Exchange Of Radionuclides Research Articles

Symkanych О.І., Коkhan О.P., Glukh О.S., Krch K.L., Lytvyn О.V., Svatiuk N.І., Butsyak І.V. MONITORING OF RADIONUCLIDE MIGRATION IN THE BOTTOM SEDIMENTS OF THE TISA BILA RIVER' SOURCE

The regularities of distribution, migration, and accumulation of natural gamma-active nuclides 40K, uranium 238U (214Pb, 214Bi), and thorium 232Th (212Pb, 212Bi, 228Ac, 208Tl) series, as well as man-made 137Cs in the sediments of the tributary of the Tysa River (Bila Tysa), have been established. It is shown that the total content of the studied radionuclides in the bottom sediments along the entire length of the Tysa River differs slightly and is proportional to the level of its siltation. And this largely depends on many factors, in particular - the intensity of radionuclide exchange processes between soil and water, the water content in the soil, organic substances, and the morphological features of the river. Fluctuations of the total specific activity of natural gamma-active radionuclides (excluding 40K) in sediments within the range of 195.5-293.9 Bq/kg were established. The highest content of these isotopes was determined at the confluence of the White and Black Tisza. Mapping of the studied territories according to the content of 40K and 137Cs has show that the area of accumulation of gamma-active nuclides is concentrated in the lower part of the river (the point of confluence of the White and Black Tisza), and the probable causes of this phenomenon were substantiated. The analysis of the degree of connection between the content of radionuclides (238U and 232Th, 40K and 137Cs series) and the territorial factor showed that for the majority of GAN there is a zonal distribution - in the bottom sediments of the river source.
 Keywords: radionuclides; gamma-active nuclides; radioecological monitoring; bottom deposits; migration; accumulation; Cs/K content; Tysa river.

Some considerations on the dependence to numerical schemes of Lagrangian radionuclide transport models for the aquatic environment

Lagrangian models present several advantages over Eulerian models to simulate the transport of radionuclides in the aquatic environment in emergency situations. A radionuclide release is simulated as a number of particles whose trajectories are calculated along time and thus these models do not require a spatial discretization (although it is always required in time). In this paper we investigate the dependence of a Lagrangian model output with the grid spacing which is used to calculate concentrations from the final distribution of particles, with the number of particles in the simulation and with the interpolation schemes which are required because of the discrete nature of the water circulation data used to feed the model. Also, a Lagrangian model may describe the exchanges of radionuclides between phases (liquid and solid), which is done in terms of transition probabilities. The dependence of these probabilities with time step is analyzed as well. It was found that the optimum grid size used to calculate concentrations should be carefully checked, and that temporal interpolation is more significant than spatial interpolation to obtain a more accurate solution. A method to estimate the number of particles required to have a certain accuracy level is proposed. Finally, it was found that for low sediment concentrations and small radionuclide kd, exact equations for the transition probabilities should be used; and that phase transitions introduce a stability condition as in Eulerian models.

Comparative Evaluation of Radiochemical and Biological Properties of 131I- and [99mTc]Tc(CO)3-Labeled RGD Analogues Planned to Interact with the αvβ3 Integrin Expressed in Glioblastoma.

Radiolabeled peptides with high specificity for overexpressed receptors in tumor cells hold great promise for diagnostic and therapeutic applications. In this work, we aimed at comparing the radiolabeling efficiency and biological properties of two different RGD analogs: GRGDYV and GRGDHV, labeled with iodine-131 (131I) and technetium-99m-tricarbonyl complex [99mTc][Tc(CO)3]+. Additionally, we evaluated their interaction with the αvβ3 integrin molecule, overexpressed in a wide variety of tumors, including glioblastoma. Both peptides were chemically synthesized, purified and radiolabeled with 131I and [99mTc][Tc(CO)3]+ using the chloramine-T and tricarbonyl methodologies, respectively. The stability, binding to serum proteins and partition coefficient were evaluated for both radioconjugates. In addition, the binding and internalization of radiopeptides to rat C6 glioblastoma cells and rat brain homogenates from normal animals and a glioblastoma-induced model were assessed. Finally, ex vivo biodistribution studies were carried out. Radiochemical yields between 95–98% were reached for both peptides under optimized radiolabeling conditions. Both peptides were stable for up to 24 h in saline solution and in human serum. In addition, the radiopeptides have hydrophilic characteristics and a percentage of binding to serum proteins around 35% and 50% for the [131I]I-GRGDYV and [99mTc]Tc(CO)3-GRGDHV fragments, respectively. Radiopeptides showed the capacity of binding and internalization both in cell culture (C6) and rat brain homogenates. Biodistribution studies corroborated the results obtained with brain homogenates and confirmed the different binding characteristics due to the exchange of radionuclides and the presence of the tricarbonyl complex. Thereby, the results showed that both radiopeptides might be considered for future clinical applications.

