György J. KötelesFrédéric Joliot-Curie National Research Institute for Radiobiologyand Radiohygiene, Budapest, Hungary
Corresponding author:Prof. Dr. György J. KötelesH-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 inChernobyl the experts and the public turned again their attentions to thelesson learned. Several international and national conferences were heldto summarize data and to draw conclusions. The present review is basedon this experience including that of the Hungarian scientists with specialattention to the extent of contamination, early and late health effectsand further problems.
INTRODUCTIONOn the occasion of the 10th anniversary of the accident of the Chernobylnuclear power plant which occurred on 26th April 1986 many internationaland national organizations contributed to get a real picture of the consequences.This is illustrated by the list of a few important conferences in Table1. Despite the efforts of thousands of experts and scientists tocollect measurement data, to use proper methods for the assessment of contaminationlevel and radiation doses and through these to reach an objective evaluation,in the public media usually such options were echoed which aggravated thesituation. It is, however, important to analyse the real consequences asthese might influence the attitude of societies interested in gaining energyresources and in deciding on nuclear energy option. The present reviewis based on the outcomes of the conferences listed on Table1 and its aim is to present a concise overview especially on healthconsequences of the radioactive release at the site and in the environmentboth locally and also in Hungary.
THE EVENTThe No. 4 reactor of the Chernobyl nuclear power plant was intended tostop for the obligatory maintenance work on 25 th April 1986. In connectionwith this, investigations were decided by the local technical personnelto observe whether the turbines will be able to produce enough electricityto operate the cooling system and the emergency facilities in case of anaccident, i.e. between the standstill of the reactor and the operationof diesel engines providing energy for emergency installations. This experiment,however, was not prepared properly, there was no information exchange andcoordination between the technical staff and the staff responsible forthe safe operation. Beside these human factors the design of the reactorcontained elements which could cause the instability of the reactor andits susceptibility for uncontrollable conditions following operationalfailures. The combination of human and engineering failures resulted ina sudden and uncontrollable energy run off on 26th April 1986, at 1.24a. m. when a chemical explosion damaged the reactor and the reactor buildingseriously. In addition, the graphite moderator applied in this reactortype together with other materials went into flames and the high temperaturecontributed to the wide spreading of radioactive materials and their prolongedrelease into the atmosphere.
The reactors of the Chernobyl nuclear power plantare of the so-called RBMK type, which is the Russian abbreviation for highproductivity channel type design. They have several economic and technicaladvantages, though their nuclear safety level is lower than that of othertypes. At present 15 of this type of reactors are in operation in the formermember states of the Soviet Union, 11 in Russia, 2 in Ukraine and 2 inLithuania. Since the time of the accident the reactor safety features ofthese were improved considerably with international co-operation as indicatedby one of the conferences in Table 1. TheNo. 1 and 2 reactors in Chernobyl were built between 1970 and 1977, theNo. 3 and 4 were completed in 1983. At the time of the accident two furtherreactors were in construction at the same site.
RELEASE, DISTRIBUTION AND DEPOSITION OF RADIONUCLIDES IN THE ENVIRONMENTThe amount of radioactive material released was appr. 4 per cent of theradioactive inventory of the reactor, and it contaminated the environmentduring 10 days in the form of gases, aerosols and fuel element particles.This protracted time period as well as the elevation of radioactive materialsup to the height of appr. 1 km was caused by the graphite fire difficultto extinguish. Thus the radioactive cloud, the fall-out of radioactivematerials reached almost the whole Northern hemisphere, though considerablecontamination could only be detected in certain parts of Europe.
The quantity and distribution of pollution proved to be very heterogenousboth in the soil and in the elements of food chains. This condition waslargely influenced by the rainfalls in the involved regions. The largestamounts of radioactivity released to the atmosphere were the cesium-137(85 Pbq), iodine-131 (1760 Pbq) and xenon-133 (6500 Pbq). The extents andlevels of soil contamination are illustrated in Table2 by a few data from the Chernobyl region and Hungary, too. Buteven higher values of cesium-137, were found in the Chernobyl region inan area of 3100 km2 with more than 1500 kBq per m2and in an area of 103 000 km2 between 40 and 200 kBq per m2.
|Country||Contamination kBq/m2||Extent km2||Population involved (million)|
In Hungary the values were between 1 and 100kBq/m2 distributed very heterogenously
Due to the great heterogeneity the authorities classified the territoriesaccording to their level of contamination as follows:
zone of occasional control 40550 kBq per m2 (~115 Ciper km2)
zone of continuous control 5501500 kBp per m2 (~1540Ci per km2)
zone of strict control above 1500 kBq per m2 (above 40Ci per km2).
