chernobyl

The accident
On April 26, 1986, Soviet’s Union Chernobyl nuclear plant exploded letting out a massive amount of radiation that all Russian citizens would debate for years to come. At exactly 1:21 am. on April 26th 1986 in Chernobyl, a city near the Pripiat River the No. 4 reactor exploded and released thirty to forty times the radiation of the Nagasaki and Hiroshima bombing. The exact causes of the explosion
are not known, however scientists and researchers, under thorough investigation, have uncovered possible causes to the explosion.

The reason
The main reason why the explosion might have occurred was that the operators of the plant were attempting to conduct an experiment with the emergency cooling system turned off, they made six fatal errors which sealed everyones fate. Soviet officials clamed that, if the technicians would have avoided at least one of those mistakes, then the plant could have been saved. The technicians began the test one day before the explosion. They started reducing the reactor’s power level so they could run the turbine experiment, however in order for the plant to run at lower power they had to turn off the automatic control system, which powered all emergency limitations that the plant should make in case it goes out of control. Turning of the cooling system was an unnecessary action and though it did not cause the explosion, it made the consequences more fatal. Just then, the operator’s receive a call from the local grid controller in Kiev who needed the power and asked the technicians to stop lowering it. Once that was done the reactor was running with out the cooling system, which was a very serious mistake. At 11:10 p.m. the grid controller said he no longer needed the power, and the operators returned to reducing the power. At twenty minutes past midnight the operators forgot to set the regulator properly, it was the second fatal error. At that point the operators would have abandoned the experiment, but they attempted to rescue it, for the next time they would be able to conduct would be in one year only.

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The senior authorities that had ordered the test would have been furious and would have found out the regulator problem, so the operators decided to pull out the stops to restore the reactor’s power. Their third fatal mistake was the pulling out of control rods. The plant’s rule was to have thirty in at all times however they left all but six. By 1:00 Am the power was still to low for the experiment, however the operators continued. In a few minutes they made their fourth fatal error, by turning on two extra pumps to join the six that were already cooling the core. This procedure under such low power caused a massive steam disorder.
Fifth was the turning off of the automatic shut off, which would turn off the reactor. At 1:23 a.m. on Saturday April 26, the workers began the actual experiment. Then they turned off the last safety system. It took the shift manager thirty-seconds to realize what was happening and shouted at other operators to press button AZ-5 which would driven all the control rods back into the core, but because the rods were melted from serious heat they didn’t fit properly into the core. As the manager looked down at the control panel several loud banging noises were heard. Immediately the one thousand ton roof of the reactor blew off sky high, and brought down the giant two hundred tone refueling crane onto the core, destroying more cooling systems. Thirty fires spread around the plant. Finally the over-heating and steam build up caused a second explosion, which destroyed the reactor and part of the building.
The graphite began to burn ferociously once exposed to air, as core reached temperatures as high as 2,800* F a massive amount of radioactive dust was let out into the air, which was picked by winds and carried thousands of miles into every direction. Previous to the testing, the technicians drew up plans, but did not discuss them with physicists or nuclear safety staff at the plant. Though they sent experiment plans to the designers of the plant, the designers never got a chance to take a look and never issued any authority or made any confirmation. All soviet officials were certain that the explosion
occurred not because of the plant, but because of human negligence. “The engineer who designed the plant and its safety systems did not include such a scenario in his project, said Valeri Legasov, first deputy director of the Kurchatov Atomic Institute. During an interview with Legasov, he stated that many discussions about the test had been going on and not everyone agreed to the test ever being conducted. However, not everyone was satisfied with the technicians theory and researchers proposed an additional theory.

Unlike Chernobyl, the power plants in the rest of the world have a contaminant structure which is a huge reinforced concrete dome designed to prevent radioactive materials from escaping during an
accident. When the reactor exploded and the core began to burn, Soviet officials tried as hard as they could to put the fire out. It took them twelve long days to finally put out the devastating fire. Unlike in any other explosion where the radioactive materials would remain buried in the ground the Chernobyl graphite fire sucked in oxygen and spewed radioactive isotopes in the air.
The evacuation
Immediately without any explanation, residents from the Chernobyl area were quickly evacuated. Kiev buses transported over 50,000 people. Only by Monday morning did people start getting suspicious. Monitoring stations in other parts of the country reported radiation levels up to one hundred times the norm. By that afternoon Swedish scientists found isotopes like krypton, xenon, iodine, cesium and cobalt in the fallout, a radioactive mix that could only have come from an accident of a reactor. The Swedes concluded that a meltdown occurred somewhere. Later on, they determined when the cloud arrived and what rout it took, so they began backtracking. They were able to draw a line going through Latvia over Moscow and into Minsk. However further testing proved that Chernobyl was the site of the meltdown.

