Editorial Review

Chernobyl: Review of Consequences 
After 10 Years

György J. Köteles

“Frédéric Joliot-Curie” National Research Institute for Radiobiology and Radiohygiene, Budapest, Hungary
 
Corresponding author:
Prof. Dr. György J. Köteles
H-1775 Budapest, POB. 101.
Tel./Fax: (36-1)226-0026

CEJOEM 1996, 2:299-308


Key words: Chernobyl, nuclear accident, health effects, contamination, further tasks

Abstract: Ten years after the nuclear power plant accident in Chernobyl the experts and the public turned again their attentions to the lesson learned. Several international and national conferences were held to summarize data and to draw conclusions. The present review is based on this experience including that of the Hungarian scientists with special attention to the extent of contamination, early and late health effects and further problems.

INTRODUCTION

On the occasion of the 10th anniversary of the accident of the Chernobyl nuclear power plant which occurred on 26th April 1986 many international and national organizations contributed to get a real picture of the consequences. This is illustrated by the list of a few important conferences in Table 1. Despite the efforts of thousands of experts and scientists to collect measurement data, to use proper methods for the assessment of contamination level and radiation doses and through these to reach an objective evaluation, in the public media usually such options were echoed which aggravated the situation. It is, however, important to analyse the real consequences as these might influence the attitude of societies interested in gaining energy resources and in deciding on nuclear energy option. The present review is based on the outcomes of the conferences listed on Table 1 and its aim is to present a concise overview especially on health consequences of the radioactive release at the site and in the environment both locally and also in Hungary.

THE EVENT

The No. 4 reactor of the Chernobyl nuclear power plant was intended to stop for the obligatory maintenance work on 25 th April 1986. In connection with this, investigations were decided by the local technical personnel to observe whether the turbines will be able to produce enough electricity to operate the cooling system and the emergency facilities in case of an accident, i.e. between the standstill of the reactor and the operation of diesel engines providing energy for emergency installations. This experiment, however, was not prepared properly, there was no information exchange and coordination between the technical staff and the staff responsible for the safe operation. Beside these human factors the design of the reactor contained elements which could cause the instability of the reactor and its susceptibility for uncontrollable conditions following operational failures. The combination of human and engineering failures resulted in a sudden and uncontrollable energy run off on 26th April 1986, at 1.24 a. m. when a chemical explosion damaged the reactor and the reactor building seriously. In addition, the graphite moderator applied in this reactor type together with other materials went into flames and the high temperature contributed to the wide spreading of radioactive materials and their prolonged release into the atmosphere.
 
Table 1.
Main Conferences dealing with the consequences of the accident of nuclear power plant in Chernobyl on the 10th anniversary
World Health Organization 1–23 November 1995 Geneve Health Consequences of the Chernobyl and other Radiological Accidents
OECD Nuclear Energy Agency/NEA November 1995 Paris Chernobyl: Ten Years of Radiological and Health Impact
European Union 18–23 March 1996 Minsk 1st International Conference of the European Union, Belarus, Russian Federation and Ukraine on the Consequences of the Chernobyl Accident
Hungarian Academy of Sciences, Natl. Atomic Energy Comm., Dept. Radiohygiene of “Haynal Imre” University of Health Sci.,“Eötvös Lóránd” Physical Soc., Radiation Protection Section, Hung. Biophys. Soc. Radiation Biology Sec., Hung. Nuclear Soc.  25–28 March 1996 Budapest The Chernobyl nuclear power plant accident after 10 years
Intl. Atomic Energy Agency UN Dept of Humanitarian Affairs 1–3 April 1996 Vienna International Forum on Nuclear Safety Aspects of RBMK Reactors
IAEA and EU, UNDHA, UNESCO, UNDP, WHO 8–12 April 1996 Vienna One Decade After Chernobyl: Summing up the Consequences

    The reactors of the Chernobyl nuclear power plant are of the so-called RBMK type, which is the Russian abbreviation for high productivity channel type design. They have several economic and technical advantages, though their nuclear safety level is lower than that of other types. At present 15 of this type of reactors are in operation in the former member states of the Soviet Union, 11 in Russia, 2 in Ukraine and 2 in Lithuania. Since the time of the accident the reactor safety features of these were improved considerably with international co-operation as indicated by one of the conferences in Table 1. The No. 1 and 2 reactors in Chernobyl were built between 1970 and 1977, the No. 3 and 4 were completed in 1983. At the time of the accident two further reactors were in construction at the same site.
 

