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Chernobyl

Chernobyl Chernobyl Biology 10 Project For Mrs. S. Kolovetsios By Dmitry Neofitides 1/05/99 Contents Introduction The accident Release of radioactive materials Reaction of national authorities Radiation dose estimates Health impact Agricultural and environmental impacts Potential residual risks Conclusion Introduction On 26 April 1986, the Chernobyl nuclear power station, in Ukraine, suffered a major accident that was followed by a contamination of the surrounding area by the large quantities of radioactive substances. The specific features of the contamination favored a widespread distribution of radioactivity throughout the Northern Hemisphere, mainly across Europe. A contributing factor was the variation of meteorological conditions and wind regimes during the period of release. Activity transported by the multiple plumes from Chernobyl was measured not only in Northern and in Southern Europe, but also in Canada, Japan and the United States. Only the Southern Hemisphere remained free of contamination.

This had serious radiological, health, social and economic consequences for the populations of Belarus, Ukraine and Russia, and to some extent they are still suffering from these consequences. Although the radiological impact of the accident in other countries was generally very low, and even insignificant outside Europe, this event enchanted public apprehension all over the world on the risks associated with the use of nuclear energy. The accident The Unit 4 of the Chernobyl nuclear power plant was to be shutdown for routine maintenance on 25 April 1986. On that occasion, it was decided to carry out a test of the capability of the plant equipment to provide enough electrical power to operate the reactor core cooling system and emergency equipment during the transition period between a loss of main station electrical power supply and the start up of the emergency power supply provided by diesel engines. Unfortunately, this test, which was to concern the non-nuclear part of the power plant, was carried out without a proper exchange of information and co-ordination between the team in charge of the test and the personnel in charge of the operation and safety of the nuclear reactor. Therefore, inadequate safety precautions were included in the test program and the operating personnel were not alerted to the nuclear safety implications and potential danger of the electrical test. This lack of co-ordination and awareness, resulting from an insufficient level of safety culture within the plant staff, led the operators to take a number of actions which deviated from established safety procedures and led to a potentially dangerous situation.

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This course of actions corresponded to the existence of significant drawbacks in the reactor design that made the plant potentially unstable and easily susceptible to loss of control in case of operational errors. The combination of these factors provoked a sudden and uncontrollable power surge that resulted in violent explosions and almost total destruction of the reactor. The consequences of this catastrophe were further worsened by the graphite moderator and other material fires that broke out in the building and contributed to a widespread release of radioactive materials to the environment. Release of radioactive materials The release of radioactive materials to the atmosphere consisted of gases, aerosols and finely fragmented nuclear fuel particles. This release was extremely high in quantity, involving a large fraction of the radioactive product inventory existing in the reactor, and its duration was unexpectedly long, lasting for more than a week.

This duration and the high altitude (about 1 km) reached by the release were largely due to the graphite fire which was very difficult to extinguish. For these reasons and frequent changes of wind direction during the release period, the area affected by the radioactive plume and the consequent deposition of radioactive substances on the ground was extremely large, contaminating the whole Northern Hemisphere, although only part of Europe had significant levels of contamination. The pattern of contamination on the ground and in foodchains however was very uneven in some areas due to the influence of rainfall during the passage of the plume. This irregularity in the pattern of deposition was particularly pronounced at large distances from the reactor site. Reactions of national authorities The scale and severity of the Chernobyl accident had not been foreseen and took most national authorities responsible for public health and emergency preparedness by surprise. The intervention criteria and procedures existing in most countries were not adequate for dealing with an accident of such scale and provided little help in decision-making concerning the choice and adoption of protective measures.

In addition, early in the course of the accident there was little information available and considerable political pressure, partially based on the public perception of the radiation danger. Within the territory of the former Soviet Union, short-term countermeasures were massive and, in general, reasonably timely and effective. However, difficulties emerged when the authorities tried to establish criteria for the management of the contaminated areas on the long term and the associated relocation of large groups of population. Various approaches were proposed and criteria were applied over the years. Eventually, criteria for population resettlement or relocation from contaminated areas were adopted in which radiation protection requirements and economic compensation were main factors.

