Fraction Of Radionuclides Research Articles

Release of Cs, Sr and Rb from two high–burnup spent nuclear fuels: Effect of the dishing and the internal grain boundaries

This work presents the results of the release of Cs, Sr and Rb from two different spent nuclear fuels (BWR fuel with a burnup of 58 GWd(tU)−1 and a PWR fuel with a burnup of 63 GWd(tU)-1). Dishing effect was observable in the experiments with a 58 GWd·(tU)−1 spent fuel but not with the 63 GWd·(tU)−1 spent fuel, perhaps due to the decrease of the gap with burnup which could block the release of the radionuclides from the void between two consecutive pellets.The fitting of the SERNI model [12] to the experimental data was found to be a useful tool in order to separate the contribution of the gap and of the internal grain boundaries. Actually, it was possible to establish the fraction of the radionuclides in the internal grain boundaries: 0.8–2.0 % for Cs, 0.22–0.89 % for strontium, and 0.36–0.90 % for rubidium. The fraction of such radionuclides in the gap was calculated to be 0.39–2.58 % for Cs, 0.04–0.20 % for strontium, and 0.05–0.27 % for rubidium. In addition, the release from internal grain boundaries was found to be relatively slow (e.g. only 18 % of the caesium was found to be already released to the solution from internal grain boundaries after 200 days).

Assessing the chronic effect of the bioavailable fractions of radionuclides and heavy metals on stream microbial communities: A case study at the Rophin mining site

This study aimed to assess the potential impact of long-term chronic exposure (69 years) to naturally-occurring radionuclides (RNs) and heavy metals on microbial communities in sediment from a stream flowing through a watershed impacted by an ancient mining site (Rophin, France). Four sediment samples were collected along a radioactivity gradient (for 238U368 to 1710 Bq.Kg−1) characterized for the presence of the bioavailable fractions of radionuclides (226Ra, 210Po), and trace metal elements (Th, U, As, Pb, Cu, Zn, Fe).Results revealed that the available fraction of contaminants was significant although it varied considerably from one element to another (0 % for As and Th, 5–59 % for U). Nonetheless, microbial communities appeared significantly affected by such chronic exposure to (radio)toxicities. Several microbial functions carried by bacteria and related with carbon and nitrogen cycling have been impaired. The high values of fungal diversity and richness observed with increasing downstream contamination (H′ = 4.4 and Chao1 = 863) suggest that the community had likely shifted toward a more adapted/tolerant one as evidenced, for example, by the presence of the species Thelephora sp. and Tomentella sp. The bacterial composition was also affected by the contaminants with enrichment in Myxococcales, Acidovorax or Nostocales at the most contaminated points.Changes in microbial composition and functional structure were directly related to radionuclide and heavy metal contaminations, but also to organic matter which also significantly affected, directly or indirectly, bacterial and fungal compositions. Although it was not possible to distinguish the specific effects of RNs from heavy metals on microbial communities, it is essential to continue studies considering the available fraction of elements, which is the only one able to interact with microorganisms.

Experimental investigation of fission gas release from spent nuclear fuels under conditions expected in a deep geological repository

