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On April 26, 1986, a catastrophic accident occurred at the Chernobyl-4 reactor near the town of Pripyat, Ukraine, 100 kilometers northwest of Kiev. Figure 1 shows the reactor location and the regions of most intense radioactive contamination. The accident destroyed the reactor and released a large amount of radioactivity into the atmosphere, particularly radioactive iodine (I-131) and radioactive cesium (Cs-137), both of which have the potential to cause cancer. Thirty-one workers at the plant died within a few weeks, most of them from receiving lethal doses of radiation while putting out fires and responding to other emergencies.

Radiation fallout caused significant contamination in parts of Belarus, Russia, and the Ukraine, resulting in the resettlement of more than 350,000 people from 4,300 square kilometers. An approximate five- to ten-fold increase in thyroid cancer has been observed in children from Belarus, Russia, and Ukraine who received a large exposure to I-131. The economic impact has also been large, not only from the direct costs of accident cleanup, decontamination, and entombing the reactor, but also for lost agricultural production from the evacuated areas, and from regions throughout Europe where the radioactive fallout resulted in restrictions on eating certain foods and on limiting imports. Continued health monitoring over many years will be required for citizens who had lived in or are currently living in contaminated areas, and for cleanup workers who received significant doses of radiation.

At the time of the accident, the Chernobyl reactors were owned and operated by the Soviet Ministry of Power and Electrification. The reactor design was a unique Soviet design called an RBMK. A schematic diagram is shown in Figure 2. Like reactors in the United States, RBMK reactors use ordinary water to cool the fuel. Unlike U.S. reactors, which use water to slow down or moderate the neutrons produced in fission, the RBMK uses graphite as the moderator. In this case the water used for the coolant is actually a neutron absorber and reducing the density of the water increases the neutron production. In addition, the ratio of uranium isotopes U-235 to U-238 in the fuel is less in the RBMK than in U.S. reactors. The effect of these differences was that at low power operation, under the right conditions, the power in the RBMK could increase in an uncontrolled manner. Reactor designs that allow power increase in an uncontrolled manner are prohibited by regulation in the United States. The type of accident that occurred was unique to the Soviet-designed RBMK reactor. Another important difference is that Soviet reactors did not have a steel-lined, thick concrete-walled containment building like those in Western Europe, North America, and Asia, using instead an industrial-type building. This final difference had profound consequences.

The Accident

The accident occurred while the operators were conducting a test simulating loss of power at the plant. The goal was to determine if power from the spinning turbines could be used to operate the pumps while backup diesel generators were brought on line. In order to conduct the test, most of the safety systems that would have provided a safe shutdown were disconnected. A test of this type that disconnected the safety systems would never be allowed in the United States, Western Europe, or Asia. The test was to be conducted at about 25 percent power, but when the power level was reduced from 100 percent to 50 percent, the test was delayed for nine hours because the electricity was needed in Kiev. While the operators waited, a strong neutron-absorbing isotope, Xenon-135, built up in the reactor. The operators did not recognize this and did not incorporate the effect into the control computer. When the test resumed, the operators could not control the reduction of power because the Xenon-135 was absorbing neutrons needed for fission and consequent power production. To keep the reactor from shutting itself down, they pulled out most of the neutron-absorbing control rods that are used to control the reactor power. This was in violation of Soviet operating procedures. Unknown to the operators, they now found themselves operating under conditions where the reactor could increase in power in an uncontrolled manner.

When the operators continued the test procedure by turning off the water coolant pumps and re-inserting the slow-moving control rods, there was still enough power to cause the water to start boiling, thereby reducing the water density and increasing the neutron production. In addition, there were graphite tips on the bottom of the control rods that added moderator when the control rods were initially inserted, and this further increased neutron production. Instead of the power level decreasing, as the operators expected, it increased rapidly, reaching approximately one hundred times full power in just a few seconds. The increased power resulted in a massive steam buildup inside the reactor leading to an explosion.

A second explosion that followed shortly lifted the large top shield above the reactor, blew off the roof and walls of the building, and dispersed burning fuel and graphite. The steel shield resettled at an angle, allowing air to enter the reactor and the argon gas that normally covers the reactor to escape. Contact with the air caused the hot graphite to ignite, propelling the volatile radioactive materials high up into the atmosphere. Firefighters who went to the room to put out the fires received a lethal dose of radiation. It took ten days to control the fire, and by that time 5 to 10 percent of the radioactive material in the core had been released to the atmosphere.

