Radioactive Particles Research Articles

Cold ion energization at separatrices during magnetic reconnection

Separatrices of magnetic reconnection host intense perpendicular Hall electric fields. The fields are produced by the decoupling of the ion and electron components and are associated with the in-plane electrostatic potential drop between the inflow and outflow regions. The width of these structures is typically less than the ion inertial length, which is small enough to demagnetize ions as they cross the layer. We investigate ion acceleration at separatrices by means of 2D particle-in-cell simulations of magnetic reconnection for two limiting cases: (1) a “GEM-like” setup (here GEM stands for geospace environmental modeling reconnection challenge) with the lobe ion thermal velocity equal to the thermal velocity of the initial current sheet ions, which is comparable to the Alfvén velocity and (2) a “cold” ion setup, in which the temperature of the background lobe ions is 1/100 of the initial current sheet temperature. The separatrix Hall electric field is balanced by the ion inertia term in the cold background simulations. The effect is indicative of the quasi-steady local perpendicular acceleration. The electric field introduces a cross field beam of unmagnetized particles, which makes the ion distribution function strongly non-gyrotropic and susceptible to sub-ion scale instabilities. This acceleration mechanism nearly vanishes in the hot ion background simulations. Our particle-in-cell simulations are complemented by one-dimensional test particle calculations. They show that the hot ion particles experience energy-scattering after crossing the accelerating layer, whereas cold ions are uniformly energized up to the energies comparable to the electrostatic potential drop between the inflow and outflow regions.

Direct measurement of thermophoretic and photophoretic force acting on hot micromotors with optical tweezers

Synthetic microparticles present exciting features owing to their customizable light-matter interaction. We hereby report on the optical trapping of two artificial plasmonic microparticles: one with isotropic nanoparticles covering the surface (homogeneous particle) used as a hot Brownian particle and an anisotropic Janus microparticle, half coated with a gold nano-layer. The homogeneous particle decorated with plasmonic nanoparticles on the surface displays features of hot Brownian dynamics as well as photophoretic motion along z dimension in the optical trap. A dielectric particle was used as a reference particle because it acts as a cold particle with only the gradient force affecting it. In general, Janus particles orient in the trap with the dielectric part in the trap center. Plasmonic gold nanostructures absorb the light energy and produce heat; the photothermal forces significantly affect the optical trapping. These hot microspheres display temperature and Janus orientation dependent position distribution significantly different from cold (purely dielectric) microparticles. The developed method allows for the first time direct determination of the photophoretic (thermal force along light propagation direction) and thermophoretic force (light propagation direction independent force) acting on the respective particles, which opens new paths for analysis and control of micromachines.

Analysis of radioactive cesium-enriched particles and measurement of their distribution in marine sediment near Fukushima Daiichi nuclear power plant

ABSTRACT Cesium-enriched particles released from the Fukushima Daiich Nuclear Power Plant (NPP1) exist in the Fukushima coastal waters and offshore, and they possibly affect the wide-area distribution of the radioactive cesium measured by the towed spectrometer. Therefore, the distribution of them in marine sediment was measured near NPP1 in November, 2016. We scanned the seafloor using a remotely operated vehicle (ROV) equipped with a NaI(Tl) scintillation detector. The sediment samples were obtained on the survey line by the ROV’s suction-type sampler. Five cesium particles, with diameters of approximately 400 m, were isolated from the samples. The radioactivity of was less than 360 Bq, and no nuclides other than , , and natural radioactive ones were found from gamma-ray spectroscopy. In the particles, titanium and calcium were commonly detected by energy-dispersive X-ray spectrometry. We also estimated the particles’ presence from the change in the total counting rate of the scintillation detector. The average particle density is found to be 3.45 m at most. The average increase in the counting rate directly above the cesium-enriched particles in the sediment was less than double. Therefore, the effect of such particles on the distribution of radioactive cesium is limited.

