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Population and Liquidators After the Accident at the Chernobyl Nuclear Power Plant
Chapter 50
Population and Liquidators After the Accident at the Chernobyl Nuclear Power Plant Chapter Outline 50.1 50.2 50.3 50.4
Introduction The Accident and the Release of Nuclides The Affected People External Exposure
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50.5 Inner Irradiation 50.6 Current Situation References
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50.1 INTRODUCTION The Chernobyl disaster, as it is sometimes commonly called, was not the first accident at a nuclear power plant and is no longer the last. The history of nuclear accidents before Chernobyl on US and Soviet nuclear facilities can be seen on the website [1]. The last in time accident of the same, the highest level of danger (the seventh) occurred at the nuclear plant “Fukushima-1” in Japan. It is going to be presented in detail in Chapter 51. But still the Chernobyl disaster remains the largest accident during the existence of nuclear power and production of nuclear weapons. This disaster was one closest to our times that affected the lives of lots of people. Regarding the assessment of the accident’s consequences, fierce debates are taking place and drastically different data get published. In April 2011, the German division of the International Physicians for the Prevention of Nuclear War (IPPNW) and the Society for the Radiation Defense (“Gesellschaft für Strahlenschutz”) published the report “Health Effects of Chernobyl: 25 years after the Disaster” [2]. Here it is claimed that the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) understated the actual data on the expected cancer mortality as compared with the data contained in the original research publications. It is well known that the statements of some politicians or some biased journalists can show an obviously preconceived attitude to some research and even deliberate distortion of the certain data. As just the opposite, there also can be found, regrettably, some unscrupulous researchers who seek to give the earliest results for the sound discovery. Let us apply the presumption of innocence to the scientists who publish research results in peer-reviewed journals. But it also has to be understood that a noticeable spread of results can occur even with absolutely honest approach toward processing and analyses of observational data. The fact is that the induction of cancer and cancer mortality, apart from the dose of radiation, also depends on a significant number of additional factors. The real impact of these factors and a competent accounting for or, on the contrary, an underestimation of their effects can significantly affect the final result. Examples of the influence on the result of studies will be given below. With the situation given, the brief review of the Chernobyl is going to contain the figures on radiation risk, morbidity, and mortality exclusively on the bases of scientific papers and data collected in the UNSCEAR and BEIR reports. As far as it is known, these organizations have never been accused of falsifying research materials.
Radiation. https://doi.org/10.1016/B978-0-444-63979-0.00050-1 Copyright © 2019 Elsevier B.V. All rights reserved.
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50.2 THE ACCIDENT AND THE RELEASE OF NUCLIDES On April 26, 1986, at 01:23:4700 because of human error and deficiencies in the construction design, the explosion of the Block-4 on the Chernobyl nuclear power plant (CNPP) occurred. On April 27, 1986, just in 2 h after the first employees affected by the explosion were hospitalized, they were taken blood probes to measure the share of sodium-24 activated by neutrons (the half-life w15.5 h). The conducted research revealed no traces of neutron activation, which meant that the accident was not caused by spontaneous chain fission reaction and that the explosion was not a nuclear one [3]. The reactor had thermal capacity of 3200 MW, the diameter of its active zone was 12 m, and its height was 7 m. By the moment of explosion, the reactor had worked with full capacity for about 3 years. It is known that the fresh but not loaded into the reactor fuel is slightly active. The fuel rods can be, in fact, assembled manually. As the reactor is running, the radioactive nuclides accumulate inside it. The activity of short-lived nuclides in several periods of half-life results in saturation: the number of newly formed radioactive nuclei becomes equal to the number of decaying nuclei. The activity of long-lived nuclides (137Cs, 90Sr) practically increases linearly over time. The activity of any nuclide can be rather simply calculated, if the reactor power, the release of a nuclide in fission, and the constant of the radioactive decay are known. At the time of the accident, the reactor contained 192 t of fuel and its decay products. By that time, the initial activity of the spent fuel was ca. 5.5 1019 Bq ¼ 55,000 PBq (1500 MCi). According to a commonly accepted estimate, inside the destroyed reactor were left about 185 t of nuclear fuel. In a molted form, mixed with molted construction materials, the fuel spread over the premises and flowed down to the lower floors. Now the total activity of the remained fuel is c. 600 PBq (16 MCi). As a result of the thermal explosion and the subsequent combustion of the core graphite from the emergency power unit, a large number of radionuclides with, in particular, microparticles of irradiated fuel, including uranium and transuranium elements 239Pu, 241Am, 242Cm, were in 10 days ejected into the atmosphere. The share of environmentally significant long-lived nuclides 131I, 90Sr, 137Cs within the release was 20%. According to the estimations, the total activity of the release, excluding the rare radioactive gases, was 3.3 1018 Bq ¼ 3300 PBq (90 MCi) [4]. The emission of radioactive nuclides is largely determined by their volatility. The radioactive rare gases Kr and Xe, volatile by any temperature, were practically completely blown out by the explosion. The isotopes of I and Te are highly volatile at a temperature greater than 100 C, their emission was dozens of percents from their content in active area. Then, as less volatile, follow Cs, Ba, Sr, Ce, Zr, and Nb. The volatility of Pu and U is the least, and the emission of plutonium is estimated at a few percent. The emission activity at the CNPP was slowly reducing in the first 5 days since the accident, but starting by May 2, it sharply went up dangerously due to overheating by the fuel residual heat. Filling the ruins of the reactor with boroncontaining mixtures from helicopters allowed to stop this growth. After May 10, the emissions fell sharply. On May 11, they turned almost 100 times weaker than the day before. During the explosion and in the first 10 days from the active area, w1760 PBq 131I (T1/2 ¼ 8.04 days), w85 PBq 137Cs (T1/2 ¼ 30 years), w10 PBq 90Sr (T1/2 ¼ 29.12 years), isotopes of uranium, plutonium, iodine, cesium, strontium, and others were emitted. In fact, a lot of other radioactive nuclides were released into the environment, but with short half-lives on the order of days or even hours. There were also released rather long-lived nuclides, such as w 0.013 PBq 239Pu with the half-life of T1/2 w24,000 years. Besides, among the nuclear fission products occurred two noble gasses, w33 PBq 85Kr (T1/2 ¼ 10.72 years) and w6500 PBq 133Xe (T1/2 ¼ 5.25 days). Because of its relatively long half-life, krypton-85 accumulates in atmosphere, it rather quickly mixes up with the air of northern hemisphere, and then, yet not so fast, it gets into the southern hemisphere. By contrast, for all the period of atmospheric testing of nuclear weapons, 675,000 PBq 131I and 948 PBq 137Cs were released into the environment. All radioactive nuclides, but one, decay and their concentration decreases over time. 241Am appears in the environment after the decay of 241Pu. Maximal activity of 241Am will be reached approximately in 2058, and then it will slowly decline with the half-life of 432.2 years. At its peak, the activity of 241Am will be about 1000 times less than activity of 137Cs by that time.