Evacuation and Health Effects

Evacuation of residents from the nearby town of Pripyat took place the following day, but evacuation from adjacent contaminated areas did not take place for several days, nor did the Soviet government quickly inform the residents or the world what had happened. The radiation release was first made public after the airborne radiation from the accident was detected in Sweden. In 1986 about 116,000 people were relocated from areas surrounding the reactor, and an additional 220,000 people from Belarus, the Russian Federation, and Ukraine were relocated after 1986.

The World Health Organization (WHO) has continually monitored those exposed to radiation, including the residents and 600,000 "liquidators" who came to clean up the accident. Two hundred thousand liquidators built a cooling system under the reactor and a shield building—commonly called the sarcophagus—around the damaged reactor. They received doses of 100 millisieverts (10 rem) or more, with 20,000 receiving doses of at least 250 millisieverts. For comparison, this is five times the U.S. total effective dose limit for radiation workers. Another 400,000 liquidators, who arrived after 1987, received much lower doses.

Extensive analyses of the public health effects from Chernobyl have been conducted by United Nations organizations including WHO. A comprehensive summary is available in a report by the United Nations Scientific Commission on the Effects of Atomic Radiation (UNSCEAR) published in 2000, which concludes that the only radiation-related effect to that date was an increase in thyroid cancer, largely in children. Through the years 1990–1998 there were about 1,800 cases of thyroid cancer in the contaminated areas of Belarus, Russia, and Ukraine in children 0–17 years old at the time of the accident. The majority of these were related to the accident.

Additional cases of thyroid cancer are expected in the future. Thyroid cancer is generally treatable if caught early. Nonetheless, ten deaths were reported as of 2000. It is not possible to make any accurate prediction about the number of deaths that will ultimately result, because there are no models that accurately predict deaths from low levels of radiation exposure. Many reports indicating much larger numbers of cancers and deaths from the Chernobyl accident were found in the UNSCEAR review to contain misinterpretations of data or use of unsubstantiated data.

While the heaviest radiation doses were received in Belarus, Russia, and Ukraine, the release of radioactivity from the Chernobyl reactor went high into the atmosphere and spread throughout Europe and then around the whole northern hemisphere. Figure 3 shows the dispersion of the radioactive cloud. The fallout in Europe varied considerably among the countries, depending on wind patterns and rain during the ten days the reactor was releasing radioactivity to the atmosphere. The largest doses were received in Poland, followed by Sweden, Germany, Italy, Finland, and Czechoslovakia. While such fallout caused great concern with the governments and the population, the doses received by the populations were relatively low, although there were some localized "hot spots."

Response and Lessons

Engineers from the former Soviet Union have made changes to all RBMK reactors to eliminate the possibility of repeating this type of accident. Nonetheless, in the West the RBMK is considered too unsafe to continue operation. All the Chernobyl units have been shut down. Other RBMK reactors outside Russia are being phased out of operation. However, the Russians still consider it a safe reactor and plan to continue operating all existing units. Plans to build new ones have been nevertheless cancelled.

In addition, the Soviet-designed water-cooled reactors, the VVER, built in the former Soviet Union and its satellite states, have either been shut down for inadequate safety features or modified to enhance safety. The United States and European countries have contributed millions of dollars in equipment and expertise to upgrade the safety of the existing reactors and their operation. The accident also stimulated the creation of the World Association of Nuclear Operations (WANO), whose goal is to improve safety in operations. WANO is an extension of the Institute for Nuclear Power Operations (INPO) that was formed after the accident at Three Mile Island in 1979 and was instrumental in improving safety in the operation of nuclear power plants in the United States.

While the design of the RBMK was flawed, a far greater problem was failures in human performance. How was it possible for the managers to allow the safety systems that would have prevented the accident to be disconnected during the test? How could all the control rods have been removed in violation of fundamental safety procedures? One answer is that written safety and accident response procedures actually did not exist in most RBMK control rooms before the accident. Furthermore, the operators were not trained to respond to different accident scenarios, and surely not to an accident that might occur during an experimental procedure. Importantly, there was no effective safety review of the proposed test. Moreover, the accident occurred in a society where secretiveness rather than openness was standard operating procedure, and this resulted in a lack of communication within the organization and with the public. After the accident, the Soviet government attempted to conceal it and the dangers posed to the local population and to the world.

