<p>Most of the territory of the Chernobyl Exclusion Zone (CEZ) is covered by forest. Forest of CEZ have accumulated a significant part of the radioactive release and for many years have served as a barrier to the non spreading of the radionuclide contamination outside the CEZ.</p><p>According to the classification of wildfire danger, the forests of CEZ belong to high, above average and medium classes, making cases of wildfires as quite common.</p><p>Poor, sod-podzolic soils of Ukrainian Polesye contribute to the entry the activity of <sup>90</sup>Sr and <sup>137</sup>Cs in plant biomass. During wildfires some of the radionuclides contained in combustion products of biomass are emitted into the atmosphere. Biologically important radionuclides such as <sup>90</sup>Sr, <sup>137</sup>Cs, plutonium isotopes and <sup>241</sup>Am bound to fine aerosols - combustion products - can be transported with atmospheric flows over the long range, causing secondary radioactive fallout and forming additional inhalation dose loads on the population.</p><p>Lack of the actual information on the source term (rate of emission of radionuclides) does not allow reliable modeling of the radiological impact of wildfires. To address this issue, we have proposed a methodology that allows for operational assessments of the dynamics of radionuclide emissions into the atmosphere from wildfires in the CEZ.</p><p>The basic parameters for the calculations are</p><ul><li>cartographic data on the density of radionuclide contamination of the territory of the CEZ;</li> <li>classification of the territory of the CEZ according to the distributive features of forests and meadows;</li> <li>classification of CEZ forests according to taxa characteristics to estimate amount of stored fuel biomass (kg/m<sup>2</sup>);</li> <li>experimental data on the transfer of radionuclides from soil to the main components of biomass for the calculation of radionuclide inventory in fuel biomass (Bq/m<sup>2</sup>). Thus, for meadows the main fuel component is grass turf, while for forest these are litter, wood, bark and pine needles.</li> <li>experimental data on emission factors of radionuclides from fuel biomass.</li> </ul><p>Implementation of the proposed algorithm in the form of GIS application makes it possible to assess the dynamics of radionuclide emission into the atmosphere by delineation the fire areas on the CEZ map. The NASA WorldView interactive mapping web application can be used to estimate the temporal and spatial characteristics of the wildfire while it is being developed. The contouring of the area affected by fire is carried out according to the analysis of the cluster of thermal points. Also, operational contouring of wildfire can be carried out using data delivered from unmanned aerial vehicles.</p><p>The application of the proposed algorithm for the analysis of the dynamics of <sup>137</sup>Cs emissions into the atmosphere from the April 2020 wildfire showed a good agreement with the data reported by various authors who used the method of inverse simulation. Improving the accuracy of calculations according to the proposed algorithm can be done by rectifying radionuclide emission factors and taking into account fire intensity data, which in turn can affect both the radionuclide emission factor and the degree of burnout of plant biomass.</p>

The results of the study on speciation and mobility of uranium in the ore processing residues in the Centralny Yar tailings (CY, former uranium processing site -Pridneprovsky Chemical Plant in Ukraine) are presented. Due to poor neutralization sludge material was dumped into the tailings body in acidic state. Several incidents with breakage in the pipeline transporting complex radiochemical solutions caused radioactive material spillover onto the tailings surface. Two features of radiological concern were identifiedsecondary contamination of the tailings surface amid elevated gamma dose rates, and excessive migration of radionuclides of U/Th decay series in strong acidic conditions within the tailings body. The monitoring data collected during 2005-2017 showed fast migration of uranium from the tailings body into the groundwater with specific activity varied in the range from 1 to 20 Bq/L. To support this finding the experimental studies aimed to obtain physical and chemical speciation of uranium in the tailings materials in existing and simulated conditions were undertaken. This was conducted by application of modified BCR sequential extraction methods followed by assessment of uranium speciation in equilibrium conditions, using the geochemical modeling tool MEDUSA coupled with the HYDRA database.