Abstract. In Germany, as well as several other countries (e.g. Sweden, Finland and Switzerland), the disposal of spent nuclear fuel (SNF) in deep geological formations, intertwined with a resilient multi-barrier concept, is considered to be the favourable option for the safe and profound isolation of such wastes from the biosphere. However, the intrusion of groundwater, followed by a failure of canisters and loss of cladding integrity, has to be considered in the long-term evaluation of such an underground repository. Therefore, a thorough process understanding of SNF dissolution, radionuclide source terms and alteration processes is necessary in order to evaluate the performance of SNF in the repository system. The aforementioned processes can be assigned into two steps: (i) a fast, initial release of radionuclides, located in accessible structures of the SNF upon cladding failure, and (ii) a slower, long-term release, resulting from the dissolution of the fuel matrix itself (Ewing, 2015). During the first stages of breaching of the container and the resulting contact of groundwater with the waste form, a fraction of radionuclides, located in easily accessible parts of the SNF such as grain boundaries or the pellet-cladding gap, will be released relatively quickly. This fraction is comprised of mostly volatile radionuclides, such as 79Se, 129I, 135Cs, and the fission gases Kr and Xe. Especially the release of fission gases from SNF is often correlated to the release properties of safety-relevant radioisotopes such as 129I or 135Cs and is, therefore, an indicator of their release rates. In particular, 129I shows a release behaviour similar to the fission gases. Within our contribution, we provide results regarding the release of fission gases during the dissolution process of two different types of SNF, i.e. UOX (50.4 GWd tHM-1) and mixed-oxide (MOX) (38.0 GWd tHM-1, where HM denotes heavy metals) fuels, under simulated geochemical conditions, as they are expected in a deep geological repository. Both examined fuel types were irradiated in commercial pressurised water reactors in Switzerland and Germany during the 1980s. The shown data were compiled over more than a decade during experimental campaigns performed at the Institute for Nuclear Waste Disposal at Karlsruhe Institute of Technology (KIT-INE) within the framework of several international programmes. Results obtained in our study indicate that, independent of the type of SNF, a comparable, fast initial release of fission gases is evident in all experiments. However, throughout the experiments, this prompt release slows down significantly, although a continuous release can be observed. Furthermore, the obtained data on fission gas release are compared to the release behaviour of iodine and caesium. An attempt is made to identify and qualify the role of fission gas release rates as indicator of the radionuclide source term for SNF by comparing and interpreting respective data collected over various experimental campaigns.

Method for solving atmospheric dispersion parameters of radioactive aerosols based on wind-tunnel laser measurement experiments

Certain fraction of radionuclides was inevitably discharged into the atmosphere during the normal operation of nuclear power plants. Therefore, the atmospheric dispersion of these airborne radioactive aerosols is an essential part of radiation environmental assessment during the siting, construction, and operation of nuclear power plants. Gaussian plume model is the most widely used method for this assessment. Evaluation uncertainty of this method mainly depends on the selection of atmospheric dispersion parameters. In this paper, the laser measurement method was carried out in the atmospheric wind-tunnel dispersion experiments of aerosols, and a method for solving atmospheric dispersion parameters based on high-resolution laser scattering images of plumes was proposed. Firstly, a full-frame statistical image of aerosol atmospheric plume trajectories was obtained through high-resolution laser measurement. Secondly, image processing was performed to remove noise, then to acquire light intensity of image pixels, and to make 95.45% (2σ) of the total light intensity fall within the plume trajectory to determine the plume boundary line at last. Finally, the atmospheric dispersion parameters were determined by optimal fitting, using the Gaussian plume model as a benchmark. Compared with the commonly used method for solving atmospheric dispersion parameters based on single-point densitometer detection experiments, the method based on laser measurement proposed in this work has advantages in reflecting directly realistic plume trajectory of both aerosols and particles with large sizes. This study can provide technical support for the accurate evaluation of aerosols or particles atmospheric dispersion.

The theory and practice in application of methods for investigation on radionuclide speciation in soils

The paper provides a comparison of the various techniques for investigation of radionuclide speciation in soils based on fractionation of radionuclides bonded with different soil components. The dates on speciation of environmentally signifшcant technogenic and natural radionuclides in soils contaminated from testing of nuclear weapons, accidents or incidents at radiation dangerous objects, mining and mineral products processing are presented. The review looks at inf uence of natural and anthropogenic factors on the forms of the radionuclide compounds like the radionuclide and soil properties, type of radioactive fallout and the time elapsed af er fallout on soil. It has been demonstrated that experimental details of radionuclide speciation provide the basis for estimates and projections their mobility in soils, availability for plants and development of recommendations on reducing their penetration into food chains.