Models for predicting the transport of radionuclides in the Red Sea

Two radionuclide transport models for the Red Sea are described: a Lagrangian model to deal with emergency situations and a Eulerian model better suited to longer term simulations, as for instance required in case of chronic radionuclide releases. Baroclinic circulation is obtained for both transport models from HYCOM ocean model. The Lagrangian model also includes tides, which are obtained from a standard tidal model customized to the Red Sea, and currents induced by local winds. Both models describe exchanges of radionuclides between water and sediments. A number of simulations were carried out to illustrate capabilities of the models. Additionally, flushing times over the Red Sea were evaluated with the Eulerian model, as another example of model use.

Regional specificity of radionuclide fixation in river basins due to soil petrology and mineralogy

The main goal of this research was to compare and reveal the difference in the character of Cs-137 distribution and fixation in fine fractions of alluvial soils formed by the rivers draining areas of different geochemical origin with the corresponding mineral composition of clay fraction and to discuss the results in light of possible ecological perspectives. Alluvial soil samples were collected in the Yenisey (Central Siberia) and Iput (the East European Plain) river basin areas contaminated by 137Cs. Granulometric fine fractions (>0.01, 0.01–0.005, 0.005–0.001, <0,001 mm) were obtained by pipette technique; clay minerals were determined by a universal Carl-Zeiss Jena X-ray diffractometer (Germany); and 137Cs activity was measured by a CANBERRA gamma spectrometer with HPGe detector (USA). Clay mineralogy demonstrated regional specificity of its composition due to different origins of the soil-forming rocks. Clay fraction of alluvial soil samples collected in the Yenisey river floodplain consists mainly of chlorite-vermiculite and chlorite-smectite interstratifications while in the Iput river basin it is mainly composed of hydromicas and mica-smectite interstratifications. We infer that this may result in a higher potential ability of clay fraction for the radionuclide exchange and release in the former region. Specificity of local clay minerals as radionuclide sorbents should be of particular ecological concern in relation to long-term exchange processes and involvement of the radioisotope in local biogeochemical cycles including its transfer to food chains. The phenomenon is considered in light of the developed scientific field inaugurated as petro-mineralogical ecology and needs further investigation.

Luminescence dating and associated analyses in transition landscapes of the Alto Ribatejo, central Portugal

Artefacts and regolith (soils, sediments, colluvia, etc.) from passage tombs, pit fills, stone scatter and clay structures, related to the transition to agro-pastoralism in the Alto Ribatejo, were analysed by optically stimulated luminescence, neutron activation analysis, field and high-resolution gamma spectrometry, and X-ray diffraction. Indications of anthropogenic, autogenic, and allogenic site formation and diagenetic processes, including radionuclide exchange, were applied to interpret 28 date estimates from the 9th to 1st millennia BC. Results from regolith samples relate to different phases of landscape activation and stability from the late 6th millennium BC to the Roman conquest. However, simple archaeological questions were best answered using heated materials, where present. Different chronological phases were often represented by different sample types in sites with multi-phase stratigraphies, indicating the importance of parallel analyses. Results from a fire pit coincide with the first indications of clearance in the regional pollen record (late 9th millennium BC): these features appear promising to map early Holocene human presence in the Alto Ribatejo landscape.