Western nations learned the lessons of Three Mile Island, but states of the former Soviet Union did not. Specifically, they did not incorporate the fundamental lesson that safety is the most important responsibility of the operators, and that management from the top down must emphasize, encourage, and incorporate this thinking into plant operation. A culture that fosters "safety-first thinking" throughout the organization is necessary if nuclear power is to reach its potential to benefit humanity.

Since Chernobyl, nations of the former Soviet Union (FSU) have made significant improvements in both operations and design. Assistance from the United States and Europe led to the establishment of new training facilities, enhanced operator training, improved procedures for responding to accidents, and upgraded plant equipment. New Russian designs of the VVER type have added safety features and a containment building so they now meet safety standards used elsewhere in the world. There has been a change in management philosophy and an increased emphasis on operations safety. Regulatory agencies are improving in their capabilities. Nonetheless, the culture change needed to reach the safety standards of the United States and Western Europe will be a continuing challenge in the FSU countries.

The Chernobyl accident showed dramatically that an accident anywhere represents an accident everywhere, for it reflects on the ability of nuclear power to serve society as a trustworthy technology. This is a high standard and it raises the question: Can nations throughout the world that desire to use nuclear power maintain this level of attention to safety? Even though future reactors may be designed and built that prevent a catastrophic accident, it is important that an emphasis on a culture of safety be maintained. Ultimately it will reflect on the capacity of the world nuclear industry to serve civilization.

The accident was also global in the sense that radioactive fallout was present throughout the northern hemisphere and caused local contamination in many European countries that were not prepared for such an accident. The reactions of national authorities varied greatly on issues such as restrictions on consumption and marketing of foodstuffs. There was no uniformity in standards for implementation of protective actions. This could be especially disconcerting to the public in the border region when the nations on each side of the border took significantly different actions. National authorities sometimes used interpretations that responded to public fears rather than being based on sound science. This resulted in unnecessarily increasing public confusion and possibly public fears, and caused unnecessary government expense and economic loss. International efforts have been undertaken to produce more uniform regulations and criteria related to radiation accidents, and for emergency management of transnational accidents. Whether these efforts will be effective may not be known unless they are put to the test. In light of the level of terrorism that now exists in the world, and the possibility that biological and chemical agents can cross national boundaries as well as nuclear agents, it has become ever more critical that this type of emergency management be carefully developed and practiced. This could be one of the most important lessons from the Chernobyl accident.


SEE ALSO Nuclear Ethics; Three-Mile Island.


Knief, Ronald Allen. (1992). Nuclear Engineering: Theory and Technology of Commercial Nuclear Power, 2nd ed. New York: Hemisphere. Nuclear engineering textbook with a good technical discussion of the RBMK reactor, the chronology of the accident, the causes of the accident, the effects of the accident, and comparisons with the Three Mile Island accident.

Medvedev, Grigori. (1991). The Truth About Chernobyl, trans. Evelyn Rossiter. New York: Basic Books. Written by a physicist who had been a chief engineer at Chernobyl and was an investigator of the accident; presents both background material and an intimate account of the events leading to the accident and the accident itself.

Organisation for Economic Co-operation and Development, Nuclear Energy Agency. (1995). Chernobyl—Ten Years On: Radiological and Health Impact. Paris: Nuclear Energy Agency, OECD. Covers radiation releases, dose estimates, health impacts, agricultural impacts, reactions of national authorities, and other issues.


Nuclear Regulatory Commission. (2000). "Fact Sheet on the Accident at the Chernobyl Nuclear Power Plant." Available from Briefly discusses the accident and presents information on the Nuclear Regulatory Commission's post-accident activities to assist the Ukraine in dealing with the accident.

United Nations Scientific Commission on the Effects of Atomic Radiation (UNSCEAR). "Exposures and Effects of the Chernobyl Accident." In Volume II of the UNSCEAR 2000 Report. Available from Comprehensive and authoritative report on the health effects of the Chernobyl accident with data through 1998.

