Accident at Chornobyl nuclear power plant caused the most significant transboundary radioactive contamination of environment in the history of mankind. After-accident status is characterized by large-scale and multi-component structure of irradiation of population consisting of:
- external gamma irradiation from radioactive fallout to the soil;
- internal irradiation caused by consumption of the food contaminated mainly by cesium and strontium.
- irradiation of thyroid gland by radioiodine;
- irradiation by transuranium elements.
Depending on the type and duration of irradiation suffered population is split in the following groups:
- people that participated in the liquidation of the accident at Chornobyl nuclear power plant.
- residents evacuated from Prypiat and other settlements of exclusion zone.
- residents living on the radioactively contaminated territories;
- children born in 1968-1986 with irradiated thyroid gland.
Representatives of different regions and settlements of Ukraine and other republics of FSU took part in the liquidation of accident consequences. Evacuated from the exclusion zone people have been resettled over the whole territory of Ukraine. Demographic differences in the number and structure of liquidators and people relocated from contaminated zone are conditioned in the majority by intentions of the law makers to increase the level of social protection of sufferers rather than by radiological factors. Map showing the distribution of these groups of population on the territory of Ukraine is presented on the
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Impact of the catastrophe on population caused by exposure to the radioiodine lasted during the first two months after the accident. Due to physiological differences there is an age dependence of irradiation dose caused by radioiodine: the highest doses got the children born in 1986, others children doses gradually decreased with the age by the moment of accident. Adult population got insignificant radiation doses as compared with children. Maps of thyroid gland irradiation are presented for seven age groups – starting from the children under 1 year of age at the moment of accident (first age group) until the adult population (seventh age group). Maps of the territory of Ukraine are presented on a scale 1:5 000 000 (
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). Calculations of thyroid gland irradiation doses have been executed according to the methodology Calculations of thyroid gland irradiation doses have been executed according to the methodology [9].
Population living on the territories enrolled in radioactively contaminated zones as a result of Chornobyl catastrophe was exposed and still is exposed to external and internal irradiation. Dosimeteric passportization of the settlements is carried out since 1991 to ensure assessment of the impact of this irradiation on population. One of the tasks of dosimetric passportization is assessment of passport and reference doses of irradiation of population. Passport irradiation dose is a calculated effective (equivalent) dose of human irradiation.
Passport dose is one of key criteria of zoning of radioactively contaminated territories [10]. Calculations of passport dose have been executed according to the methodologies of National Commission on Radiation Protection [26, 5].
Passport dose includes the following components:
- external gamma irradiation conditioned by radioactive fallout on the Earth surface.
- internal irradiation by radioisotopes of cesium, strontium and transuranium elements.
- industrial irradiation (in the vicinity of operating NPPs).
During the late phase after the accident at Chornobyl NPP the external gamma irradiation dose was formed mainly by radioisotopes of cesium, first of all cesium-137. During the initial phase after the accident the dose has been formed by not less than 19 radionuclides and radioisotopes of niobium, zirconium, iodine, lanthanum, barium made the main contribution. But in aggregate cesium radioisotopes made 70% contribution to the dose obtained from external gamma irradiation during the whole time span after the accident.
Internal irradiation during the activity of accidental source has been caused mainly by cesium radioisotopes. Irradiation by strontium radioisotope during the first twenty years after Chornobyl accident was 7-10 times less and by transuranium elements tens of times less than by cesium radioisotopes (both by average annual dose rate and by doses accumulated during different time spans).
Methodology for calculation of passport and predicted irradiation doses for settlements enrolled in the radioactive contamination zones is presented in respective methodological guides [26, 5]. Doses for 2161 settlements have been calculated according to these guides. For other settlements where dosimetric passportization has not been performed the dose values have been calculated following the methodology for assessment of retrospective-predictive irradiation doses based on the system of referential functions, relations and parameters that by-turn reconstruct the most generic and universal regularities for the whole territory including lognormal law for distribution of used referential values.
