Ядерна фізика та енергетика Nuclear Physics and Atomic Energy   ISSN: 1818-331X (Print), 2074-0565 (Online)   Publisher: Institute for Nuclear Research of the National Academy of Sciences of Ukraine   Languages: Ukrainian, English   Periodicity: 4 times per year   Open access peer reviewed journal

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D. M. Holiaka^1,*, S. E. Levchuk¹, M. O. Hrechaniuk¹, V. V. Illienko¹, M. A. Holiaka¹, V. P. Protsak², V. O. Kashparov<sup>1

1</sup> National University of Life and Environmental Science of Ukraine, Kyiv, Ukraine
² Ukrainian Hydrometeorological Institute, State Emergency Service of Ukraine and National Academy of Sciences of Ukraine, Kyiv, Ukraine

^*Corresponding author. E-mail address: holiaka@nubip.edu.ua

Abstract: Wildfires in radioactively contaminated territories in northern Ukraine have intensified over the past decade, raising concerns about the atmospheric resuspension of technogenic radionuclides, particularly ¹³⁷Cs. Despite numerous studies on this topic, empirical data on radionuclide emissions from burning combustible materials in near-natural environments remain limited. This study provides new estimates of ¹³⁷Cs release during the combustion of moss, herbaceous vegetation, forest litter layers, and green pine branches collected at six Chornobyl sites representing pine and birch forests as well as meadows. Using a custom-built aerosol filtration system, we quantified ¹³⁷Cs activity in smoke aerosols and determined its fraction of release relative to both fuel activity and the total ecosystem inventory. The results revealed a clear dependence of the cesium radioisotope release on the vertical position within the pine litter profile during burning: the upper layers (moss and fresh litter) contributed a greater amount to the atmospheric release, despite having a lower total ¹³⁷Cs activity compared to the deeper humified layer. An increase in moisture content (from 5-13 % to 15-29 %) significantly reduced radionuclide emissions from pine litter (by approximately one order of magnitude), whereas combustion of green pine branches with moisture contents exceeding 100 % had unexpectedly high ¹³⁷Cs releases (up to 24 %). The mean proportion of cesium radioisotope release increased along the sequence: pine forest - birch forest - meadow (0.075-0.45 %) for mechanically intact and dried above-ground layers of moss/grass vegetation and litter/detritus. The obtained ¹³⁷Cs release factors relative to its total activity in the studied sites generally align with empirical estimates and modelling results for the spring 2020 Chornobyl wildfires, where this parameter has been estimated to range between 0.01 and 0.4 %. Our materials indicate that ¹³⁷Cs release in the Chornobyl landscapes is unlikely to exceed 1 % of its gross inventory in ecosystems, even during large-scale wildfires.

Keywords: radionuclide, radioactive aerosol, emission, wildfires, combustible materials.

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