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EXECUTIVE SUMMARY

Chapter I. THE SITE AND ACCIDENT SEQUENCE
  • The site
  • The RBMK-1000 reactor
  • Events leading to the accident
  • The accident
  • The graphite fire

Chapter II. THE RELEASE, DISPERSION AND DEPOSITION OF RADIONUCLIDES

  • The source term
  • Atmospheric releases
  • Chemical and physical forms
  • Dispersion and deposition
  • Within the former Soviet Union
  • Outside the former Soviet Union

Chapter III. REACTIONS OF NATIONAL AUTHORITIES

  • Within the former Soviet Union
  • Outside the former Soviet Union

Chapter IV. DOSE ESTIMATES

  • The liquidators
  • The evacuees from the 30-km zone
  • Doses to the thyroid gland
  • Whole-body doses
  • People living in the contaminated areas
  • Doses to the thyroid gland
  • Whole-body doses
  • Populations outside the former Soviet Union

Chapter V. HEALTH IMPACT

  • Acute health effects
  • Late health effects
  • Thyroid cancer
  • Other late health effects
  • Other studies
  • Psychological effects
  • Within the former Soviet Union
  • Outside the former Soviet Union

Chapter VI. AGRICULTURAL AND ENVIRONMENTAL IMPACTS

  • Agricultural impact
  • Within the former Soviet Union
  • Within Europe
  • Environmental impact
  • Forests
  • Water bodies

Chapter VII. POTENTIAL RESIDUAL RISKS

  • The Sarcophagus
  • Radioactive waste storage sites

Chapter VIII. LESSONS LEARNED

  • Operational aspects
  • Scientific and technical aspects

EXPLANATION OF TERMS

LIST OF ACRONYMS

Chapter III

REACTIONS OF NATIONAL AUTHORITIES

The scale and severity of the Chernobyl accident with its widespread radioactive contamination had not been foreseen and took by surprise most national authorities responsible for emergency preparedness. No provisions had been made for an accident of such scale and, though some radiation protection authorities had made criteria available for intervention in an accident, these were often incomplete and provided little practical help in the circumstances, so that very few workable national guidelines or principles were actually in place. Those responsible for making national decisions were suddenly faced with an accident for which there were no precedents upon which to base their decisions. 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, was being exerted on the decision-makers. In these circumstances, cautious immediate action was felt necessary, and measures were introduced that tended to err, sometimes excessively so, on the side of prudence rather than being driven by informed scientific and expert judgement.

Within the former Soviet Union

TheThe town of Pripyat was not severely contaminated by the initial release of radionuclides, but, once the graphite fire started, it soon became obvious that contamination would make the town uninhabitable. Late on 26 April it was decided to evacuate the town, and arrangements for transport and accommodation of the evacuees were made. The announcement of evacuation was made at 11:00 hr the following day. Evacuation began at 14:00 hr, and Pripyat was evacuated in about two and one half hours. As measurements disclosed the extensive pattern of deposition of radionuclides, and it was possible to make dose assessments, the remainder of the people in a 30-km zone around the reactor complex were gradually evacuated, bringing the total evacuees to about 135,000.

Other countermeasures to reduce dose were widely adopted (Ko90). Decontamination procedures performed by military personnel included the washing of buildings, cleaning residential areas, removing contaminated soil, cleaning roads and decontaminating water supplies. Special attention was paid to schools, hospitals and other buildings used by large numbers of people. Streets were watered in towns to suppress dust. However, the effectiveness of these countermeasures outside the 30-km zone was small. An attempt to reduce thyroid doses by the administration of stable iodine to block radioactive uptake by the thyroid was made (Me92), but its success was doubtful.

The Soviet National Committee on Radiation Protection (NCRP) proposed a 350-mSv lifetime dose intervention level for the relocation of population groups (Il87). This value was lower by a factor of 2 to 3 than that recommended by the International Commission on Radiological Protection (ICRP) for the same countermeasure. Nevertheless, this value proposed by the NCRP was strongly criticised as being a very high level. The situation was further complicated by the political and social tension in the Soviet Union at that time. As a result, the NCRP proposal was not adopted by the Supreme Soviet. Later, a special Commission was established which developed new recommendations for intervention levels. These recommendations were based on the levels of ground contamination by the radionuclides caesium-137, strontium-90 and plutonium239. As has been mentioned above, large areas were contaminated mainly by caesium-137 and a ground contamination level by this radionuclide of 1,480 kBq/m2 was used as the intervention criterion for permanent resettlement of population, and of 555 to 1,480 kBq/m2 for temporary relocation.

People who continued to live in the heavily contaminated areas were given compensation and offered annual medical examinations by the government. Residents of less contaminated areas are provided with medical monitoring. Current decisions on medical actions are based on annual doses. Compensation is provided for residents whose annual dose is greater than 1mSv. The use of locally produced milk and mushrooms is restricted in some of these areas. Relocation is considered in Russia for annual doses above 5 mSv.

As is mentioned in the section on psychological effects, in Chapter V, the Soviet authorities did not foresee that their attempts to compensate those affected by the accident would be misinterpreted by the recipients and increase their stress, and that the label of "radiophobia" attributed to these phenomena was not only incorrect, but was one that alienated the public even more. Some of these initial approaches have been recognised as being inappropriate and the authorities are endeavouring to rectify their attitude to the exposed population.

Outside the former Soviet Union

The progressive spread of contamination at large distances from the accident site has caused considerable concern in Member countries, and the reactions of national authorities to this situation have been extremely varied, ranging from a simple intensification of the normal environmental monitoring programmes, without adoption of any specific countermeasures, to compulsory restrictions concerning the marketing and consumption of foodstuffs. This variety of responses has been accompanied by significant differences in the timing and duration of the countermeasures.