2-D numerical simulation of radionuclide transport in the lower Yangtze River

The assessment of the radiological impact of the liquid discharges from nuclear power plants is a major issue for the environmental protection. In this study, a numerical model for the radionuclide transport in the aquatic environment is built, based on the hydrodynamic equations, including the complete set of Saint-Venant equations, the sediment transport equations, with consideration of several different particle sizes and the deposition and erosion of the suspended sediments, and the radionuclide transport equations. The exchanges of radionuclides between water, suspended matter and bed sediments are described in terms of kinetic transfer coefficients. The model is used to simulate the transport of the radionuclides discharged from a planned nuclear power plant project to be sited along the lower Yangtze River. From the model results, one may see the detailed temporal-spatial evolution of the radionuclide contamination in the solution, in the suspended matter and in the bed sediments. The model can be used as a basic tool for studying the environmental impacts of the liquid discharges from nuclear facilities on a river system.

Radiological risk assessment and biosphere modelling for radioactive waste disposal in Switzerland

Long-term safety assessments for geological disposal of radioactive waste in Switzerland involve the demonstration that the annual radiation dose to humans due to the potential release of radionuclides from the waste repository into the biosphere will not exceed the regulatory limit of 0.1 mSv. Here, we describe the simple but robust approach used by Nagra (Swiss National Cooperative for the Disposal of Radioactive Waste) to quantify the dose to humans as a result to time-dependent release of radionuclides from the geosphere into the biosphere. The model calculates the concentrations of radionuclides in different terrestrial and aquatic compartments of the surface environment. The fluxes of water and solids within the environment are the drivers for the exchange of radionuclides between these compartments. The calculated radionuclide concentrations in the biosphere are then used to estimate the radiation doses to humans due to various exposure paths (e.g. ingestion of radionuclides via drinking water and food, inhalation of radionuclides, external irradiation from radionuclides in soils). In this paper we also discuss recent new achievements and planned future work.

Effect of colloids on transfer of radionuclides by subsurface water

The fluid transfer of radionuclides in the geologic medium is considered under conditions when radionuclides are contained in fluids not only as solutes but also as colloids. The effect of colloidal transport of radionuclides on the rate of spreading of radioactive contamination in an underground medium is estimated, with assessment of this effect in mathematical models describing the transport of radionuclides by subsurface water. For this purpose, the exchange of radionuclides between subsurface water, colloid, and an immobile solid phase is considered, taking into account the precipitation of colloidal particles on both the immobile solid phase and other colloidal particles and their recurrent mobilization into the liquid phase. It is noted that, in real colloidal transfer, the heterogeneity of the geologic medium and colloidal particles in subsurface water is of great importance. The known models of colloidal transfer of radionuclides are evaluated on the basis of the analysis performed.

Simulation of radioecological processes in mountain ecosystems specific to Ukraine

To analyze and simulate radioecological processes in mountain ecosystems typical for regions of Ukraine the method of the box (chamber) models is used. The real values of the rate of radionuclide exchange between the elements of a mountain landscape are specified on the basis of the literature data and the data of experts. Our results on simulation of slope ecosystems were adopted for mountain landscape with considerable greater rate of redistribution of radionuclides (Cs–137). Estimation of ecological safety for a mountain landscape contaminated with radionuclides is carried out on the basis of estimation of the radioactive doses affected people making use of a typical mountain ecosystem for production activity and recreation.It is shown that in a mountain ecosystem there is a rapid accumulation of the limit human radiation dose which may account for 6 – 17% of the initial amount in the ecosystem. It is shown that the events where not only the mountain top but all the elements of the mountain landscape are exposed to initial contamination are the most dangerous.

