident." However, while undetectable, they estimate, based on the linear no threshold model of cancer effects, that 16,000 excess cancer deaths could be expected from the effects of the Chernobyl accident up to 2065. Their estimates have very wide 95% confidence intervals from 6,700 deaths to 38,000 .

French legal action

Since March 2001, 400 lawsuits have been filed in France against "X" by the French Association of Thyroid-affected People, including 200 in April 2006. These persons are affected by thyroid cancer or goitres, and have filed lawsuits alleging that the French government, at the time led by Prime Minister Jacques Chirac, had not adequately informed the population of the risks linked to the Chernobyl radioactive fallout. The complaint contrasts the health protection measures put in place in nearby countries (warning against consumption of green vegetables or milk by children and pregnant women) with the relatively high contamination suffered by the east of France and Corsica. Although the 2006 study by the French Institute of Radioprotection and Nuclear Safety said that no clear link could be found between Chernobyl and the increase of thyroid cancers in France, it also stated that papillary thyroid cancer had tripled in the following years .

Comparison with other disasters

The Chernobyl disaster has been compared to the 1984 Bhopal disaster. On December 3, 1984, a Union Carbide chemical plant in Bhopal, India leaked 40 tons of toxic methyl isocyanate gas, which killed at least 15,000 people, and injured anywhere from 150,000 to 600,000 others.

Other manmade disasters with very high death tolls include:

• Johnstown Flood, 1889, 2,209 killed.
• Banqiao Dam, 1975, in China, 171,000 killed.
• Great Smog of 1952, London, England about 12,000 killed.

Other nuclear and radiation accidents have occurred during the years, although none approached the proportions of the Chernobyl's catastrophe. Civilian nuclear accidents involving known fatalities happened in a fuel recovery plant in Charlestown, Rhode Island (US) on July 24, 1964 (one death) ; in an experimental facility in Buenos Aires, Argentina, on September 23, 1983 (one death) , and most recently in the Japanese Tokaimura nuclear fuel reprocessing plant, on September 30, 1999 (two deaths). Previous serious commercial nuclear power plant incidents include the 1957 fire of the Windscale reactor in England and the 1979 meltdown at the Three Mile Island US nuclear power plant, both with no known fatalities.

Chernobyl after the disaster

The trouble at the Chernobyl plant itself did not end with the disaster in reactor 4. The damaged reactor was sealed off and 200 metres of concrete were placed between the disaster site and the operational buildings. The Ukrainian government continued to let the three remaining reactors operate because of an energy shortage in the country. A fire broke out in reactor 2 in 1991; the authorities subsequently declared the reactor damaged beyond repair and had it taken offline. Reactor 1 was decommissioned in November 1996 as part of a deal between the Ukrainian government and international organizations such as the IAEA to end operations at the plant. In November 2000, Ukrainian President Leonid Kuchma personally turned off the switch to reactor 3 in an official ceremony, shutting down the entire plant.

The need for future repairs

The sarcophagus is not an effective permanent enclosure for the destroyed reactor. Its hasty construction, in many cases conducted remotely with industrial robots, is aging badly. If it collapses another cloud of radioactive dust could be released. The sarcophagus is so badly damaged that a small earthquake or severe wind could cause the roof to collapse. A number of plans have been discussed for building a more permanent enclosure.

According to official estimates, about 95% of the fuel (about 180 tonnes) in the reactor at the time of the accident remains inside the shelter, with a total radioactivity of nearly 18 million curies (670 PBq). The radioactive material consists of core fragments, dust, and lava-like "fuel-containing materials" (FCM) that flowed through the wrecked reactor building before hardening into a ceramic form. By conservative estimates, there are at least four tons of radioactive dust inside the shelter. However, more recent estimates have strongly questioned the previously held assumptions regarding the quantity of fuel remaining in the reactor. Some estimates now place the total quantity of fuel in the reactor at only about 70% of the original fuel load, however the IAEA maintains that less than 5% of the fuel was lost due to the explosion. Moreover, some liquidators estimate that only 5–10% of the original fuel load remains inside the sarcophagus.

Water continues to leak into the shelter, spreading radioactive materials throughout the wrecked reactor building and potentially into the surrounding groundwater. The basement of the reactor building is slowly filling with water that is contaminated with nuclear fuel and is considered high-level radioactive waste. Though repairs were undertaken to fix some of the most gaping holes that had formed in the roof, it is by no means watertight, and will only continue to deteriorate.