World Nuclear Association. (2001). "Chernobyl." Available from (Go to Document inf07.) Site has a set of detailed and authoritative documents discussing many facets of the accident and its consequences. There are also maps of the area. Document inf07 describes the accident and its consequences in detail and gives direct access to three short reports on health effects from the accident.

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On 26 April 1986 one of the four nuclear reactors at the Chernobyl nuclear power plant near Kiev, Ukraine, exploded. The explosion generated a huge fire that spewed tons of radioactive material into the atmosphere and made the surrounding towns of Chernobyl and Pripyat uninhabitable. The explosion released four hundred times more radiation than the atom bombs dropped on Hiroshima and Nagasaki during World War II. Most of the radioactive material fell in Ukraine and the surrounding countries of Belarus and Russia, while lighter contaminated material blew as far away as Scandinavia and other parts of Europe, as far south as Greece and Yugoslavia.

The implications of the Chernobyl explosion lie not only in the fact that it was the worst nuclear accident of the modern age but also that it was a significant trigger for the collapse of the Soviet Empire and the communist bloc. Mikhail Gorbachev, the Soviet general secretary at the time of the accident, came to power in 1985 at a time when the world was still dominated by a bipolar geopolitical structure led by the United States and the Soviet Union. For centuries the Russians, during the tsarist monarchies and later under the Soviets, had a tradition of intense secrecy and lack of transparency in their governing bodies. Gorbachev announced a new policy of openness (glasnost) and restructuring (perestroika) soon after he came to power. But old habits die hard, and Chernobyl was a test of Gorbachev's ability to follow through on his promise to be more progressive. Despite the goals for a more open, democratic society, the Chernobyl accident revealed the extremely conservative and rigid nature of the Soviet government. Gorbachev had made a powerful impression on the Soviet people when he first came to office. He was by far the most accessible leader they had ever known. Chernobyl threw Gorbachev off course and he was never able to fully recover.

Firefighters and volunteers were not able to bring the fire and meltdown under control for nine days, and Gorbachev waited for eighteen days before publicly addressing the catastrophe. On 27 April, thirty-six hours after the accident, residents of Pripyat, a town four kilometers away and closest to the reactors, were evacuated. Residents in other surrounding villages were not informed of the accident and continued to go about their daily lives unaware of the fatal levels of exposure. Forty-eight hours after the accident Moscow authorities admitted there had been an explosion but insisted that the radiation situation was not harmful to inhabitants in the area. May Day festivities with parades and speeches in the surrounding villages (except Pripyat) went on as if nothing had happened. Not until after the May Day celebrations, from 2 to 4 May, were more than 100,000 people living in villages within a thirty-kilometer radius informed of the contamination and forced to leave their homes immediately and resettle. On 14 May, in a speech that revealed nothing about the causes or the impact of the accident, Gorbachev slid back into an anti-Western diatribe that claimed the United States used the accident as a launching point for an anti-Soviet campaign. This speech, the lack of transparency in revealing the true extent of the radiation poisoning, the denial and delay in evacuating residents and alerting the world, all added to the Soviet public's deep distrust and suspicion of its leaders.


The official explanation for the accident is that it was the result of a flawed reactor design that was operated by inadequately trained personnel. The less publicized explanation for the catastrophe is far more complex and dates back to the Soviet Union's rush to industrialize the nation in the 1920s and 1930s after the Bolshevik Revolution. Dozens of giant hydroelectric plants, factories, and later, nuclear plants were rushed prematurely into service. Historically the Soviet Union's occupational accident rate was the worst of any industrialized nation.

The reactor that exploded was known to have a problematic design structure; there were many of this same model in use and scheduled to be built all over the Soviet Union. The inadequacies and deficiencies of the reactor design were ignored and hidden by managers of the plant in order to fulfill the demands of the nation's economic plans for more nuclear energy. Following the accident, these design problems were acknowledged and no more of this model were built.


The terrible environmental contamination resulted in the forced resettlement of hundreds of thousands of people and the loss of crops and cropland in the rich area of the Belarusian and Ukrainian black earth region known as the breadbasket of the Soviet Union. Over the next year another 300,000 inhabitants were forced to leave their homes and resettle. More than two thousand villages and towns were razed and covered over to prevent further radiation exposure. Hundreds of other villages were abandoned and still lie empty in 2006. Billions of rubles have been spent on the cleanup, decontamination efforts, and the resettlement and health care costs of the hundreds of thousands of people who suffered radiation poisoning.