Modelling the dispersion of radionuclides by a river plume: Application to the Rhone river

A numerical model to simulate the transport of radionuclides in a river plume has been developed. The model solves the hydrodynamic equations, including baroclinic terms and a 1-equation turbulence model, suspended matter equations, including several particle sizes and deposition and erosion of sediments, and the radionuclide dispersion equations. The exchanges of radionuclides between water, suspended matter and bed sediments are described in terms of kinetic transfer coefficients. The dependence of these coefficients with water salinity is explicitly included in the model since in a river plume it changes from freshwater to seawater values. The model has been applied to the Rhone River plume, where radionuclides have been mainly discharged from a nuclear fuel reprocessing plant. Four particle sizes have been considered. Computed currents, salinity patterns, suspended sediment distributions and sedimentation rates are, in general, in agreement with observations. The model has been applied to simulate the transport of 125Sb, 137Cs and 239 , 240 Pu in the river plume. The model provides realistic radionuclide distributions in water, suspended matter and bottom sediments. Other valuable information, as fractions of radionuclides in suspended particles and distribution coefficients, can also be provided by the model.

Redissolution of caesium and plutonium from Irish Sea sediments: A comparison between different modelling approaches

Two models with different conceptual and numerical approaches have been used to simulate the dispersion of radionuclides released from Sellafield nuclear fuel reprocessing plant. The first is a long-term box-model for simulating dispersion from Sellafield to the Arctic environment in which water fluxes between boxes are obtained from basic oceanographic information. Water-sediment radionuclide exchanges are described through sedimentation and remobilisation processes on the basis of equilibrium distribution coefficients. The second model is a 3D high-resolution model that explicitly solves tidal mixing and suspended sediment transport in the Irish Sea. Exchanges of radionuclides between the liquid and solid phases are now described in terms of kinetic rates. Thus, this model has a general applicability and can be used in situations out from equilibrium. Both models have been used to simulate the dispersion of Cs and Pu in the Irish Sea. Results from the two models are comparable, being differences in the results smaller than should be expected from the very different modelling approaches.

Modelling the flux of radionuclides from the Rhone River into the Mediterranean Sea

A numerical model has been developed to simulate the input of radionuclides into the Mediterranean Sea through the Rhone River plume. The model is fully 3D. It solves the hydrodynamic equations, which include baroclinic terms and a turbulence model, together with the suspended sediment equations and radionuclide dispersion equations. The suspended sediment sub-model includes four particle classes, settling and deposition. The radionuclide equations include the exchanges of radionuclides between water, suspended sediments and bed sediments, described using a kinetic model. The effect of salinity changes upon uptake kinetics has also been included. Computed water circulation, salinity pattern, suspended sediment distribution and sedimentation rates are in agreement with observations in the area. The model has been applied to simulate the dispersion of 137 Cs and 239,240 Pu through the plume. Computed specific activities in water, suspended matter and bottom sediments are in agreement with the measured distributions. The model can also be applied to calculate distribution coefficients. Although some water circulation models for the Rhone River plume exist in current literature, this is the first time in which a detailed hydrodynamic and suspended sediment model has been applied to simulate the dispersion of radionuclides in the plume.

Modelling the transport of suspended particulate matter by the Rhone River plume (France). Implications for pollutant dispersion

A model to simulate the transport of suspended particulate matter by the Rhone River plume has been developed. The model solves the 3D hydrodynamic equations, including baroclinic terms and a 1-equation turbulence model, and the suspended matter equations including advection/diffusion of particles, settling and deposition. Four particle classes are considered simultaneously according to observations in the Rhone. Computed currents, salinity and particle distributions are, in general, in good agreement with observations or previous calculations. The model also provides sedimentation rates and the distribution of different particle classes over the sea bed. It has been found that high sedimentation rates close to the river mouth are due to coarse particles that sink rapidly. Computed sedimentation rates are also similar to those derived from observations. The model has been applied to simulate the transport of radionuclides by the plume, since suspended matter is the main vector for them. The radionuclide transport model, previously described and validated, includes exchanges of radionuclides between water, suspended matter and bottom sediment described in terms of kinetic rates. A new feature is the explicit inclusion of the dependence of kinetic rates upon salinity. The model has been applied to 137Cs and 239,240Pu. Results are, in general, in good agreement with observations.

