[en] The assessment of the fluctuating asymmetry based on measurement of the parameters of left and right parts of silver birch (Betula pendula (L.) Roth.) leaves and relative sizes of pairs of Scots pine (Pinus sylvestris L.) needles from the Chernobyl Exclusion Zone (ChEZ) was carried out. Twelve samples of both birch leaves and pairs of needles were collected from 10 trees at 5 sites in the Chernobyl Exclusion Zone and also at one control site located outside the ChEZ. Values of gamma dose rate in the air varied between the sites from 0.1 to 40 μGy h^-1. Activity concentrations of ⁹⁰Sr and ¹³⁷Cs in the birch leaves varied over the range of 0.9÷2460 kBq kg^-1 and 0.1÷339 kBq·kg^-1 (DW), respectively. In addition to the above, in the Scots pine needles, these ranges were 0.7 ÷1970 kBq kg^-1f for ⁹⁰Sr and 0.1÷78 kBq kg^-1 (DW) for ¹³⁷Cs. From the values of the radionuclides activity concentrations in the plants, the internal dose rate is estimated to be in the range of 0.1 ÷ 274 μGy h^-1. The main sources of the internal dose rate were radiation of ⁹⁰Sr and ⁹⁰Y. Indices of fluctuating asymmetry of silver birch leaves and Scots pine needles varied over the range of 0.048 ± 0.007 ÷ 0.060 ± 0.009 and 0.014 ± 0.002 ÷ 0.018 ± 0.002, respectively, and did not statistically differ for all experimental sites. The indices also did not depend on the external or internal dose rate of ionizing radiation for plants. The above findings seem to be consistent with other research effort in terms of understanding the response of organisms to chronic pollutant exposure and the long-term effects of large scale nuclear accidents. (authors)

[en] The effects of radiation on radial growth of Scots pine (Pinus sylvestris L.) affected by the Chernobyl accident were studied at five sites with different deposition levels. The study sites were chosen along a high gradient of depositions at the distance of a few hundred meters in the forests with similar forest characteristics. Air dose rates varied at the sites from the background values up to 30 μGy h^-1 as of December 1, 2016. Scots pine trees exposed to sub-lethal doses of 8.6–13.2 Gy at the “Red Forest” site did not demonstrate deviations in formation of annual rings 30 years after the Chernobyl accident compared to trees with lower doses and control trees. Variation with time in annual rings thickness did reveal that the effect of radiation in trees growing at the sites with different contamination not detectable in 1986 and 1987. Conversely, the effects were clear observed in a later period in 1989–1991, i.e. 3–5 years after the accident. Until 2000, there were statistically significant differences in the annual rings growth rates of Scots pine trees exposed to external absorbed dose rates of 4.4–6.7 mGy h^-1 as estimated for June 1, 1986 (or 19.5–30.0 μGy h^-1 as of December 1, 2016) compared with the trees of the other sites studied. The results comply with the conclusions from research with acute pine exposure conducted in the Kyshtym area in 1975–1984.

[en] A series of different nuclear sources associated with the nuclear weapon and fuel cycles have contributed to the release of radioactive particles to the environment. Following nuclear weapon tests, safety tests, conventional destruction of weapons, reactor explosions and fires, a major fraction of released refractory radionuclides such as uranium (U) and plutonium (Pu) were present as entities ranging from sub microns to fragments. Furthermore, radioactive particles and colloids have been released from reprocessing facilities and civil reactors, from radioactive waste dumped at sea, and from NORM sites. Thus, whenever refractory radionuclides are released to the environment following nuclear events, radioactive particles should be expected. Results from many years of research have shown that particle characteristics such as elemental composition depend on the source, while characteristics such as particle size distribution, structure, and oxidation state influencing ecosystem transfer depend also on the release scenarios. When radioactive particles are deposited in the environment, weathering processes occur and associated radionuclides are subsequently mobilized, changing the apparent Kd. Thus, particles retained in soils or sediments are unevenly distributed, and dissolution of radionuclides from particles may be partial. For areas affected by particle contamination, the inventories can therefore be underestimated, and impact and risk assessments may suffer from unacceptable large uncertainties if radioactive particles are ignored. To integrate radioactive particles into environmental impact assessments, key challenges include the linking of particle characteristics to specific sources, to ecosystem transfer, and to uptake and retention in biological systems. To elucidate these issues, the EC-funded COMET and RATE projects and the IAEA Coordinated Research Program on particles have revisited selected contaminated sites and archive samples. This COMET position paper summarizes new knowledge on key sources that have contributed to particle releases, including particle characteristics based on advanced techniques, with emphasis on particle weathering processes as well as on heterogeneities in biological samples to evaluate potential uptake and retention of radioactive particles.

