.. 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.
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.