FREE ESSAY ON 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. 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 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 wasn't
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 
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