Mechanism of resuspension of radiocesium in summer and autumn

Atmosphere, 2022

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The Analyst, 1998

When radioactive particles are released into the environment, information on the size distribution pattern, radionuclide and matrix composition, morphology and structure is essential for assessing weathering and the subsequent mobilisation and biological uptake of associated radionuclides. The particle characteristics will depend on the source in question in addition to the release scenario, dispersion processes and deposition conditions. Following high temperature accident scenarios associated with nuclear installations (e.g., Chernobyl accident) a range of different uranium fuel particles and condensed particles were observed, varying in composition, morphology and structure (e.g., crystalline and amorphous phases). Following low temperature releases (e.g., prefire Winscale releases), flake-like uranium fuel particles significantly different from those collected at Chernobyl were identified. Furthermore, a major fraction of radionuclides in effluents from reactors and reprocessing plant during normal operations are associated with particles and colloids. Hence the presence of radioactive particles or colloids in releases from nuclear sources occurs more frequently than usually expected. After deposition, weathering of particles occurs and associated radionuclides are mobilised with time. Hence the transfer of mobilised radionuclides within the ecosystem will be delayed until weathering takes place, and the assessment of short term consequences of releases may be overestimated if particles are present. The weathering rate will depend on the particle composition (e.g., UO 2 fuel), structural changes occurring during the event (e.g., transformation from UO 2 to U 3 O 8) and chemical conditions after deposition (e.g., pH, redox). Unless the impact of particle weathering is taken into account, assessment of mobilisation, transfer and long-term consequences of radionuclide releases may be underestimated. In order to improve the predicting power of transport models, ecosystem transfer models and dose assessment models, experimental information is required with respect to source term radionuclide speciation and in particular the association of radionuclides with particles and colloids, influencing mobility and biological uptake. This work was therefore focused on analytical techniques applicable to the fractionation, identification and characterisation of radioactive particles and colloids (e.g., hollow fibre fractionation, electron microscopic techniques and reactivity studies) released from a source and deposited in the environment. Results from research carried out during several years at the authors' laboratory are presented to illustrate the usefulness of the techniques.

Science of The Total Environment, 1997

Dynamics of the 13'Cs content in the components of the forests in the 30-km zone around the Chernobyl nuclear power plant (NPP) in 1986-1994 are associated mainly with such factors as the size of radioactive particles in the fallout, ecosystem humidification and soil type, tree age. The influence of particle size was especially noticable between 1986--1987 and was displayed by low biological availability of radionuclides in the near part of the zone (within the IO-km radius circle around the NPP) in comparison with more distant regions (within the 30-km radius circle). Later. the expression of this influence decreased and transfer factor (the ratio of i3'Cs content in overground phytomass to the soil contamination density) became approximately the same for all plots with similar ecological and fallout characteristics. Humidity of landscape and soil type determined the velocity of radionuclide vertical migration in the soil and '37Cs biological availability. These parameters were maximum for the hydromorphic soils of wet landscapes enriched in organic substance and poor clayey minerals. Differences of '37Cs accumulation in overground phytomass of trees caused by tree age are displayed in the higher '37Cs concentration in structural parts of young trees as compared with old ones. Copyright 0 1997 Elsevier Science B.V.

Research Square (Research Square), 2021

The deposition of insoluble radiocesium bearing microparticles (CsMPs), which were released from the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident in March 2011, has resulted in the widespread contamination of eastern Japan. Obviously, these deposited insoluble CsMPs may become the secondary contamination sources by atmospheric migration or other environmental transferring process, however, the understanding of the transport mechanism remains non-elucidation, and the relevant evidence has not been directly provided. This study, for the rst time, provides the direct evidence for the resuspension of these insoluble CsMPs to the atmosphere from 1) proximity of 137 Cs radioactivity and resemblance of the morphology and the elemental compositions of CsMPs in the samples of soil and aerosol derived from the same sampling site, 2) the special characteristics of the resuspended CsMPs of which the ratios of Na/Si, K/Si and/or Cs/Si were smaller than those from the initially released CsMPs collected at either long distance or near F1NPP, which can be ascribed to the slowly natural corrosion of CsMPs by the loss of the small amount of soluble contents in CsMPs and 3) high CsMPs concentration of 10 granules/gram in the surface soil of our sampling site and the observed resuspension of surface soil dust at wind gust speed higher than 4 m s-1. Speci cally, fteen single CsMPs were successfully isolated from the aerosol lters collected by unmanned high-volume air samplers at a severely polluted area in Fukushima Prefecture, about 25 km away from F1NPP, from January 2015 to September 2019. The mean diameter of these CsMPs was 1.8 ± 0.5 μm, and the average 137 Cs radioactivity was 0.35 ± 0.23 Bq/granule. The contribution rate of the resuspended CsMPs to the atmospheric radiocesium was estimated from the ratio of 137 Cs radioactivity of a single CsMP to that of the aerosol lter to be of 23.9 ± 15.3%. There has been no considerable decreasing trend in the annual CsMP resuspension frequency. 1. Introduction 1.1. Accident The Fukushima Daiichi Nuclear Power Plant (F1NPP) accident was triggered by the 9.0-magnitude Tohoku-Oki earthquake and the subsequent tsunami on March 11, 2011, 1, 2 which resulted in the complete loss of all power and over-pressurization of Units 1-3 (there are 6 Units in F1NPP and Units 4-6 had been "shut down" for regular maintenance prior to the earthquake 3). Over the subsequent several days, although venting operations