Nuclear Melt Glass from Experimental Field, Semipalatinsk Test Site

Investigation of shocked materials provides unique information about behavior of substances in extreme thermodynamic conditions. Near surface nuclear tests have induced multiple transformations of affected soils. Examination of nuclear glasses and relics of entrapped minerals provides a unique database on their behavior under an intense temperature flash. In this work, several types of nuclear fallout particles from historic tests at the Semipalatinsk test site are investigated using complementary analytical methods. Distribution of radionuclides in all types of samples is highly heterogeneous; domains with high content of radionuclides are often intermixed with non-active materials. There is no general correlation between chemical composition of the glassy matrix and content of radionuclides. In aerodynamic fallout, the main fraction of radionuclides is trapped in the outer glassy shell. Relics of quartz grains are always devoid of radionuclides, while glass regions of high activity have different composition. In contrast to underground tests, iron-rich minerals are not necessarily radioactive. In most cases, the glassy matrix in anhydrous and is strongly polymerized, and the Q3 silicate groups dominate. Temperature-induced transformations of entrapped minerals are discussed. Investigation of zircon grains shows absence of a direct correlation between degree of decomposition into constituting oxides, morphology of resulting baddeleyite, and maximum experienced temperature. For the first time, temperature history of a nuclear ground glass is estimated from Zr diffusion profiles from decomposing zircon grain.

Analysis of the vertical distribution of 137Cs and 239,240Pu in waterlogged and non-boggy soils by the sequential extraction method

Mobile capabilities of 137Cs, 239,240Pu and some stable element physicochemical forms were studied in soil layers at a depth of 6–8 cm (maximum concentrations of radionuclides) of non-boggy and waterlogged soil cores sampled on the shores of Lake Bedugnis (Lithuania). Soil samples were acidic with small amount of clay (muscovite). The radionuclide activity concentrations were about 2.5 times higher in non-boggy soil. It was explained by different conditions of deposition of radioactive fallout at these sampling sites and density of the soil samples. The value of the exchangeable fraction of radionuclides is shown to be an indicator of their migration capabilities in the soil. Under anaerobic conditions in waterlogged soil (stagnant pore water conditions) and due to the presence of clay admixture, ∼90% of 137Cs was concentrated in the residual fraction and its mobility was low. 239,240Pu was concentrated mainly in organic matter with rather large exchangeable fractions (∼9.6–∼13.9%). Under oxidizing conditions in non-boggy soil (dynamic pore water conditions in the case of rain), 239,240Pu was mostly concentrated in the oxide fraction. Its exchangeable fractions were less than those in waterlogged soil and, respectively, its mobility was lower. In non-boggy soils, exchangeable fractions of 137Cs were large and varied in the range of 10.1–12.2%, which indicated its high mobility. In the case, 137Cs adsorption by clay materials was reduced and its residual fraction did not exceed 71.3%. The obtained data show that in the area of Lake Bedugnis, the migration capabilities of 137Cs and 239,240Pu change in antiphase.

Review of Instant Release Fractions of Long-lived Radionuclides in CANDU and PWR Spent Nuclear Fuels Under the Geological Disposal Conditions

Review of Instant Release Fractions of Long-lived Radionuclides in CANDU and PWR Spent Nuclear Fuels Under the Geological Disposal Conditions