The long-term health effects of such high radiation exposure are still a subject of intense debate. In 1986 and 1987 an estimated 200,000 "liquidators" from all over the Soviet Union came to help control the fire and clean up the area so the remaining reactors could continue to operate. The workers who were either forced or volunteered to help with the immediate cleanup operation in the early days before the fire was contained either died soon after the accident or died prematurely, primarily from cancer. The other liquidators also suffered high rates of cancers, but there is no conclusive data on all of them. In 2005, a report by a group of experts called the Chernobyl Forum attributed a total of fifty-six deaths directly to the explosion and the immediate aftermath. The Forum also greatly reduced the estimate of subsequent deaths related to radiation poisoning to 4,000 from previous estimates as high as 100,000. Children are disproportionately affected by radiation poisoning because they are more physically vulnerable. Although there have been extremely high rates of thyroid and other cancers among children exposed to the Chernobyl fallout, and very high rates of congenital birth defects and mental retardation, the link between radiation and these health consequences is still debated by nuclear experts in Russia, Ukraine, Belarus, and other countries. As the Chernobyl Forum report reveals, debates about death rates and the effects of radiation poisoning remain inconclusive and will continue for decades after the disaster.


Because there were many signs of decay in the Soviet economy and society even before the Chernobyl accident, the explosion acted as a catalyst that propelled the Soviet Union toward collapse by 1991. Imminent signs of the breakup included rising national consciousness in the fifteen republics of the Soviet Union, a failing war in Afghanistan that had caused deep-seated anger among the populace, and an economy that had been stagnating and declining for at least twenty years. Environmental damage and its impact on human health were hidden under Soviet rule and never publicly discussed nor acknowledged. For seventy years Soviet policies had wantonly destroyed the environment through the overuse of pesticides and chemicals for agriculture, the rush to industrialize, and the buildup of a militaryindustrial complex to compete with the United States in the Cold War. The nuclear accident at Chernobyl sent shock waves through the country that were irreparable. Chernobyl forced the issue into the public sphere and led to a widespread civil awakening. After the accident, for the first time in Soviet history, civil society spoke up, protesting and forming environmental associations to protect the Soviet Union's remaining natural resources. No peaceful civil gatherings of this nature were allowed before.


After the fire was contained, a concrete sarcophagus was constructed to keep the radioactive material from leaking out. The sarcophagus was supposed to last for twenty to thirty years, but began to show dangerous signs of decay in the 1990s. A new shelter was scheduled to be completed by 2009, which is supposed to contain the reactor and the hazardous material for another hundred years. The remaining three reactors continue to operate. Concerns about possible leaks from leftover nuclear fuel in these three reactors remain.

After the Chernobyl accident the world became far more cautious about the use of nuclear energy and the design of nuclear power plants. International nuclear commissions were formed not only to research and examine the accident and the mechanisms for cleanup but also to ensure that this kind of accident never happens again. Globally, public trust in nuclear energy as an alternate source of power declined dramatically after Chernobyl, and that faith in the potential for nuclear power to solve the world's energy needs has never been fully restored.

See alsoAtomic Energy; Gorbachev, Mikhail; Soviet Union.


"Chernobyl Children's Project International." Available from

"Chernobyl Information." Available from

Coleman, Fred. The Decline and Fall of the Soviet Empire: Forty Years That Shook the World, from Stalin to Yeltsin. New York, 1996.

Feshbach, Murray, and Alfred Friendly Jr. Ecocide in the USSR: Health and Nature under Siege. New York, 1992.

Gale, Peter, and Thomas Hauser. Final Warning: The Legacy of Chernobyl. New York, 1988.

"International Atomic Energy Agency." Available from

Kaiser, Robert G. Why Gorbachev Happened: His Triumphs and His Failure. New York, 1991.

Medvedev, Zhores. The Legacy of Chernobyl. New York, 1990.

Volkogonov, Dmitri. Autopsy for an Empire: The Seven Leaders Who Built the Soviet Regime. New York, 1998.