RELEASE, DISTRIBUTION AND DEPOSITION OF RADIONUCLIDES IN THE ENVIRONMENT

The amount of radioactive material released was appr. 4 per cent of the radioactive inventory of the reactor, and it contaminated the environment during 10 days in the form of gases, aerosols and fuel element particles. This protracted time period as well as the elevation of radioactive materials up to the height of appr. 1 km was caused by the graphite fire difficult to extinguish. Thus the radioactive cloud, the fall-out of radioactive materials reached almost the whole Northern hemisphere, though considerable contamination could only be detected in certain parts of Europe.

The quantity and distribution of pollution proved to be very heterogenous both in the soil and in the elements of food chains. This condition was largely influenced by the rainfalls in the involved regions. The largest amounts of radioactivity released to the atmosphere were the cesium-137 (85 Pbq), iodine-131 (1760 Pbq) and xenon-133 (6500 Pbq). The extents and levels of soil contamination are illustrated in Table 2 by a few data from the Chernobyl region and Hungary, too. But even higher values of cesium-137, were found in the Chernobyl region in an area of 3100 km2 with more than 1500 kBq per m2 and in an area of 103 000 km2 between 40 and 200 kBq per m2.
 

Table 2. The extent of soil contamination by cesium-137
Country Contamination kBq/m2 Extent km2 Population involved (million)
Belarus
>37
38 400
2.2
Ukraine
3>1.85
22 100
0.235
Russia
>37
56 800
2.2
In Hungary the values were between 1 and 100 kBq/m2 distributed very heterogenously

Due to the great heterogeneity the authorities classified the territories according to their level of contamination as follows:

– zone of occasional control 40–550 kBq per m2 (~1–15 Ci per km2)
– zone of continuous control 550–1500 kBp per m2 (~15–40 Ci per km2)
– zone of strict control above 1500 kBq per m2 (above 40 Ci per km2).

    Hungary got the contamination in two waves. The first release which moved toward North-West from Chernobyl reached Hungary on 29th April passing Scandinavia, Poland and Czechoslovakia and it was washed out from the atmosphere between 29 April and 1 May at the Northern and North-Western region of the country. The second major cloud which started into the Southern direction from Chernobyl has reached Hungary on 7th of May through Romania and Yugoslavia and was washed out by the substantial rainfall on 8th May to the soil, including the pastures. The latter was important as the milk food chain was considered the main route of radiation burden in the early period, when mostly the concentrations of iodine-131, rutenium-103 and the technetium-129m were the highest. Then after a few weeks the radioisotopes of cesium became dominant. As far as the surface contamination is concerned the highest values were presented by the tellurium-132 (60 kBq per m2) in the early phase. The maximum values of iodine-131 were between 20 and 30 kBq per m2 in the first week of May.

    The activity concentration values of the most important contributors for long-run, i.e. of the cesium-137 was between 1 and 10 kBq per m2. For comparison: this value in the Alps and South Germany was between 40 and 60 kBq per m2, in some areas of Scandinavia it even reached 100 kBq per m2. At certain inhabited parts of the former Sowiet republics the surface contamination was 1 MBq per m2 or even more than that.

HEALTH DAMAGES ON THE SITE

The explosion and the first radioactive release have caused the deaths of 31 persons. Out of these 28 cases were due to radiation sickness, 1 died because of burn injuries, 1 was covered by the ruins, 1 has got cardiac infarction during transportation to the hospital. 499 persons were hospitalized from those present at the time of the accident – fire brigade and emergency services. Out of this group 134 cases have got the diagnosis of acute radiation sickness. From the latter group 14 persons have died during the last 10 years, but only a few deaths can be attributed to radiation injury. All the others died because of cardiac infarction, traffic accidents, etc.

The severity of radiation sickness, in various dose-ranges, i.e. dose – effect relationship of the deterministic effect of radiation is reflected in Table 3 where the number of persons, the various dose-ranges, the death cases and the number of survivors are listed.
 