In general, the most widespread countermeasures were those which were not expected to impose, in the short time for which they were in effect, a significant burden on lifestyles or the economy. These included advice to wash fresh vegetables and fruit before consumption, advice not to use rainwater for drinking or cooking, and programmes of monitoring citizens returning from potentially contaminated areas. In reality, experience has shown that even these types of measures had, in some cases, a negative impact which was not insignificant.

Protective actions having a more significant impact on dietary habits and imposing a relatively important economic and regulatory burden included restrictions or prohibitions on the marketing and consumption of milk, dairy products, fresh leafy vegetables and some types of meat, as well as the control of the outdoor grazing of dairy cattle. In some areas, prohibitions were placed on travel to areas affected by the accident and on the import of foodstuffs from the Soviet Union and Eastern European countries. In most Member countries, restrictions were imposed on the import of foodstuffs from Member as well as non-Member countries.

The range of these reactions can be explained primarily by the diversity of local situations both in terms of uneven levels of contamination and in terms of national differences in administrative, regulatory and public health systems. However, one of the principal reasons for the variety of situations observed in Member countries stems from the criteria adopted for the choice and application of intervention levels for the implementation of protective actions. In this respect, while the general radiation protection principles underlying the actions taken in most Member countries following the accident have been very similar, discrepancies arose in the assessment of the situation and the adoption and application of operational protection criteria. These discrepancies were further enhanced by the overwhelming role played in many cases by non-radiological factors, such as socio-economic, political and psychological, in determining the countermeasures.

This situation caused concern and confusion among the public, perplexities among the experts and difficulties to national authorities, especially in maintaining their public credibility. This was, therefore, identified as an area where several lessons should be learned from the accident and efforts directed towards better international harmonisation of the scientific bases and co-ordination of concepts and measures for the protection of the public in case of emergency.

Nowhere was this problem better illustrated than by the way that contaminated food was handled. In some countries outside the Soviet Union the main source of exposure to the general population was the consumption of contaminated food. Mechanisms to handle locally produced as well as imported contaminated food had to be put in place within a few weeks of the accident. National authorities were in an unenviable position. They had to act quickly and cautiously to introduce measures to protect the "purity" of the public food supply and, what is more, they had to be seen to be effective in so doing. This inevitably led to some decisions which even at the time appeared to be over-reactions and not scientifically justified. In addition, dissenting opinions among experts added to the difficulties of the decision-makers.

Some countries without nuclear power programmes and whose own food was not contaminated, argued that they did not need to import any "tainted" food and refused any food containing any radionuclides whatsoever. This extreme and impracticable measure might well have been regarded as an example of how well the authorities of those countries were protecting the health of their population. Sometimes this attitude appeared to promote a neighbourly rivalry between countries to see which could set the more stringent standards for food contamination, as though, by so doing, their own citizens were more protected. The result was that often slightly contaminated food was destroyed or refused importation to avoid only trivial doses.

In 1986, the EC imposed a ban on the importation of food containing more than 370 Bq/kg of radiocaesium for milk products and 600 Bq/kg for any other food, regardless of the quantity consumed in the average European diet. Thus, food items with a trivial consumption (and dose), such as spices, were treated the same as items of high consumption such as vegetables. However, these values were later relaxed for some food items in order to remove inconsistent treatment of food groups.

In some special circumstances, decisions had to be made based on the local situation. For example, in some Northern European communities, reindeer meat is a major component of the diet; due to the ecological circumstances, these animals tend to concentrate radiocaesium, which will then expose the populations which depend on them. Special countermeasures, such as pasturing reindeer in areas of lower contamination, were introduced in some countries to avoid this exposure.

The variety of solutions led to confusion and made any international consensus on Derived Intervention Levels for food extremely difficult to achieve, and it was only with the WHO/FAO Codex Alimentarius Meeting in Geneva in 1989 that any agreement was reached on guideline values for the radioactivity of food moving in international trade (Table 2).


Table 2. Codex Alimentarius Guideline values for food moving in international trade (FA91).
FOODS FOR GENERAL CONSUMPTION
RadionuclideLevel (Bq/kg)
americium-241, plutonium-239
strontium-90
iodine-131, caesium-134, caesium-137
10
100
1,000
INFANT FOODS AND MILK
americium-241, plutonium-239
iodine-131, strontium-90
caesium-134, caesium-137
1
100
1,000


It should be remembered that these guideline values were developed to facilitate international trade in food, and should be regarded as levels "below regulatory concern". Levels above these do not necessarily constitute a health hazard, and if found, the competent national authority should review what action should be taken.

Often the national authorities were not able accurately to predict the public response to some of their advice and pronouncements. For example, in some European countries, soon after the accident the public were advised to wash leafy vegetables. The national authority felt that this was innocuous advice as most people washed their vegetables anyway, and they were unprepared for the public response which was to stop buying these vegetables. This resulted in significant economic loss to local producers which far outweighed any potential benefit in terms of radiological health.

In some countries, the public was told that the risks were very small but, at the same time, were given advice on how to reduce these low risks. It was very difficult to explain this apparently contradictory advice, and the national authority came under criticism from the media (Sj87). Outside the Soviet Union, the initial confusion led to inconsistent and precipitate actions which, although understandable, were sometimes ill-advised and unjustified.

However, it should be emphasised that great progress has been made since this early confusion. As a result of the actions of the international organisations to harmonise intervention criteria and the willingness of countries to cooperate in this endeavour, a firm groundwork for uniform criteria based on accepted radiation protection principles has been established, so that relative consistency can hopefully be expected in their implementation in the event of a possible future nuclear accident.

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.


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