Behavior Of Radionuclides Research Articles

An experimental study on natural weathering of radionuclides from urban surfaces for aerosols deposited in wet and dry conditions

The European Model for Inhabited Areas (ERMIN) predicts long-term doses and other consequences following contamination of built-up areas by airborne radioactivity. Central to ERMIN are empirical models of the long-term behaviour of radionuclides on building and other surfaces in the environment. Experiments in which building materials were contaminated, and weathered outdoors for up to 1 year following contamination have enhanced the data on weathering from surfaces that can be used in ERMIN. New data have been obtained for the elements americium, cadmium, caesium, cobalt, iodine, ruthenium and strontium and for the surfaces brick, concrete and clay roof tiles, concrete slabs, glass, sandstone, tarmac and wood cladding. The results have highlighted some differences between the retention of aerosols on surfaces, particularly for glass. This paper presents a summary of the results and identifies the main differences in retention observed.

Application of zonality conceptual model of chronic effects of ionizing radiation for studying the behavior of Sr-90 in terrestrial ecosystems

Behavior of Sr-90 radionuclide in the system of «soil-plants-mollusc shells» was investigated on the example of biotope of regional radioactive waste storage facility. The purpose of the study was to examine the possibility of applying the conceptual model of zonality of chronic effects of ionizing radiation in natural populations in the investigation of behavior of radioactive strontium in terrestrial ecosystems and to identify radioecological zones of biological effects of chronic exposure to ionizing radiation of the mollusc population based on of the bio-geochemical regularities of technogenic migration of Sr-90 within the «soil-plants-mollusc shells» system. The study was conducted on the experimental site which represented the biotope of the regional radioactive waste storage facility. Analysis of samples of soil, plant (Urtica dioica) and terrestrial molluscs was implemented by the method of radiochemical separation followed with measuring the activity of the radionuclide using scintillation spectrometer «BETA-01C». Annual exposures to external beta-radiation received by tissues of molluscs irradiated by Sr-90 and its daughter radionuclide Y-90 contained in the shells were calculated using Levinger and Marinelli formula.It was discovered that dose rates of irradiation of molluscs Bradybaena Fruticicola fruticum are within 0.03–1.60 Gy/year. Structuring of experimental data was implemented based on the obtained data on the specific activity of Sr-90 in the system under study in accordance with model by G.G.Polikarpov. Three ecological zones were identified on the experimental site with regular variation of specific activity of Sr-90 in mollusс shells. In the zone of physiological masking concentration of radionuclide in mollusc shells can be by one order of magnitude and even more higher than in the plant. In the zone of ecological masking and the zone of pronounced environmental effects specific activities of the radionuclide are reduced as compared to its concentration in plants by 8 and 40 times, respectively (no decrease of specific activities of the radionuclide in the plant is regisrered). The implemented studies allow formulating the conclusion on the possibility of adaptation of indicators of Sr-90 migration in terrestrial ecosystems.

Thermodynamic analysis of radionuclides behaviour in products of vapour phase hydrothermal oxidation of radioactive graphite

The behaviour of radionuclides was studied by the method of thermodynamic modelling in the wide temperature range 400–3200 K during interaction of radioactive graphite with water vapour, taken in the ratio C (s):H2O (g) = 1:10 and 1:20 (by mass). It was determined that the main components of the gaseous phase over the whole temperature range are H2O vapour, H2, gaseous CO and CO2 containing radioactive 14C. Their partial pressures exceed 103 Pa. Cs, Sr, Ca, Be, Ni radionuclides, which radioactive graphite contains, form volatile hydroxides, U, Pu radionuclides—volatile oxides. The partial pressure of these radionuclides does not exceed 10−1 Pa.