Kate Schecter

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The disaster at Chernobyl (Ukrainian spelling: Chornobyl) on April 26, 1986 occurred as a result of an experiment on how long safety equipment would function during shutdown at the fourth reactor unit at Ukraine's first and largest nuclear power station. The operators had dismantled safety mechanisms at the reactor to prevent its automatic shutdown, but this reactor type (a graphitemoderated Soviet RBMK) became unstable if operated at low power. An operator error caused a power surge that blew the roof off the reactor unit, releasing the contents of the reactor into the atmosphere for a period of about twelve days.

The accident contaminated an area of about 100,000 square miles. This area encompassed about 20 percent of the territory of Belarus; about 8 percent of Ukraine; and about 0.5-1.0 percent of the Russian Federation. Altogether the area is approximately the size of the state of Kentucky or of Scotland and Northern Ireland combined. The most serious radioactive elements to be disseminated by the accident were Iodine-131, Cesium-137, and Strontium-90. The authorities contained the graphite fire with sand and boron, and coal miners constructed a shelf underneath it to prevent it from falling into the water table.

After the accident, about 135,000 people were evacuated from settlements around the reactor, including the town of Pripyat (population 45,000), the home of the plant workers and their families, and the town of Chernobyl (population 10,000), though the latter remained the center of the cleanup operations for several years. The initial evacuation zone was a 30-kilometer (about 18.6 miles) radius around the destroyed reactor unit. After the spring of 1989 the authorities published maps to show that radioactive fallout had been much more extensive, and approximately 250,000 people subsequently moved to new homes.

Though the Soviet authorities did not release accurate information about the accident, and classified the health data, under international pressure they sent a team of experts to a meeting of the IAEA (The International Atomic Energy Agency) in August 1986, which revealed some of the causes of the accident. The IAEA in turn was allowed to play a key role in improving the safety of Soviet RBMK reactors, though it did not demand the closure of the plant until 1994. A trial of Chernobyl managers took place in 1987, and the plant director and chief engineer received sentences of hard labor, ten and five years respectively.

Chernobyl remains shrouded in controversy as to its immediate and long-term effects. The initial explosion and graphite fire killed thirty-one operators, firemen, and first-aid workers and saw several thousand hospitalized. Over the summer of 1986 up until 1990, it also caused high casualties among cleanup workers. According to statistics from the Ukrainian government, more than 12,000 "liquidators" died, the majority of which were young men between the ages of twenty and forty. A figure of 125,000 deaths issued by the Ukrainian ministry of health in 1996 appears to include all subsequent deaths, natural or otherwise, of those living in the contaminated zone of Ukraine.

According to specialists from the WHO (World Health Organization) the most discernible health impact

of the high levels of radiation in the affected territories has been the dramatic rise in thyroid gland cancer among children. In Belarus, for example, a 1994 study noted that congenital defects in the areas with a cesium content of the soil of onefive curies per square kilometer have doubled since 1986, while in areas with more than fifteen curies, the rise has been more than eight times the norm.

Among liquidators and especially among evacuees, studies have demonstrated a discernible and alarming rise in morbidity since Chernobyl when compared to the general population. This applies particularly to circulatory and digestive diseases, and to respiratory problems. Less certain is the concept referred to as "Chernobyl AIDS," the rise of which may reflect more attention to medical problems, better access to health care, or psychological fears and tension among the population living in contaminated zones. Rises in children's diabetes and anemia are evident, and again appear much higher in irradiated zones. The connection between these problems and the rise in radiation content of the soil have yet to be determined.

To date, the rates of leukemia and lymphoma though they have risen since the accidentremain within the European average, though in the upper seventy-fifth percentile. One difficulty here is the unreliability or sheer lack of reporting in the 1970s. The induction period for leukemia is four to fifteen years, thus it appears premature to state, as some authorities have, that Chernobyl will not result in higher rates of leukemia.

As for thyroid cancer, its development has been sudden and rapid. As of 2003 about 2,000 children in Belarus and Ukraine have contracted the disease and it is expected to reach its peak in 2005. One WHO specialist has estimated that the illness may affect one child in ten living in the irradiated zones in the summer of 1986; hence ultimate totals could reach as high as 10,000. Though the mortality rate from this form of cancer among children is only about 10 percent, this still indicates an additional 1,000 deaths in the future. Moreover, this form of cancer is highly aggressive and can spread rapidly if not operated on. The correlation between thyroid gland cancer and radioactive fallout appears clear and is not negated by any medical authorities.

