Chernobyl : TEN YEARS ON

OECD Nuclear Energy Agency has published a study of the research done on the accident and its aftermath, useful background for those not familiar with the broader issues and stuffed full of useful references:

Areas covered by the main body of the radioactive cloud on various days during the release


In summary, the Chernobyl accident was the product of a lack of « safety culture ». The reactor design
was poor from the point of view of safety and unforgiving for the operators, both of which provoked a
dangerous operating state. The operators were not informed of this and were not aware that the test
performed could have brought the reactor into explosive conditions. In addition, they did not comply with
established operational procedures. The combination of these factors provoked a nuclear accident of
maximum severity in which the reactor was totally destroyed within a few seconds.

In summary it can be stated that there is now a fairly accurate estimate of the total release. The
duration of the release was unexpectedly long, lasting more than a week with two periods of intense
release. Another peculiar feature was the significant emission (about 4 per cent) of fuel material which also
contained embedded radionuclides of low volatility such as cerium, zirconium and the actinides. The
composition and characteristics of the radioactive material in the plume changed during its passage due to
wet and dry deposition, decay, chemical transformations and alterations in particle size. The area affected
was particularly large due to the high altitude and long duration of the release as well as the change of
wind direction. However, the pattern of deposition was very irregular, and significant deposition of
radionuclides occurred where the passage of the plume coincided with rainfall. Although all the Northern
hemisphere was affected, only territories of the former Soviet Union and part of Europe experienced
contamination to a significant degree.

In summary, the Chernobyl accident took authorities by surprise as regards extent, duration and
contamination at long distance. As no guidelines were available for such an accident, little information was
available and great political and public pressure to do something were experienced, overprecautious
decisions were often taken in and outside the Soviet Union. The psychological impact of some official
decisions on the public were not predicted and variable interpretations or even misinterpretations of ICRP
recommendations, especially for intervention levels for food, led to inconsistent decisions and advice.
These added to public confusion and provoked mistrust and unnecessary economic losses. However, there
were exceptions and very soon international efforts started to harmonise criteria and approaches to
emergency management.

In summary, a large number of people received substantial doses as a result of the Chernobyl

  • Liquidators – Hundreds of thousands of workers, estimated to amount up to 800,000, were
    involved in clean-up operations. The most exposed, with doses of several grays, were the workers
    involved immediately after the beginning of the accident and the scientists who have performed
    special tasks in the sarcophagus. The average doses to liquidators are reported to have ranged
    between 170 mSv in 1986 and 15 mSv in 1989.
  • Evacuees – More than 100,000 persons were evacuated during the first few weeks following the
    accident. The evacuees were exposed to internal irradiation arising from inhalation of
    radioiodines, especially iodine-131, and to external irradiation from radioactivity present in the
    cloud and deposited on the ground. Thyroid doses are estimated to have been, on average, about
    1 Sv for small children under 3 years of age and about 70 mSv for adults. Whole-body doses
    received from external irradiation prior to evacuation from the Ukrainian part of the 30-km zone
    showed a large range of variation with an average value of 15 mSv.
  • People living in contaminated areas of the former Soviet Union – About 270,000 people live in
    contaminated areas with caesium-137 deposition levels in excess of 555 kBq/m2. Thyroid doses,
    due mainly to the consumption of cow’s milk contaminated with iodine-131, were delivered
    during the first few weeks after the accident; children in the Gomel region of Belarus appear to
    have received the highest thyroid doses with a range from negligible levels up to 40 Sv and an
    average close to 1 Sv for children aged 0 to 7. Because of the control of foodstuffs in those areas,
    most of the radiation exposure since the summer of 1986 is due to external irradiation from the
    caesium-137 activity deposited on the ground; the whole-body doses for the 1986-1989 time
    period are estimated to range from 5 to 250 mSv with an average of 40 mSv. In areas without
    food control, there are places, such as the Rovno region of Ukraine, where the transfer of
    caesium137 from soil to plant is very high, resulting in doses from internal exposure being greater
    than those from external exposure.
  • Populations outside the former Soviet Union – The radioactive materials of a volatile nature (such
    as iodine and caesium) that were released during the accident spread throughout the entire
    northern hemisphere. The doses received by populations outside the former Soviet Union were
    relatively low, and showed large differences from one country to another depending mainly upon
    whether rainfall occurred during the passage of the radioactive cloud.

