ABSTRACT Fires significantly affect the structure and diversity of vegetation. Natural recovery of vegetation after fires in the Chornobyl Exclusion Zone is of special interest because of its status as a nuclear disaster area. This is the first assessment of the potential for natural regrowth of forest and post-fire succession after the catastrophic fires of 2020 that scorched 62 000 ha of forest across the territory. Most of these areas (>80%) have high potential for natural regeneration but, in the first instance, forest species are commonly replaced by wasteland weeds, some of them invasive; 10 alien plant species were identified in the studied plots. Megafires facilitate vegetation shifts and opportunities for invasive species, especially in the early stages of succession.

Concentration-discharge relationships are widely used to understand the hydrologic processes controlling river water chemistry. We investigated how hydrological processes affect radionuclide concentrations (137Cs and 90Sr) in surface water in the headwater catchment at the Chornobyl exclusion zone in Ukraine. In flat wetland catchment, the depth of saturated soil layer changed little throughout the year, but changes in saturated soil surface area during snowmelt and immediately after rainfall affected water chemistry by changing the opportunities for contact between suface water and the soil surface. On the other hand, slope catchments with little wetlands, the water chemistry in river water is formed by changes in the contribution of "shallow water" and "deep water" due to changes in the water pathways supplied to the river. Dissolved and suspended 137Cs concentrations did not correlate with discharge rate or competitive cations, but the solid/liquid ratio of 137Cs showed a significant negative relationship with water temperature, and further studies are needed in terms of sorption/desorption reactions. 90Sr concentrations in surface water were strongly related to water pathways for each the catchments. The contact between surface water and the soil surface and the change in the contribution of shallow and deep water to stream water could changes 90Sr concentrations in surface water for in wetland and slope catchments, respectively. In this study, we revealed that the radionuclide concentrations in rivers in Chornobyl is strongly affected by the water pathways at headwater catchments.

The wildfires in the Chornobyl Exclusion Zone (ChEZ) have caused widespread public concern about the potential risk of radiation exposure from radionuclides resuspended and redistributed due to the fires in 2020. The wildfires were also confirmed in ChEZ in the spring of 2022, and its impact needed to be estimated accurately and rapidly. In this study, we developed a tuning-free burned area detection algorithm (TuFda) to perform rapid detection of burned areas for the purpose of immediate post-fire assessment. We applied TuFda to detect burned areas in the ChEZ during the spring of 2022. The size of the burned areas in February and March was estimated as 0.4 km2 and 70 km2, respectively. We also applied the algorithm to other areas outside the boundaries of the ChEZ and detected land surface changes totaling 553 km2 in northern Ukraine between February and March 2022. These changes may have occurred as a result of the Russian invasion. This study is the first to identify areas in northern Ukraine impacted by both wildfires and the Russian invasion of Ukraine in 2022. Our algorithm facilitates the rapid provision of accurate information on significant land surface changes whether caused by wildfires, military action, or any other factor.

Abstract The article presents data from the study of vegetation dynamics in the Chornobyl Exclusion Zone 30 years after the nuclear disaster and the resettlement of its local people. The 1993 prognostic data on the further development of grass and forest community groups in this area was only partially correct. The new prognosis for demutation successions reflects deviations from the linear development with a possible horizontal "shift", depending on climatic conditions, bio-ecological features of plants, as well as the impact of fires. Based on the analysis of recent data from geobotanical studies of the vegetation, the values of ecofactors that determine the course of demutation of communities were calculated. In particular, the classic course of succession is now inherent in the former settlements of the exclusion zone where the formation of forests takes place. In the old fallow lands, the previously prevailing Elytrigia repens has lost its dominant position, and has been replaced by Calamagrostis epigejos, which we associate with a certain deficiency of nitrogen compounds in the soil. The allelopathic properties of cereals inhibit the process of replacing grass communities with forest ones, which affects the course of succession. The issues of demutation of residential areas of the Exclusion Zone are considered and the sequence of changes in different habitats is described. Post-pyrogenic changes in the forest vegetation are noted and the capacity of invasive plant species to invade natural ecosystems are characterized. It is emphasized that frequent and large-scale fires cause a significant imbalance in forest ecosystems, and result in the appearance of a largenumber of alien species.

SFC is a work package in Eurad that investigates issues related to the properties of the spent nuclear fuel in the back-end of the nuclear fuel cycle. Decay heat, nuclide inventory, and fuel integrity (mechanical and otherwise), and not least the related uncertainties, are among the primary focal points of SFC. These have very significant importance for the safety and operational aspect of the back-end. One consequence is the operation economy of the back-end, where deeper understanding and quantification allow for significant optimization, meaning that significant parts of the costs can be reduced. In this paper, SFC is described, and examples of results are presented at about half-time of the work package, which will finish in 2024. The DisCo project started in 2017 and finished in November 2021 and was funded under the Horizon 2020 Euratom program. It investigated if the properties of modern fuel types, namely doped fuel, and MOX, cause any significant difference in the dissolution behavior of the fuel matrix compared with standard fuels. Spent nuclear fuel experiments were complemented with studies on model materials as well as the development of models describing the solid state, the dissolution process, and reactive transport in the near field. This research has improved the understanding of processes occurring at the interface between spent nuclear fuel and aqueous solution, such as redox reactions. Overall, the results show that from a long-term fuel matrix dissolution point of view, there is no significant difference between MOX fuel, Cr+Al-doped fuel, and standard fuels.