After pressure from the countries of the G7, Ukraine first imposed a moratorium on any new nuclear reactors (lifted in 1995) and then closed down the Chernobyl station at the end of the year 2000. The key issue at Chernobyl remains the construction and funding of a new roof over the destroyed reactor, the so-called sarcophagus. The current structure, which contains some twenty tons of radioactive fuel and dust, is cracking and is not expected to last more than ten years. There are fears of the release of radioactive dust within the confines of the station and beyond should the structure collapse.

It is fair to say that the dangers presented by former Soviet nuclear power stations in 2003 exceed those of a decade earlier. In the meantime, some 3.5 million people continue to live in contaminated zones. From a necessary panacea, evacuation of those living in zones with high soil contamination today has become an unpopular and slow-moving process. Elderly people in particular have returned to their homes in some areas.

See also: atomic energy; belarus and belarusians; ukraine and ukrainians


Marples, David R. (1988). The Social Impact of the Chernobyl Disaster. London: Macmillan.

Medvedev, Zhores. (1992). The Legacy of Chernobyl. New York: Norton.

Petryna, Adriana. (2002). Life Exposed: Biological Citizens after Chernobyl. Princeton, NJ: Princeton University Press.

Shcherbak, Yurii. (1988). Chernobyl: A Documentary Story. London: Macmillan.

Yaroshinskaya, Alla. (1995). Chernobyl: The Forbidden Truth. Lincoln: University of Nebraska Press.

David R. Marples

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On April 26, 1986, at 1:23 a.m., an accident occurred during a test of a turbine generator on the Unit 4 reactor at the Chernobyl nuclear power station in the Ukraine. The accident resulted from the improper withdrawal of control rods and the inactivation of important safety systemsin violation of the operating ruleswhich caused the reactor to overheat, explode, and catch fire. Because the facility lacked an adequate containment structure, the damage to the reactor core and control building allowed large quantities of radiation and millions of curies of krypton-85, xenon-133, iodine-131, tellurium-132, strontium-89, strontium-90, plutonium-240, and other radionuclides from the rector core to be released during the ensuing ten days, necessitating the evacuation of tens of thousands of people and farm animals from the surrounding area and resulting in radiation sickness and burns in more than two hundred emergency personnel and firefighters, thirty-one of whom were injured fatally.

The heaviest contamination occurred in the vicinity of the reactor itself and, to a lesser extent, in neighboring countries of eastern Europe. Those living in the vicinity of the reactor were given potassium iodide preparations to inhibit the thyroidal uptake of radioactive iodine, but infants in a number of areas elsewhere in eastern Europe are estimated to have received sizeable radiation doses to the thyroid gland, largely through ingestion of radioiodine via cow's milk, and the incidence of thyroid cancer in such persons has since risen dramatically in Belarus and in Ukraine. In areas outside Belarus, Russia, and Ukraine, organs other than the thyroid typically received only a small fraction of the radiation dose normally accumulated each year from natural background radiation. For example, the highest average effective dose in such areas during the first year was received in Bulgaria, where it is estimated to have approximated slightly less than one-third of the average annual effective dose received from natural sources. Because of the small magnitude of the average dose to a given individual, the ultimate health impacts of the accident cannot be predicted with certainty. However, nonthreshold risk models for the carcinogenic effects of radiation imply that the collective dose to the population of the northern hemisphere may cause up to thirty thousand additional cancer deaths during the next seventy years.

The accident, by far the worst nuclear reactor accident to date, highlighted flaws in the design, as well as the operation, of the Chernobyl reactor. The reactor's lack of adequate containment and its positive void coefficient, which made the reactor potentially unstable at low-risk power levels, prompted the International Atomic Energy Agency subsequently to recommend the decommissioning of all Chernobyl-type reactors, a recommendation yet to be fully implemented throughout eastern Europe. In spite of the fact that the accident also prompted reassessment and upgrading of the safety of nuclear power systems everywhere, nuclear power has fallen into disfavor in most countries because of the magnitude of the disaster. To many experts, nevertheless, nuclear power still compares favorably with other sources of energy in its impact on human health and the environment, and it is expected to continue to play a role in helping to meet the world's rapidly growing demands for energy.