The sarcophagus, while not airtight, heats up much more readily than it cools down. This is contributing to rising humidity levels inside the shelter. The high humidity inside the shelter continues to erode the concrete and steel of the sarcophagus.

Further, dust is becoming an increasing problem within the shelter. Radioactive particles of varying size, most of similar consistency to ash make up a large portion of the debris inside the shelter. Convection currents compounded with increasing intrusion of outside airflow are increasingly stirring up and suspending the particles in the air inside the shelter. The installation of air filtration systems in 2001 has reduced the problem, but not eliminated it.

Consequences of further collapse

The present shelter is constructed atop the ruins of the reactor building. The two "Mammoth Beams" that support the roof of the shelter are resting upon the structurally unsound west wall of the reactor building that was damaged by the accident. If the wall of the reactor building and subsequently the roof of the shelter were to collapse, then tremendous amounts of radioactive dust and particles would be released directly into the atmosphere, resulting in a devastating new release of radiation into the surrounding environment.

A further threat to the shelter is the concrete slab that formed the "Upper Biological Shield" (UBS), and rested atop the reactor prior to the accident. This concrete slab was thrown upwards by the explosion in the reactor core and now rests at approximately 15° from vertical. The position of the upper bioshield is considered inherently unsafe, in that only debris is supporting it in a nearly upright position. The collapse of the bioshield would further exacerbate the dust conditions in the shelter, would probably spread some quantity of radioactive materials out of the shelter, and could damage the shelter itself.

The sarcophagus was never designed to last for the 100 years needed to contain the radioactivity found within the remains of reactor 4. While present designs for a new shelter anticipate a lifetime of up to 100 years, that time is minuscule compared to the lifetime of the radioactive materials within the reactor. The construction of a permanent sarcophagus that can entomb the remains of reactor 4 will undoubtedly present a daunting challenge to engineers for many generations to come.

The Chernobyl Fund and the Shelter Implementation Plan

The Chernobyl Shelter Fund was established in 1997 at the Denver G7 summit to fund the Shelter Implementation Fund. The Shelter Implementation Plan (SIP) calls for transforming the site into an ecologically safe condition through stabilisation of the sarcophagus, followed by construction of a New Safe Confinement (NSC). The original cost estimate for the SIP was US$768 million. The SIP is being managed by a consortium of Bechtel, Battelle, and Electricité de France, and conceptual design for the NSC consists of a movable arch, constructed away from the shelter to avoid high radiation, to be slid over the sarcophagus. The NSC will be the largest movable structure ever built, and is expected to be completed in early 2008. Dimensions Span: 270 m Height: 100 m Length: 150 m

Chernobyl in the popular consciousness

The Chernobyl accident riveted international attention. Around the world, people read the story and were profoundly affected. As a result, "Chernobyl" has entered the public consciousness in a number of different ways.