Modeling Transport of Radioactive Products of Corrosion in Loops with Sodium Coolant

A phenomenological model is proposed for finding the relationship between the observed behavior of corrosion radionuclides in liquid sodium and the experimental conditions. Reactor and extra-reactor experimental data are used to find the temperature and rate dependences of the model parameters so that the model reflects a wide range of experimental conditions. Most of the experimental data were obtained using domestic fast reactors and, to a lesser extent, foreign reactors. The design code Al’fa-M, which is based on the proposed model, is described. The code was tested on the BN-600 reactor. It was shown that the proposed modeling approach makes it possible to solve the problem of calculating the removal from the core and the distribution in the tank of a power reactor of activated products of corrosion with satisfactory accuracy within the framework of the problem at hand. In addition, discrepancies between the calculations and experiments, requiring further improvements to the model are found.

Behaviour of radionuclides during microbially-induced mining of nickel at Talvivaara, Eastern Finland

The Talvivaara mine in Eastern Finland utilizes microbe-induced heap leaching to recover nickel and other valuable metals (Zn, Cu, Co) from a black schist ore. In addition to the target metals, the ore contains uranium at a concentration of 17 mg/kg, incorporated as uraninite (UO2). Uranium oxidizes from the U(IV) to U(VI) state during leaching and dissolves as the uranyl ion (UO22+) in the acidic pregnant leach solution. Mobilisation of uranium has caused sufficient concern that plans have been developed for uranium recovery. The aim of this study is to generate new data leading to a better understanding of the fate of its radiotoxic daughter nuclides, primarily 226Ra, 210Pb and 210Po, in the mining process.It is shown that uranium daughters mostly remain in the heaps during the leaching process and are associated with secondary minerals, including jarosite, goethite and gypsum. Thorium and progeny (232Th plus 228Th, 228Ra) are also mainly retained. High sulphate concentrations in the acidic solutions limit the solubility of radium by incorporation in the crystal lattices of precipitated secondary sulphates. Electron probe microanalysis shows that goethite in the heaps is uraniferous, resulting from the adsorption of U(VI).After recovery of target metals, the pregnant leach solution is neutralized to further remove metal contaminants and the resulting slurries stored in a bunded tailings pond. The activity concentrations of thorium, radium, lead and polonium isotopes are generally low in the pond owing to prior retention by secondary minerals in the heaps. However, 238U activity concentrations range up to 3375 Bq/kg, which exceeds the permitted value (1000 Bq/kg) for natural radionuclides of the 238U series.

불포화 암반 파쇄대를 통한 핵종 이동

Adsorption experiments for radionuclides such as , and were conducted using fractured rock collected in unsaturated zone. The released radionuclide through artificial barrier from the near surface repository can be transported by the flow of rainfall or pore water through fractures in unsaturated zone and reach to groundwater flow. Therefore, it is important to investigate transport behavior (retardation) of radionuclides through fractured rock for the safety assessment and long-term performance of repository. Fractured rock samples were collected and characterized by X-ray microtomography (XMT) analysis, which can be used to develop a more robust unsaturated fracture transport model. When fracture-filling materials are exist, distribution coefficient of is higher than without fracture-filling materials. In this study, batch sorption distribution coefficient () of radionuclide was determined and used to increase our understanding of radionuclide retardtion through fracture-filling materials.

Radioactivity and the environment: technical approaches to understand the role of arbuscular mycorrhizal plants in radionuclide bioaccumulation.

Phytoaccumulation of radionuclides is of significant interest with regards to monitoring radionuclide build-up in food chains, developing methods for environmental bioremediation and for ecological management. There are many gaps in our understanding of the characteristics and mechanisms of plant radionuclide accumulation, including the importance of symbiotically-associated arbuscular mycorrhizal (AM) fungi. We first briefly review the evidence that demonstrates the ability of AM fungi to enhance the translocation of 238U into plant root tissues, and how fungal association may prevent further mobilization into shoot tissues. We then focus on approaches that should further advance our knowledge of AM fungi–plant radionuclide accumulation. Current research has mostly used artificial cultivation methods and we consider how more ecologically-relevant analysis might be performed. The use of synchrotron-based X-ray fluorescence imaging and absorption spectroscopy techniques to understand the mechanisms of radionuclide transfer from soil to plant via AM fungi is evaluated. Without such further knowledge, the behavior and mobilization of radionuclides cannot be accurately modeled and the potential risks cannot be accurately predicted.