The coverup and aftermath
In Kiev things were going smooth; joggers jogged, kids played outside, and life was going on just the same. However other countries were well aware of what was going on and immediately evacuated more then 200 tourists out of Kiev. But even so, the Soviet Union claimed that it was not dangerous to be outside. Radiation levels soared, and the government gave out an iodine solution to children under 16, and as far as Tokyo it was recommended in newspapers not to drink rainwater. In an interview in Hamburg, it was said that 49,000 people have been evacuated and that 20 to 25 people were seriously ill, and that 40 more people received fatal doses of radiation “but definitely not hundreds or thousands as reported by the Western press.” However, the festivities in Kiev were in progress and parades with flashing red flags covered the streets. Poland was the country worst affected by the radiation in all of Europe toddlers were treated with iodine and milk was dumped out. In other countries radiation spread as well. In Italy border patrols halted thirty-two freight cars loaded with cattle, sheep and horses from Poland. After a week they send it back and banned all imports of meat, livestock and vegetables. In Britain, Members of the London Festival Ballet canceled the Soviet Union tour, which would have been the first one in twenty-five years.
Besides all that, a concern spread through all European countries about milk and water. In West Germany, citizens were urged to keep children inside and stay out of the rain, which carried radiation. In Minsk all were advised to stay inside, shut the windows and wash often, as well not to eat leafy vegetables, not too much meat, and also stay out of the rain.
Iodine pills were distributed among all. Radiation spread as far as Ottawa, Canada where radiation was six times as much as normal rates. With the worry of citizens, all shipment of fruit from Europe was
stopped. Even in upstate New York radiation was found and many went out to buy iodine tablets.

Even With all the radiation killing and injuring people, the Soviet Union successfully covered up the truth from all its citizens and reporters for a long time and left its people wander the streets of death. Only after violent protests from Sweden and some Western countries did the Soviet Union admit that the disaster occurred. However they told such limited information that awful rumors began to spread. Some said that more than 2,000 people died and were bulldozed into large graves. Most Soviet citizens were disappointed in the president, because Gorbachev promised that once he became president all secrecy was to end. However when Gorbachev was asked to tell more, the Kremlin shut it’s doors and acted same as they did many years ago. It was bad enough that the Kremlin covered up the deaths, and put the people in imminent danger only for saving their face, but to others outside the Soviet Union the cover-up was of no surprise.
Disasters ranging from plane crashes to fires were never admitted to anyone. In 1957 a nuclear-waste pant exploded and spewed contaminants over hundreds of square miles in the southern Ural Mountains. More then hundreds of people died, and for years afterward the area was a radioactive wasteland. Only in the 1970s did a Russian scientist in exile, Zhores Medvedev, publish the story. Even then, the Kremlin did not acknowledge that the explosion ever happened. Many Russians accept the Soviet government’s actions to cover-up any bad things.

Sources
msn Encarta > http://encarta.msn.com/encyclopedia_761563993/Chernobyl%e2%80%99_Accident.html
BBC Worlds report on the Chernobyl Disaster > http://www.chernobyl.co.uk/

http://www.nea.fr/html/rp/chernobyl/chernobyl.html
Dr. Meshkati’s Page on Chernobyl ; http://www-bcf.usc.edu/~meshkati/chernobyl.html

Chernobyl

.. medical observation of the population has not revealed any increase in other cancers, as well as in leukemia, congenital abnormalities, adverse pregnancy outcomes or any other radiation caused disease that could be attributed to the Chernobyl accident. Large scientific and epidemiological research programs, some of them sponsored by international organizations such as the WHO and the EC, are being conducted to provide further insight into possible future health effects. However, the population dose estimates generally tend to indicate that, with the exception of thyroid disease, it is unlikely that the exposure would lead to discernible radiation effects. In the case of the liquidators this forecast should be taken with some caution. An important effect of the accident, which has a bearing on health, is the appearance of a widespread status of psychological stress in the populations affected. The severity of this phenomenon, which is mostly observed in the contaminated regions of the former Soviet Union, appears to reflect the public fears about the unknowns of radiation and its effects, as well as its mistrust towards public authorities and official experts, and is certainly made worse by the disruption of the social networks and traditional ways of life provoked by the accident and its long-term consequences.