Spread of contamination at large distances from the accident site caused considerable concern in many countries outside the former Soviet Union and the reactions of the national authorities to this situation were extremely varied, ranging from a simple intensification of the normal environmental monitoring programs, without adoption of specific countermeasures, to compulsory restrictions on the marketing and consumption of food Apart from the differences of contamination levels and public health systems between countries, one of the main reasons for the different situations observed in the different countries comes from the different criteria taken for the choice and use of intervention and implementation of protective actions. These differences were in some cases due to misinterpretation and misuse of international radiation protection guidelines, especially in the case of food contamination, and were further enhanced by the overwhelming role played in many cases by non-radiological factors, such as social, economic, political and psychological ones. This situation caused concern and confusion among the public, arguing among the experts and difficulties to national authorities. These problems were particularly felt in areas close to international borders due to different reactions of the authorities and media in bordering countries. However, all these issues were soon identified as an area where several lessons should be learned and international efforts were undertaken to harmonize measures of emergency management. Radiation dose estimates Most of the population of the Northern Hemisphere was exposed to the radiation from the Chernobyl accident. After several years calculations of data from all available sources it is now possible to tell ranges of doses received by the various groups of population affected by the accident.

The main doses are those of the thyroid due to external irradiation and inhalation and ingestion of radioactive iodine isotopes and those to the whole body due to external irradiation from and ingestion of radioactive cesium isotopes. According to current calculations, the situation for the different exposed groups is the following: Evacuees – More than 100,000 persons were evacuated, mostly from the 30-km radius area around the accident site, during the first few weeks following the accident. These people received significant doses both to the whole body and to the thyroid, although the distribution of those doses was variable among them and depended on their places around the accident site and the delays of their evacuation. Doses to the thyroid ranging from 70 millisieverts to adults up to about 1,000 millisieverts (1sievert) to young children and an average individual dose of 15 millisieverts to the whole body were estimated to have been absorbed by these people before they were evacuated. Many of them continued to be exposed, although to a lesser extent depending on the sites of their relocation, after their evacuation from the 30-km zone. Liquidators – Up to 800,000 workers and military personnel, were involved in the emergency actions on the site during the accident and the clean-up operations that lasted for a few years.

These workers were called liquidators. A small number, about 400, of plant staff, firemen and medical aid personnel, were on the site during the accident and its immediate aftermath and received very high doses from a variety of sources. Among them were all those who developed acute radiation syndrome and required emergency medical treatment. The doses to these people ranged from a few grays to well above 10 grays to the whole body from external irradiation and comparable or even higher internal doses, in particular to the thyroid, from incorporation of radionuclides. A number of scientists, who periodically performed technical actions inside the destroyed reactor area during several years, accumulated over time doses of similar magnitude.

The largest group of liquidators participated in clean-up operations for variable duration over a number of years after the accident. Although they were not operating anymore in emergency conditions and were submitted to controls and dose limitations, they received significant doses ranging from tens to hundreds of millisieverts. People living in contaminated areas of the former Soviet Union. About 270,000 people continue to live in contaminated areas with radiocaesium deposition levels in excess of 555 kilobecquerels per square meter [kBq/m2], where protection measures still continue to be required. Children in the Gomel region of Belarus appear to have received the highest thyroid doses with a range from negligible levels up to 40 sieverts and an average of about 1 sievert for children aged 0 to 7. Because of the control of food in those areas, most of the radiation exposure since the summer of 1986 is due to external irradiation from the radiocaesium activity deposited on the ground. The whole-body doses for the 1986-89 time period are estimated to range from 5 to 250 mSv with an average of 40 mSv.

People outside the former Soviet Union. The radioactive materials of a volatile nature (such as iodine and cesium) that were released during the accident spread throughout the entire Northern Hemisphere. The doses received by populations outside the former Soviet Union are relatively low, and show large differences from one country to another depending mainly upon whether rainfall occurred during the passage of the radioactive cloud. These doses range from a lower extreme of a few microsieverts or tens of microsieverts outside Europe, to an upper extreme of 1 or 2 mSv in some European countries. Health impact The health impact of the Chernobyl accident can be described in terms of early health effects (death, severe health impairment), late health effects (cancers) and psychological effects.

The acute health effects occurred among the plant personnel and the persons who intervened in the emergency phase to fight fires, provide medical aid and immediate clean-up operations. A total of 31 people died as a consequence of the accident, and about 140 people suffered various degrees of radiation sickness. No members of the general public suffered these kinds of effects. As for the late health effects there was a possible increase of cancer incidence. In the decade following the accident there has been a real and significant increase of carcinomas of the thyroid among the children living in the contaminated regions of the former Soviet Union, which should be attributed to the accident until proved otherwise.

There might also be some increase of thyroid cancers among the adults living in those regions. From the observed trend of the increase of thyroid cancers it is expected that the peak has not yet been reached and that this kind of cancer will still continue for some time to show an excess above its natural rate in the area. On the other hand, the scientific and …

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