Are there any pristine comets? Constraints from pebble structure

ABSTRACT We show that if comets (or any small icy planetesimals such as Kuiper belt objects) are composed of pebble piles, their internal radiogenic as well as geochemical heating results in considerably different evolutionary outcomes compared to similar past studies. We utilize a 1D thermophysical evolution code, modified to include state-of-the-art empirical measurements of pebble thermal conductivity and compression, the latter obtained through a new laboratory experiment presented here for the first time. Results indicate that due to the low pebble thermal conductivity, the peak temperatures attained during evolution are much higher than in any previous study given the same formation time. Assuming meteoritic radiogenic abundances, we find that only extremely small, sub-kilometre comets have the potential to retain the primordial, uniform, and thermally unprocessed composition from which they formed. Comets with radii in excess of about 20 km are typically swept by rapid and energetically powerful aqueous hydration reactions. Across the full range of comet sizes and formation times, evolutions result in the processing and differentiation of various volatile species, and a radially heterogeneous nucleus structure. Our computations however also indicate that the assumed fraction of radionuclides is a pivotal free parameter, because isotopic analyses of the only available cometary samples suggest that no 26Al was ever present in comet 81P/Wild 2. We show that if comets formed early in the protoplanetary disc (within 1–3 Myr), the radionuclide abundances indeed must be much smaller than those typically assumed based on meteoritic samples. We discuss the importance of our findings for the formation, present-day attributes and future research of comets.

Radiological Risk Assessment of Vehicle Transport Accidents Associated with Consumer Products Containing Naturally Occurring Radioactive Materials

Natural and artificial ionizing radiation can be harmful to human health when they come into contact with people and the environment. Transport of naturally occurring radioactive materials (NORMs) and consumer products containing NORM in the public domain is inevitable owing to their potential applications. This study evaluates the dose and risk to the public from transport accidents of NORM and consumer products. Radiological and physical data were obtained from previous literature. The median and maximum values of radioactivity concentration were applied to consumer products and NORM data, which serve as an input. An external dose rate at 1 m from a transported shipment was calculated using Microshield® Pro version 12.11 code, which serves as input to RADTRAN 6 code. Based on developed transport accident scenarios, a RADTRAN 6 code was used to estimate collective dose and risk. The sensitivity analysis was conducted by considering the variation of release, aerosol, and respirable fractions of radionuclides at 0.1%, 1%, 10%, and 100% from the transported shipment during an accident, respectively. The results of dose and risk to the general public because of the damage of the shipment container following a fire accident are below the annual regulatory limits of 1 man-Sv recommended by IAEA transport regulation of 2018. The sensitivity results of all NORMs and associated consumer products are also below the regulatory limits. Therefore, radiological safety can be ensured in the event of a transport accident involving the transit of NORM and consumer products containing NORM.

Localised solution environments drive radionuclide fractionation in uraninite

We explore the role of various solution environments – chloride brines, acid mine drainage (sulfate) and groundwater (carbonate), as well as pore pressure in producing secular disequilibrium among the various radionuclides (RN) in the U-decay series upon leaching of uraninite – the most abundant U-ore and a widespread accessory mineral in U-rich rocks. We observed that the end products of the U-decay chain, 206Pb and 207Pb, exist primarily at the surface/edges of grains or within large pores in the uraninite. In contrast, the intermediate daughters 226Ra, 210Pb, 210Po, and 234/230Th, exist primarily within the bulk of uraninite, requiring breakdown by leaching for subsequent mobility to occur. Overall, pore pressure had little effect on RN mobility, with solution environment being the primary factor in creating significant mobility and disequilibrium among the RN, as it drives the initial breakdown of uraninite and influences the subsequent differential solubility of individual RNs. This was particularly the case for carbonate-bearing fluids, leading to significant fractionation of the various daughter RN arising from variable complexation and sorption phenomena. Understanding the geochemical behaviour of the RN in the U-decay series is important for predicting and managing the risks associated with RN in both environmental (acid-mine drainage) and engineered (metallurgical extraction) processes. Effective modelling of long-term RN behaviour should incorporate this strong relative fractionation caused by contrasting geochemical behaviour of individual RN during and after their release into the water from uraninite and subsequent interaction with the surrounding aquifer host rocks.