Agricultural and environmental impacts The impact of the accident on agricultural practices, food production and use and other aspects of the environment has been and continues to be much more widespread than the direct health impact on humans. Several techniques of soil treatment and decontamination to reduce the accumulation of radioactivity in agricultural produce and cow’s milk and meat have been experimented with positive results in some cases. Nevertheless, within the former Soviet Union large areas of agricultural land are still excluded from use and are expected to continue to be so for a long time. In a much larger area, although agricultural production activities are carried out, the food produced is subjected to strict controls and restrictions of distribution and use. Similar problems of control and limitation of use, although of a much lower severity, were experienced in some countries of Europe outside the former Soviet Union, where agricultural and farm animal production were subjected to restrictions for variable duration after the accident. Most of these restrictions have been lifted several years ago. However, there are some areas in Europe where restrictions on slaughter and distribution of animals are in force.

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A kind of environment where special problems were and continue to be experienced is the forest environment. Because of the high filtering characteristics of trees, deposition was often higher in forests than in other areas. An extreme case was the so-called red forest near to the Chernobyl site where the irradiation was so high as to kill the trees that had to be destroyed as radioactive waste. In more general terms, forests, being a source of timber, wild game, berries and mushrooms as well as a place for work and recreation, continue to be of concern in some areas and are expected to constitute a radiological problem for a long time. Water bodies, such as rivers, lakes and reservoirs can be, if contaminated, an important source of human radiation exposure because of their uses for recreation, drinking and fishing.

In the case of the Chernobyl accident this segment of the environment did not contribute significantly to the total radiation exposure. It was estimated that the component of the individual and collective doses that can be attributed to the water bodies and their products did not exceed 1 or 2 percent of the total exposure resulting from the accident. The contamination of the water system has not posed a public health problem during the last decade. Nevertheless there are large quantities of radioactivity deposited in the catchment area of the system of water bodies in the contaminated regions around Chernobyl and there will continue to be for a long time a need for careful monitoring to ensure that washout from the catchment area will not contaminate drinking-water supplies. Outside the former Soviet Union, no concerns were ever warranted for the levels of radioactivity in drinking water.

On the other hand, there are lakes, particularly in Switzerland and the Nordic countries, where restrictions were necessary for the consumption of fish. These restrictions still exist in Sweden, for example, where thousands of lakes contain fish with a radioactivity content that is still higher than the limits established by the authorities for sale on the market. Potential risks Within seven months of the accident, the destroyed reactor was encased in a massive concrete structure, known as the sarcophagus. This was done to provide some form of containment of the damaged nuclear fuel, destroyed equipment and reduce the likelihood of further releases of radioactivity to the environment. This structure however wasnt intended as a permanent containment, rather as a provisional barrier until more radical solution for the elimination of the destroyed reactor and the safe disposal of the highly radioactive materials was to be found.

Nine years after its erection, the sarcophagus structure, although still generally sound, raises concerns for its long-term resistance and represents a potential risk. In particular, the roof of the structure had for a long time numerous cracks with leaks and penetration of large quantities of rainwater that is now highly radioactive. This also creates conditions of high humidity producing corrosion of metallic structures that support the sarcophagus. Some massive concrete structures, after the reactor explosion, are unstable and their failure, due to further degradation or to external events, could provoke a collapse of the roof and part of the building. According to various analyses, a number of potential accidental scenarios could be predicted. They include a criticality excursion due to change of configuration of the melted nuclear fuel masses in the presence of water leaked from the roof, a resuspension of radioactive dusts provoked by the collapse of the enclosure and the long-term migration of radionuclides from the enclosure into the groundwater.