50.3 THE AFFECTED PEOPLE All the people exposed to the radiation because of the accident are divided into the following groups: 1. Liquidators. It is believed that the main stage of the accident’s resulting liquidation lasted 3 years (1986e89). 2. People evacuated from the town of Pripyat and from 30 km area around the destroyed reactor.
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3. The population living in the affected area under strict control. The contamination with 137Cs in this area exceeded 555 kBq/m2 (15 Ci/km2). 4. The population living in the area with 137Cs contamination exceeding 37 kBq/m2 (1 Ci/km2). In 1986e87, about 440,000 people were involved in the liquidation of the accident aftermath. Later their number increased up to w800,000. These people were called liquidators. A special medical register contains data as for 2008 on more than 500,000 liquidators. In the 30 km zone about 200,000 people worked. Note that the number of liquidators included not only the workers, engineers, scientists, and military personnel, who were actually engaged in the liquidation of consequences of the accident, but also everyone who worked in the contaminated territories, including doctors, teachers, cooks, interpreters, and so on. The average additional dose for all contingents of liquidators received during the whole operation was 0.083 Gy [5]. During the spring and summer, 1986, 115,000 people were evacuated from 188 settlements in the affected areas and 220,000 more afterward. 7500 settlements with the population of 2.6 million on the Russian territory were subjected to contamination. Toward 2011 due to decontamination and natural decay, the number of contaminated settlements was reduced to 4000 (1.5 million inhabitants). The contaminated territories of the former Soviet Union with the total area of 150 km2 are still supporting by now up to 5 million people. Immediately on the accident three employees of CNPP were killed for reasons not related to radiation. Among the people who were carrying out emergency works, 134 cases of acute radiation sickness (ARS) were registered. By the end of 1986, 28 people died of ARS. In the years that followed, 13 more people died. The information on the early effects can be found in the report [6].
50.4 EXTERNAL EXPOSURE It is known that high radiation doses cause acute radiation sickness. Such cases because of Chernobyl disaster were relatively not many (134 people). All other radiation effects, which are discussed below, are stochastic, that is, they manifest themselves in long-term effects with different latent periods. The main effect is cancer. The development of various kinds of cancer in time is shown in Fig. 36.5. It is known that as a result of acute exposure, in a relatively short period (several years), leukemia develops. The maximum probability of disease is reached approximately in 6 years after irradiation. By now, the maximum for leukemia should already be passed. The induction of new leucosis practically equals zero in about 30 years after irradiation. The latent period of other cancers is about 10 years, and the maximum is reached in 30e40 years. The doses of outer irradiation are determined by contamination level of the area, and the contamination is caused by the fallouts of radioactive substances released by blast, fire, and the following processes in the destroyed reactor. The fallouts vary considerably depending on the mechanism of emitting and sizes. There is a near fallout zone, a central spot around the reactor with radius up to 60 km, which was caused by dry fallouts on April 26e27, and a far fallout zone, which is Gomel-Mogilev spot, contaminated by raining fallouts of April 28e29, with the center removed about 200 km north-north-east from CNPP. In the near zone, the ratio of activity of many refractory nuclides to activity of 137Cs is 1e5 and of 131I is about 10 [7]. In the distant zone the ratio of refractory nuclides to 137Cs was c. 0.06e0.11 and of 131I is c. 10 [7]. The maps of distribution of contamination by 137Cs in Europe are collected in the Atlas [8]. The Atlas contains about 100 colored maps of various scales showing distribution of contamination in Europe on the whole, within state borders, and in certain areas with particularly high contamination. Total amount of 137Cs that fell out in Europe was 8∙1016 Bq. The fallouts were distributed among the states in the following proportion: Belarus 33.5%, Russia 24%, Ukraine 20%, Sweden 4.4%, Finland 4.3%, Bulgaria 3.8%, Austria 2.7%, Norway 2.3%, Romania 2.0%, Germany 1.1%, and in the other European countries less than 1%. The studies showed that in Europe the contamination by 137Cs with surface activity exceeding 20 kBq/m2 covers about 6% of its territory, with activity exceeding 40 kBq/m2 it covers 2% of its territory, and with activity exceeding 1480 kBq/ m2 it covers less than 0.03% of its territory. The boundary values of surface activity as 37 kBq/m2 (1 Ci/km2) were set when mapping fallouts and determining their hazard. The level of contamination by 137Cs exceeds the limit of 37 kBq/m2 on 45,000 km2 on the territory of Europe (for reference, the area of, e.g., Germany is w357,000 km2 and Belarus 207,000 km2) [9]. Coefficient of connection of surface activity with dose rate for 137Cs equals 2.55 106 (mGy/hour)/(kBq/m2). Thus, the dose rate by contamination 37 kBq/m2 is w0.1 mGy/h w1 mGy/year. As is known, the annual dose for personnel must not be more than 50 mSv/year and for the population not more than 5 mSv/year.
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Therefore, it is evident that by such activity of 137Cs, a person who may constantly appear in the field of irradiation would get an annual dose less than 1 mGy, which complies with radiation safety standards. On the fields with activity lower than 37 kBq/m2, it is possible to conduct economic activities. The value 555 kBq/m2 (15 Ci/km2) is stated as a hazardous boundary limit. By activity exceeding this value, an annual dose for a person exceeds official dose limit for the population and gets closer to the dose limit for the personnel. The UNSCEAR report in 2008 provides information about the doses received by different groups, accounting for amendments relating to the improvement of treatment of dose recording techniques [9]. The average effective dose received by the liquidators during 1986e90 mainly because of external radiation is about 120 mSv. Registered doses range from 10 mSv to more than 1000 mSv, although approximately 85% of the workers received doses in the range 20e500 mSv. Estimates of uncertainty in individual doses range from 50% to five times. The experts noted that the doses received by military personnel are likely to have been understated. Average additional effective dose received by the 6 million people living in the most contaminated area of Belarus, Ukraine, and Russia during 1986e2005 from external exposure was about 9 mSv. For the 98 million people living in the three republics, who received 1.3 mSv, a third of the dose was received in 1986. These values are only slightly higher than the natural radiation background in the same period (w50 mSv). Over a 20-year period, about 70% of the population received an effective dose of less than 1 mSv and about 20% between 1 and 2 mSv. However, 150,000 people living in the affected area during the 20-year period received an effective dose of more than 50 mSv. For the 500 million inhabitants of other countries in Europe, the average effective dose is estimated at 0.3 mSv over this period. Detailed information on the effects of low-dose radiation after Chernobyl nuclear disaster can be found in the book of E. Burlakova and V. Naiditch [10]. Relatively recently it was found that radioactive contamination has reduced the rate of litter mass loss in Chernobyl forests, increased accumulation of litter, and affected growth conditions for plants [11].