Design and off-design performance comparison of supercritical carbon dioxide Brayton cycles for particle-based high temperature concentrating solar power plants

Concentrated solar power (CSP) plants using dense particle suspension as heat transfer fluid and particles as the storage medium are considered as a promising solution to provide the high temperature required for the supercritical carbon dioxide (S-CO2) Brayton cycle. During plant operation, variations in the heat transfer fluid temperature and ambient temperature would significantly affect system performance. Determining the suitable S-CO2 Brayton cycle configuration for this particle-based CSP plant requires accurate prediction and comprehensive comparison on the system performance both at design and off-design conditions. This study presents a common methodology to homogeneously assess the plant performance for six 10 MW S-CO2 Brayton cycles (i.e. simple regeneration, recompression, precompression, intercooling, partial cooling and split expansion) integrated with a hot particles thermal energy storage and a dry cooling system. This methodology includes both design and off-design detailed models based on the characteristic curves of all components. The optimal design for each thermodynamic cycle has been determined under the same boundary design constrains by a genetic algorithm. Then, their off-design performances have been quantitatively compared under varying particle inlet temperature and ambient temperature, in terms of cycle efficiency, net power output and specific work. Results show that the variation in ambient temperature contributes to a greater influence on the cycle off-design performance than typical variations of the heat transfer fluid temperature. Cycles with higher complexity have larger performance deterioration when the ambient temperature increases, though they could present higher peak efficiency and specific work at design-point. In particular, the cycle with maximum efficiency or specific work presents significant changes in different ranges of ambient temperature. This means that for the selection of the best configuration, the typical off-design operation conditions should be considered as well. For integrating with high-temperature CSP plants and dry cooling systems, the simple regeneration and the recompression cycles are the most suitable S-CO2 Brayton cycle configurations due to their fewer performance degradations at ambient temperatures above 30 °C, which is a frequent environmental condition in sunny areas of the world.

New highly radioactive particles derived from Fukushima Daiichi Reactor Unit 1: Properties and environmental impacts

A contaminated zone elongated toward Futaba Town, north-northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains highly radioactive particles released from reactor Unit 1. There are uncertainties associated with the physio-chemical properties and environmental impacts of these particles. In this study, 31 radioactive particles were isolated from surface soils collected 3.9 km north-northwest of the FDNPP. Two of these particles have the highest particle-associated 134+137Cs activity ever reported for Fukushima (6.1 × 105 and 2.5 × 106 Bq per particle after decay-correction to March 2011). The new, highly-radioactive particle labeled FTB1 is an aggregate of flaky silicate nanoparticles with an amorphous structure containing ~0.8 wt% Cs, occasionally associated with SiO2 and TiO2 inclusions. FTB1 likely originates from the reactor building, which was damaged by a H2 explosion, after adsorbing volatilized Cs. The 134+137Cs activity in the other highly radioactive particle labeled FTB26 exceeded 106 Bq. FTB26 has a glassy carbon core and a surface that is embedded with numerous micro-particles: Pb–Sn alloy, fibrous Al-silicate, Ca-carbonate or hydroxide, and quartz. The isotopic signatures of the micro-particles indicate neutron capture by B, Cs volatilization, and adsorption of natural Ba. The composition of the micro-particles on FTB26 reflects the composition of airborne particles at the moment of the H2 explosion. Owing to their large size, the health effects of the highly radioactive particles are likely limited to external radiation during static contact with skin; the highly radioactive particles are thus expected to have negligible health impacts for humans. By investigating the mobility of the highly radioactive particles, we can better understand how the radiation dose transfers through environments impacted by Unit 1. The highly radioactive particles also provide insights into the atmospheric conditions at the time of the Unit 1 explosion and the physio-chemical phenomena that occurred during reactor meltdown.

Experimental research and numerical simulation of gel fuel ignition by a hot particle

The research investigates interdependent physical and chemical processes, occurring when a typical gel fuel is ignited by a hot particle. In the conducted experiments, high-speed video recording made it possible to establish the consistent patterns and characteristics of the ignition of gel fuel, based on an organic polymer thickener, by a disc-shaped steel particle 5 mm in radius and height. The fuel ignition delay times are 0.5–2.5 s when the initial temperature of the steel particle is varied from 1230 to 1500 K. A mathematical model of the investigated process was developed using experimental data obtained. It describes the interdependent processes of conductive heating and melting of gel fuel, melt evaporation, cooldown of the particle and its gradual immersion in the near-surface layer of the fuel, formation of a combustible gas–vapor mixture around the local heating source and its ignition under the conditions of diffusion-convective heat and mass transfer. The numerical simulation results are in good agreement with the experimental data. The developed mathematical model can be used in practice to predict the characteristics of gel fuel ignition by hot particles, when a group of factors in the particle – fuel – air system is varied in wide ranges.