Table 3.
Persons hospitalized in the site due to acute radiation sickness
Assessed dose Number of patients Number of deaths
6–16 21 20
4–60 21 07
2–40 55 01
<20 140* 00
Total 237* 28
* The more detailed clinical investigations resulted
in the diagnosis of mild acute radiation sickness only in 37 cases.

LATE HEALTH EFFECTS OF RADIATION IN THE MEMBER STATES OF THE FORMER SOVIET UNION

For the last 10 years – or mostly for the recent 5 years – the only well-detectable phenomenon has been the increase of thyroid cancer frequency especially in the population of children in Belorus, Ukraine and Russia. Until the end of 1995 appr. 800 cases were reported in children under 15 years of age within that 400 cases in Belorus. In the Gomel region of Belorus the present frequency is 100 cases per 106 child per year, the frequency value in Belorus in non-contaminated areas is 14.6. A further increase of frequency is expected in the forthcoming decades among those persons who were children at the time of accident. The assessed expected number of cases is a few thousand but the uncertainty in risk assessment is rather large. The increasing tendency is shown in Figure 1. It has to be mentioned also that the morbidity rate of this illness is rather low when proper medical treatment is provided. Until now 3 children have died because of thyroid cancer.
 

Fig. 1. Increase of frequency of thyroid cancer in children at the most contaminated sites (BfS 1996).

In the Gomel region of Belorus the thyroid dose of radiation was found very high. There were more than 32 000 children of ages up to 7 years and out of this population the thyroid dose assessment in 300 cases resulted in 10 to 40 Sv, in 3100 cases between 2 and 10 Sv and in 13 900 cases between 0.3 and 2 Sv.

In the frequency of other types of malignant diseases no statistically significant changes were found. Based on the probability values of stochastic radiation effects, however, it can be assessed that the number of leukemic cases will increase. Appr. 200 cases are expected from the population of 3.7 million living at the relevant contaminated areas, and further 200 cases can be expected in the population of liquidators of a group of appr. 200 000 persons working on the stabilization of conditions at the site in 1986–1987. The number of such liquidators have increased to appr. 800 000 during the recent 10 years. The morbidity statistics of these groups might change in the future. The average dose values of the various population groups mentioned are given in Table 4.

It has to be emphasized that various health changes and illnesses were also detected in the involved population which are not consequences of radiation but which might otherwise be related to the accident like anxieties, mental depressions, various psycho-somatic symptoms. Among the etiological factors beside the accident the profound social and economic alterations might be mentioned which are also connected with the fall of the former political structure.
 

Table 4.
Average dose values of various groups of population
Evacues Number of persons Doses
until August 1985 116 000 >50 mSv
  666 800 >100 mSv6
until August 1995 210 000 >50 mSv
liquidators in 1986–87 200 000 100 mSv
during 10 years 800 000 in average
  620 000 250 mSv
  64 000 500 mSv

RADIATION BURDEN OF THE HUNGARIAN POPULATION AND THE ASSESSMENT OF HEALTH RISK

The contamination levels were very heterogenous also over the country. Consequently, the exposures of population groups were also different. The radiation levels in the early period over the country are shown in Fig.2. The average values of dose rates based on 123 measuring points in open air were 26 per cent higher in May and June of 1986 than 1 year earlier.

It could also be observed that the average value of dose rate in open air sites in the first year was 40 per cent higher at the North of the Trans-Danubian region, 26 per cent higher at the South of the Trans-Danubian region, 12 per cent higher between the Danube and Tisza rivers and in the Trans-Tisza region than in the earlier 3 years.

The increment had decreased to its half by 1988. After 1992 the dose rate values were higher than the fluctuation of natural background values, only at parts with larger contamination.

The radiation burden of the population was due mainly to the cesium-137 and -134, and iodine-131 radioisotopes. From external sources the urban population has got in average 150 mSv while from internal sources 60 mSv. The external exposure of population in villages was in average 300 mSv, the internal dose was the same as that in the urban population. The weighted average for the whole population of the country was from external exposure 225 mSv and from internal 90 mSv, i.e. altogether 300 mSv.
 