References

1. "Geographical location and extent of radioactive contamination". Swiss Agency for Development and Cooperation. {{cite web}}: Cite has empty unknown parameter: |1= (help) (quoting the "Committee on the Problems of the Consequences of the Catastrophe at the Chernobyl NPP: 15 Years after Chernobyl Disaster", Minsk, 2001, p. 5/6 ff., and the "Chernobyl Interinform Agency, Kiev und", and "Chernobyl Committee: MailTable of official data on the reactor accident")
2. "TORCH report (The Other Report on Chernobyl)" (PDF). European Greens. April 2006. Retrieved April 2006. {{cite web}}: Check date values in: |accessdate= (help); Cite has empty unknown parameter: |1= (help)
3. ^ See also here for an animated Flash map of radioactive fallout caesium-137, produced by the French Institut de radioprotection et de sûreté nucléaire
4. Comparison of Damage among Hiroshima/Nagasaki, Chernobyl, and Semipalatinsk
5. ^ "IAEA Report". In Focus: Chernobyl. Retrieved 2006-03-29.
6. "Greenpeace rejects Chernobyl toll". BBC News. April 18, 2006.
7. Template:Ru icon Глава 4. КАК ЭТО БЫЛО
8. Template:Ru icon Фатахов Алексей Чернобыль как это было - 2
9. Chernobyl source term, atmospheric dispersion, and dose estimation, EnergyCitationsDatabase, November 1, 1989
10. OECD Papers Volume 3 Issue 1, OECD, 2003
11. The Social Impact of the Chernobyl Disaster, 1988, p166, by David R. Marples ISBN 0333481984
12. "Chernobyl's silent graveyards". BBC News. BBC. April 20,2006. {{cite news}}: Check date values in: |date= (help)
13. ^ Template:Fr icon "Tchernobyl, 20 ans après". RFI. April 24, 2006. Retrieved April 24, 2006.
14. ^ "TORCH report executive summary" (PDF). European Greens and UK scientists Ian Fairlie PhD and David Sumner. April 2006. Retrieved April 21, 2006. (page 3)
15. Chapter IV: Dose estimates, Nuclear Energy Agency, 2002
16. "Post-Chernobyl Monitoring and Controls Survey Report" (PDF). UK Food Standards Agency. Retrieved April 19, 2006.
17. "Chernobyl fallout: internal doses to the Norwegian population and the effect of dietary advice", Strand P, Selnaes TD, Boe E, Harbitz O, Andersson-Sorlie A., National Institute of Radiation Hygiene, Osteras, Norway
18. Wildlife defies Chernobyl radiation, by Stefen Mulvey, BBC News
19. For full coverage see the IAEA Focus Page (op.cit.) and joint IAEA/WHO/UNDP September 5, 2005 press release Chernobyl: The True Scale of the Accident
20. ^ "Special Report: Counting the dead". Nature. April 19, 2006. Retrieved April 21, 2006.
21. TORCH report executive summary, op.cit., p.4
22. Concerning human minisatellite mutation rate after the Chernobyl accident, the Nature April 2006 article also quotes "Human minisatellite mutation rate after the Chernobyl accident". Nature n° 380. April 25, 1996. Retrieved April 21, 2006. {{cite news}}: Unknown parameter |authors= ignored (help)
23. WHO Chernobyl report 2006 pdf
24. Wall Street Journal, 27 April 2006
25. Spiegel, The Chernobyl body count controversy
26. "20 years after Chernobyl - The ongoing health effects". IPPNW. April , 2006. Retrieved April 24, 2006. {{cite web}}: Check date values in: |date= (help)
27. "20 years after Chernobyl - The ongoing health effects, PDF report" (PDF). IPPNW. April 2006. Retrieved April 24, 2006.
28. Chernobyl 'caused Sweden cancers', BBC News, November 20, 2004
29. Increase of regional total cancer incidence in north Sweden due to the Chernobyl accident?
30. UNSCEAR 2000, Vol II, Annex J. Exposures and effects of the Chernobyl Accident
31. Template:Fr "Selon un rapport indépendant, les chiffres de l'ONU sur les victimes de Tchernobyl ont été sous-estimés (According to an independent report, UN numbers on Chernobyl's victims has been underestimated)". Le Monde. April 7, 2006.
32. Abstract of April 2006 IARC report 'Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident'
33. IARC Press release on the report 'Estimates of the cancer burden in Europe from radioactive fallout from the Chernobyl accident'
34. Briefing document:Cancer burden in Europe following Chernobyl
35. Template:Fr icon "Nouvelles plaintes de malades français après Tchernobyl". RFI. April 26, 2006. Retrieved April 26, 2006. (includes Audio files, with an interview with Chantal Loire, president of the French Association of Thyroid-Affected People, as well as interviews with member of the CRIIRAD
36. FAS.org PDF file pg27
37. NRC.gov
38. "Tokaimura Criticality Accident". World Nuclear Association. June 2000. Retrieved 2006-04-20.