The dispersion of 137Cs and 239,240Pu in the Rhone River plume: a numerical model

A numerical three dimensional model to simulate the transport of Cs and Pu by the Rhone River plume has been developed. The model solves the hydrodynamic equations, including baroclinic terms (that account for density variations) and a turbulence model, the suspended matter equations, including several particle classes simultaneously, settling, deposition and erosion of the sediment, and the radionuclide dispersion equations. Exchanges of radionuclides between the liquid and solid phases are described in terms of kinetic transfer coefficients. The dependence of these coefficients with water salinity is explicitly included in the model since it changes from freshwater to seawater values in the model domain. Computed activity levels in water, suspended matter and bed sediments are, in general, in agreement with measurements in the area. The model can also give a wide amount of information, as distribution coefficients for total suspended matter and sediments and for each particle class, fractions of radionuclides fixed to solid particles, and vertical profiles of radionuclides and distribution coefficients.

Bioaccumulation of silver‐110m, cobalt‐60, cesium‐137, and manganese‐54 by the freshwater algae Scenedesmus obliquus and Cyclotella meneghiana and by suspended matter collected during a summer bloom event

Laboratory experiments were done to assess 110mAg, 60Co, 137Cs, and 54Mn uptake by two phytoplankton species, the chlorophyte Scenedesmus obliquus and the small diatom Cyclotella meneghiana. Mn and Co were characterized by similar uptake kinetic rates, 20–30 d−1, whatever the algal species, whereas depuration rates were 3–60 d−1. Silver uptake and depuration rates were very high (144–293 d−1). However, Cs accumulation and depuration were very slow, with kinetic constants of 0.6–5 d−1. Mn, Co, and Ag were more strongly accumulated by C. meneghiana than S. obliquus and vice versa for Cs. To evaluate the extrapolation of the kinetic rates fitted for S. obliquus and C. meneghiana to natural conditions, suspended solids were also collected during a bloom event and contaminated. Radionuclide exchange between three distinct compartments among the suspended solids was modeled: the kinetic rates fitted for S. obliquus and C. meneghiana were used to represent chlorophyte and bacillariophyte contamination, whereas kinetic rates describing a third compartment were estimated when possible. A third compartment was evidenced only for Mn and Co, whereas, for Ag, the chlorophyte and bacillariophyte compartments were sufficient to describe the particulate phase. For Cs, algae kinetic rates could not be used, so a single compartment was fitted. These experiments confirm the low affinity of Cs for phytoplankton and the high bioavailability of Ag. In the case of Co and Mn, several processes acting simultaneously govern the contamination of natural suspended solids.

Radionuclides concentrations in the Loire river system resulting from routine discharges of five nuclear power plants: assessment of dose to man

Low level radioactive liquid discharges have been carried out in the Loire river since 1963. Since then, the number of power plants located on the Loire river and its tributaries has been steadily increasing to reach, in the year 2000, 14 reactors operating on 5 different sites. The question arose to evaluate to what extent the addition of several nuclear power plants on the same river system could increase the concentrations in radionuclides in the environment and affect the dose to the public. To address this issue, EDF initiated in 1998 the “Loire river and estuary radioecology” program with the focus on assessing possible accumulation of radionuclide in river bottom sediments or on river shores. The following radionuclides were considered because of their importance in power plant liquid discharges: tritium, 14C, 58Co, 60Co, Ag, 134Cs, 137Cs, 54Mn, 124Sb, and 131I. Radionuclide concentrations in the dissolved, particulate and sedimentary forms were evaluated using the CRESCENDO model. The development and validation of this model required a multi-step process. The first step was to design a 350-km long 1D hydraulic and water transport based on currently available tools and data. Next, daily tritium concentrations measured in Angers, at the downstream limit of the river, were compared with computed values. The following step was to calibrate the sediment transport model. Areas where fine particles settled (dams and river shores) were monitored to improve our understanding of sediment dynamics. Then equations representing radionuclide exchange between water and particles were derived from laboratory experiments and included in the model. After each step the computed values were compared to measure data sets to ensure the model adequately described the processes involved. In the final step, the CALVADOS model was used to calculate dose to the public at different locations along the Loire river.

