Experience in studying the consequences of the Chernobyl accident in a rural settlement: case study of the village of Novye Bobovichi, Novozybkovsky district, the Bryansk region

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Introduction Academician R.M. Aleksakhin often called the accident at the Chernobyl Nuclear Power Plant (ChNPP) in 1986 an agricultural disaster, meaning that the main troubles caused by the consequences of the accident fell on the shoulders of agricultural producers and villagers.[5] It is difficult to disagree with the opinion of an authoritative scientist, observing the changes that occurred in the radioactively contaminated territories after the accident. In the first two years, villagers had little understanding of what had happened and therefore felt a sense of oppressive fear. The measures taken by the state more often caused additional anxiety, and the seconded specialists working in some villages could not relieve it and reassure the population adequately. These circumstances caused the first wave of outflow of young people and specialists (doctors, teachers, zootechnicians, etc.) working in rural areas. About three years after the accident, when social tensions seemed to be subsiding and life was returning to its usual course, an anti-communist campaign swept across the country, in which rural residents unwittingly became the main hostages. The public consciousness trained during the Cold War, oriented towards the nuclear threat as the most powerful force for the destruction of life, was now used consciously or not, in some cases, as a means of fighting against communist power. At the same time there was a substitution of notions: the frightening nuclear danger was replaced by radiation danger. Attempts by individual scientists to explain the difference between the two were crushed by a militant group - the so-called democrats - who took over most of the media. All this bacchanalia around the unfolding power struggle further undermined the country’s economy and hit the countryside the hardest. In neighbouring Belarus, a second wave of mass resettlements took place, partly affecting the Bryansk region as well. Materials and methods Despite state support for the territories classified as affected by the radiation accident, the general decline in production, coupled with demographic problems, was eroding and destroying established rural life. In the Novozybkovsky District of the Bryansk region, only 60 out of 120 settlements (1986) remained 15 years later, and the rural population dropped from 18,424 (1989)[6] to 10,815 (2022) people.[7] The article considers the situation on the example of one settlement of Novozybkovsky District - the village of Novye Bobovichi and the collective farm located in it - state farm “Reshitelny”. Figure 1 shows the dynamics of the population of the village in the period from 01.01.1986 to 01.01.2023 according to the records in the house books. Figure 1. Number of officially registered of the village of Novye Bobovichi in the period 1986-2022 Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko. The decline in production and deterioration of living conditions of the population occurred not only in Novozybkovsky District, but also in the whole country. For the villagers of some farms located on the radioactively contaminated territories, for a short period of the early 1990s there was even some improvement of the situation due to the state support of the contaminated areas. During this period, due to the receipt of fertilisers and agricultural machinery, grain yields increased, milk yields and overall milk production increased (Figures 2, 3). However, this surge was short-lived; the collapse of the USSR and the general economic recession, perhaps, had the sharpest impact on agricultural producers. A period of sharp decline in the quality of life on the poor lands of Novozybkovsky District, aggravated by demographic problems, began. There was an outflow of young people and qualified personnel in the period 1986-1988 and in 1990, which, due to the lack of meaningful prospects, has not been completed to the present day. If the total milk yield in the farm was 2,209 tonnes in 1991, in 2000 it decreased to 891 tonnes, in 2010 - to 360 tonnes, in 2020 - to 135 tonnes, and in 2021 - to 63 tonnes, i.e. milk production has decreased 35 times in 30 years. In 1986, there were 248 dairy cows in private farms in the village, of which only one cow remained in 1990. In 2022, only one private farm had 7 cows; dairy products produced in this farm were mainly used for the needs of individual villagers. The rest of the villagers used purchased dairy products. The experience of the past years has shown that the most