Ukraine has all the preconditions to increase the sugar beet yield, but, at present, comprehensive studies of spatio-temporal variation in the yield of sugar beet in the country have not been conducted. Though, such research is essential for the formation of crop management and yield forecasting in the future. The study aim is to analyze the general spatio-temporal dynamics of sugar beet yield within 10 regions of Ukraine, to identify the determinants of this trend and to characterize the areas of Ukraine regarding the sugar beet yield. Several statistical methods have been applied to the average sugar beet yields data which were provided by the State Statistics Service of Ukraine. The Akaike Information Criterion (AIC) was used to estimate the likelihood of a statistical model to the observed data. To calculate the global spatial autocorrelation coefficient, I-Moran statistics were computed using the Geoda095i program. A spatial database was created in ArcGIS 10.2. The average sugar beet yields within the study area ranged from 154.5 dt/ha to 495.7 dt/ha. The spatio-temporal trend of sugar beet yield has been described by a fourth-degree polynomial. It was determined that the overall trend of sugar beet yields is determined by agroeconomic and agro-technological factors, whose contribution to the yield variation is 72-96%. The areas where high sugar beet yields are ensured by favorable natural conditions, such as soil fertility, were identified, as well as areas with high crop yield potential provided that agricultural and breeding techniques are adequately used.

This original study aims to quantify the human factor uncertainties in radiation doses for Chernobyl cleanup workers that are associated with errors in direct or proxy personal interviews due to poor memory recall a long time after exposure. Two types of doses due to external irradiation during cleanup mission were calculated independently. First, a "reference" dose, that was calculated using the historical description of cleanup activities reported by 47 cleanup workers shortly after the completion of the cleanup mission. Second, a "current" dose that was calculated using information reported by 47 cleanup workers and respective 24 proxies (colleagues) nominated by cleanup workers during a personal interview conducted more recently, as part of this study, i.e., 25-30 years after their cleanup missions. The Jaccard similarity coefficient for reference and current doses was moderate: the arithmetic mean ± standard deviation was 0.29 ± 0.18 (median = 0.31) and 0.23 ± 0.18 (median = 0.22) for the cleanup worker's and proxy's interviews, respectively. The agreement between two doses was better if the cleanup worker was interviewed rather than his proxy: the median ratio of current to reference dose was 1.0 and 0.56 for cleanup workers and proxies, respectively. The present study has shown that human factor uncertainties lead to underestimation or overestimation of the "true" reference dose for most cleanup workers up to 3 times. In turn, the potential impact of these errors on radiation-related risk estimates should be assessed.

Although soil organisms are essential for ecosystem function, the impacts of radiation on soil biological activity at highly contaminated sites has been relatively poorly studied. In April-May 2016, we conducted the first largescale deployment of bait lamina to estimate soil organism (largely soil invertebrate) feeding activity in situ at study plots in the Chernobyl Exclusion Zone (CEZ). Across our 53 study plots, estimated weighted absorbed dose rates to soil organisms ranged from 0.7 μGy h-1 to 1753 μGy h-1. There was no significant relationship between soil organism feeding activity and estimated weighted absorbed dose rate. Soil biological activity did show significant relationships with soil moisture content, bulk density (used as a proxy for soil organic matter) and pH. At plots in the Red Forest (an area of coniferous plantation where trees died because of high radiation exposure in 1986) soil biological activity was low compared to plots elsewhere in the CEZ. It is possible that the lower biological activity observed in the Red Forest is a residual consequence of what was in effect an acute high exposure to radiation in 1986.

Despite the ubiquity of pollutants in the environment, their long‐term ecological consequences are not always clear and still poorly studied. This is the case concerning the radioactive contamination of the environment following the major nuclear accident at the Chernobyl nuclear power plant. Notwithstanding the implications of evolutionary processes on the population status, few studies concern the evolution of organisms chronically exposed to ionizing radiation in the Chernobyl exclusion zone. Here, we examined genetic markers for 19 populations of Eastern tree frog (Hyla orientalis) sampled in the Chernobyl region about thirty years after the nuclear power plant accident to investigate microevolutionary processes ongoing in local populations. Genetic diversity estimated from nuclear and mitochondrial markers showed an absence of genetic erosion and higher mitochondrial diversity in tree frogs from the Chernobyl exclusion zone compared to other European populations. Moreover, the study of haplotype network permitted us to decipher the presence of an independent recent evolutionary history of Chernobyl exclusion zone's Eastern tree frogs caused by an elevated mutation rate compared to other European populations. By fitting to our data a model of haplotype network evolution, we suspected that Eastern tree frog populations in the Chernobyl exclusion zone have a high mitochondrial mutation rate and small effective population sizes. These data suggest that Eastern tree frog populations might offset the impact of deleterious mutations because of their large clutch size, but also question the long‐term impact of ionizing radiation on the status of other species living in the Chernobyl exclusion zone.