[en] The novel approach for optimising soil sampling strategies in areas affected by radionuclides is suggested. Major factors influencing the efficiency of soil sampling strategies, including (number of samples, sampling area size, sampling depth and spatial resolution of the sample sites are examined to provide optimisation of the soil sampling plan. The experimental field studies to validate the suggested approach were performed in 25 sampling units ranging from 1.2 x 1.2 m to 60 x 60 m size. The sampling units were selected on arable farmlands, natural meadow and former agricultural land), as well as coniferous and deciduous forests with contamination density of ¹³⁷Cs ranging from 2.8 kBq-m^-2 to 24.5 MBq-m^-2. The studied areas were contaminated by both the global fallout and the Chernobyl radioactive particles of different types. To determine the values of standard deviation of the log of the soil contamination density of ¹³⁷Cs, 25 to 256 soil samples were collected with an increment of 0.07-10 m within each sampling unit. It was found that the values of standard deviation of the log of the soil contamination density of ¹³⁷Cs were not dependent on the mean contamination density, the type of radioactive deposition and the landscape features. The mean value of standard deviation calculated for all sites studied was estimated as 0.44 ± 0.15 and 0.30 ± 0.10 for the sampling area 0.001 m² (∅37 mm) and 0.005 m² (∅80 mm) at the relative measurement uncertainties lower than 10% (CI = 95%). Concentrations of ¹³⁷Cs in the soil samples were statistically independent when sampling points were situated at a distance larger than 1 m one from each other. A simple method was developed for assessing minimum sample sizes required for estimation of the median or the geometric mean of radionuclide soil contamination with a relative uncertainty set by the user. The approach was also suggested for estimation of the uncertainty of soil contamination for the case of composite samples. The approach was implemented in the Ukrainian national requirements for assessment of quality of the soil.

[en] Possibility of the economical utilization of forests in the radioactive contaminated areas depends on compliance of the radionuclide activity concentrations in wood with the hygiene norms or national standards that are established by the governments or regulators. Since such regulations consider wood as a whole, development of the sampling methods for assessment of compliance of wood to the norms or standards requires the adequate addressing the issues related to heterogeneity of the radionuclide distributions within the three trunks. In this paper we present spatial distributions of the ⁹⁰Sr and ¹³⁷ Cs activity concentrations in the trunk wood of mature Scots pine (Piluts sylvestris L.) trees in the Chernobyl exclusion zone in the late stage (30 years) after the deposition. Four 52- 53 year old model trees were sampled in the forest stand located in approximately 5 km from the accidental nuclear reactor. The radionuclide concentrations were measured in 156 wood samples collected from the wood disks cut off the trees trunks at the set of heights. To address variability of the tree sizes and radionuclide concentrations between the individual trees, we applied the corresponding relative indices enabling identification of the general patterns of the spatial distributions of ⁹⁰Sr and ¹³⁷Cs. We demonstrated significant differences in bioavailability and distribution trends between the studied radionuclides. ¹³⁷Cs is translocated to the younger parts of the trees trunk, while the ⁹⁰Sr concentrations are higher in heartwood and in senescing tissues, which is explained by the different chemical properties of Cs and Sr and by different physiological roles played in plant development by their chemical analogs and major plant nutrition elements, Ca and K respectively. In this reason, the principal distribution patterns of the studied radionuclides in the trunk wood do not significantly change with time, and the results of om study generally are in good agreement with those obtained in the earlier stage after the deposition. The above trends are clearly expressed in both radial and longitudinal directions and result in systematic deviations of the concentrations estimated based on core sampling from the average concentrations in the whole tree trunk. (authors)