Modification of 137Cs transfer to rape (Brassica napus L.) phytomass under the influence of soil microorganisms

After nuclear accidents, such as those experienced in Chernobyl and Fukushima, microorganisms may help purify contaminated soils by changing the mobility of radionuclides and their availability for plants by altering the physical and chemical properties of the substrate. Here, using model experiments with quartz sand as a substrate we investigate the influence of microorganisms on 137Cs transfer from substrate to plants. The highest transition of 137Cs from substrate to plants (50% increase compared to the control) was observed after Brassica napus L. seeds were inoculated by Azotobacter chroococcum. The best results for reducing the accumulation of 137Cs radionuclides (30% less) were noted after the inoculation by Burkholderia sp.. Furthermore, Bacillus megaterium demonstrated an increased ability to accumulate 137Cs. This research improves our prediction of the behavior of radionuclides in soil and may contribute towards new, microbiological countermeasures for soil remediation following nuclear accidents.

Integrated watershed modeling for simulation of spatiotemporal redistribution of post-fallout radionuclides: Application in radiocesium fate and transport processes derived from the Fukushima accidents

Simulation of the watershed-scale fate and transport of radionuclides is required in order to predict the consequences of contamination redistribution. Integrated watershed modeling is a suitable technique for this task, but it requires fully coupled investigation of radionuclide behavior in surface water, suspended sediment and subsurface aquifers. We developed a novel simulator for computing the spatiotemporal redistribution of fallout radionuclides in watersheds. The simulator was applied to an actual reservoir basin contaminated by fallout radionuclides from the Fukushima Dai-Ichi Nuclear Power Plant accident in 2011. As a result, the simulated 137Cs concentration in bottom sediment showed a reasonably close match with the measurement data. The distribution coefficient of 137Cs consistent with the latest measurement data was identified as being at least 400,000 L/kg, and it was estimated that more than 90% of the total 137Cs distributed in the fallout remains in the catchment area.

Microbial bioremediation processes for radioactive waste

Microbial processes can affect the environmental behavior of priority radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes and can contribute to the remediation of radionuclide-contaminated land. Underlying mechanisms that can control radionuclide solubility in biogeochemical systems can range from biosorption and biomineralization process, through direct (enzymatic) and indirect redox transformations. The mechanisms of enzyme-mediated reduction of problematic actinides, in principal, uranium (U), but including neptunium (Np), plutonium (Pu) and Americium (Am), are described in this review. In addition, the mechanisms by which the fission products technetium (Tc), cesium (Cs), and strontium (Sr) are removed from a solution by microorganisms are also described. The present review discusses the status of these microbiological processes, and the potential for cost-effective and scalable in situ remediation of radioactive waste.

The Distribution of 137Cs, 90Sr, and 241Am in Waterbodies of Different Origins in the Belarusian Part of Chernobyl Exclusion Zone

The accident at the Chernobyl Nuclear Power Plant (ChNPP) resulted in the radioactive contamination of vast regions of Belarus including waterbodies of various types found within the watershed of the Pripyat River. The purpose of the work reported upon here was to conduct a comparative analysis of the distribution, form, and behavior of contaminant radionuclides (137Cs, 90Sr, 241Am) within components of two aqueous ecosystems of different origins found within the territory of the Belarusian part of the Chernobyl exclusion zone: a natural floodplain pond and a flooded area covering former agricultural lands. Despite the contamination densities being practically the same for the catchment areas of the two waterbodies studied, differences were observed in the levels of radionuclides in various components of the two ecosystems and in their behavior with respect to sediments of the waterbodies. Assessment of the surface runoff of radionuclides from the catchment areas as an input to the waterbodies indicates that ingress of 137Cs, 90Sr, and 241Am into the floodplain pond exceeds that for the flooded wetland. Results indicate that this input is most relevant for waterbodies of small area and that the input of 90Sr is most intensive. However, additional inputs of 137Cs and 90Sr into the waterbodies do not lead to substantial secondary contamination as the rate of decrease in concentration of these radionuclides due to physical decay is greater than the rates of input by this mechanism. There is however the possibility of accumulation of long-lived transuranic radionuclides due to runoff inputs.