Potential of hemp (Cannabis sativa L.) for paired phytoremediation and bioenergy production

AbstractHemp (Cannabis sativa L.) is a multi‐use crop that has been investigated for its potential use in phytoremediation of heavy metals, radionuclides, and organic contaminants, and as a feedstock for bioenergy production. A review of research literature indicates that hemp is a suitable crop for phytoremediation, and a competitive option for bioenergy. Coupling phytoremediation and bioenergy production from a single hemp crop is a potential solution to overcoming the economic constraints of phytoremediation projects. The current challenge is ensuring that the extracted contaminants are not introduced into the consumer marketplace. After several decades of limited research on hemp in the United States, the purpose of this review is to identify the knowledge available for hemp applications in phytoremediation or in production of bioenergy, and if and how those two purposes have been combined. The literature shows that hemp growth has been demonstrated successfully at the field scale for phytoremediation and in several bioenergy conversion technologies. Little is known about the fate of contaminants during hemp growth or during post‐harvest processing, especially the relationships between hemp genetics, metabolomics, and contaminant partitioning. Complicating the understanding is the expectation that contaminant fate will be dependent on the contaminant type, the concentration in the material, and the processing methods. Before hemp from phytoremediation applications can be used for bioenergy, the fractionation of heavy metals, radionuclides, and/or organic compounds during transesterification, anaerobic digestion, fermentation, and/or combustion of hemp must be evaluated.

Contribution of phases segregated from the UO2 matrix to the release of radionuclides from spent nuclear fuel and duration of the Instant Release Fraction (IRF)

During the dissolution of the spent nuclear fuel (SNF) some radionuclides are released to the solution simultaneously from different sources in the fuel. This is of particular importance to some radionuclides that contribute to the Instant Release Fraction (IRF), which govern the initial radiation dose during the dissolution of the SNF. In this work a model that is able to discriminate between the different contributions responsible for the total concentration of a radionuclide in solution was developed. The model permits to establish that uranium and radionuclides that dissolved congruently with the UO2 matrix came from two sources as a function of time: oxidized phases on the surface of the SNF including fines and the matrix itself. Other radionuclides such as Ru and Rh were released from metallic precipitates with dissolution rates lower than the matrix dissolution rate.In the case of radionuclides that were expected to contribute to the IRF, this work showed that Cs, Rb and Sr had initial release rates higher than uranium because a fraction of such radionuclides were segregated from the matrix during the irradiation. Actually it was calculated that the fraction of those radionuclides in the grain boundaries in a BWR SNF powder sample from the center part of a pellet (burnup 42 MWd/kgU) was 2.1%, 0.9%, and 0.6% for Cs, Rb, and Sr, respectively. In addition, the model permitted to calculate the duration of their contribution to the IRF, matrix dissolution governed the release of such radionuclides after 137 days, 75 days, and 164 days for Cs, Rb, and Sr, respectively (at these times, the contribution of the release from grain boundaries was lower than the 0.1%).

Environmental behaviour of radioactive particles from chernobyl

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 90Sr 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 (UO2+x) has occurred and about half of the non-oxidized chemically stable fuel particles (UO2) 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 90Sr 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-Zry-Ox) 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 90Sr activity remained as part of the non-dissolved UO2 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-Zry-Ox) 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 90Sr, 241Am 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 238Pu associated with fuel particles released during the Chernobyl accident amounted to 1.8 × 1013Bq (1.2% of the activity in the reactor) and 90Sr amounted to 2.6 × 1015Bq (1.5% of the activity in the reactor).

Investigation of the dependence of the activity concentration of natural and artificial radionuclides on particle size in surface soil

Surface soil radioactivity is being studied at NED-NTUA since almost thirty years. The last few years this research has expanded to the study of soil particle size fractionation of radionuclides. The purpose of the present work was to study the tendency of many radionuclides to accumulate in the smaller particle size fractions. To this end, soil samples were collected from an area in the NTUA Campus where 241Am contamination, due to a failed 241Am-tipped lightning rod, had been previously detected. The samples were separated into size fractions using a sieving machine and analyzed by gamma spectrometry to determine 210Pb, 241Am, 234Th, 228Ra, 228Th, 226Ra, 7Be, 137Cs and 40K. The activity concentrations of these nuclides were found to significantly differ among the size fractions examined.