The first two accident scenarios would result in the release of radionuclides into the atmosphere that would produce a new contamination of the surrounding area within a radius of several tens of kilometers. It is not expected, however, that such accidents could have serious radiological consequences at longer distances. As far as the leaching of radionuclides from the fuel into the groundwater, it is expected to be very slow and it has been estimated that, for example, it will take 45 to 90 years for certain radionuclides such as strontium90 to migrate underground up to the Pripyat River catchment area. The expected radiological significance of this phenomenon is not known with certainty and a careful monitoring of the situation of the groundwater will need to be carried out for a long time. The accident recovery and clean-up operations have resulted in the production of large quantities of radioactive wastes and contaminated equipment which are currently stored in about 800 sites within and outside the 30-km exclusion zone around the reactor.

These wastes and equipment are partly buried in trenches and partly conserved in containers isolated from groundwater by clay or concrete screens. A large number of contaminated equipment, engines and vehicles are also stored in the open air. All these wastes are a potential source of contamination of the groundwater that will require close monitoring until a safe disposal into an appropriate repository is implemented. In general, it can be concluded that the sarcophagus and the proliferation of waste storage sites in the area constitute a series of potential sources of release of radioactivity that threatens the surrounding area. However, any such releases are expected to be very small in comparison with those from the Chernobyl accident in 1986 and their consequences would be limited to a relatively small area around the site.

On the other hand, concerns have been expressed by some experts that a much more important release might occur if the collapse of the sarcophagus should induce damage in the Unit 3 of the Chernobyl power plant, which currently is still in operation. In any event, initiatives have been taken internationally, and are currently underway, to study a technical solution leading to the elimination of the sources of potential risk on the site. Lessons learned The Chernobyl accident was very specific in nature and it should not be seen as a reference accident for future emergency planning purposes. However, it was very clear from the reactions of the public authorities in the various countries that they were not prepared to deal with an accident of this magnitude and that technical and/or organizational deficiencies existed in emergency planning in almost all countries. The lessons that could be learned from the Chernobyl accident were, therefore, numerous and evolve all areas, including reactor safety and severe accident management, intervention criteria, emergency procedures, communication, medical treatment of irradiated persons, monitoring methods, radioecological processes, land and agricultural management, public information, etc. However, the most important lesson learned was probably the understanding that a major nuclear accident has inevitable transboundary implications and its consequences could affect, directly or indirectly, many countries even at large distances from the accident site.

This led to an extraordinary effort to expand and reinforce international co-operation in areas such as communication, harmonization of emergency management criteria and co-ordination of protective actions. Major improvements were achieved in this decade and important international mechanisms of co-operation and information were established, such as the international conventions on early notification and assistance in case of a radiological accident, by the IAEA and the EC, the international nuclear emergency exercises (INEX) program, by the NEA, the international accident severity scale (INES), by the IAEA and NEA and the international agreement on food contamination, by the FAO and WHO. At the national level, the Chernobyl accident also stimulated authorities and experts to a radical review of their understanding of and attitude to radiation protection and nuclear emergency issues. This prompted many countries to establish nationwide emergency plans in addition to the existing structure of local emergency plans for individual nuclear facilities. In the scientific and technical area, besides providing new surge to the nuclear safety research, especially on the management of severe nuclear accidents, this new climate led to renewed efforts to expand knowledge on the harmful effects of radiation and their medical treatment and to revitalize radioecological research and environmental monitoring programs.

Substantial improvements were also achieved in the definition of criteria and methods for the information of the public, an aspect whose importance was particularly evident during the accident and its aftermath. Conclusion The history of the modern industrial world has been affected on many occasions by catastrophes comparable or even more severe than the Chernobyl accident. However this accident, due not only to its severity but especially to the presence of ionizing radiation, had a significant impact on human society. Not only it produced severe health consequences and physical, industrial and economic damage in the short term, but, also, its long-term consequences in terms of social, economic disruption, psychological stress and damaged image of nuclear energy, are expected to be long standing. However, the international community has demonstrated a remarkable ability to understand and value the lessons that were drawn from this event.

Now it is better prepared to cope with a challenge of this kind, if ever a severe nuclear accident should ever happen again. Bibliography Begichev S.N., Borovoy A.A., Burlakov E.V. Radioactive Release due to Chernobyl Accident. Fission Products Transport Processes in Reactor Accidents World Conference Vienna 1996. Chernobyl: 10 years afterwards.

Kurchatov research institute. Chernobyl: Causes and Aftermath. www.prypat.com Microsoft Encarta 99 Bibliography Included in the Paper Science Essays.

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