Arthur C. Upton

(see also: Nuclear Power; Nuclear Waste; Radiation, Ionizing; Three Mile Island )


Eisenbud, M., and Gesell, T. (1999). Environmental Radioactivity: From Natural, Industrial, and Military Sources, 4th edition. San Diego, CA: Academic Press.

Heidenreich, W. F.; Kenigsberg, J.; Jacob, P.; Buglova, E.; Goulko, G.; Paretzke, H. G.; Demidchik, E. P.; and Golovneva, A. (1999). "Time Trends of Thyroid Cancer Incidence in Belarus After the Chernobyl Accident." Radiation Research 181:617625.

Krewitt, W.; Hurley, F.; Trukenmuller, A.; and Friedrich, R. (1998). "Health Risks of Energy Systems." Risk Analysis 18:377385.

Rhodes, R., and Beller, D. (2000). "The Need for Nuclear Power." Foreign Affairs 79:3044.

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CHERNOBYL , town on the River Pripet, Kiev district, Ukraine. It had one of the oldest Jewish settlements in the Ukraine, dating from the end of the 17th century. It was originally under the jurisdiction of the Lithuanian Council and attached in 1710 to the *Council of the Four Lands. In 1691 a Cossack gang killed many Jews and pillaged their property. There were 695 Jewish poll taxpayers in Chernobyl and the surrounding villages in 1765. In the late 18th century, Menahem Nahum (1730–1787), a disciple of *Israel b. Eliezer Ba'al Shem Tov, settled there. He was the author of Me'or Einayim and Yismaḥ Lev, both printed in Slavuta in 1798. His son Mordecai founded a dynasty of ẓaddikim and made Chernobyl a center of Ḥasidism (see *Twersky family). Mordecai's many sons also founded ḥasidic courts, the most famous being R. Duvidl of Talnoye. The community numbered 3,482 in 1847 and 5,526 in 1897 (59.4% of the total). Many engaged in trade in agricultural products and crafts. The Jews in Chernobyl suffered from pogroms in October 1905, when Jewish property was pillaged, and from April 7 to May 2, 1919, at the hands of the Struk peasant gangs, who killed 150 Jews, injured many, and burned down most of the Jewish shops and houses. With the establishment of the Soviet government in 1920, communal, social, and religious life came to an end. The Jewish population numbered 3,165 in 1926 (39% of the total), dropping to 1,783 in 1939 (total population 8,470). In 1939 most of the Jews worked in eight artisan cooperatives. There were also two Jewish kolkhozes and a Yiddish school in operation. The Germans occupied Chernobyl on August 25, 1941. On November 7 they executed a large group of Jews. Jews returned after the war. In 1965, when there was no synagogue and prayers had to be held in private, Jewish private prayer groups were dispersed by the militia and religious articles were confiscated. After the Jews complained to the central authorities in Kiev, only prayer shawls were returned to their owners. The Jewish population in 1970 was estimated at 150 families.


A.D. Rosenthal, Megillat ha-Tevaḥ, 3 (1938), 118–25; R. Yanait Ben-Zvi, in: He-Avar, 9 (1962), 116–7; B. Hurwitz, ibid., 17 (1970), 110–4; E. Tcherikower, Di Ukrainer Pogromen in Yor 1919 (1965), 77–80. add. bibliography: pk Ukrainah. s.v.

[Yehuda Slutsky /

Shmuel Spector (2nd ed.)]

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Chernobyl (Chornobyl) City on the River Pripyat River, n central Ukraine. It is 20km (12mi) from the Chernobyl power plant. On April 26, 1986, an explosion in one of the plant's reactors released eight tonnes of radioactive material into the atmosphere. Within the first few hours, 31 people died. Fallout spread across e and n Europe, contaminating agricultural produce. The long-term effects of contamination are inconclusive, but 25,000 local inhabitants have died prematurely. Two of the three remaining reactors were reworking by the end of 1986. In 1991 Ukraine pledged to shut down the plant, but energy needs dictated its continued output. With aid from the West, the plant finally closed in December 2000.

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Chernobyl a town near Kiev in Ukraine where, in April 1986, an accident at a nuclear power station resulted in a serious escape of radioactive material, and the subsequent contamination of Ukraine, Belarus, and other parts of Europe. (See also cultural Chernobyl.)

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