large-scale consequences of the accident were realised not in the radiological, but in the socio-economic sphere. This is confirmed by the recommendations formulated in the report of the UN mission “Humanitarian consequences of the accident at Chernobyl NPP: rehabilitation strategy”,[8] and the conclusions of the Chernobyl Forum, presented at the final conference on 6-7 September 2006 in Vienna [1]. The Chernobyl Forum emphasises the need to place economic development aimed at the economic and social viability of the territories affected by the accident at the core of the strategy for overcoming the consequences of the accident at the ChNPP in the medium and long term. Изображение выглядит как текст, линия, диаграмма, снимок экрана Автоматически созданное описание Figure 2. Dynamics of milk yield per cow in the best farms of the Novozybkovsky District: “Wave of Revolution” (1945-1985) and “Resolute” (1986-2010) in comparison with the average data for the Russian Federation Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko. Изображение выглядит как текст, снимок экрана, линия, диаграмма Автоматически созданное описание Figure 3. Dynamics of milk production in the collective farm “Reshitelny” (in the village of Novye Bobovichi) and in the Novozybkovsky district of the Bryansk region, 1986-2010 Source: Muratova NA. (ed.) et al. Chernobyl a quarter of a century ago. Statistical collection. Feder. government service. Statistics (Rosstat), the Territorial body of the Federal State Statistics Service for the Bryansk Region. Bryansk: Bryanskstat; 2011. 175 p. It is important that this approach was based not only on the opinion of international experts and the governments of the three countries (Belarus, Russia, Ukraine) most affected by the Chernobyl accident, it also responded to the urgent problems and concerns of the residents themselves.[9] However, the situation after such recommendations and individual efforts undertaken has not changed dramatically. The question about the prospects and even about the further existence of the settlement is still extremely topical. Regardless of the described course of events, the assessment of received radiation doses of the population living in the most radioactively contaminated territories and preserving the established way of life, along with other indicators, is of undoubted both scientific and social interest. The present work deals with the results of long-term farmstead surveys in Novye Bobovichi village in terms of external dose estimates. These studies were based on the radiation parameters measured in the period 1986-2022, as well as on various data on the village residents, obtained on the basis of records in house books. Radiation situation and household surveys in Novye Bobovichi village The study of the radiation situation in Novye Bobovichi village due to radioactive fallout from the accident at ChNPP started with the measurement of contamination levels of generalised milk from the state farm on 12 May 1986. However, to some extent due to coincidence in the area of the Experimental Station (branch of the All-Russian Institute of Fertilizer and Agrosoil Science) in the town of Novozybkov, which can be considered as settlements of “the same fate”, the first measurements of the exposure dose rate were made on the day following the radioactive fallout that formed the contamination of the territory under consideration as a result of heavy precipitation in the evening of 28 April 1986. Subsequent dose rate measurements performed until the end of May showed a rapid decline due to the decay of short-lived radionuclides (Figure 4). The calculated values of the dose rate in Novozybkov town were made using the results of cluster analysis in reconstruction of radionuclide composition of fallout in Gomel (north-eastern part), Mogilev (south-eastern part) and Bryansk (western part) regions[10] (Table 1). The levels of 137Cs deposition in Novozybkov (697 kBq/m2) and at the Experimental Station (1 050 kBq/m2) were noticeably higher than 370 kBq/m2. On this basis, the radionuclide composition of the deposition characteristic of the area was reconstructed, from which the exposure dose rate in Novozybkov was estimated using the coefficients from [2] for early deposition. It can be assumed with great confidence that the parameters of the radiation situation in Novye Bobovichi village were similar to the situation in Novozybkov, which allows us to estimate the dose rate based on the proportion of 137Cs depositions in these territories. Изображение выглядит как текст, линия, снимок экрана, диаграмма Автоматически созданное описание Figure 4. Measured and calculated values of exposure dose rate in Novozybkov in April-May 1986 Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko Table 1. Ratio of a number of radionuclides in fallout in the Mogilev Region (eastern part), Gomel Region (north-eastern part) and Krasnogorsk District of Bryansk Region (as of 26.04.1986) 137Cs contamination density, kBq/m2 Mogilev region (eastern part) Gomel region (north-eastern part) Krasnogorsky District, Bryansk Region 131I / 137Cs 95Zr / 137Cs 90Sr / 137Cs 18 38.2 0.71 0.3 115 12.8 0.16 0.05 370 10.5 0.09 0.022 1580 7.6 0.04 0.013 Source: compiled by S.V. Panchenko based on [7]. It was previously shown that the initial deposition of 137Cs was [3]: - to the territory of Novye Bobovichi village 1095 ± 261 kBq/m2; - to agricultural land around 1100 ± 378 kBq/m2; - to nearby forests 1920 ± 310 kBq/m2. Thus, immediately after precipitation, the average gamma-ray background in Novye Bobovici (in the open area at a height of 1 m from the ground surface) was about 13 mR/h. Various aspects related to the formation and evolution of radiation environment parameters have been discussed in more detail in the scientific works[11] and [2]. Materials and methods At this stage of the study, individual external doses were estimated for 984 residents (432 men and 552 women) of Novye Bobovichi village, Novozybkovsky district, Bryansk region, who lived in the village during the Chernobyl accident and did not leave in the first years after the accident. By the middle of 2023, 499 people (233 men and 263 women) from among the old residents had died. The average age of death for men was 65 years, and for women - 79 years. The calculations of external dose were based on the results obtained in the previous door-to-door surveys [3], as well as new measurements of dose rate made in July 2022 during the door-to-door surveys. All surveys to maintain similarity were conducted in accordance with the 1990 Methodological Recommendations for Assessment of Radiation Situation in Populated Areas by the year 1990.[12] In 2022 the following verified instruments of the Scientific and Technical Support Centre (STSC) of IBRAE RAS[13] were used to measure the dose rate on the ground and indoors: - DKG-02U “Arbitr” was used in this study to measure the ambient dose equivalent rate at local points; - individual dosimeter DKG-RM1610 was used as a backup for route recording of continuous γ-radiation dose equivalent rate for each of the expedition participants; - MKS-AT6101 was used for enroute gamma-ray imaging. In addition, each researcher had a Polymaster dosimeter attached to his or her belt, which continuously recorded dose rates in files with an averaging interval of 180s. All instruments measure the ambient dose rate. The lowest actual background dose rate values in the range from 0.08 to 0.22 μSv/h were recorded in the centre of asphalt roads. In the same dose range were the results of measurements in both brick and wooden houses. The highest values were recorded over areas of undisturbed soil surface. The results of dose rate measurements at local points are given in Table 2. In the course of work under the research programme on migration of 137Cs in the structure of a settlement[14] the parameter M137(t) was proposed - the ratio of the average dose rate at a height of 1 m for a characteristic surface type Pγ(137), to the density of the integral nuclide content in soil calculated at the time of dose rate measurement - s137: М137(t) = Рg(137)/s137 [], (1) where s137 - calculated density of 137Cs surface contamination, kBq/m2 at the time of dose rate measurement; Рg(137) - the difference between the measured dose rate at the point Pγ and the background value of this rate Pγ(0), which was before the accidental contamination: Pγ(137) = Pγ - Pγ(0). As Pγ(0) for Novye Bobovichi was taken the value equal to 0.09 μSv/h[15]. Table 2. Mean dose rate values at characteristic points of the village of Novye Bobovichi in July 2022, μSv/h Surface Type Number of Dimensions Mean dose rate, μSv/h Unperturbed surface 12 0.43±0.02 Grass cover from road to site 261 0.28±0.01 Bench at the gate (at home) 96 0.25±0.003 Soil on the street and in yards 16 0.27±0.01 Asphalt 87 0.15±0.01 Vegetable garden 67 0.31±0.01 Garden 27 0.30±0.01 The house is wooden 33 0.12±0.01 The house is brick 18 0.13±0.01 Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko. A relationship can be used to estimate the effective external dose (HEx) at a particular point for selected occupational and age groups: , (2) where - dose rate per year obtained by interpolation between measured Pγ(137) in individual years in the period 1990-2023; Rk - dose reduction factor, which for different population groups can be defined as: (3) where Lj - the factor of place[16], рkj - the factor of employment of the k-th