Measurement of the gross alpha activity of the fine fractions of road dust and near-roadway ambient particle matter

ABSTRACT Traffic-related air pollution, including direct exhaust emissions and road dust (RD), impacts individuals living near busy roads. We recently conducted a study to investigate the sources and composition of tailpipe and non-tailpipe traffic emissions, where we collected and analyzed samples of ambient air fine particulate matter (PM2.5) and fine RD (RD2.5) at different distances from major roadways. We analyzed a subset of the samples, including those collected at the roadside and local background, for their alpha activity level. Subsequently, we investigated whether there is a distance-related decay in the alpha activity in RD2.5 or PM2.5 similar to those observed for traffic-related species in PM2.5 and RD2.5. We found that the alpha activity of ambient air PM2.5 (Bq/mg) was more than an order of magnitude higher than the activity level of the corresponding RD2.5 sample, suggesting that PM2.5 may be more toxic than RD2.5. Using mixed-effects regression models, we found that ambient PM2.5 alpha activity was significantly higher during the cold months than during warm months, and that the background was higher than the roadside (though not significantly). In contrast, the RD2.5 alpha activity was significantly higher at the background site compared to the roadside but was not significantly affected by season. In addition to sampling position, both Zn and elemental carbon (EC) were significant predictors of RD2.5 alpha activity. In addition, the roadside RD2.5 activity levels were found to be higher at highways as compared to secondary roads. While traffic-related emissions do not appear to be significant sources of either ambient PM2.5 or RD2.5 alpha activity, the RD2.5 results suggest that traffic-related particles may contribute to RD2.5 alpha-activity. Implications: Many studies have reported the effects of traffic-related particulate matter (PM) on human health, and there is growing interest in the health effects of exposure to environmental PM alpha activity. This is the first study to report on the alpha activity of road dust (RD) or near-roadway ambient PM. We found that the alpha activity of ambient PM is twenty times higher than RD, suggesting that ambient PM may be more toxic. In PM and RD, the alpha activities were higher at background sites than at the roadside, indicating that traffic-related emissions are not a significant source of particulate radioactivity.

Rheological and Microbiological Characteristics of Hops and Hot Trub Particles Formed during Beer Production.

During the production of beer, and especially beer wort, the main wastes are spent grain and hot trub, i.e., the so-called “hot break.” Combined with yeast after fermentation, they represent the most valuable wastes. Hot trub is also one of the most valuable by-products. Studies on the chemical composition of these sediments and their rheological properties as waste products will contribute to their effective disposal and even further use as valuable pharmaceutical and cosmetic raw materials. So far, hot trub has been studied for morphology and particle distribution depending on the raw material composition and beer wort extract. However, there are no preliminary studies on the rheological properties of hot trub and hops. In particular, no attention has yet been paid to the dependence of these properties on the hop variety or different protein sources used. The aim of this study was to examine the effect of different hopping methods on hot trub viscosity and beer wort physicochemical parameters. Additionally, the hop solutions were measured at different temperatures. A microbiological analysis of hop sediments was also performed to determine the post-process survival of selected microorganisms in these wastes. For manufacturers of pumps used in the brewing industry, the most convenient material is that of the lowest viscosity. Low viscosity hot trub can be removed at lower velocities, which reduces costs and simplifies washing and transport. The sediments also had similar equilibrium viscosity values at high shear rates.