50.5 INNER IRRADIATION The distribution in the organism of the radionuclides getting into the blood is determined by biogenic significance of the stable isotopes of the given element and by the affinity of this element to certain tissues and organs. Each element participates in its metabolic transformations in the body. These transformations are influenced by the solubility of the initial compound, by chemical transformations in the gastrointestinal tract, and by absorbability. The removal of incorporated radioactive elements with metabolic products through excretory systems is similar to their stable isotopes and chemical analogs. Besides, with the appropriate half-life value, the radioactive isotope content in the body also decreases as a result of radioactive decay. The period of time during which half of the incoming amount of the element is excreted from the body is called the effective half-life period. Nuclides 90Y, 137Cs, 140Ba, 96Au, and some others are characterized by a short half-life period. A long half-life period is typical, e.g., for the nuclides 210Po, 226Ra, 232U, and 239Pu. One of the most hazardous nuclides, 137Cs, is a chemical analog of sodium and potassium. In metabolic reactions it repeats their ways, fairly evenly distributing throughout the body. Like other alkali metals, cesium is easily absorbed and excretes with urine. The biological half-life of accumulated 137Cs for humans is considered to be equal to 70 days. By even 137Cs distribution in the human organism with specific activity of 1 Bq/kg, the absorbed dose rate, according to various authors, varies from 2.14 to 3.16 mGy/year. Other hazardous radionuclide 90Sr is a chemical analog of calcium and therefore it concentrates on bones. The natural excretion of this nuclide from the body appears more slow. Iodine is concentrated in the thyroid gland; thus its radioactive isotopes, in large quantities contained in fission products, pose the greatest danger in the first weeks after radiation accidents. Rare-earth elements, cerium, lanthanum, etc., are mainly concentrated in the liver, and antimony, arsenic, bismuth, etc., are concentrated in the kidneys. The main radiation damage by inner irradiation was created mainly by the two radionuclides: the short-lived nuclide 131 I, which determined the impact on health during the first couple of months, and the gamma emitter 137Cs, the main effect of which is currently ongoing. In the first months after the accident, due to the lack, or inadequacy, of protection measures, the pollution of fresh milk by the nuclide 131I caused significant radiation doses for the thyroid gland. At that time, children were subjected to the main radiation exposure. Subsequently, the activity of iodine dropped significantly and the entire population became exposed to irradiation mainly because of 137Cs. Irradiation was both external and internal through contaminated food. However, because of protective measures, the resulting doses were relatively small. The real average annual effective dose was 31 mSv in Belarus, 17 mSv in Ukraine, the average dose in the population of Pripyat did not exceed 13 mSv, and the maximum dose could reach 50 mSv [12].
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Radiation doses received by the thyroid gland are noticeably higher. The average dose to the thyroid in 1986 was 490 mGy for the evacuees, 102 mGy for the population of contaminated area in the three USSR republics, 16 mGy for the 98 million of population in Belarus, Ukraine, and 19 regions of Russia and 1.3 mGy for people in the remote countries of Europe. It is noted that preschoolers received a dose to the thyroid that was approximately two to four times greater than the average dose got by the population. Note that, currently, science cannot distinguish a tumor that developed as a result of irradiation from a tumor occurring for any other reason. Therefore, the link between the dose and morbidity is established by statistical methods. It is important to consider the impact on the disease probability of some factors such as age, gender, and genetic characteristics of the individual, lifestyle, and many other factors that may be relevant to the disease. To obtain reliable and sound epidemiological conclusions, it is necessary to have sufficient statistical support for the research. Thyroid cancer is a rare disease in children. However, because the thyroid gland in children is quite an active organ, it has increased radiosensitivity. If a child has received a large dose of radiation to the thyroid and develops thyroid cancer several years after exposure, it is very likely that the cancer was caused by radiation. If thyroid cancer appears in an adult a few months after exposure, its relationship with exposure has very low probability. An important factor that modifies the risk of radiation-induced thyroid cancer is iodine deficiency in human consumption. E. Cardis and colleagues found that in areas with low iodine content in soil, the risk of a dose 1 Gy is 3.1 times greater than in areas with higher levels of iodine. It is considered reliably proven that the use of potassium iodide as a dietary supplement significantly reduces the risk of radiation-induced thyroid cancer. It is clear that the underestimating of iodine deficiency, of this external, nonedose-related circumstance, significantly affects the risk assessment result. The increased incidence of thyroid cancer in children began to show in 1990e91. This was pretty early for solid cancer, which is characterized by a much greater latency period, so this information initially caused doubt. However, further developments showed an obvious connection of these cancers with radiation. The number of these cancers is increasing steadily, and by 2005 no slowdown has been detected. According to the UNSCEAR report for 2008, among children who were younger than age 14 years at the time of the accident, for the period 1991e2005, a total of 5127 cases of thyroid cancer were revealed and 6848 cases among those who were younger than age 18 years. (In the UNSCEAR report for 2000, it was fewer than 1800 cases.) These numbers refer to Belarus and Ukraine wholly and to the four most affected areas of the Russian Federation. Background level of thyroid cancer in children under the age of 10 years is approximately two to four cases per year per million people. For children born after 1986, no increase in frequency of thyroid cancer has been detected; the frequency is at the background level. There is no reliable information on thyroid cancer in exposed adults [9]. There is also no evidence of any increase in the frequency of any other solid cancers among the population of Ukraine and the Russian Federation [9]. At the International Conference “Fifteen years after the Chernobyl disaster, Lessons Learned” in April 2001, it was noted that the mortality rate among liquidators and residents of contaminated territories does not exceed the statistical average data in the three countries. However, to assess such an exposure effect as mortality, the time that had passed after the disaster was still too short. The report [13] shows a table with an overview of 51 environmental studies on the population performed by domestic and foreign environmentalists. In most studies, an increased number of thyroid cancers are noted. In early works executed before 1995, no other types of cancer, including leukemia, were recorded, and only the subsequent papers reported of leukemia cases and some noncancerous diseases. Most of the researchers and experts point out that regardless of the exposure, the Chernobyl disaster has significantly changed the lives of millions of people, especially in Belarus, Russia, and Ukraine, who live in the most contaminated areas. Forced evacuation, limitations in usual activities, other countermeasures, and conflicting information about the possible consequences of the accident have radically changed people’s lives and led to psychological problems, worsened the quality of life, and could significantly affect health. The total incidence of disease among adults living in contaminated areas is significantly higher than the national average, although in the vast majority of cases the causes of the disease cannot be attributed to the effects of radiation. Significantly higher than the national average is suicide rate among the liquidators. Obviously, competent processing of epidemiologic data should not encourage to dismiss the unpleasant consequences at the expense of the accident to radiation phobia. On the other hand, the psychological aspects of the accident and postaccident conditions should be taken into account. The study of the Chernobyl disaster is now ongoing [14]. The third issue of the volume 56 for 2016 of the journal “Radiation Biology, Radioecology” is entirely devoted to the 30th anniversary of the events. Note here the article of I.V. Oradovskaya [15] about change of immune status under action of radiation. L.M. Rozhdestvenskiy paid attention to the fact that insufficient consideration was given to nonradiological factors having an effect on the
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psychoemotional state of the people [16]. A.N. Micheev considered the role of radiophobia in the psychosomatic diseases of population in the area of strict radiation control [17].
