COMPREHENSIVE RADIATION AND HYGIENIC MONITORING IN POPULATION OF THE RIVNE OBLAST RADIOLOGICALLY CONTAMINATED TERRITORIES

Objective. The key factors identification in radiation dose formation in population of radiologically contaminated areas of Rivne oblast in the current period of accident through comprehensive radiation and hygienic monitoring in reference settlements in 2020 and estimation of their impact on dose formation were the study objectives. Materials and methods. Comprehensive radiation and hygienic monitoring of settlements in Rivne oblast (province) was provided in Stare Selo, Vezhytsia, Perekhodychi, and Drozdyn villages of Rokytne district, where the highest radiation doses were registered after the ChNPP accident. Studies were conducted in September 2020. Measurements (n=696, 318 adults, and 378 children) were performed using the whole body counters (WBC) to determine the internal radiation doses. The 48 samples of milk, 45 samples of potatoes and vegetables, and 35 samples of wild products were collected in local farms and measured for the 137Cs and 90Sr content. Residents of the studied settlements (n=229, 140 adults, and 89 children) were interviewed about the levels of consumption of staple foodstuffs. External radiation doses were evaluated in all the studied settlements. Mathematical, dosimetric, and radiochemical methods were applied. Results and conclusions. Annual effective radiation doses of the Rivne oblast population in 2020 were formed mainly due to internal radiation ones that not exceeded 1.24 mSv · year-1 in adults and 0.65 mSv · year-1 in children against the RCT criterion of 1 mSv · year-1. Further 1.2–1.9-fold decrease in the annual internal radiation doses vs. the results of WBC-monitoring in autumn of 2017 was registered in the surveyed settlements. The latter confirmed a time pattern of radiation levels gradual reduction at the current stage of Chornobyl accident since 2011. Intake of 137Cs with milk and wild mushrooms, which traditionally occupy a significant part of diet in the Rivne Polissya area and have consistently high levels of radioactive cesium contamination, remains a key factor of internal radiation dose forming in residents of the surveyed settlements of Rivne oblast. The Scientific Council meeting of NAMS approved the NRCRM Annual Report. Key words: radiologically contaminated territories, comprehensive radiation and hygienic monitoring, internal radiation dose, whole body counter, 137Cs and 90Sr content, food.

90Sr Content in the Stemwood of Forests within Ukrainian Polissya

The consequences of the Chernobyl disaster continue to threaten humans and ecosystems across fallout gradient in Northern Ukraine and nearby. Forest ecosystems contain substantial stocks of long-lived radionuclide 90Sr which was leached from the fuel matrix during the disaster. Nowadays, there is a lack of information about current transfer factors (TF) of this radionuclide from soil to the stemwood of native tree species. We have estimated 90Sr content in the forest stemwood of three tree species utilizing models of their growth and yield and collected woody samplings. TFs provided here vary greatly across studied tree species (18.0 × 2.1±1, 8.7 × 2.8±1, and 10.4 × 6.0±1 n × 10−3 m2·kg−1 (geometrical mean (GM) ± geometrical standard deviation, GSD) for the above species, respectively) and together with indicators of soil contamination allow us to reliably assess local stocks in the stemwood. Silver birch stands are estimated to deposit the highest 90Sr stocks. Herewith, at 25 years old Black alder stands could accumulate higher stocks (up to 35 MBq·ha−1) under rich growth conditions. TFs obtained in this study substantially exceed values provided by the International Atomic Energy Agency for studied tree species and thus could entail respective restrictions on use of firewood across large areas in Ukrainian Polissya. Data provided here may be harnessed to support decisions of respective stakeholders to provide credibly safe management of the contaminated forest ecosystems.

GROUNDWATER SELF-CLEARING FROM 90SR WITHIN BACKGROUND AREA AND OWING TO ARTIFICIAL CONTAMINATION

The main idea of the presented results is the determination of spatial-temporal regularities of 90Sr content in groundwaters within Chornobyl Exclusion Zone. Utilization of formal kinetic regularities (of I order for irreversible process) for monitoring data analyses has been substantiated. Rate constants of groundwater self-clearing from 90Sr in dependence of type of contamination are calculated by iteration method. Graphic interpretation of data has been realized using package for analysis of Microsoft Excel and Statistica software. Self-clearing of groundwaters is carried out owing to three main processes: sorption as function of water containing medium dispercity, dispersion due to water exchange, concentration dilution (dissolving) of radionuclides in specified volume, and physical decay. considered Self-clearing is considered to be an important element both for the security and vulnerability of groundwaters. Data on 90Sr content in groundwater of background areas, in affected zone of radioactive waste storage, zone of groundwater nutrition from cooling pond of Chornobyl NPP, spots of primarily radioactive contamination, and of groundwater secondary contamination owing to well drilling are discussed. Rate constants for groundwater self-clearing from 90Sr are calculated from experimental data both for non-stationary (rapid) and stationary (slow) processes. The “half-decontamination” period (in analogy to half-life) is less than 0.5 year. The rate constant for unstable process two times, and for established one time exceeds the decay constant. The rates of groundwater self-clearing from strontium-90 owing to water exchange and geochemically immobilization are determined. The equilibrium of sorption-desorption within water saturated zone is generally depended on the rate of water exchange and radionuclides concentration in upper stream, i.e. from concentration gradient.