Simulation study of radionuclide atmospheric transport after wildland fires in the Chernobyl Exclusion Zone in April 2020

This paper presents model results for the dispersion of radionuclides released into the atmosphere by intense forest fires in the Chernobyl Exclusion Zone in April 2020. The 137Cs activity concentration in the surface air is calculated on a regional scale (in Ukraine) and a local scale (within the Chernobyl Exclusion Zone). The 137Cs activity in the surface air of Kyiv was found to have reached 2–4 mBq m−3 during the period April 4–20. The results presented in this paper are generally consistent with measured data pertaining to radioactive contamination in Kyiv and areas around several nuclear power plants in Ukraine. The total effective dose to the population of Kyiv during the fire period was estimated to be 5.7 nSv from external exposure and the inhalation of 137Cs and 90Sr, rising to 30 nSv by the end of 2020. This is about 0.003% of the annual permissible level of exposure of the population. A committed effective dose of about 16 nSv was estimated for the personnel of the Chernobyl nuclear power plant from the inhalation of 137Cs and 90Sr during the 2020 forest fires. A method for estimating the radionuclide activity emissions during wildland fires in radioactively contaminated areas is proposed. This method is based on satellite measurement data of the fire radiative power, the radionuclide inventory in the fire area, and an emission factor for radioactive particles.

Bench testing of noninvasive ventilation masks with viral filters for the protection from inhalation of infectious respirable particles

During the beginning of the SARS-CoV-2 pandemic, there was a shortage of masks and respirators for the protection of health care professionals. Masks for noninvasive ventilation (NIV) in combination with viral-proof filters, worn by healthcare workers, could serve as an alternative protection measure. We determined the simulated protection factor (SPF) of such devices in comparison to conventional surgical masks, N95, and FFP3 respirators. Masks and respirators were mounted on a ventilated mannequin head in a test-chamber. Isotonic saline containing 150 MBq 99mTC-DTPA (99mTc-diethylenetriamine pentaacetate (DTPA) was nebulized inside the box. The aerosol had a mass median aerodynamic diameter of 0.6 ± 0.4 µm. SPFs were measured using radioactive DTPA particles in the mannequin test system by calculating the ratio of unfiltered particles (Pu) and filtered particles (Pf) for each tested device (SPF = Pu/Pf). Simulated protection factors were 15.6 ± 3.6 for a ResMed AcuCare mask plus filter, 3.5 ± 0.2 for a ResMed Mirage Quattro FX mask plus filter, 9.5 ± 0.8 for a Loewenstein JOYCEclinc FF mask plus filter, 1.9 ± 0.2 for a surgical mask with a rubber band, 2.7 ± 0.7 for a surgical mask with ribbons, 2.3 ± 0.3 for an FFP3 respirator, and 3.6 ± 1.3 for an N95 respirator. The ResMed AcuCare and the Loewenstein JOYCEclinic FF mask were more effective than any other of the tested devices (p < 0.001). In conclusion, masks normally used for NIV with viral-proof filters can effectively filter respirable particles.

Gas-solid mixing and heat transfer performance in alternating spout deflection

Spout deflection has long been regarded as a threat to efficient gas-solid interactions in spout fluidised beds, as it may break the stable symmetrical particle circulation in the spout-fluidisation flow pattern. In this paper, the so-called alternating spout deflection (ASD) is evaluated and compared with the spout-fluidisation (SF) flow pattern in terms of gas-solid hydrodynamics, mixing and heat transfer performance at particle scale by means of a Computer Fluid Dynamic-Discrete Element Method (CFD-DEM) model. The comparisons show in the SF over ~40% particles are in a densely packed state, whereas in the ASD the proportion of particles in a packing state is less than 20%; Then their mixing performance are compared using the improved Lacy index, indicating that the mixing speed and final state of the mixing process are similar. Further, the two patterns are compared in terms of heat transfer. It is indicated that in the ASD flow pattern, the mean particle temperature drops quicker; moreover, the homogeneity of the heat transfer is also better in terms of mean square error of particle temperature, compared to the SF. The underlying mechanism is also explored: in the ASD the hot particle cores can be mitigated due to the spout incoherence phenomena, which is however unavoidable in the SF. This paper corrects the negative view that the alternating spout deflection is not as effective as the spout-fluidisation pattern in terms of gas-solid mixing and heat transfer performance.