Journal of Environmental Radioactivity, 2019

Long-term environmental behaviour of radioactive particles released during the Chernobyl accident and deposited in sandy topsoil in Ivankiv district of Kyiv Region (Ukraine), in radioactive trench waste materials from the Red forest, and in bottom sediments from the Cooling pond has been assessed. The efficiency of the models describing the dissolution/weathering rates of U fuel particles developed 15-20 years ago was tested, and their predictions for the dynamics of remobilization, mobility and plants uptake of 90 Sr were confirmed. It was found that at present in the topsoil and in radioactive trench waste material, total dissolution of fuel particles of low chemical stability (UO 2+x) has occurred and about half of the non-oxidized chemically stable fuel particles (UO 2) has also dissolved, indicating radiological stabilization of the environment and that the mobile fraction of radionuclides would be reduced in the future. The biological availability of 90 Sr in topsoil due to fuel particles dissolution has reached maximum values and further decrease is expected. The presence of chemically extra-stable fuel particles (U-Zr y-O x) in environments should be taken into account when the total radionuclides activity concentrations are assessed during radioactive materials management. It was shown that nearly half of the 90 Sr activity remained as part of the non-dissolved UO 2 fuel particles at the time of the study. Taking into consideration that 31 ± 4% of the radionuclide activities were still associated with non-dissolved chemically extra-stable particles (U-Zr y-O x) in radioactive trench waste materials from the Red forest, increased dissolution should not be expected in the near future. The physico-chemical form of radionuclides in air exposed sediments from the Cooling pond were determined, and results showed that about 70-80% of total 90 Sr, 241 Am and plutonium isotopes activity were associated with U fuel particles. The low dissolution rate of radionuclides from the pond sediments is attributed to prolonged slightly alkaline pH in the medium due to zebra mussel residues. According to new data, the emission value of 238 Pu associated with fuel particles released during the Chernobyl accident amounted to 1.8 × 10 13 Bq (1.2% of the activity in the reactor) and 90 Sr amounted to 2.6 × 10 15 Bq (1.5% of the activity in the reactor).

Environmental Science & Technology, 2013

Analysis of 137 Cs trapped in biomass in highly contaminated zones is crucial in predicting the long-term fate of 137 Cs following the explosion at the Fukushima Daiichi Nuclear Power Plant. We surveyed forest 20−50 km from the plant in July and September 2011 to evaluate 137 Cs trapped in biomass within 20 km of the plant. We determined the ambient dose rate and collected forest soils and twigs at 150 sampling points. Removability from the canopy was evaluated by washing leaves and branches with water and organic solvents. The biomass of the forest canopy was then calculated. 137 Cs fallout was simulated with an atmospheric transport model. The modeled dose rate agreed with observations (n = 24) (r = 0.62; p < 0.01). Washing experiments demonstrated that unremovable portions accounted for 53.9 ± 6.4% of 137 Cs trapped by deciduous canopy (n = 4) and 59.3 ± 13.8% of 137 Cs trapped by evergreen canopy (n = 10). In total, it was estimated that 74.5 × 10 12 Bq was trapped by canopy in the forest within the no-go zone, with 44.2 × 10 12 Bq allocated to unremovable portions, and that 0.86% of the total release was trapped in biomass as of September 2011.

Scientific Reports, 2020

it is the conventional understanding that rain removes aerosols from the atmosphere. However, the question of whether rain plays a role in releasing aerosols to the atmosphere has recently been posed by several researchers. in the present study, we show additional evidence for rain-induced aerosol emissions in a forest environment: the occurrence of radiocaesium-bearing aerosols in a Japanese forest due to rain. We carried out general radioactive aerosol observations in a typical mountainous village area within the exclusion zone in fukushima prefecture to determine the impacts and major drivers of the resuspension of radiocaesium originating from the nuclear accident in March 2011. We also conducted sampling according to the weather (with and without rain conditions) in a forest to clarify the sources of atmospheric radiocaesium in the polluted forest. We found that rain induces an increase in radiocaesium in the air in forests. With further investigations, we confirmed that the fungal spore sources of resuspended radiocaesium seemed to differ between rainy weather and nonrainy weather. Larger fungal particles (possibly macroconidia) are emitted during rainy conditions than during nonrainy weather, suggesting that splash generation by rain droplets is the major mechanism of the suspension of radiocaesium-bearing mould-like fungi. The present findings indicate that radiocaesium could be used as a tracer in such research fields as forest ecology, meteorology, climatology, public health and agriculture, in which fungal spores have significance. We found a novel rain-related mechanism of bioecological resuspension of radiocaesium in a contaminated area in Japan. The research background is described below. It is widely known that atmospheric aerosols are removed by rain (wet removal, including in-cloud and below-cloud scavenging). However, in recent atmospheric studies, several examples of atmospheric aerosol releases supposedly related to rain have been reported 1-8. The existence of odours known as petricor 9 and geosmin 10 , which occur with the start of rain or with light rain, has been acknowledged for a long time, but their formation mechanism was revealed very recently 3,7,8. In these cases, the suspension flux from the surface overwhelms the deposition flux of the aerosols in question in the near-surface air layer. The underlying mechanisms include (1) microbubbles bursting inside raindrops upon contact with the Earth's dried porous surface 3,7 , (2) active fungal spore dispersion due to high humidity (e.g., ref. 2,4), and (3) aerosol bursts caused by the splashing of raindrops (e.g. ref. 11). Details of these phenomena are given in the Discussion section. Through such mechanisms, soil organics, fungal spores, bacteria and their fragments/contents