 


Fig. 2. Increases of doses in air until July 1986 in Hungary (Sztanyik 1992).

Taking into account the probability risk factors of the ICRP (1990) and the latency period of solid tumours for 10 to 30 years the expected values of fatal cancer cases are appr. 5 to 15 per year. It has to be mentioned, however, that out of the population of 10 million, nowadays more than 30 000 persons die due to malignant diseases of various origin yearly. The unfortunate increasing tendency of frequency of malignant diseases has begun already before the accident in Chernobyl as shown on Table 5. Neither the leukemic cases, nor the thyroid diseases in children have increased in Hungary since the accident.
 

Table 5.
Number of fatal cancer cases in Hungary
Year Male Female Total
1970 12.010 10.629 22.639
1980 15.359 12.578 27.937
1990 17.644 11.577 31.212
1992 18.465 14.211 32.676
1993 18.218 14.323 32.541
1994 18.602 14.391 32.993
Népegészségügy (Public Health), 76:22, 1995.

Concerning the risk assessment it has also to be mentioned that there is a great discrepancy between the real and the presumed risk assessment and perception of the population. This raises the necessity of proper and objective information because it might influence the decisions on the acceptance of nuclear technology in energy production as well as the relieving of the people of their unjustified fears.

FURTHER PROBLEMS AND TASKS

From the technical and engineering points of view the main problem is the condition of “sarcophagus”, the building isolating the damaged reactor from the surroundings. Further steps are needed to stabilize it as it was not built as a final and permanent protection. There is a risk of collapse in the process of rebuilding and of local release of radioactivity.

On the biological effects detailed deeper investigations have began only in the recent years. These involved the flora and fauna. For instance, increased frequency of cytochrom b gene mutations were detected in rodents (Baker et al. 1996) and cytogenetic injuries in bank vole populations (Goncharova and Ryabokon 1995) as compared to those animals living in non-contaminated areas. These are probably due to the radio-iodine and radiocesium contamination, but there are considerable uncertainties in the epidemiological aspects like the freqency values before the accident, the information on population dynamics of these animals, the presence of chemical mutagens. Among plants perdition at large scale were detected on contaminated fields, the inactivation of growth zones, metabolic disorders, cytogenetic and various morphological alterations were already observed (Grodzinsky 1995).

On the human health conditions beside the mentioned stochastic and deterministic effects as well as the psychosomatic effects new data were published. For instance, observations were made on the increase of initial cataracts in children living in contaminated areas (Day et al. 1995). Qualitative and quantitative changes of immunocompetent cells were found, the activation of CD4+ and CD5+, the proportion of CD4+/CD8+, increased ratio of T suppressor:killer cells (Oradovskaya et al. 1995). There is an increase in the frequency of autoimmune inflammation of thyroid glands among children at strongly radioiodine-contaminated areas (Poverenny et al. 1995). The increase of frequency of p53 tumor suppressor gene mutations were observed in children with thyroid cancer (Hillebrandt et al. 1996). Satellite mutations were demonstrated in gonad cells of children from Belorus, though no known health effects are attributed to these mutations (Dubrova et al. 1996).

In the sera of liquidators a so-called “clastogenic factor” was observed although not identified chemically until now which might play a role in the increased level of chromosome aberrations (Oganesian 1995).

The international meetings identified certain priorities of tasks for national and international bodies as follows:

– the injured persons have to be treated for many years;
– the emergency preparedness has to be developed further;
– the accident has turned the attention to improvement of reactor safety, medical handling, intervention criteria, information flow, radioecological monitoring;
– it became obvious that the research and development works need internationally coordinated efforts as the consequences of accidents transgress political frontiers.

The examples listed suggest that further research activities and analyses are needed to study and reveal the biological effects. It was also concluded that further medical-biological research is needed for the better handling of radiation accident patients both on diagnostic and therapeutic fields.

As a final conclusion, it can be drawn that in the history of our modern industrialized world there were already several catastrophes comparable in consequences with the Chernobyl accident. But the latter was taken more seriously due to the involvement of ionising radiation. It caused not only health effects, and also physical, industrial and economic detriments but it caused long-term consequences in social and economic conditions, psychological stress effects and the alteration of images of applicability of nuclear energy.