group of population [3]. For each age and occupational group the values of the parameter - pkj are selected (Table 3). The analysed data from the house books of Novye Bobovichi village. Novye Bobovichi, as well as the desire to use the known dependence of dose coefficient values on the age of residents [2] allowed us to identify 6 main population groups. Group No. 1 - preschool children up to 7 years of age were included. Group No. 2 - school-age children. Children aged 7 to 17 years. Group No. 3 - people older than 17 years, constantly working outdoors: shepherds, tractor drivers, field workers, etc. Group No. 4 - people over the age of 17 who work outdoors intermittently rather than continuously. Group No. 5 - people over 17 years old, their lifestyle can be called “work-home”, as they spend 9 hours working indoors, 2 hours travelling (including visits to shops and other places), and the rest of the time is taken up by household chores. Group No. 6 - pensioners who also have a lifestyle that is not typical for other groups. It was accepted that until 9 o’clock representatives of the group spend up to 9 hours in the fresh air, doing work in the vegetable garden, communicating with other pensioners, and the rest of the time they spend at home. For the reference members of each population group, the distribution of living time in different locations is presented in Table 3. Table 3. Time spent by different population groups in different locations, hour/year Localization Population group 1 2 3 4 5 6 Unperturbed surface 2053 1369 Grass cover from road to site 1800 1721 Bench at the gate (at home) 182 Soil on the street and in yards 885 391 319 684 339 365 Asphalt 274 456 157 913 Vegetable garden 600 194 259 Garden 5475 5280 6068 6205 5632 7117 The house is wooden 1174 46 46 2373 183 ∑ hours 8760 8760 8760 8760 8760 8760 Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko. To estimate the dose rate before 1990, we will use the dependence [4]: , (4) where si - the initial density of surface contamination with the i-th radionuclide (kBq/m2); Gi(t) - conversion rate from si to dose rate i as a function of time, (nSv/h)/(kBq/m2); λi - the radioactive decay constant of the i-th radionuclide; t - the time after contamination. Conversion rate (Gi(t)) for 1986 were taken for a 3 mm soil layer, and for subsequent years (1987-1989) for a 5 cm layer from [2]. The parameter M137 (t) was used to estimate external doses after the year 1990. Results and discussion Figure 5 presents the dynamics of the M137 parameter value for different localisations of Novye Bobovichi village over the entire observation period, considering the data obtained in 2022 (36 years after the accident). The points for the first numbers of May 1986 (initial points) are taken from reference publications. Figure 5. Change in the value of the M137 parameter for different localizations of the village of Novye Bobovichi due to the migration of 137Cs in the period 1986-2022 Source: compiled by K.V. Gupalo-Osadchaia, S.V. Panchenko. As can be seen from Figure 5, the general characteristic of the processes is the actual cessation of the decline in the values of the parameter M137 for all localisations after 2001. In other words, after 15 years the migration of 137Cs, which influenced the formation of the external dose rate in the settlement in the first years, actually ceases, and only the decay of this isotope remains. For the subsequent stages of reconstruction of the accumulated dose due to external exposure, the absolute value of the anthropogenic component for each characteristic point of localisation also matters. Therefore, the dynamics of these values (Figure 5) is an important parameter for calculating the accumulated dose to the inhabitants of the settlement. The following expression was used to calculate the average annual dose loads for the j-th recipient: , (5) where ti - the time spent by the j-th recipient at a particular point, in fractions of a year. In our case the following local points are defined: undisturbed surface (forest), grass cover, bench, ground in front of the house, vegetable garden, asphalt, wooden and brick houses. To estimate

About the authors

Ksenia V. Gupalo-Osadchaia

Nuclear Safety Institute of the Russian Academy of Sciences

Email: gupalo.kv@ibrae.ac.ru
ORCID iD: 0009-0004-0791-4638

Engineer of the Radioecology Laboratory

52 Bolshaya Tulskaya St, Moscow, 115191, Russian Federation

Sergey V. Panchenko

Nuclear Safety Institute of the Russian Academy of Sciences

Author for correspondence.
Email: panch@ibrae.ac.ru
ORCID iD: 0000-0002-2750-0940
SPIN-code: 6148-6635

Head of the Laboratory of Radioecology

52 Bolshaya Tulskaya St, Moscow, 115191, Russian Federation

References