A novel radioactive particle tracking algorithm based on deep rectifier neural network

Radioactive particle tracking (RPT) is a minimally invasive nuclear technique that tracks a radioactive particle inside a volume of interest by means of a mathematical location algorithm. During the past decades, many algorithms have been developed including ones based on artificial intelligence techniques. In this study, RPT technique is applied in a simulated test section that employs a simplified mixer filled with concrete, six scintillator detectors and a137Cs radioactive particle emitting gamma rays of 662 keV. The test section was developed using MCNPX code, which is a mathematical code based on Monte Carlo simulation, and 3516 different radioactive particle positions (x,y,z) were simulated. Novelty of this paper is the use of a location algorithm based on a deep learning model, more specifically a 6-layers deep rectifier neural network (DRNN), in which hyperparameters were defined using a Bayesian optimization method. DRNN is a type of deep feedforward neural network that substitutes the usual sigmoid based activation functions, traditionally used in vanilla Multilayer Perceptron Networks, for rectified activation functions. Results show the great accuracy of the DRNN in a RPT tracking system. Root mean squared error for x, y and coordinates of the radioactive particle is, respectively, 0.03064, 0.02523 and 0.07653.

Microparticles with diverse sizes and morphologies from mechanical and laser cutting of fuel debris simulants and geopolymer as a covering material

ABSTRACT During the decommissioning of Fukushima Daiichi nuclear power plant, the dismantling of massive fuel debris is important for the defueling process. The production and dispersion of radioactive microparticles highly depends on the cutting technique implemented. Previous studies have been conducted on the development of cutting techniques and the treatment of radioactive particles generation during the cutting process. Besides, adequate understanding of the microparticle products during the cuttings of fuel debris is of vital necessity. Nowadays, geopolymer application is proposed as a covering material during the fuel debris retrieval in order to keep the structural integrity of damaged components. In this study, the microparticle products during mechanical and laser cutting of fuel debris simulants (Hafnium oxide and Tungsten(IV) oxide pellets) and geopolymer material were investigated. The cuttings have been carried out for samples of the simulants, geopolymer, and simulants with geopolymer covering. The generated particles were collected and investigated by laser diffraction particle size analyzer and Scanning Electron Microscope with X-ray spectrometry. Particles with diverse sizes and morphologies were observed from the products of each sample. It also appears that particles with unique sizes and morphologies can generate from the laser cuttings due to the thermal effect of laser cutting.

Monte Carlo Simulation Study of Hot-Particle Detection in Voluminous Samples by Gamma Spectrometry

In this work, we addressed the inhomogeneity problem in gamma spectrometry caused by hot particles, which are dispersed into environment from large nuclear reactor accidents such as at Chernobyl and Fukushima. Using Monte Carlo simulation, we have determined the response of a gamma spectrometer to individual and grouped hot particles randomly distributed in a soil matrix of 1-L and 0.6-L sample containers. By exploring the fact that the peak-to-total ratio of efficiencies in gamma spectrometry is an empirical parameter, we derived and verified a power-law relationship between the peak efficiency and peak-to-total ratio. This enabled creation of a novel calibration model which was demonstrated to reduce the bias range and bias standard deviation, caused by measuring hot particles, by several times, as compared with the homogeneous calibration. The new model is independent of the number, location, and distribution of hot particles in the samples. In this work, we demonstrated successful performance of the model for a single-peak 137Cs radionuclide. An extension to multi-peak radionuclide was also derived.

Gamma Spectrometry of Inhomogeneous Samples Using Peak-Ratio Method

In gamma spectrometry of voluminous samples, inhomogeneous distribution of radioactivity caused by the presence of hot particles can create significant Bias in the results of activity determinations. We developed a novel method to reduce this Bias using the gamma-peak ratio. We show that the peak area ratio of two gamma peaks of different energies, emitted by the same radionuclide, is a sensitive measure of emitting source location and thus the inhomogeneity. A new calibration formula was then derived for true gamma efficiency pi as a function of efficiency ratio pi/pj of two peaks. This approach was verified by Monte Carlo simulations for a sample of 1-L volume containing from 1 up to 2048 of hot particles randomly distributed in a soil matrix. A 152Eu radionuclide was selected for calculations and we used various combinations of two gamma spectral peaks selected from three gamma energies of 121.8, 344.3, and 1408.0 keV. This new method is shown to reduce the Bias range and Bias standard deviation by several times when compared with the traditional homogeneous calibration applied to measuring hot particles. The method is independent of the number, location, and distribution of hot particles in the samples, and can be applied to a mixture of radionuclides. It complements our previous calibration model based on the peak-to-total ratio.

