FEATURES Chernobyl — Ten years after Global experts clarify the facts about the 1986 accident and its effects by n 26 April 1986, a catastrophic explosion at international conference on One Decade after Abel J. González OUnit 4 of the Chernobyl nuclear power Chernobyl: Summing up the Consequences of plant in the Ukrainian Republic — close to the the Accident, held at the Austria Center in point marking the three-way border with the Vienna. The Chernobyl Conference was a Republics of Belarus and Russia — sent a very model of international co-operation: six organi- large amount of radioactive material into the zations of the UN family, including the IAEA, atmosphere. The event was to become one of the and two important regional agencies were most protracted and controversial themes of the involved in its organization. (See boxes on pages modern technological era. The Chernobyl acci- 8 and 17.) dent caused widespread concern over its radio- Between the accident in 1986 and this logical consequences, and also focused attention Chernobyl conference, the IAEA participated in on nuclear safety generally. The accident's a range of scientific endeavours which sought to aftermath evolved together with the unfolding quantify the actual consequences. (See boxes on of glasnost and perestroika in the former USSR pages 5,6,7 and 8). and soon became bound up with many misun- The aim of the Chernobyl Conference was to derstandings and apprehensions about the consolidate "an international consensus on the radioactive release and its real or perceived accident's consequences, to agree on proven sci- effects. entific facts, and to clarify information and There was initial secrecy and confusion prognoses in order to dispel confusion". The about the accident — candidly reported in Prof. results of the Conference speak for themselves. Leonid Ilyin's book, Chernobyl: Myths and (See the following article for Highlights of the Reality. The people living in the affected areas Chernobyl Conference: Summary of Results). learned about the event mainly from hearsay Some important issues have been summarised rather than from authoritative reporting. The here and are separately analysed in reports fea- first evidence of the accident outside the USSR tured in this edition of the IAEA Bulletin. resulted from measurements in Nordic countries Radioactive fallout. Although even today showing an unexpected increase in environmen- there is no complete consensus on the amount of tal radioactivity. This initial lack of transparen- radioactive material released by the Chernobyl cy had an impact on public confidence, and sub- accident, the best estimates — which are of the sequently so did the confusing and at times con- magnitude of 10 international units of activi- tradictory nature of the information released. ty, called becquerels — are illustrative of the Perceptions of the catastrophe ranged from catastrophic nature of the accident. Two chemi- those who believed that Chernobyl had been one cal elements in the radioactive plume formed by of the world's worst ever disasters to those who the materials released dominated the radiologi- saw it as a relatively limited health problem cal consequences: iodine and caesium. There is despite the tragic circumstances. a family of mainly short-lived radioactive iso- A decade later, in April 1996, more than 800 topes of iodine: a significant one is iodine-131. experts from 71 countries and 20 organizations whose activity falls by half every eight days. — observed by over 200 journalists — met to Radioiodines were mainly responsible for irradi- review the Chernobyl accident's actual and pos- ation of the thyroid gland of the people living in sible future consequences, and to put these into nearby regions shortly after the accident. Of the proper perspective. They came together at the radioactive caesiums, the most significant is cae- sium-137. a long-lived nuclide whose activity falls by half every 30 years. Caesium-137 was Mr. González ¡s Director of the IAEA Division of Radiation and Waste Safety, Department of Nuclear Safety. transported through the atmosphere for long dis- IAEA BULLETIN, 3/1996 FEATURES Release of radioactive material into the environment 1 Q he destroyed reactor released a very large amount of radioac- About 10 becquerels of iodine-131 were released by the acci- Ttive material into the environment: lCr" international units dent. Iodine is mainly absorbed by a person's thyroid gland after of activity, termed becquerels. Although the discharge included inhalation or after consumption of contaminated foodstuffs such many radioactive chemical elements, just two of them — iodine as milk products; its short range beta particles irradiate the gland (in the short term) and caesium (in the long term) — were par- from the inside. Uptake of iodine by the thyroid is very easy to ticularly significant from a radiological point of view. prevent, for example by banning consumption of contaminated food for a few weeks until the iodine-131 decays sufficiently or by administering small amounts of non-radioactive