50.6 CURRENT SITUATION The destroyed reactor continuously emitted radioactive substances into the environment. By November 1986, above the destroyed reactor a protective structure was erected, officially called “Shelter,” though more widely known as “Sarcophagus.” But this protection was constructed in haste and thus contained lots of gaps. Partly the constructions erected in 1986 were built on the destroyed sections of the Block-4 of CNPP, the endurance of which was not then accurately determined because of difficulties of radiation situation and blockages. The use of remote methods of concreting led to the situation when large masses of concrete spread over the floors of the building overloading them. Remote installation in some cases did not provide tight fit of structures to each other and reliable connection of structures with supports. The total area of cracks in the roof and walls of the object was about 1000 m2 at the time of the object’s delivery. Despite the efforts made during the entire period of operation of the Sarcophagus, the state of safety decreased over time. Constantly there was a process of degradation of building structures under the influence of moisture and water due to ingress of precipitation. On February 15, 2013, the suspending slabs over the engine room of the power unit with an area of several hundred square meters collapsed [18]. Useful material on the first sarcophagus can be found on the website [19]. At the end of November 2016, the destroyed reactor with the old sarcophagus over it was covered with a new mobile protective arch.
REFERENCES [1] Chernobyl Nuclear Power Plant and Exclusion Zone. Chernobyl, Pripyat. http://chornobyl.in.ua/istoria-avariy.html. [2] Health Effects of Chernobyl 25 years after the reactor catastrophe, IPPNW (International Physicians for the Prevention of Nuclear War) and GFS (Gesellshaft für Strahlenschutz), 2011. Report, http://www.ippnw.org/pdf/chernobyl-health-effects-2011-english.pdf. [3] L.A. Il’in, Realities and Myths of Chernobyl «ALARA Limited», 1994. [4] Y.V. Sivintsev, A.A. Khrulev, Estimation of radioactive release at 1986 accident on the 4-th block of Chernobyl NPP, At. Energ. 78 (6) (1995) 403e416. [5] Chernobyl disaster. Ideas and problems of overcoming its consequences in Russia 1986e2001, Rus. Nat. Report, in: History of Atomic Energy of the Soviet Union and Russia, Issue 4, AT Publ. (JieAT), Moscow, 2002, pp. 487e536, 539 p. [6] UNCSCEAR 1988 Report, Annex G. Early Effects in Man of High Dose Radiation. http://www.unscear.org/unscear/en/publications/1988.html. [7] K.V. Kotenko, S.M. Shinkarev, Y.V. Abramov, E.O. Granovskaya, V.N. Yazenko, Y.I. Gavrilin, et al., Comparative analysis of the radionuclide composition of deposition in the near and far zones after the accident at the Chernobyl NPP and in the near zone after the accident at the Fukushima1 NPP, Occup. Med. Ind. Ecol. (10) (2012) 1e5 (Russian Journal: Nfejxjoa truea j Vrpn9zmfooa> ;lpmp[j>). [8] Atlas of Cesium Deposition on Europe after Chernobyl Accident. EUR 1673 EN/RU, European Commission, 1998, 65 pp. http://cricket.biol.sc.edu/ chernobyl/UN-reports/Atlas.pdf. [9] UNSCEAR 2008 Report, v.II, Annex D. Health Effects due to Radiation from the Chernobyl Accident, p. 45e219 - http://www.unscear.org/unscear/ en/publications/2008_2.html. [10] E. Burlakova, V. Naiditch, The Effects of Low Dose Radiation: New Aspects of Radiobiological Research Prompted by the Chernobyl Nuclear Disaster, CRC Press, 2004, 420 pp. [11] T.A. Mousseau, G. Milinevsky, J. Kenney-Hunt, A.P. Møller, Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas, Oecologia 175 (1) (2014) 429e437. [12] A.K. Guskova, V.I. Krasnyuk, Health consequences in overexposed persons after the Chernobyl accident: basic resume and unsolved problems, Occup. Med. Ind. Ecol. (10) (2012) 11e17. [13] BEIR VII Phase 2, Population Exposed from the Chernobyl Accident, 2006, p. 215. https://www.nap.edu/read/11340/chapter/11#214. [14] A.I. Gorsky, M.A. Maksioutov, K.A. Tumanov, N.V. Shchukina, S.Y. Chekin, V.K. Ivanov, Non-parametric analysis of radiation risks of mortality among Chernobyl clean-up workers, Radiats Biol. Radioecol. 56 (2) (2016) 138e148. [15] I.V. Oradovskaya, 30 years of tragedy in Chernobyl. Clinical and immunological effects of liquidators of consequences of the accident at Chernobyl NPP. Main results of multiyear monitoring, Rad. Biol. Radioecol. 53 (3) (2016) 251e273 (in Russian). [16] L.M. Rozhdestvenskiy, Results of the Chernobyl accident at 30 years of distance, Rad. Biol. Radioecol. 53 (3) (2016) 274e284 (in Russian). [17] A.N. Micheev, Low “doses” of radioecology, Rad. Biol. Radioecol. 53 (3) (2016) 336e350 (in Russian). [18] Sarcophagus Above the Reactor (Object Shelter). http://4ernobyl.ru/publ/katastrofa/likvidacija/sarkofag_nad_reaktorom_obekt_quot_ukrytie_quot/ 5-1-0-4. [19] Truth about Chernobyl. Object “Shelter” (Sarcophagus). http://stopatom.slavutich.kiev.ua/1-2-2a.htm.