До сплеску активності 137Cs в повітрі під об’єктом «Арка» 17 жовтня 2019 р.

The construction of a New Safe Confinement (NSC) is one of the main stages in the transformation of the Chornobyl nuclear power plant 4th power unit into an ecologically safe system. On the one hand, this system is designed to ensure the safety of personnel, the population and the environment, on the other — to allow safe work with the remnants of the unit. At the same time, the project allows quite high levels of bulk activity of radioactive aerosols inside the NSC — up to 210 Bq/m3 for total β-activity. The sharp increase in the volumetric air activity, observed on October 17–19, 2019 in a number of rooms of the Shelter object and in the space under the “Arch” object in the absence of a burst of activity outside these objects, can be considered as a successful kind of spontaneous test of the NSC isolation systems. The chronology of the dynamics of volume activity according to the act of official investigation of the precedent is given. The results of studies of aerosol filters exposed in the near zone of the Chornobyl NPP before and after the burst of activity in the air under the “Arсh” object are presented. Autoradiograms of fragments of these filters demonstrate a significant (≈2 orders of magnitude) increase in the number of hot particles immediately after the fall of the concrete fragment of the floor in the room 402/3. The analysis of features of the hot particles after the collapse indicates a significant contribution to the total activity of a large number of low-activity particles (0.005÷5 Bq), and the low 137Cs/241Am ratio that indicates their fuel nature. Based on the assumption about the fuel nature of hot particles, their minimum possible aerodynamic diameters were calculated, which are in the range 2.91&lt;d&lt;36.7 μm, which does not exclude the presence of smaller hot particles on the filter that are not visible using this method. The contribution of particles with aerodynamic diameters less than 10 μm, determined using the impactor, did not exceed 20% of the total beta activity of the aerosol.

Experimental investigation and optimization on machined surface of Si3N4 ceramic using hot SiC abrasive in HAJM

Abstract Machining of advance engineering ceramic materials are extremely demanded in present day precision industries as it has a wide and potential application in various fields i.e. automobile, aerospace and biomedical engineering. Silicon nitride ceramics (Si3N4) are difficult to machine in conventional machining methods. Hot abrasive jet machining (HAJMing) is a state-of-art technology which practically facilitates the machining in all the engineering materials. This experimental research deals with the investigation on optimization of process parameters of HAJMing of Si3N4 with hot SiC abrasive particles. The surface roughness, overcut and flaring diameter were studied against the HAJMing process parameters, namely, compressed air pressure, nozzle-tip- distance and abrasive temperature. Contribution of these constraints on outcomes was determined by analysis of variance. Also, Regression models were obtained for all the outcomes. CFD simulation for material erosion mechanism of HAJMing was used to obtain the nature of produced workpiece surface profile. Moreover, microstructures of HAJMed surface s were analyzed using scanning electron microscopic images. The outcomes of RSM data validated through experimentation and RSM predictive model. In addition, a multi-objective optimization problem has been employed based on empirical model objective functions and solved by multii objective genetic algorithm (GA). The RSM with GA was used to find out the optimum machining constraint value for an exact HAJMing condition in Si3N4 ceramic materials.

Tethered tracer in a mixture of hot and cold Brownian particles: can activity pacify fluctuations?

We study how an interacting mixture of components with differing levels of activity can affect the fluctuations of an embedded object such as a tracer. In particular, we consider a simple model of a tracer that is harmonically bound within a mixture of hot and cold Brownian particles, which, like a mixture of active and passive particles, can phase separate. By measuring the fluctuations of the tracer, we find that this collective behavior gives rise to an effective temperature for the tracer. Additionally, we find that there is an increased tendency for cold particles to accumulate on the surface of the tracer due to the hot particles, potentially dampening its fluctuations and decreasing its effective temperature. These results suggest that the phase separation of a mixture of hot/cold or active/passive particles may have strong effects on the fluctuations of an embedded object. We discuss potential implications of these results for experiments on fluctuations of nuclear envelope affected by the activity in the chromatin.