Kinetics of the adsorption and desorption of radionuclides of Co, Mn, Cs, Fe, Ag and Cd in freshwater systems: experimental and modelling approaches

The sorption and release kinetics of 54Mn, 58Co, 59Fe, 109Cd, 110mAg and 134Cs by freshwater suspended particles were investigated to better identify the biogeochemical processes involved and to obtain suitable data for improving models describing radionuclide migration in freshwater streams. In order to observe any seasonal variability in the interaction of radionuclides with natural particles, experiments were performed both in winter and in summer during a phytoplanktonic bloom. Two kinetic models are compared in this paper: the “one-step reversible” model, based on the hypothesis that the transfer of radionuclides between water and suspended solids is governed by a reversible reaction, and the “two-successive-step reversible” model, which assumes two distinct types of sites or reactions on the solid phase. The “one-step reversible” model is generally unable to describe properly the exchange kinetics; this result shows that at least two processes are generally involved in radionuclide exchange between water and suspended particles. On the contrary, a model involving the existence of two successive reversible reactions properly simulates both the sorption and release kinetics. The determination of the kinetic coefficients allows quantitative assessment of the relative importance and kinetics of the processes. In particular, it has been shown that, except for Cs and Cd, major fractions of the radionuclides are associated at equilibrium with particulate sites involving strong interactions. The kinetics to reach this equilibrium depend on seasonal conditions, especially for Co and Mn: the transfer of Co and Mn to particulate sites involving strong interactions is much slower in winter. The distribution of the radionuclides between water and particulate sites involving weak interactions also shows seasonal variations for Co, Mn, Fe and Ag: the capacity to associate radionuclides is much higher in summer for Co and Mn, while the inverse tendency is observed for Fe and Ag. For Cs and Cd, no significant seasonal differences were observed.

Three-dimensional modelling of the tidal dispersion of non-conservative radionuclides in the marine environment. Application to 239,240Pu dispersion in the eastern Irish Sea

A three-dimensional model to simulate the tidal dispersion of non-conservative radionuclides in a marine environment has been developed. The model solves the three-dimensional hydrodynamic equations using normalized σ coordinates in the vertical and a flow dependent formulation for the eddy viscosity. Simultaneously, the suspended matter equation is also solved in σ coordinates, which includes advective–diffusive transport of particles plus settling. Erosion and deposition are incorporated into the sea bed boundary condition of the equation. It is considered that radionuclides can be present in three phases: solution, suspended matter particles and bottom sediments. Three equations have been formulated, whose solutions give the time evolution of specific activity into each phase. The exchanges of radionuclides between the liquid and solid phase (suspended matter and sediments) have been described in terms of kinetic transfer coefficients, so that the model can be applied under non-equilibrium conditions. The model has been applied to simulate the dispersion of 239,240Pu in the eastern Irish Sea, which is released from Sellafield nuclear fuel reprocessing plant. Computed and measured suspended matter concentrations have been compared for several points in the sea to test the suspended matter sub-model. Also, computed and observed 239,240Pu distributions in water, suspended matter and sediments have been compared for several years. k d distribution coefficients have been computed as well. Model results are, in general, in good agreement with observations.

Basic microscopic theory of the distribution, transfer and uptake kinetics of dissolved radionuclides by suspended particulate matter — part II: Applications

From recent experimental findings on dissolved radionuclide adsorption by suspended particulate matter, some further theoretical effort is needed to explain both the wide k d variability range and the factors affecting uptake kinetics. In the previous paper we have studied the uptake of dissolved radionuclides by suspended particles from a microscopic viewpoint. We developed a mathematical description of the kinetic transfer and the k d distribution coefficients. The most relevant contribution is the assumption that exchange of radionuclides occurs across a specific surface layer of non-zero thickness on particles. A wide range of experimental findings can be explained by this theory as will be demonstrated here using literature data. Also, the derived governing equations can be solved using a finite differences method to illustrate the effects of particle size spectra, temperature, suspended load concentrations, pH and salinity, amongst other factors, on radionuclide partitioning.