In summary, it can be stated that:

  • Thirty-one people died in the course of the accident or soon after and another 137 were treated
    for the acute radiation syndrome.
  • Extensive psychological effects are apparent in the affected regions of the former Soviet Union,
    manifested as anxiety and stress. Severe forms induce a feeling of apathy and despair often
    leading to withdrawal. In the rest of the world these individual effects were minimal.
  • In the last decade, there has been a real and significant increase in childhood and, to a certain
    extent, adult carcinoma of the thyroid in contaminated regions of the former Soviet Union
    (Wi940) which should be attributed to the Chernobyl accident until proven otherwise.
  • In children, the thyroid cancers are:
    – largely papillary and particularly aggressive in nature often self presenting with local invasion and/or distant metastases,
    – more prevalent in children aged 0 to 5 years at the time of the accident, and in areas assessed to be the more heavily contaminated with iodine-131,
    – apparently characterised by a shorter latent period than expected and,
    – still increasing.
    – There has been no increase in leukemia, congenital abnormalities, adverse pregnancy outcomes or any other radiation induced disease in the general population either in the contaminated regions or in Western Europe, which can be attributed to this exposure. It is unlikely that surveillance of the general population will reveal any significant increase in the incidence of cancer.

In summary,

  • Many countermeasures to control the contamination of agricultural products were applied with
    varying levels of efficacy. 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 and farm animal activities are carried out, the food produced is
    subject to strict controls and restrictions of distribution and use;
  • Similar problems, 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 controls and limitations for variable durations after the accident. Most of these
    restrictions have been lifted several years ago. However, there are still some areas in Europe
    where restrictions on slaughter and distribution of animals are in force. This concerns, for
    example, several hundreds of thousands of sheep in the United Kingdom and large numbers of
    sheep and reindeer in some Nordic countries.
  • Produce from forests may continue to be a radiological protection problem for a long time.
  • At present drinking water is not a problem. Contamination of groundwater, especially with
    strontium-90, could be a problem for the future in the catchment basins downstream of the
    Chernobyl area.
  • Contaminated fish from lakes may be a long-term problem in some countries.


In summary, the sarcophagus was never intended to be a permanent solution to entomb the stricken
reactor. The result is that this temporary solution may well be unstable in the long term. This means that
there is the potential for collapse which needs to be corrected by a permanent technical solution.
The accident recovery and clean-up operations have also resulted in the production of very 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 are partly conserved in
containers and partly buried in trenches or stored in the open air.

In general, it has been assessed 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 accidental releases from the sarcophagus are expected to be very small in comparison with
those from the Chernobyl accident in 1986 and their radiological 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 more important release might occur if the collapse of the Sarcophagus should induce damage in the
Unit 3 of the Chernobyl power plant.

As far as the radioactive wastes stored in the area around the site are concerned, they are a potential
source of contamination of the groundwater which will require close monitoring until a safe disposal into
an appropriate repository is implemented. Initiatives have been taken internationally, and are currently
underway, to study a technical solution leading to the elimination of these sources of residual risk on the


In summary, besides providing new impetus to nuclear safety research, especially on the management
of severe nuclear accidents, the Chernobyl accident stimulated national authorities and experts to a
radical review of their understanding of, and attitude to radiation protection and nuclear emergency

This led to expand knowledge on radiation effects and their treatment and to revitalise radioecological
research and monitoring programmes. emergency procedures, and criteria and methods for the
information of the public.

Moreover, a substantial role in these improvements was played by multiple international co-operation
initiatives, including revision and rationalisation of radiation protection criteria for the management of
accident consequences, as well as reinforcement or creation of international communication and assistance
mechanisms to cope with the transboundary implications of potential nuclear accidents.

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