Оцінка внеску пилової бурі 16 квітня 2020 р. в радіоактивне забруднення атмосфери в період лісових пожеж у зоні відчуження Чорнобильської АЕС

On April 16, 2020, a strong dust storm was observed in the northern regions of Ukraine, which coincided with the period of intense wildland fires in the Chornobyl exclusion zone. The activity of 137Cs in aerosol particles released into the atmosphere as a result of resuspension from burned areas in the meadow biocenoses in the exclusion zone is evaluated in the article. Resuspension of radioactively contaminated particles from burned areas formed after fires in meadow biocenoses of the exclusion zone can be a powerful source of air contamination in the zone itself, as well as increase of the radionuclides transport outside it. The total 137Cs activity that entered the atmosphere during the dust storm was estimated to be about 162 GBq, i. e. up to 20% of the total activity emitted in the air during the entire period of forest fires on April 3–20, 2020. The 137Cs emission from burned areas during the dust storm on April 16 and 17 amounted to 0.24% of the total stock of 137Cs activity in this territory. According to the results of modeling, the relative contribution of wildland fires and resuspension due to the dust storm on April 16 and 17 significantly depends on the distance to the emission sources. It was found that the resuspension of radioactive particles from burned areas during the dust storm determined 80–95% of the 137Cs activity concentration in the surface air near Chornobyl nuclear power plant and in Chornobyl city and the rest was due to the continuing forest fires in neighboring territories. The maximum 3-hour averaged value of the 137Cs activity concentration in the air due to resuspension from the burned areas was obtained for the location of the monitoring post VRP-750 of SSE “Ecocenter” to be about 28 mBq/m3 for the period 9–12 hours on April 16. In Kyiv, the 3-hour averaged 137Cs activity concentration due to the dust storm in the Exclusion Zone was calculated as 44 μBq/m3 in the period from 9 to 12 hours on April 17, 2020. This value was only about 4% of the total 137Cs activity in the air in this period.

Propagation Analysis of Pu Radionuclides as a Result of Fire Incidents in the Exclusion Zone of the Chernobyl NPP in April 2020

In consequence of nuclear accidents that have occurred in various parts of the world, radioactive contamination of the environment is observed. The risks of spreading pollution can increase during floods, fires and some natural disasters. The lack of effective measures that aimed at eliminating possible sources of fire in the meadow zone and forest lands in the Chernobyl exclusion zone (ChEZ) leads to a high risk of fire emergence. The temporal and spatial distribution of fires shows that they occur throughout the ChEZ, including in the most contaminated areas. The risk of fires increases with climate change and measures to prevent them should be considered in emergency programs. ChEZ area is contaminated with long-lived radionuclides such as 137Cs, 90Sr, Pu isotopes (238Pu, 239 + 240Pu, 241Pu) and 241Am. As a result of forest fires radionuclides contained in wood and underlying surface are carried out into the atmosphere along with smoke. Diseases arising under the influence of ionizing radiation from Pu and 241Am isotopes pose a serious problem for human health. To assess of the spatial distribution of Pu isotopes and 241Am we used data on forest fires that occurred in the Chernobyl zone in April 2020. To evaluatе the dynamics of the release of radioactive substances into the atmosphere during fire incidents on the ChEZ territory, the following software products were used: NASA WorldView, HYSPLIT program. The HYSPLIT program allows to reconstruct the trajectories of radionuclide propagation in the atmosphere using meteorological data and to obtain a reliable picture of the distribution of radionuclides in the study area. The maps of the volumetric activity of Pu isotopes in the air and the fallout on the soil as a result of fires were obtained. It was found that the radioactivity due to the presence of this element in the air and during the fallout of radioactive particles on the soil is low (it reaches 1.0E-7...0.1 Bq/m3 in the air, 1.0E-6...1 Bq/m2 on the soil). The analysis of the propagation of Pu isotopes as a result of the movement of air masses in the places of fires in the exclusion zone of the Chernobyl nuclear power plant and the associated dangers for the population and the environment has been carried out.