Hungary got the contamination in two waves. The firstrelease which moved toward North-West from Chernobyl reached Hungary on29th April passing Scandinavia, Poland and Czechoslovakia and it was washedout from the atmosphere between 29 April and 1 May at the Northern andNorth-Western region of the country. The second major cloud which startedinto the Southern direction from Chernobyl has reached Hungary on 7th ofMay through Romania and Yugoslavia and was washed out by the substantialrainfall on 8th May to the soil, including the pastures. The latter wasimportant as the milk food chain was considered the main route of radiationburden in the early period, when mostly the concentrations of iodine-131,rutenium-103 and the technetium-129m were the highest. Then after a fewweeks the radioisotopes of cesium became dominant. As far as the surfacecontamination is concerned the highest values were presented by the tellurium-132(60 kBq per m2) in the early phase. The maximum values of iodine-131were between 20 and 30 kBq per m2 in the first week of May.
The activity concentration values of the most importantcontributors for long-run, i.e. of the cesium-137 was between 1 and 10kBq per m2. For comparison: this value in the Alps and SouthGermany was between 40 and 60 kBq per m2, in some areas of Scandinaviait even reached 100 kBq per m2. At certain inhabited parts ofthe former Sowiet republics the surface contamination was 1 MBq per m2or even more than that.
HEALTH DAMAGES ON THE SITEThe explosion and the first radioactive release have caused the deathsof 31 persons. Out of these 28 cases were due to radiation sickness, 1died because of burn injuries, 1 was covered by the ruins, 1 has got cardiacinfarction during transportation to the hospital. 499 persons were hospitalizedfrom those present at the time of the accident fire brigade and emergencyservices. Out of this group 134 cases have got the diagnosis of acute radiationsickness. From the latter group 14 persons have died during the last 10years, but only a few deaths can be attributed to radiation injury. Allthe 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 reflectedin Table 3 where the number of persons, thevarious dose-ranges, the death cases and the number of survivors are listed.
|Assessed dose||Number of patients||Number of deaths|
in the diagnosis of mild acute radiation sickness only in 37 cases.
LATE HEALTH EFFECTS OF RADIATION IN THE MEMBER STATES OF THE FORMERSOVIET UNIONFor the last 10 years or mostly for the recent 5 years the only well-detectablephenomenon has been the increase of thyroid cancer frequency especiallyin the population of children in Belorus, Ukraine and Russia. Until theend of 1995 appr. 800 cases were reported in children under 15 years ofage within that 400 cases in Belorus. In the Gomel region of Belorus thepresent frequency is 100 cases per 106 child per year, the frequency valuein Belorus in non-contaminated areas is 14.6. A further increase of frequencyis expected in the forthcoming decades among those persons who were childrenat the time of accident. The assessed expected number of cases is a fewthousand but the uncertainty in risk assessment is rather large. The increasingtendency is shown in Figure 1. It has to bementioned also that the morbidity rate of this illness is rather low whenproper medical treatment is provided. Until now 3 children have died becauseof thyroid cancer.
In the Gomel region of Belorus the thyroid dose of radiation was foundvery high. There were more than 32 000 children of ages up to 7 years andout of this population the thyroid dose assessment in 300 cases resultedin 10 to 40 Sv, in 3100 cases between 2 and 10 Sv and in 13 900 cases between0.3 and 2 Sv.