"Referential" values characterizing the radioecological situation in a settlement are the densities of radioactive contamination of soil by cesium-137, strontium-90 and plutonium-239, -240, averaged for territories of settlement and its vicinity. Coefficients of transition of cesium-137 from soil to milk also have been considered as well as a proportion of activities of main discharged gamma emitters in the fallouts (presented as of 26.04.86). Cesium-137 transition coefficient will be changed insignificantly during the next years. Highest transition coefficients are inherent to organogenic (peat) soils with excessive water saturation mostly found on the north east of Ukraine . These coefficients are in tens and even hundreds times more than in mineral soils (see soil map on
). For strontium-90 the speed of migration deep down is lower or comparable by profile with cesium-137. Cesium radioisotopes taken with contaminated food have a dominant contribution to internal irradiation of population. The main dose-forming product is milk produced in private sector. Levels of cesium in milk can differ in several times even within the same settlement. Weather conditions have significant influence of the content of radionuclides. Cesium content in milk is higher during rainy years rather than during the dry ones. Therefore the maps on milk contamination are variable in space and in time. Milk contamination level trends show decrease with the years and are is presented on the maps with annual averages by the results of sampling taken in the most contaminated areas
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To prepare the measures on liquidation of catastrophe consequences and minimization of population irradiation levels it is important to assess not only the part of the dose already received by population but also the dose they would receive in future when living on contaminated territories. Map of retrospective total effective irradiation doses received by population for 20 years (1986-2006) is presented on
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map of predictive total effective irradiation doses for 70 years (1986-2055) is shown on
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Total doses are calculated considering the values of passport and retrospective-predictive doses for separate years. For 25 years after the accident the zone of settlements has been formed on the territory of Ukraine where received irradiation doses exceed 10 and even 50 mSv. Insignificant increasing of this dose on 5-10 mSv and in many cases less than on 1 mSv will be observed during next decades. Doses received by population for 25 years practically coincide with data for 20 years. Distribution of settlements by dose value for 70 years not significantly differs from the distribution for 20 years and in many cases even for 12 years. Therefore application of such measures of accident consequences minimization as relocation and resettlement is not justified anymore since population already got the main part of Chornobyl irradiation on contaminated territories during the first years after the accident and expenses related to resettlement are inadequate to potential harm caused by excessive irradiation in case if people stay on this territory.
Determination of statistically significant impact of irradiation on the morbidity of people is one of the main tasks for studies of accident consequences. It is supposed that the most sensitive factor of this impact is increasing of oncological diseases among suffered population. Multiple factors and details pertaining to this problem do not allow constructing spatial distribution of a number of oncological diseases conditioned by Chornobyl accident. Assessments of risks related to radio-induced malignant tumors occurred among population suffered as a result of Chornobyl catastrophe are more correct. Summarized values of these assessments are presented in table 2.1.
Table 2.1. Assessment of absolute and relative radiation risk related to Chornobyl irradiation for population of radioactively contaminated territories of Ukraine for 12 years after the accident [28]
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Average spontaneous level of lethal oncological diseases in Ukraine is 2000 per year per one million of population [28], whereas estimated absolute spontaneous level in irradiated subpopulation for 12 years after the accidents equals 94.8 thousand occurrences. Chornobyl factor adds to spontaneous level less than 0.8% (751 cases). Despite the fact that increasing of Chornobyl cancers for studied contingent is not observed statistically for those subgroups having received individual dose more than 100 mSv and more the local increase for 12 years can reach 10%. Comprehensive data characterizing the influence of Chornobyl accident on general values of population morbidity are published in the special references [29, 34]. Analysis of medical monitoring system in Ukraine, trends and character of influence of irradiation on different categories of suffered population are also presented in these books.
There are two classifications of suffered people. Social classification has been established in national legislation in 1991 (see section III). Medical classification has been introduced by the Ministry of Health of USSR and it is still in force in Ukraine. According to medical classification citizens exposed to radiation resulted from the accident at Chornobyl NPP are divided into four groups of primary accounting. First accounting group consists of the persons participated in the works on liquidation of the accident at Chornobyl NPP or its consequences in exclusion zone. Second group consists of the people evacuated from exclusion zone. Third group consists of the people living on the territories enrolled in radioactive contamination zones (according to actual legislation). Fourth group consists of the children born from those enrolled in the 1-3 groups of primary accounting.
Information on the health status of population is being collected in the framework of permanent medical monitoring and is input in the medical sub-register of National register of population suffered as a result of the accident at Chornobyl NPP. Main issues of monitoring of the health status of suffered population are regulated by articles 16, 17 of the Law of Ukraine "On Status and Social Protection of Population Suffered from Chornobyl Catastrophe" [14]. Issues of organization and functioning of State (National) register is regulated by relevant Provisions [31].
Ukrainian military register and its sections supported by the Ministry of Defense of Ukraine, Ministry of Internal Affairs of Ukraine and Security Service of Ukraine are constituent part of State register. Analysis of medical statistical data is regularly published in scientific publications of medical and biological profile [29, 34], National reports of Ukraine [3, 35]. Materials of the Center of Medical Statistics of the Ministry of Health of Ukraine [29, 34] have been used as a basis for statistical maps of population morbidity, structure of general morbidity, prevalence of diseases among suffered population and structures of prevalence of diseases among suffered population as a result of the accident at Chornobyl NPP
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In general available monitoring data and its cartographical interpretation indicate on the presence of certain trend regarding the negative impact of radioactive contamination on the health of people by the data of morbidity of population suffered as a result of the accident at Chornobyl NPP. Conclusions and problems related to assessment of this impact are presented in mentioned publications [28, 29, 34] and in [32, 33, 35] and other scientific publications.
Maps of the section have been developed by the following group of authors: I.A. Likhtaryov, V.V. Berkovsky, I.A. Kairo, L.M. Kovgan, V.M. Shpak, L.Ya. Tabachnyi, O.Ye. Lytvynenko, S.V. Davydchuk, V.I. Reshetnyk, O.R. Savchuk, S.O. Sotnikov.
I.A. Likhtaryov, L.M. Kovgan, L.Ya. Tabachnyi, O.Ye. Lytvynenko, O.R. Savchuk