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Purpose: Justification the possibility of safe re-use and recycling of the residues of Uranium-containing raw material processing as an element of the remediation strategy for bringing the site of the former "Prydniprovsky Chemical Plant" (PChP)to a safe state. Methods: Site specific field studies and analytical methods for determining of the radionuclides of Uranium-Thorium series, as well as useful mineral elements in the residues of Uranium production, assessment of safe management and possible options for its re-use and recycling. Results: According to the results of monitoring studies on the radionuclide and hydrochemical composition of groundwater at the PChP industrial site for the period from 2009 to 2021 year, a high content of sulfates and an increased content of uranium in groundwater under the body of the Dniprovske tailing dump, which has a phosphogypsum coating on its surface, was revealed. Phosphogypsum is considered, on the one hand, as a source of groundwater pollution, and on the other, as a potential resource for its possible reuse and processing. The results of experimental studies of the content of natural radionuclides and the elemental composition of mineral residues of ore production at the site of the former uranium ore processing plant "PChP" are also provided, as well as an safety assessment of their handling and the options of their possible processing as an element of the strategy for bringing the site to a safe state. Conclusions: The possibility and necessity of safe processing of phosphogypsum on the surface of the tailings "Dniprovske" with its simultaneous replacement by a new soil cover is proved.

Problems Statement and Purpose. The territory of the former Uranium production facility “Prydniprovsky Chemical Plant” (“PChP”) are located in Kamensky city, Dnipropetrovsk region, occupy the area of the upper and lower terraces of the Dnieper River (more than 300 hectares), where the remained legacy facilities and residues of the former uranium ore processing are located. After 1991 the production of Uranium concentrates ceased without remediated. Thus, up to 40 million tons of radioactive and chemical mineral residues of uranium production have accumulated within its industrial site and at the adjacent territories. Systemic monitoring studies began only in 2005. The studied environment characteristics were soils contamination, the tailings facilities where Uranium ore processing residues had accumulated, as well as atmospheric contamination by airborne aerosols. The purpose of this study stage is a comprehensive analysis of the spatial distribution of radionuclides of Uranium series at the legacy site territory and factors that can lead to a significant expansion of the contaminated area and scale of chronic environmental pollution under the influence of atmospheric transport and human exposure by inhalation. Data & Methods. The field sampling and analytical methods (gamma, alpha spectrometry and liquid scintillation counting methods) for determination of radionuclides of U-Th decay series were in use for this study. Soils samples from the top layers (0–5 cm) and gamma-dose rate surveys performed. A two-week continues integrated sampling data on the radioactive aerosols ambient activity concentrations and radioactive atmospheric fallout from 7-th locations at the legacy site and adjacent areas used for the environment radioactivity site-specific analyses. For determination of radionuclides in the environment samples (aerosols, soils and in the raw ore mineral residues) the low background gamma-spectrometry method with HPGe detectors have been in use. The content of metals associated with aerosols measured on filters using atomic absorption spectrometry methods. The data analysis for longterm series of observations (2005–2017) carried out using statistical methods. The compliance environment contamination analyses for the legacy site were carried comparing averaged observed data with the established safety criteria and regional background observation data. Results. The main current sources of radiation emission to the environment at the legacy site are open dispersed residues of Uranium production accumulated at the tailings facilities and at the former U‑extraction infrastructure. The spatial analyses of the gamma dose rate at the U‑production legacy site and its soil chemical contamination showed that about 30% of its territory requires decontamination. It is shown that the effects of aerosol radioactive particles dispersion from the contaminated “hot spots” at the territory such as tailings and former U‑production infrastructure are local and do not extend significantly beyond the industrial site. The greatest effects of wind re-suspension and propagation observed during the period of earthworks during construction of the U‑tailings covers and residues management at the contaminated facilities. In worst cases during earthwork at the U‑tailings facilities specific activity concentrations of 238U, 226Ra associated with aerosols (dust) nearby the tailings facilities may exceed 100 times above background radioactivity concentrations level observed at the distance about 10 km from the legacy site in the Kamyanske city. However, the air contamination with radioactive dusts in the worst meteorological conditions (dry windy period observation) did not exceed safe level of air concentrations according national radiation safety standards of Ukraine. The content of metals associated with aerosol particles can also increase by 2–10 times, but also their transfer by wind at the site is local and does not have a significant impact on residential areas of the city. Significant inhalation risks may arise during the dismantling of production equipment and buildings of former uranium production. Therefore, during implementation of any engineering remediation works, it is advisable to provide dust suppression control and to remove all dispersed materials from the former Uranium extraction before dismantling of the contaminated buildings and U‑production equipment. The introduced methods of air sampling at the PChP legacy site and low background analytical methods for radionuclide determination in the laboratories allow to recommend them for site specific environment monitoring programs bringing the radioactive contamination PChP site in a safe state