In the frequency of other types of malignant diseases no statisticallysignificant changes were found. Based on the probability values of stochasticradiation effects, however, it can be assessed that the number of leukemiccases will increase. Appr. 200 cases are expected from the population of3.7 million living at the relevant contaminated areas, and further 200cases can be expected in the population of liquidators of a group of appr.200 000 persons working on the stabilization of conditions at the sitein 19861987. The number of such liquidators have increased to appr. 800000 during the recent 10 years. The morbidity statistics of these groupsmight change in the future. The average dose values of the various populationgroups mentioned are given in Table 4.
It has to be emphasized that various health changes and illnesses werealso detected in the involved population which are not consequences ofradiation but which might otherwise be related to the accident like anxieties,mental depressions, various psycho-somatic symptoms. Among the etiologicalfactors beside the accident the profound social and economic alterationsmight be mentioned which are also connected with the fall of the formerpolitical structure.
RADIATION BURDEN OF THE HUNGARIAN POPULATION AND THE ASSESSMENTOF HEALTH RISKThe contamination levels were very heterogenous also over the country.Consequently, the exposures of population groups were also different. Theradiation 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 openair 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 openair sites in the first year was 40 per cent higher at the North of theTrans-Danubian region, 26 per cent higher at the South of the Trans-Danubianregion, 12 per cent higher between the Danube and Tisza rivers and in theTrans-Tisza region than in the earlier 3 years.
The increment had decreased to its half by 1988. After 1992 the doserate 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-137and -134, and iodine-131 radioisotopes. From external sources the urbanpopulation 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 weightedaverage for the whole population of the country was from external exposure225 mSv and from internal 90 mSv, i.e. altogether 300 mSv.
Taking into account the probability risk factors of the ICRP (1990)and the latency period of solid tumours for 10 to 30 years the expectedvalues 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 30000 persons die due to malignant diseases of various origin yearly. Theunfortunate increasing tendency of frequency of malignant diseases hasbegun already before the accident in Chernobyl as shown on Table5. Neither the leukemic cases, nor the thyroid diseases in childrenhave increased in Hungary since the accident.
Concerning the risk assessment it has also to be mentioned that thereis a great discrepancy between the real and the presumed risk assessmentand perception of the population. This raises the necessity of proper andobjective information because it might influence the decisions on the acceptanceof nuclear technology in energy production as well as the relieving ofthe people of their unjustified fears.
FURTHER PROBLEMS AND TASKSFrom the technical and engineering points of view the main problemis the condition of sarcophagus, the building isolating the damaged reactorfrom the surroundings. Further steps are needed to stabilize it as it wasnot built as a final and permanent protection. There is a risk of collapsein the process of rebuilding and of local release of radioactivity.
On the biological effects detailed deeper investigations havebegan only in the recent years. These involved the flora and fauna. Forinstance, increased frequency of cytochrom b gene mutations were detectedin rodents (Baker et al. 1996) and cytogenetic injuries in bank vole populations(Goncharova and Ryabokon 1995) as compared to those animals living in non-contaminatedareas. These are probably due to the radio-iodine and radiocesium contamination,but there are considerable uncertainties in the epidemiological aspectslike the freqency values before the accident, the information on populationdynamics of these animals, the presence of chemical mutagens. Among plantsperdition at large scale were detected on contaminated fields, the inactivationof growth zones, metabolic disorders, cytogenetic and various morphologicalalterations were already observed (Grodzinsky 1995).
On the human health conditions beside the mentioned stochasticand deterministic effects as well as the psychosomatic effects new datawere published. For instance, observations were made on the increase ofinitial cataracts in children living in contaminated areas (Day et al.1995). Qualitative and quantitative changes of immunocompetent cells werefound, the activation of CD4+ and CD5+, the proportion of CD4+/CD8+, increasedratio of T suppressor:killer cells (Oradovskaya et al. 1995). There isan increase in the frequency of autoimmune inflammation of thyroid glandsamong children at strongly radioiodine-contaminated areas (Poverenny etal. 1995). The increase of frequency of p53 tumor suppressor gene mutationswere 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 (Dubrovaet al. 1996).
In the sera of liquidators a so-called clastogenic factor was observedalthough not identified chemically until now which might play a role inthe increased level of chromosome aberrations (Oganesian 1995).
The international meetings identified certain priorities of tasks fornational 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, radioecologicalmonitoring;
it became obvious that the research and development works need internationallycoordinated efforts as the consequences of accidents transgress politicalfrontiers.