Population and Liquidators After the Accident at the Chernobyl Nuclear Power Plant Chapter Outline 50.1 50.2 50.3 50.4
Introduction The Accident and the Release of Nuclides The Affected People External Exposure
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50.5 Inner Irradiation 50.6 Current Situation References
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50.1 INTRODUCTION The Chernobyl disaster, as it is sometimes commonly called, was not the first accident at a nuclear power plant and is no longer the last. The history of nuclear accidents before Chernobyl on US and Soviet nuclear facilities can be seen on the website [1]. The last in time accident of the same, the highest level of danger (the seventh) occurred at the nuclear plant “Fukushima-1” in Japan. It is going to be presented in detail in Chapter 51. But still the Chernobyl disaster remains the largest accident during the existence of nuclear power and production of nuclear weapons. This disaster was one closest to our times that affected the lives of lots of people. Regarding the assessment of the accident’s consequences, fierce debates are taking place and drastically different data get published. In April 2011, the German division of the International Physicians for the Prevention of Nuclear War (IPPNW) and the Society for the Radiation Defense (“Gesellschaft für Strahlenschutz”) published the report “Health Effects of Chernobyl: 25 years after the Disaster” [2]. Here it is claimed that the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) understated the actual data on the expected cancer mortality as compared with the data contained in the original research publications. It is well known that the statements of some politicians or some biased journalists can show an obviously preconceived attitude to some research and even deliberate distortion of the certain data. As just the opposite, there also can be found, regrettably, some unscrupulous researchers who seek to give the earliest results for the sound discovery. Let us apply the presumption of innocence to the scientists who publish research results in peer-reviewed journals. But it also has to be understood that a noticeable spread of results can occur even with absolutely honest approach toward processing and analyses of observational data. The fact is that the induction of cancer and cancer mortality, apart from the dose of radiation, also depends on a significant number of additional factors. The real impact of these factors and a competent accounting for or, on the contrary, an underestimation of their effects can significantly affect the final result. Examples of the influence on the result of studies will be given below. With the situation given, the brief review of the Chernobyl is going to contain the figures on radiation risk, morbidity, and mortality exclusively on the bases of scientific papers and data collected in the UNSCEAR and BEIR reports. As far as it is known, these organizations have never been accused of falsifying research materials.
Radiation. https://doi.org/10.1016/B978-0-444-63979-0.00050-1 Copyright © 2019 Elsevier B.V. All rights reserved.
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50.2 THE ACCIDENT AND THE RELEASE OF NUCLIDES On April 26, 1986, at 01:23:4700 because of human error and deficiencies in the construction design, the explosion of the Block-4 on the Chernobyl nuclear power plant (CNPP) occurred. On April 27, 1986, just in 2 h after the first employees affected by the explosion were hospitalized, they were taken blood probes to measure the share of sodium-24 activated by neutrons (the half-life w15.5 h). The conducted research revealed no traces of neutron activation, which meant that the accident was not caused by spontaneous chain fission reaction and that the explosion was not a nuclear one [3]. The reactor had thermal capacity of 3200 MW, the diameter of its active zone was 12 m, and its height was 7 m. By the moment of explosion, the reactor had worked with full capacity for about 3 years. It is known that the fresh but not loaded into the reactor fuel is slightly active. The fuel rods can be, in fact, assembled manually. As the reactor is running, the radioactive nuclides accumulate inside it. The activity of short-lived nuclides in several periods of half-life results in saturation: the number of newly formed radioactive nuclei becomes equal to the number of decaying nuclei. The activity of long-lived nuclides (137Cs, 90Sr) practically increases linearly over time. The activity of any nuclide can be rather simply calculated, if the reactor power, the release of a nuclide in fission, and the constant of the radioactive decay are known. At the time of the accident, the reactor contained 192 t of fuel and its decay products. By that time, the initial activity of the spent fuel was ca. 5.5 1019 Bq ¼ 55,000 PBq (1500 MCi). According to a commonly accepted estimate, inside the destroyed reactor were left about 185 t of nuclear fuel. In a molted form, mixed with molted construction materials, the fuel spread over the premises and flowed down to the lower floors. Now the total activity of the remained fuel is c. 600 PBq (16 MCi). As a result of the thermal explosion and the subsequent combustion of the core graphite from the emergency power unit, a large number of radionuclides with, in particular, microparticles of irradiated fuel, including uranium and transuranium elements 239Pu, 241Am, 242Cm, were in 10 days ejected into the atmosphere. The share of environmentally significant long-lived nuclides 131I, 90Sr, 137Cs within the release was 20%. According to the estimations, the total activity of the release, excluding the rare radioactive gases, was 3.3 1018 Bq ¼ 3300 PBq (90 MCi) [4]. The emission of radioactive nuclides is largely determined by their volatility. The radioactive rare gases Kr and Xe, volatile by any temperature, were practically completely blown out by the explosion. The isotopes of I and Te are highly volatile at a temperature greater than 100 C, their emission was dozens of percents from their content in active area. Then, as less volatile, follow Cs, Ba, Sr, Ce, Zr, and Nb. The volatility of Pu and U is the least, and the emission of plutonium is estimated at a few percent. The emission activity at the CNPP was slowly reducing in the first 5 days since the accident, but starting by May 2, it sharply went up dangerously due to overheating by the fuel residual heat. Filling the ruins of the reactor with boroncontaining mixtures from helicopters allowed to stop this growth. After May 10, the emissions fell sharply. On May 11, they turned almost 100 times weaker than the day before. During the explosion and in the first 10 days from the active area, w1760 PBq 131I (T1/2 ¼ 8.04 days), w85 PBq 137Cs (T1/2 ¼ 30 years), w10 PBq 90Sr (T1/2 ¼ 29.12 years), isotopes of uranium, plutonium, iodine, cesium, strontium, and others were emitted. In fact, a lot of other radioactive nuclides were released into the environment, but with short half-lives on the order of days or even hours. There were also released rather long-lived nuclides, such as w 0.013 PBq 239Pu with the half-life of T1/2 w24,000 years. Besides, among the nuclear fission products occurred two noble gasses, w33 PBq 85Kr (T1/2 ¼ 10.72 years) and w6500 PBq 133Xe (T1/2 ¼ 5.25 days). Because of its relatively long half-life, krypton-85 accumulates in atmosphere, it rather quickly mixes up with the air of northern hemisphere, and then, yet not so fast, it gets into the southern hemisphere. By contrast, for all the period of atmospheric testing of nuclear weapons, 675,000 PBq 131I and 948 PBq 137Cs were released into the environment. All radioactive nuclides, but one, decay and their concentration decreases over time. 241Am appears in the environment after the decay of 241Pu. Maximal activity of 241Am will be reached approximately in 2058, and then it will slowly decline with the half-life of 432.2 years. At its peak, the activity of 241Am will be about 1000 times less than activity of 137Cs by that time.