GEOCHEMICAL JOURNAL, 2012

that the power plant released approximately 3.5 × 10 16 Bq of 137 Cs following the accident. Radionuclides from the power plant were dispersed in the air and ocean and deposited on land . 134 Cs and 137 Cs were transported from the power plant to Taiwan (up to ~1.5 × 10 -13 Bq/m 3 in aerosol samples; Huh et al., 2011), and airborne radionuclides were detected in Europe from . reported that approximately 22% of the 137 Cs emitted from the power plant was deposited in Japan in March 2011. The Japanese Government reported the radionuclide activity concentrations in soils (0-5 cm depth) collected from Fukushima and southern Miyagi Prefecture (within a 100-km radius of the power plant) following the accident (MEXT, 2011a). On April 28, 2011, relatively high 134 Cs and 137 Cs activity concentrations (up to 8800 and 9400 Bq/kg, respectively;

Environmental Science &amp; Technology, 2015

The Fukushima nuclear accident (March 11, 2011) caused the widespread contamination of Japan by direct deposition of airborne radionuclides. Analysis of weekly air filters has revealed sporadic releases of radionuclides long after the Fukushima Daiichi reactors were stabilized. One major discharge was observed in August 2013 in monitoring stations north of the Fukushima Daiichi nuclear power plant (FDNPP). During this event, an air monitoring station in this previously scarcely contaminated area suddenly reported 137 Cs activity levels that were 30-fold above the background. Together with atmospheric dispersion and deposition simulation, radionuclide analysis in soil indicated that debris removal operations conducted on the FDNPP site on August 19, 2013 are likely to be responsible for this late release of radionuclides. One soil sample in the center of the simulated plume exhibited a high 90 Sr contamination (78 ± 8 Bq kg −1) as well as a high 90 Sr/ 137 Cs ratio (0.04); both phenomena have usually been observed only in very close vicinity around the FDNPP. We estimate that through the resuspension of highly contaminated particles in the course of these earthmoving operations, gross 137 Cs activity of ca. 2.8 × 10 11 Bq has been released.

Environmental Science & Technology, 2013

Segregation and radioactive analysis of aerosols according to their aerodynamic size were performed in France, Austria, the Czech Republic, Poland, Germany, and Greece after the arrival of contaminated air masses following the nuclear accident at the Fukushima Dai-ichi nuclear power plant in March 2011. On the whole and regardless of the location, the highest activity levels correspond either to the finest particle fraction or to the upper size class. Regarding anthropogenic radionuclides, the activity median aerodynamic diameter (AMAD) ranged between 0.25 and 0.71 μm for 137 Cs, from 0.17 to 0.69 μm for 134 Cs, and from 0.30 to 0.53 μm for 131 I, thus in the "accumulation mode" of the ambient aerosol (0.1−1 μm). AMAD obtained for the naturally occurring radionuclides 7 Be and 210 Pb ranged from 0.20 to 0.53 μm and 0.29 to 0.52 μm, respectively. Regarding spatial variations, AMADs did not show large differences from place to place compared with what was observed concerning bulk airborne levels registered on the European scale. When air masses arrived in Europe, AMADs for 131 I were about half those for cesium isotopes. Higher AMAD for cesium probably results from higher AMAD observed at the early stage of the accident in Japan. Lower AMAD for 131 I can be explained by the adsorption of gaseous iodine on particles of all sizes met during transport, especially for small particles. Additionally, weathering conditions (rain) encountered during transport and in Europe in March and April contributed to the equilibrium of the gaseous to total 131 I ratio. AMAD slightly increased with time for 131 I whereas a clear decreasing trend was observed with the AMADs for 137 Cs and 134 Cs. On average, the associated geometric standard deviation (GSD) appeared to be higher for iodine than for cesium isotopes. These statements also bear out a gaseous 131 I transfer on ambient particles of a broad size range during transport. Highest weighted activity levels were found on the 0.49−0.95 μm and on the 0.18−0.36 μm size ranges in France and in Poland, respectively. The contribution from resuspension of old deposited 137 Cs was assessed for the coarse particle fractions only for the first sampling week.