[en] This paper examines the distributions of several anthropogenic radionuclides (^239+240Pu, ²⁴¹Am, ¹³⁷Cs, ⁹⁰Sr, ⁶⁰Co and ³H) at a legacy trench disposal site in eastern Australia. We compare the results to previously published data for Pu and tritium at the site. Plutonium has previously been shown to reach the surface by a bath-tubbing mechanism, following filling of the former trenches with water during intense rainfall events. This has led to some movement of Pu away from the trenched area, and we also provide evidence of elevated Pu concentrations in shallow subsurface layers above the trenched area. The distribution of ²⁴¹Am is similar to Pu, and this is attributed to the similar chemistry of these actinides and the likely in-situ generation of ²⁴¹Am from its parent ²⁴¹Pu. Concentrations of ¹³⁷Cs are mostly low in surface soils immediately above the trenches. However, similar to the actinides, there is evidence of elevated ¹³⁷Cs and ⁹⁰Sr concentrations in shallow subsurface layers above the trenched area. While the subsurface radionuclide peaks suggest a mechanism of subsurface transport, their interpretation is complicated by the presence of soil layers added following disposals and during the subsequent years. The distribution of ⁹⁰Sr and ¹³⁷Cs at the ground surface shows some elevated levels immediately above the trenches which were filled during the final 24 months of disposal operations. This is in agreement with disposal records, which indicate that greater amounts of fission products were disposed in this period. The surface distribution of ^239+240Pu is also consistent with the disposal documents. Although there is extensive evidence of a mobile tritium plume in groundwater, migration of the other radionuclides by this pathway is limited. The data highlight the importance of taking into account multiple pathways for the mobilisation of key radioactive contaminants at legacy waste trench sites. (author)

[en] There are two different ways to model reactive transport: ad hoc and innovative reaction-based approaches. The former, such as the Kd simplification of adsorption, has been widely employed by practitioners, while the latter has been mainly used in scientific communities for elucidating mechanisms of biogeochemical transport processes. It is believed that innovative mechanistic-based models could serve as protocols for environmental remediation as well. This paper reviews the development of a mechanistically coupled fluid flow, thermal transport, hydrologic transport, and reactive biogeochemical model and example-applications to environmental remediation problems. Theoretical bases are sufficiently described. Four example problems previously carried out are used to demonstrate how numerical experimentation can be used to evaluate the feasibility of different remediation approaches. The first one involved the application of a 56-species uranium tailing problem to the Melton Branch Subwatershed at Oak Ridge National Laboratory (ORNL) using the parallel version of the model. Simulations were made to demonstrate the potential mobilization of uranium and other chelating agents in the proposed waste disposal site. The second problem simulated laboratory-scale system to investigate the role of natural attenuation in potential off-site migration of uranium from uranium mill tailings after restoration. It showed inadequacy of using a single Kd even for a homogeneous medium. The third example simulated laboratory experiments involving extremely high concentrations of uranium, technetium, aluminum, nitrate, and toxic metals (e.g.,Ni, Cr, Co). The fourth example modeled microbially-mediated immobilization of uranium in an unconfined aquifer using acetate amendment in a field-scale experiment. The purposes of these modeling studies were to simulate various mechanisms of mobilization and immobilization of radioactive wastes and to illustrate how to apply reactive transport models for environmental remediation. The second problem simulated laboratory-scale system to investigate the role of natural attenuation in potential off-site migration of uranium from uranium mill tailings after restoration. It showed inadequacy of using a single Kd even for a homogeneous medium