See also

• Nuclear and radiation accidents
• Three Mile Island
• Zone of alienation – the restricted zone formed around the accident site.
• Yuri Bandazhevsky
• Valeri Legasov
• Ignalina Nuclear Power Plant

External links

General information

• 2006 TORCH full report (in pdf)
• Chernobyl's Legacy (PDF, 902KB) by the Chernobyl Forum (UN) updated in 2006
  • Health, Environmental and Socio-Economic Impacts – a summary for non-specialists of the above UN report by GreenFacts
• The Chernobyl Catastrophe: Consequences on Human Health (PDF, 1.8MB) by Greenpeace International, April 2006.
• Better World Links on the Chernobyl Disaster – 100 links
• BBC h2g2 giving a detailed description of events
• Fall-out data in 19 zones from Austria to Eastern USA
• The International Chernobyl Research and Information Network
• Frequently Asked Chernobyl Questions, by the IAEA
• Official UN Chernobyl site
• The Human Consequences of the Chernobyl Accident: A Strategy for Recovery – UN Report, 2002 (PDF, 350KB)
• Chernobyl – A Canadian Perspective (PDF 405KB) – A brochure describing nuclear reactors in general and the RBMK design in particular, focusing on the safety differences between them and CANDU reactors. Published by the CANDU organization.
• Annotated bibliography for Chernobyl from the Alsos Digital Library for Nuclear Issues

Event & technical analysis

• Template:En icon/Template:Fr icon Surveillance sanitaire en France en lien avec l’accident de Tchernobyl – Bilan actualisé sur les cancers thyroïdiens et études épidémiologiques en cours en 2006, April 2006 report by the French Institut de veille sanitaire on Chernobyl's consequences in France and thyroid cancers
• Template:En icon/Template:Fr icon Various reports (Chernobyl 5 years after, 10 years after, 20 years after, etc. by the Institut de radioprotection et de sûreté nucléaire (English version - click on top right)
• Detailed analysis of the events, Georgia State University
• Another account of the incident, World Nuclear Association
• Technical information concerning the accident, as well as a contrast between the RBMK reactor design that of American reactors, University of Pittsburgh
• Harvard Medical School study on Radiation and Chernobyl
• Radioecology and the Chernobyl Disaster, January 2003. Covers impact on the UK
• Template:Ru icon Alternative opinion about the Chernobyl catastrophe reasons – The English version is being prepared.
• Details of the events leading up to the accident and the aftermath
• Template:Pl icon Czarnobyl
• WNC reactor Issue Brief – Short technical analysis of the RBMK reactor design and changes made after accident, World Nuclear Association

Witness accounts (before and after)

• 20 Years 20 Lives – Eyewitness accounts in words and photographs
• A female tourist's account, in photos, the veracity of which has been questioned. See Elena Filatova
• Interview with Sasha Yuvchenko – an engineer working in Chernobyl on 26th April 1986
• Mary Mycio's Account of the Zone – Wormwood Forest: A Natural History of Chernobyl

Photography/Videography/Infography

• Chernobyl Legacy, 2006. By photojournalist Paul Fusco. Narrated interactive essay, focused on the continuing human tragedy in Belarus.
• Animated Flash map—2 minutes and 30 seconds—of Caesium-137 contamination published by the French Institut de radioprotection et de sûreté nucléaire (IRSN)
• Photographs of Pripyat and Chernobyl
• Photos from Pripyat city and Chernobyl zone 2 trips in 2005
• Nuclear Nightmares: Twenty Years Since Chernobyl
• BBC On This Day: Including recordings of the first public announcement
• Template:Ru icon More Dead Zone pictures
• 2006 images of Chernobyl today
• Chernobyl Gallery – Several images, many from inside the reactor.
• Chernobyl Heart (2003) – Academy Award-winning documentary
• Stone, Richard (2006-03-28). "The Long Shadow of Chernobyl". National Geographic. p. 32. Retrieved 2006-03-28. {{cite news}}: More than one of |author= and |last= specified (help); More than one of |pages= and |page= specified (help)
• Nine Network Australia, 60 Minutes, 'Inside Chernobyl', airdate April 16, 2006. Reporter Richard Carlton goes inside the control centre at Chernobyl and also visits the exclusion zone surrounding the plant. Focuses on the 1986 incident, the failing 'sarcophagus' and yet-to-be–realised plans to replace it, and the affected children in orphanages in nearby Belarus
• Satellite view of Chernobyl, Google Maps
• Various videos from Chernobyl, Czech language

Charitable and voluntary organizations concerned with the effects

• Chernobyl Children's Project International – subject of documentary "Chernobyl Heart."
• Aratta – Public organisation supporting children and families

Template:Link FA Template:Link FA Template:Link FA

• Chernobyl disaster
• Engineering failures
• Nuclear accidents
• Industrial disasters
• 1986
• History of the Soviet Union and Soviet Russia
• History of Belarus
• History of Ukraine