50.3 THE AFFECTED PEOPLE All the people exposed to the radiation because of the accident are divided into the following groups: 1. Liquidators. It is believed that the main stage of the accident’s resulting liquidation lasted 3 years (1986e89). 2. People evacuated from the town of Pripyat and from 30 km area around the destroyed reactor.
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3. The population living in the affected area under strict control. The contamination with 137Cs in this area exceeded 555 kBq/m2 (15 Ci/km2). 4. The population living in the area with 137Cs contamination exceeding 37 kBq/m2 (1 Ci/km2). In 1986e87, about 440,000 people were involved in the liquidation of the accident aftermath. Later their number increased up to w800,000. These people were called liquidators. A special medical register contains data as for 2008 on more than 500,000 liquidators. In the 30 km zone about 200,000 people worked. Note that the number of liquidators included not only the workers, engineers, scientists, and military personnel, who were actually engaged in the liquidation of consequences of the accident, but also everyone who worked in the contaminated territories, including doctors, teachers, cooks, interpreters, and so on. The average additional dose for all contingents of liquidators received during the whole operation was 0.083 Gy [5]. During the spring and summer, 1986, 115,000 people were evacuated from 188 settlements in the affected areas and 220,000 more afterward. 7500 settlements with the population of 2.6 million on the Russian territory were subjected to contamination. Toward 2011 due to decontamination and natural decay, the number of contaminated settlements was reduced to 4000 (1.5 million inhabitants). The contaminated territories of the former Soviet Union with the total area of 150 km2 are still supporting by now up to 5 million people. Immediately on the accident three employees of CNPP were killed for reasons not related to radiation. Among the people who were carrying out emergency works, 134 cases of acute radiation sickness (ARS) were registered. By the end of 1986, 28 people died of ARS. In the years that followed, 13 more people died. The information on the early effects can be found in the report [6].
50.4 EXTERNAL EXPOSURE It is known that high radiation doses cause acute radiation sickness. Such cases because of Chernobyl disaster were relatively not many (134 people). All other radiation effects, which are discussed below, are stochastic, that is, they manifest themselves in long-term effects with different latent periods. The main effect is cancer. The development of various kinds of cancer in time is shown in Fig. 36.5. It is known that as a result of acute exposure, in a relatively short period (several years), leukemia develops. The maximum probability of disease is reached approximately in 6 years after irradiation. By now, the maximum for leukemia should already be passed. The induction of new leucosis practically equals zero in about 30 years after irradiation. The latent period of other cancers is about 10 years, and the maximum is reached in 30e40 years. The doses of outer irradiation are determined by contamination level of the area, and the contamination is caused by the fallouts of radioactive substances released by blast, fire, and the following processes in the destroyed reactor. The fallouts vary considerably depending on the mechanism of emitting and sizes. There is a near fallout zone, a central spot around the reactor with radius up to 60 km, which was caused by dry fallouts on April 26e27, and a far fallout zone, which is Gomel-Mogilev spot, contaminated by raining fallouts of April 28e29, with the center removed about 200 km north-north-east from CNPP. In the near zone, the ratio of activity of many refractory nuclides to activity of 137Cs is 1e5 and of 131I is about 10 [7]. In the distant zone the ratio of refractory nuclides to 137Cs was c. 0.06e0.11 and of 131I is c. 10 [7]. The maps of distribution of contamination by 137Cs in Europe are collected in the Atlas [8]. The Atlas contains about 100 colored maps of various scales showing distribution of contamination in Europe on the whole, within state borders, and in certain areas with particularly high contamination. Total amount of 137Cs that fell out in Europe was 8∙1016 Bq. The fallouts were distributed among the states in the following proportion: Belarus 33.5%, Russia 24%, Ukraine 20%, Sweden 4.4%, Finland 4.3%, Bulgaria 3.8%, Austria 2.7%, Norway 2.3%, Romania 2.0%, Germany 1.1%, and in the other European countries less than 1%. The studies showed that in Europe the contamination by 137Cs with surface activity exceeding 20 kBq/m2 covers about 6% of its territory, with activity exceeding 40 kBq/m2 it covers 2% of its territory, and with activity exceeding 1480 kBq/ m2 it covers less than 0.03% of its territory. The boundary values of surface activity as 37 kBq/m2 (1 Ci/km2) were set when mapping fallouts and determining their hazard. The level of contamination by 137Cs exceeds the limit of 37 kBq/m2 on 45,000 km2 on the territory of Europe (for reference, the area of, e.g., Germany is w357,000 km2 and Belarus 207,000 km2) [9]. Coefficient of connection of surface activity with dose rate for 137Cs equals 2.55 106 (mGy/hour)/(kBq/m2). Thus, the dose rate by contamination 37 kBq/m2 is w0.1 mGy/h w1 mGy/year. As is known, the annual dose for personnel must not be more than 50 mSv/year and for the population not more than 5 mSv/year.
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Therefore, it is evident that by such activity of 137Cs, a person who may constantly appear in the field of irradiation would get an annual dose less than 1 mGy, which complies with radiation safety standards. On the fields with activity lower than 37 kBq/m2, it is possible to conduct economic activities. The value 555 kBq/m2 (15 Ci/km2) is stated as a hazardous boundary limit. By activity exceeding this value, an annual dose for a person exceeds official dose limit for the population and gets closer to the dose limit for the personnel. The UNSCEAR report in 2008 provides information about the doses received by different groups, accounting for amendments relating to the improvement of treatment of dose recording techniques [9]. The average effective dose received by the liquidators during 1986e90 mainly because of external radiation is about 120 mSv. Registered doses range from 10 mSv to more than 1000 mSv, although approximately 85% of the workers received doses in the range 20e500 mSv. Estimates of uncertainty in individual doses range from 50% to five times. The experts noted that the doses received by military personnel are likely to have been understated. Average additional effective dose received by the 6 million people living in the most contaminated area of Belarus, Ukraine, and Russia during 1986e2005 from external exposure was about 9 mSv. For the 98 million people living in the three republics, who received 1.3 mSv, a third of the dose was received in 1986. These values are only slightly higher than the natural radiation background in the same period (w50 mSv). Over a 20-year period, about 70% of the population received an effective dose of less than 1 mSv and about 20% between 1 and 2 mSv. However, 150,000 people living in the affected area during the 20-year period received an effective dose of more than 50 mSv. For the 500 million inhabitants of other countries in Europe, the average effective dose is estimated at 0.3 mSv over this period. Detailed information on the effects of low-dose radiation after Chernobyl nuclear disaster can be found in the book of E. Burlakova and V. Naiditch [10]. Relatively recently it was found that radioactive contamination has reduced the rate of litter mass loss in Chernobyl forests, increased accumulation of litter, and affected growth conditions for plants [11].