iodine prophylactically to block the thyroid gland. About 10' ' becquerels of radioactive caesiums were released, and precipitated over a vast area (see map MEPHOBblilbCKMM flPOEKT on page 5). Exposure to caesium is difficult to pre- 3KCnEPTH3A PAAHOJIOTHMECKHX vent. Once it is deposited in the soil, its long range H OL4EHKA 3AtHHTHblX gamma rays can expose anybody in the area. To clean UTOrOBAfl EPOWIOPA the surfaces is difficult and, if the concentration of caesium is high, often the only feasible countermea- sure is to evacuate the inhabitants. Caesium in the soil can also be transferred into agricultural products and grazing animals. For iodine-131, there is no clear information on where the release went, who was exposed to it and to which levels, or whether iodine uptake was effective- ly prevented. Indirect estimations gave firm indica- tion that very high thyroid doses were incurred by some population groups. Children, who are particu- larly sensitive because of their normally high inges- tion of milk products and their small thyroids, received higher doses. In 1990 the International Chernobyl Project (see box, page 7) had predicted that, with high doses, a signif- icant increase in the incidence of the relatively rare cancer of the thyroid would occur in affected children after a few years. The cover of the Russian edition of a booklet describing the International Chernobyl Project, which was conducted by teams of international scientists in 1990 and 1991. tances, deposited variably over vast areas, mainly sequences for people and ecosystems in and in Europe and — to a minor but measurable near the Chernobyl plant site. Radiation damage extent — elsewhere over the whole northern correlates with the radiation dose incurred by hemisphere. The deposited caesium became the people and biota. Dose is a quantity related to main cause of whole body radiation exposure in the amount of radiation energy absorbed by the the long term. (Sec box above and map on pai>e 51. mass of biological matter. The dose incurred by Radiation doses. The release of radioactive people is expressed in Sieverts and. most com- material was expected to have severe direct con- monly, in the submultiple millisieverts — one IAEA BULLETIN, 3/1996 FEATURES Environmental damage. Lethal radiation Direct effects of radiation on the doses were reached in some radiosensitive local natural environment ecosystems, within a few kilometres of the acci- dent, notably in coniferous trees and for voles. n the first few weeks following the accident, Doses fell sharply within a few months and the Ilethal doses were reached in local biota, ecosystems eventually recovered. No sustained notably for coniferous trees and voles (small severe impacts on the environment have been mice) in the area within a few kilometers of the observed so far. (See box on the left). A report reactor. By autumn 1986, dose rates had fallen by M. Dreicer and R. Alexakhin addresses the by a factor of 100, and by 1989, these local environmental consequences of the accident in ecosystems had begun to recover. No sustained more detail. (Page 24). severe impacts on animal populations or A by-product of the environmental contami- ecosystems have been observed. Possible long- nation was the contamination of foodstuffs pro- term genetic impacts and their significance duced in the affected areas. Although for some remain to be studied. time after the accident key foodstuffs showed activity levels exceeding the maximum levels permitted by the Codex Alimentarius,* no food now produced by collective farms exceeds these levels. Exceptionally, wild food products — such as mushrooms, berries and game — from forests in the more affected areas as well as fish from some European lakes remain above Codex levels. An important aspect in controlling the contami- nation of the human habitat was the agricultural countermeasures undertaken in the affected areas; these are examined by J. Richards and R. Hance in a related report. (Page 38). Health effects. Health effects attributed to the accident have commanded the most concern on the part of the public, decision-makers and political authorities, and the Chernobyl Conference devoted a great deal of time to the topic. Clinically observed (and individually attributable) effects were discussed separately millisievert being a thousandth of a sievert (for from long-term effects which can only be attrib- comparison purposes, people receive on average uted to radiation after long studies of a statisti- an annual dose of 2.4 millisieverts from natural cal epidemiological nature of large popula- background radiation). Many of the plant work- tions.** (See box on page 10). Among the latter, ers and many people who helped to deal with thyroid effects is a special case that was treated the accident's aftermath — who were called separately from other longer term health effects. 'liquidators' — received high doses, some of Clinically observed effects. The number of thousands of millisieverts, and suffered clinical people who suffered clinically observed health radiation syndromes.