Analysis of the vertical distribution and size fractionation of natural and artificial radionuclides in soils in the vicinity of hot springs

ABSTRACTLead-210 is a naturally occurring radionuclide of great importance for environmental studies. Its vertical distribution in soil combined with that of Radium–226 may provide useful information on radon exhalation from the ground, or radon carried by ground water. Previous research has shown that natural radioactivity levels–in particular Lead–210 and Radium–226 activity in the ground–may be higher near hot springs. In this work two different locations near hot springs were selected for soil sampling: Kamena Vourla and Thermopylae, both in Greece. Depending on the special soil characteristics of each sampling location, it was decided to collect soil cores up to a depth of 20 cm from Kamena Vourla, and surface soil from Thermopylae. The soil cores were then sectioned into 1 cm slices, while the surface soil samples were separated into seven particle size fractions by dry sieving. All samples were analysed by high resolution gamma-ray spectrometry at the Nuclear Engineering Department of the National Technical University of Athens, using an XtRa germanium detector and a Low Energy germanium detector, to determine: (a) the terrestrial natural radionuclides Thorium–234, Radium–226, Lead–210, Radium–228, Thorium–228 and Potassium–40, (b) the cosmogenic radionuclide Beryllium–7, and (c) the artificial radionuclides Cesium–137 and Ruthenium–106. It is worth mentioning that, the Ruthenium–106 that was detected in samples collected from both sampling locations is the result of an accidental release over Europe, apparently originated in Russia, a few days before the sampling took place. The vertical profile of the radionuclides obtained from the core sample analysis indicated a disturbance in the first 7 cm of soil, while at greater depth the concentrations for all radionuclides were as expected. Lead-210 activity was higher than that of Radium–226, showing a disruption in the radioactive equilibrium, as expected. The analysis of the size-fractionated samples showed a higher activity concentration of Lead–210 and Cesium–137 in the finer fractions. The radioactive equilibrium between Thorium–234, Radium–226, and Lead–210 was found to be significantly disturbed in all size fractions.

Consequence analysis of a transportation accident of radioactive spent resin waste from a heavy water-cooled reactor to a the Gyeongju radioactive waste disposal facility

Radiological assessments of hypothetical accidents resulting in the dispersion of radioactive material are needed to ensure the safety of the public, especially during the transport of waste to disposal facilities. Therefore, a radiological impact assessment was conducted, assessing a hypothetical accident near the Wolsong receiving area during the transportation of radioactive spent resin waste from a heavy water-cooled reactor to the Gyeongju disposal facility. The HotSpot Health Physics code was used in this case study. It Because of the variability in transportation conditions, eight accident scenarios were considered based on waste type (cement solidification and dry spent resin), waste activity (low and intermediate level waste), and accident severity (1% or 10% radionuclide release). From the results, the form of the radioactive waste was the most important factor in determining the total effective dose equivalent (TEDE), because the aerosol fractions of dispersed radionuclides differed among the radioactive waste forms. Among the scenarios, the 10% release fraction and radioactive waste of dry spent resin scenario resulted in the highest TEDE of 1.4E-3 Sv within 10 min of exposure at a distance of 0.03 km, which was higher than the 1E-3 Sv/year dose limit for the public. A radiological impact assessment of spent resin waste transportation for the public was completed based on the specific scenarios.