[en] After performing a first multi-model exercise in 2015 a comprehensive and technically more demanding atmospheric transport modelling challenge was organized in 2016. Release data were provided by the Australian Nuclear Science and Technology Organization radiopharmaceutical facility in Sydney (Australia) for a one month period. Measured samples for the same time frame were gathered from six International Monitoring System stations in the Southern Hemisphere with distances to the source ranging between 680 (Melbourne) and about 17,000 km (Tristan da Cunha). Participants were prompted to work with unit emissions in pre-defined emission intervals (daily, half-daily, 3-hourly and hourly emission segment lengths) and in order to perform a blind test actual emission values were not provided to them. Despite the quite different settings of the two atmospheric transport modelling challenges there is common evidence that for long-range atmospheric transport using temporally highly resolved emissions and highly space-resolved meteorological input fields has no significant advantage compared to using lower resolved ones. As well an uncertainty of up to 20% in the daily stack emission data turns out to be acceptable for the purpose of a study like this. Model performance at individual stations is quite diverse depending largely on successfully capturing boundary layer processes. No single model-meteorology combination performs best for all stations. Moreover, the stations statistics do not depend on the distance between the source and the individual stations. Finally, it became more evident how future exercises need to be designed. Set-up parameters like the meteorological driver or the output grid resolution should be pre-scribed in order to enhance diversity as well as comparability among model runs.

[en] Highlights: • Radiation emergency medical staff were surveyed about the risk perception. • It was agreed that low dose radiation exposure does not pose any health risks. • Staff with a higher level of knowledge were less concerned about radiation risks. Radiation emergency medical (REM) staff respond to many types of disasters such as radiological and nuclear accidents as well as environmental radioactivity exposure. The objective of this study was to evaluate the risk perception of REM staff on radiation exposure in various situations and to analyze the factors that affect their risk perception. A questionnaire was given to 284 REM staff affiliated with various organizations, including nuclear power generation, nuclear fuel manufacturing, large-scale irradiation, and radiation-waste disposal facilities, as well as research and development institutions. To determine the substantially influential factors for risk perception, we analyzed the questionnaire responses using ordinal logistic regression, Kruskal-Wallis, and Spearman correlation analyses. It was generally perceived by REM staff that low-dose radiation exposure in daily life and work environments does not pose any health risks. A higher level of radiation knowledge was tightly associated with a lower risk perception of REM staff on extremely low-dose (several mSv) radiation exposure, thus exhibiting an inverse correlation. In contrast to radiation researchers, the work experience of REM staff was not a contributing factor to their risk perception. In our study, REM staff with a high level of radiation knowledge did not have any health concerns in their work environments. Efforts to enhance the radiation knowledge of REM staff through proper education and training would result in analytical risk evaluation, which may also improve their willingness to help meet surge capacity needs in large-scale radiological events.

[en] Highlights: • An online monitoring system was developed to evaluate air activation in proton accelerators. • Monte Carlo simulation was performed to provide proportion of O-15, N-13 and C-11. • Gamma spectrum was directly measured and radionuclides activity were calculated according to the process of air flow and radionuclides decay. • Radiation safety of staff and the public from activated air was evaluated. During the operation of high-energy proton accelerators, the air in the tunnel is activated with the production of radionuclides. For CSNS (China Spallation Neutron Source), the first pulsed neutron source in China for multidisciplinary research, an online air activation monitoring system was developed to evaluate the radiation safety of the staff and the public, which consisted of a NaI detector, Pb shielding, an MB container and a control system. With the monitoring system, gamma spectra of the activated air from controlled areas are measured, and the activity concentration and immersion dose rates of radionuclides in air are calculated and displayed in real time. The system has been in stable operation since February 2020, and results have been obtained for the evaluation of the radiation risk from activated air.