The examples listed suggest that further research activities and analysesare needed to study and reveal the biological effects. It was also concludedthat further medical-biological research is needed for the better handlingof radiation accident patients both on diagnostic and therapeutic fields.
As a final conclusion, it can be drawn that in the history ofour modern industrialized world there were already several catastrophescomparable in consequences with the Chernobyl accident. But the latterwas taken more seriously due to the involvement of ionising radiation.It caused not only health effects, and also physical, industrial and economicdetriments but it caused long-term consequences in social and economicconditions, psychological stress effects and the alteration of images ofapplicability of nuclear energy.
This might last long. Nevertheless, it has to be admitted that the internationalcommunity could react quickly and based on the gained experience it isprepared for even improved responses to similar challenges if such casesmight occur again.
REFERENCESBAKER, 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 380:707708.
BfS (1996). Tschernobyl 10 Jahre danach. Gesundheitliche Folgen ineuropaischen Ländern, insbesondere in den GUS-Staaten Infoblatt Bundesamtfür 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; StrahlenschutzPraxis 1:338.
DAY, R., GORIN, M. B. and ELLER, A. W. (1995). Prevalence of lens changesin Ukrainian children residing apound Chernobyl. Health Phys. 68:632642.
DUBROVA, Y. E., NESTEROV, V. N., KROUCHINSKY, N. G., OSTAPENKO, V. A.,NEUMANN, R., NEIL, D. L. and JEFFREYS, A. J. (1996). Human minisatellitemutation rate after the Chernobyl accident. Nature 380:683686.
GONCHAROVA, R. I. and RYABOKON, N. I. (1995). Dynamics of cytogeneticinjuries in natural populations of bank vole in the Republic of Belarus.Radiat. prot. Dosim. 62. 3740.
GRODZINSKY, D. M. (1995). Late effects of chronic irradiation in plantsafter the accident at the Chernobyl nuclear power station. Radiat. Prot.Dosim. 62. 4143.
Health Statistical data in Hungary ed. A. Paksy (in Hungarian). Népegészségügy(Public Health) 76: 22, 1995.
HILLEBRANDT, S., STREFFER, C., REINERS, Chr. and DEMIDCHIK, E. (1996).Mutations in the p53 tumour suppressor gene in thyroid tumours of childrenfrom areas contaminated by the Chernobyl accident. Int. J. Radiat. Biol.69. 3945.
ICRP 1990: Recommendations of the International Commission on RadiologicalProtection. Annals of the ICRP, vol. 21. 1991. Pergamon Press.
KÖTELES, G. J. (1996). Chernobyl: the review of consequences after10 years (In Hungarian) Biokémia, in press.
OECD/NEA (1995): Chernobyl. Ten Years On Radiological and Health Impact.OECD/&NEA, Paris, 1995.
OGANESIAN, N. M. (1995). The state of health of Chernobyl NPP accidentliquidators. Radiat. Prot. Dosim. 62:6970.
ORADOVSKAYA, I. V., FADEEVA, I. D., ULYANOVA, N. V., CHERNETSOVA, L.F., NIKONOVA, M. F. and LITVINA, M. M. (1995). Six-year observation ofimmune state of persons affected by the Chernobyl accident. Radiat. Prot.Dosim. 62. 6367.
POVERENNY, A. M., SHINKARKINA, A. P., PODGORODNICHENKO, V. K., MATVEENKO,E. G. and TSYB, A. F. (1995). Signs of autoimmune thyroiditis in childrenand juveniles affected by the Chernobyl accident. Radiat. Prot. Dosim.62. 7576.
SZTANYIK, B. L. (1992). Health consequences of the Chernobyl accidentin Hungary (In Hungarian) Fizikai Szemle 42. 382385.
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 10years after the accident of Chernobyl nuclear power plant Proceedingsof the Hungarian Conference, 2528. March 1996. Budapest
VOIGT, G. and PARETZKE, H. G. (1996). Scientific recommendations forthe reconstruction of radiation doses due to the reactor accident at Chernobyl.Radiat. Environ. Biophys. 35:19.