Estimation of Radioactivity Caused by Chemical Fertilizers on Trakya Sub-Region Soils and Its Potential Risk on Ecosystem

Exposure to terrestrial radioactivity depends primarily on geological conditions and soil types. Phosphate, nitrogen and potassium fertilizers, which are used predominantly in order to increase crops in agriculture, provide basic nutrients to plants. Radionuclides in phosphate fertilizer belonging to 232 Th and 238 U from phosphate rocks series as well as radioisotope of potassium ( 40 K) are the major contributors of outdoor terrestrial natural radiation. The plants take some fractions of radioactivity and radionuclides enter the food chain in this way. Trakya sub-region, located in northwestern Turkey, constitutes one of the significant agricultural centers, 65% of this area is used for agricultural purposes. This is the region which uses the most fertilizer per unit area, with an average of 145 kg per hectare and approximately 20% of the fertilizer consumed in Turkey is used in the region. The main objective of this study is to evaluate Trakya Sub-region from the point of potential environmental effects of radionuclides which may be caused by phosphate fertilizers used in agricultural areas. For this purpose, it is aimed to determine the priority areas for the monitoring studies by analyzing the results of the use of temporal and spatial fertilizers and the studies performed in the region. Keywords: Radioactivity, chemical fertilizers, Trakya Sub-region, soil

Environmental assessment of risks associated with the Ordovician Dictyonema shale in the eastern part of the Baltic Klint

The results of research considered in this article made it possible to expand the understanding of the environmental risks associated with the highly radioactive bituminous argillites of the Baltic Sea region. The natural patterns of the distribution of natural radionuclides 226Ra, 232Th and 40K are established along the strike and thickness of layers. The average value of the effective specific activity (ESA) for all samples in the Koporka River valley amounted 1270 Bq/kg. The minimum value of ESA was 650 Bq/kg (the closest to the seam roof level), and the maximum value was 3750 Bq/kg (the second from the seam floor level). Conversion to mass fractions of natural radionuclides (NRN) showed that the average content of uranium in the sample amounted up to 90.7 g/t, thorium up to 11.4 g/t and of potassium up to 4.1%. The high heterogeneity of the content distribution of NRN along the strike of the Dictyonema shale seam was confirmed by studies of separate outcrops of highly radioactive rocks along the banks of the Tosna River. In general, the level of the argillites radioactivity has abnormally high value and exceeds the natural background more than ten times. The average annual values of the effective dose amounted from 5,8 to 10,7 mSv/year, that should be classified as the territories of emergency ecological danger and zones of ecological disaster.

Importance of coccolithophore‐associated organic biopolymers for fractionating particle‐reactive radionuclides (234Th, 233Pa, 210Pb, 210Po, and 7Be) in the ocean

AbstractLaboratory incubation experiments using the coccolithophore Emiliania huxleyi were conducted in the presence of 234Th, 233Pa, 210Pb, 210Po, and 7Be to differentiate radionuclide uptake to the CaCO3 coccosphere from coccolithophore‐associated biopolymers. The coccosphere (biogenic calcite exterior and its associated biopolymers), extracellular (nonattached and attached exopolymeric substances), and intracellular (sodium‐dodecyl‐sulfate extractable and Fe‐Mn‐associated metabolites) fractions were obtained by sequentially extraction after E. huxleyi reached its stationary growth phase. Radionuclide partitioning and the composition of different organic compound classes, including proteins, total carbohydrates (TCHO), and uronic acids (URA), were assessed. 210Po was closely associated with the more hydrophobic biopolymers (high protein/TCHO ratio, e.g., in attached exopolymeric substances), while 234Th and 233Pa showed similar partitioning behavior with most activity being distributed in URA‐enriched, nonattached exopolymeric substances and intracellular biopolymers. 234Th and 233Pa were nearly undetectable in the coccosphere, with a minor abundance of organic components in the associated biopolymers. These findings provide solid evidence that biogenic calcite is not the actual main carrier phase for Th and Pa isotopes in the ocean. In contrast, both 210Pb and 7Be were found to be mostly concentrated in the CaCO3 coccosphere, likely substituting for Ca2+ during coccolith formation. Our results demonstrate that even small cells (E. huxleyi) can play an important role in the scavenging and fractionation of radionuclides. Furthermore, the distinct partitioning behavior of radionuclides in diatoms (previous studies) and coccolithophores (present study) explains the difference in the scavenging of radionuclides between diatom‐ and coccolithophore‐dominated marine environments.