This might last long. Nevertheless, it has to be admitted that the international community could react quickly and based on the gained experience it is prepared for even improved responses to similar challenges if such cases might occur again.
 

REFERENCES

BAKER, R. J., Van Den BUSSCHE, R., WRIGHT, A. J., WIGGINS, L. E., HAMILTON, M. J., REAT, E. P., SMITH, M. M., LOMAKIN, M. D. and CHESSER, R. K. (1996). “High levels of genetic change in rodents of Chernobyl.” Nature 380:707–708.

BfS (1996). “Tschernobyl – 10 Jahre danach. Gesundheitliche Folgen in europaischen Ländern, insbesondere in den GUS-Staaten” Infoblatt Bundesamt für Strahlenschutz 24 April.

BAUCHINGER, M., BAYER, A., BIKO, J., GROSCHE, B., HEINEMANN, G., HILL, P., HILLE, R., HILLEBRANDT, S., KARTHEIN, R., KAUL, A., MÜLLER, W-U., NARROG, J., PARETZKE, H. G., PETERS, H. P., PFOB, H., REINERS, Ch., SAUERMANN, P. F., SCHNADT, H., STREFFER, Ch., VOIGT, G. and ZITELSBERGER, H. (1996). Die Folgen von Tschernobyl: Was wissen wir 10 Jahre danach; Strahlenschutz Praxis 1:3–38.

DAY, R., GORIN, M. B. and ELLER, A. W. (1995). “Prevalence of lens changes in Ukrainian children residing apound Chernobyl.” Health Phys. 68:632–642.

DUBROVA, Y. E., NESTEROV, V. N., KROUCHINSKY, N. G., OSTAPENKO, V. A., NEUMANN, R., NEIL, D. L. and JEFFREYS, A. J. (1996). “Human minisatellite mutation rate after the Chernobyl accident.” Nature 380:683–686.

GONCHAROVA, R. I. and RYABOKON, N. I. (1995). “Dynamics of cytogenetic injuries in natural populations of bank vole in the Republic of Belarus.” Radiat. prot. Dosim. 62. 37–40.

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HILLEBRANDT, S., STREFFER, C., REINERS, Chr. and DEMIDCHIK, E. (1996). “Mutations in the p53 tumour suppressor gene in thyroid tumours of children from areas contaminated by the Chernobyl accident.” Int. J. Radiat. Biol. 69. 39–45.

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ORADOVSKAYA, I. V., FADEEVA, I. D., ULYANOVA, N. V., CHERNETSOVA, L. F., NIKONOVA, M. F. and LITVINA, M. M. (1995). “Six-year observation of immune state of persons affected by the Chernobyl accident.” Radiat. Prot. Dosim. 62. 63–67.

POVERENNY, A. M., SHINKARKINA, A. P., PODGORODNICHENKO, V. K., MATVEENKO, E. G. and TSYB, A. F. (1995). “Signs of autoimmune thyroiditis in children and juveniles affected by the Chernobyl accident.” Radiat. Prot. Dosim. 62. 75–76.

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SZTANYIK, B. L., VAJDA, Gy., SZATMÁRY, Z., GADÓ, J., RÓNAKY, J., SIMON, A., STUR, D., GUCZI, J., SZABÓ, Gy., KURTÁCS, E., SZERBIN,, P., ZOMBORY P., KANYÁR, B., ANDRÁSI, A., MASCHEK, I., NIKL, I., VÉGVÁRI, I., KEREKES, A., TARJÁN, S., ÖRDÖGH, J., FEHÉR, I., SÁGI, L., KÖTELES, G. J., APJOK, E., FEKETE, Gy., SCHULER, D., PÉTER, F., PÉTER, Z., KOBLINGER, L. and CHOCH, Á. (1996). “Experience collected 10 years after the accident of Chernobyl nuclear power plant” Proceedings of the Hungarian Conference, 25–28. March 1996. Budapest

VOIGT, G. and PARETZKE, H. G. (1996). “Scientific recommendations for the reconstruction of radiation doses due to the reactor accident at Chernobyl.” Radiat. Environ. Biophys. 35:1–9.

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Posted: 19 December 1998