50.5 INNER IRRADIATION The distribution in the organism of the radionuclides getting into the blood is determined by biogenic significance of the stable isotopes of the given element and by the affinity of this element to certain tissues and organs. Each element participates in its metabolic transformations in the body. These transformations are influenced by the solubility of the initial compound, by chemical transformations in the gastrointestinal tract, and by absorbability. The removal of incorporated radioactive elements with metabolic products through excretory systems is similar to their stable isotopes and chemical analogs. Besides, with the appropriate half-life value, the radioactive isotope content in the body also decreases as a result of radioactive decay. The period of time during which half of the incoming amount of the element is excreted from the body is called the effective half-life period. Nuclides 90Y, 137Cs, 140Ba, 96Au, and some others are characterized by a short half-life period. A long half-life period is typical, e.g., for the nuclides 210Po, 226Ra, 232U, and 239Pu. One of the most hazardous nuclides, 137Cs, is a chemical analog of sodium and potassium. In metabolic reactions it repeats their ways, fairly evenly distributing throughout the body. Like other alkali metals, cesium is easily absorbed and excretes with urine. The biological half-life of accumulated 137Cs for humans is considered to be equal to 70 days. By even 137Cs distribution in the human organism with specific activity of 1 Bq/kg, the absorbed dose rate, according to various authors, varies from 2.14 to 3.16 mGy/year. Other hazardous radionuclide 90Sr is a chemical analog of calcium and therefore it concentrates on bones. The natural excretion of this nuclide from the body appears more slow. Iodine is concentrated in the thyroid gland; thus its radioactive isotopes, in large quantities contained in fission products, pose the greatest danger in the first weeks after radiation accidents. Rare-earth elements, cerium, lanthanum, etc., are mainly concentrated in the liver, and antimony, arsenic, bismuth, etc., are concentrated in the kidneys. The main radiation damage by inner irradiation was created mainly by the two radionuclides: the short-lived nuclide 131 I, which determined the impact on health during the first couple of months, and the gamma emitter 137Cs, the main effect of which is currently ongoing. In the first months after the accident, due to the lack, or inadequacy, of protection measures, the pollution of fresh milk by the nuclide 131I caused significant radiation doses for the thyroid gland. At that time, children were subjected to the main radiation exposure. Subsequently, the activity of iodine dropped significantly and the entire population became exposed to irradiation mainly because of 137Cs. Irradiation was both external and internal through contaminated food. However, because of protective measures, the resulting doses were relatively small. The real average annual effective dose was 31 mSv in Belarus, 17 mSv in Ukraine, the average dose in the population of Pripyat did not exceed 13 mSv, and the maximum dose could reach 50 mSv [12].
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Radiation doses received by the thyroid gland are noticeably higher. The average dose to the thyroid in 1986 was 490 mGy for the evacuees, 102 mGy for the population of contaminated area in the three USSR republics, 16 mGy for the 98 million of population in Belarus, Ukraine, and 19 regions of Russia and 1.3 mGy for people in the remote countries of Europe. It is noted that preschoolers received a dose to the thyroid that was approximately two to four times greater than the average dose got by the population. Note that, currently, science cannot distinguish a tumor that developed as a result of irradiation from a tumor occurring for any other reason. Therefore, the link between the dose and morbidity is established by statistical methods. It is important to consider the impact on the disease probability of some factors such as age, gender, and genetic characteristics of the individual, lifestyle, and many other factors that may be relevant to the disease. To obtain reliable and sound epidemiological conclusions, it is necessary to have sufficient statistical support for the research. Thyroid cancer is a rare disease in children. However, because the thyroid gland in children is quite an active organ, it has increased radiosensitivity. If a child has received a large dose of radiation to the thyroid and develops thyroid cancer several years after exposure, it is very likely that the cancer was caused by radiation. If thyroid cancer appears in an adult a few months after exposure, its relationship with exposure has very low probability. An important factor that modifies the risk of radiation-induced thyroid cancer is iodine deficiency in human consumption. E. Cardis and colleagues found that in areas with low iodine content in soil, the risk of a dose 1 Gy is 3.1 times greater than in areas with higher levels of iodine. It is considered reliably proven that the use of potassium iodide as a dietary supplement significantly reduces the risk of radiation-induced thyroid cancer. It is clear that the underestimating of iodine deficiency, of this external, nonedose-related circumstance, significantly affects the risk assessment result. The increased incidence of thyroid cancer in children began to show in 1990e91. This was pretty early for solid cancer, which is characterized by a much greater latency period, so this information initially caused doubt. However, further developments showed an obvious connection of these cancers with radiation. The number of these cancers is increasing steadily, and by 2005 no slowdown has been detected. According to the UNSCEAR report for 2008, among children who were younger than age 14 years at the time of the accident, for the period 1991e2005, a total of 5127 cases of thyroid cancer were revealed and 6848 cases among those who were younger than age 18 years. (In the UNSCEAR report for 2000, it was fewer than 1800 cases.) These numbers refer to Belarus and Ukraine wholly and to the four most affected areas of the Russian Federation. Background level of thyroid cancer in children under the age of 10 years is approximately two to four cases per year per million people. For children born after 1986, no increase in frequency of thyroid cancer has been detected; the frequency is at the background level. There is no reliable information on thyroid cancer in exposed adults [9]. There is also no evidence of any increase in the frequency of any other solid cancers among the population of Ukraine and the Russian Federation [9]. At the International Conference “Fifteen years after the Chernobyl disaster, Lessons Learned” in April 2001, it was noted that the mortality rate among liquidators and residents of contaminated territories does not exceed the statistical average data in the three countries. However, to assess such an exposure effect as mortality, the time that had passed after the disaster was still too short. The report [13] shows a table with an overview of 51 environmental studies on the population performed by domestic and foreign environmentalists. In most studies, an increased number of thyroid cancers are noted. In early works executed before 1995, no other types of cancer, including leukemia, were recorded, and only the subsequent papers reported of leukemia cases and some noncancerous diseases. Most of the researchers and experts point out that regardless of the exposure, the Chernobyl disaster has significantly changed the lives of millions of people, especially in Belarus, Russia, and Ukraine, who live in the most contaminated areas. Forced evacuation, limitations in usual activities, other countermeasures, and conflicting information about the possible consequences of the accident have radically changed people’s lives and led to psychological problems, worsened the quality of life, and could significantly affect health. The total incidence of disease among adults living in contaminated areas is significantly higher than the national average, although in the vast majority of cases the causes of the disease cannot be attributed to the effects of radiation. Significantly higher than the national average is suicide rate among the liquidators. Obviously, competent processing of epidemiologic data should not encourage to dismiss the unpleasant consequences at the expense of the accident to radiation phobia. On the other hand, the psychological aspects of the accident and postaccident conditions should be taken into account. The study of the Chernobyl disaster is now ongoing [14]. The third issue of the volume 56 for 2016 of the journal “Radiation Biology, Radioecology” is entirely devoted to the 30th anniversary of the events. Note here the article of I.V. Oradovskaya [15] about change of immune status under action of radiation. L.M. Rozhdestvenskiy paid attention to the fact that insufficient consideration was given to nonradiological factors having an effect on the
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psychoemotional state of the people [16]. A.N. Micheev considered the role of radiophobia in the psychosomatic diseases of population in the area of strict radiation control [17].
50.6 CURRENT SITUATION The destroyed reactor continuously emitted radioactive substances into the environment. By November 1986, above the destroyed reactor a protective structure was erected, officially called “Shelter,” though more widely known as “Sarcophagus.” But this protection was constructed in haste and thus contained lots of gaps. Partly the constructions erected in 1986 were built on the destroyed sections of the Block-4 of CNPP, the endurance of which was not then accurately determined because of difficulties of radiation situation and blockages. The use of remote methods of concreting led to the situation when large masses of concrete spread over the floors of the building overloading them. Remote installation in some cases did not provide tight fit of structures to each other and reliable connection of structures with supports. The total area of cracks in the roof and walls of the object was about 1000 m2 at the time of the object’s delivery. Despite the efforts made during the entire period of operation of the Sarcophagus, the state of safety decreased over time. Constantly there was a process of degradation of building structures under the influence of moisture and water due to ingress of precipitation. On February 15, 2013, the suspending slabs over the engine room of the power unit with an area of several hundred square meters collapsed [18]. Useful material on the first sarcophagus can be found on the website [19]. At the end of November 2016, the destroyed reactor with the old sarcophagus over it was covered with a new mobile protective arch.
REFERENCES [1] Chernobyl Nuclear Power Plant and Exclusion Zone. Chernobyl, Pripyat. http://chornobyl.in.ua/istoria-avariy.html. [2] Health Effects of Chernobyl 25 years after the reactor catastrophe, IPPNW (International Physicians for the Prevention of Nuclear War) and GFS (Gesellshaft für Strahlenschutz), 2011. Report, http://www.ippnw.org/pdf/chernobyl-health-effects-2011-english.pdf. [3] L.A. Il’in, Realities and Myths of Chernobyl «ALARA Limited», 1994. [4] Y.V. Sivintsev, A.A. Khrulev, Estimation of radioactive release at 1986 accident on the 4-th block of Chernobyl NPP, At. Energ. 78 (6) (1995) 403e416. [5] Chernobyl disaster. Ideas and problems of overcoming its consequences in Russia 1986e2001, Rus. Nat. Report, in: History of Atomic Energy of the Soviet Union and Russia, Issue 4, AT Publ. (JieAT), Moscow, 2002, pp. 487e536, 539 p. [6] UNCSCEAR 1988 Report, Annex G. Early Effects in Man of High Dose Radiation. http://www.unscear.org/unscear/en/publications/1988.html. [7] K.V. Kotenko, S.M. Shinkarev, Y.V. Abramov, E.O. Granovskaya, V.N. Yazenko, Y.I. Gavrilin, et al., Comparative analysis of the radionuclide composition of deposition in the near and far zones after the accident at the Chernobyl NPP and in the near zone after the accident at the Fukushima1 NPP, Occup. Med. Ind. Ecol. (10) (2012) 1e5 (Russian Journal: Nfejxjoa truea j Vrpn9zmfooa> ;lpmp[j>). [8] Atlas of Cesium Deposition on Europe after Chernobyl Accident. EUR 1673 EN/RU, European Commission, 1998, 65 pp. http://cricket.biol.sc.edu/ chernobyl/UN-reports/Atlas.pdf. [9] UNSCEAR 2008 Report, v.II, Annex D. Health Effects due to Radiation from the Chernobyl Accident, p. 45e219 - http://www.unscear.org/unscear/ en/publications/2008_2.html. [10] E. Burlakova, V. Naiditch, The Effects of Low Dose Radiation: New Aspects of Radiobiological Research Prompted by the Chernobyl Nuclear Disaster, CRC Press, 2004, 420 pp. [11] T.A. Mousseau, G. Milinevsky, J. Kenney-Hunt, A.P. Møller, Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas, Oecologia 175 (1) (2014) 429e437. [12] A.K. Guskova, V.I. Krasnyuk, Health consequences in overexposed persons after the Chernobyl accident: basic resume and unsolved problems, Occup. Med. Ind. Ecol. (10) (2012) 11e17. [13] BEIR VII Phase 2, Population Exposed from the Chernobyl Accident, 2006, p. 215. https://www.nap.edu/read/11340/chapter/11#214. [14] A.I. Gorsky, M.A. Maksioutov, K.A. Tumanov, N.V. Shchukina, S.Y. Chekin, V.K. Ivanov, Non-parametric analysis of radiation risks of mortality among Chernobyl clean-up workers, Radiats Biol. Radioecol. 56 (2) (2016) 138e148. [15] I.V. Oradovskaya, 30 years of tragedy in Chernobyl. Clinical and immunological effects of liquidators of consequences of the accident at Chernobyl NPP. Main results of multiyear monitoring, Rad. Biol. Radioecol. 53 (3) (2016) 251e273 (in Russian). [16] L.M. Rozhdestvenskiy, Results of the Chernobyl accident at 30 years of distance, Rad. Biol. Radioecol. 53 (3) (2016) 274e284 (in Russian). [17] A.N. Micheev, Low “doses” of radioecology, Rad. Biol. Radioecol. 53 (3) (2016) 336e350 (in Russian). [18] Sarcophagus Above the Reactor (Object Shelter). http://4ernobyl.ru/publ/katastrofa/likvidacija/sarkofag_nad_reaktorom_obekt_quot_ukrytie_quot/ 5-1-0-4. [19] Truth about Chernobyl. Object “Shelter” (Sarcophagus). http://stopatom.slavutich.kiev.ua/1-2-2a.htm.