Development of the <sup>137</sup>Cs, <sup>90</sup>Sr and <sup>3</sup>H Concentrations in the Hydrosphere in the Vicinity of NPP Temelín (South Bohemia)

The paperfocuses on an analysis of the results of long-term monitoring of the concentrations of 137Cs, 90Sr and 3H in hydrosphere in the vicinity of Temelín Nuclear Power Plant (Temelín plant). The radionuclides were monitored in surface water, river sediments, aquatic flora and fish species. The main objective of the study was to analyze and integrate all of the knowledge on concentrations and behaviour of these radionuclides, which originate mainly from residual contamination, in order to assess the impacts of Temelín Nuclear Power Plant on hydrosphere in these indicators during its standard operation and possible accidents. The radionuclides were analyzed in terms of spatial and temporal variability in their concentrations and their inflows and outflows, mainly into and from Orlík Reservoir. The analysis included standard radioecological characteristics, which were applicable for assessing long-term development and behavior of radionuclides in the environment affected by their possible accidental releases on the territory of the Czech Republic or outside this territory. For all of the components of the environment, the concentrations of 137Cs and 90Sr which were used for calculation of their effective and ecological half-time, were decreasing. For 137Cs in surface water and fish, the rates of the decrease in the first and second monitoring period were different. The rate of the decrease in 90Sr concentration was invariable. The results of the monitoring showed that 86% of suspended solids and 62% of 137Cs inflowing into Orlík Reservoir accumulated in the reservoir while accumulation of 90Sr was not substantiated. Outflows of 137Cs and 90Sr activities were assessed in relation to their concentrations that were accumulated in individual basins until 1986 consequently to Chernobyl accident and tests of atmospheric nuclear weapons. The results for the whole area of the Vltava, Luznice and Otava River basins upstream from the Vltava River at Solenice showed that during the period 1986-2013 only 0.49% of 137Cs activity and 3.6% of 90Sr activity that accumulated in the basins were washed and flowed out from the area. Distribution coefficients derived from summary analysis of sediments and concentration factors for biota were calculated. Concentrations of 3H in river sites not affected by Temelín plant were slowly decreasing and their values were substantially below those from the sites affected by the plant.

Radionuclide exposure in animals and the public health implications

Living tissues are usually exposed to varying degrees of radiation from natural and manmade radioactive substances. Depending on the type of radiation emitted and rate and dose of absorption, all radioactive substances are potentially hazardous. Previous researches on the biological effects of radiation as well as preventive measures have focused on human subjects, being the most radiosensitive species. However, exposure of animals to ionizing irradiation may negatively influence their production performance, resulting in some level of economic loss. In addition, many food animals may represent a significant pathway for transfer of radionuclides to humans, thereby adding to the exposure burden. The current review aims at evaluating the effects of ionizing radiation on animals as important components of human food chain, and some preventive measures. A proper understanding of radioactivity and the behavior of important radionuclides in livestock animals will serve as an informational tool in livestock management as well as consumers' dietary choices.

ICONE23-1463 IDENTIFYING RESEARCH ISSUES ON DISSOLUTION BEHAVIOR OF RADIONUCLIDES FROM THE VITRIFIED HIGH-LEVEL RADIOACTIVE WASTE IN JAPAN

The vitrified high-level radioactive waste from reprocessing spent fuels is planned to be disposed of within a stable geological environment at least 300m below ground surface. The evaluation of the individual dose rate caused by the waste to the biosphere is the primary issue for evaluating the safety of geological disposal. The radionuclide dissolution behavior from the vitrified waste is an especially critical processes for calculating the dose rate. The dissolution model proposed by Japan Nuclear Fuel Cycle (JNC, now JAEA) in the second progress report (H12 report)(JNC, 1999) has been used in Japan. However, various dissolution models have been proposed by researchers and implementers since the H12 report. This paper presents the recent progress of the glass matrix dissolution research and identifies four issues of the dissolution behavior of radionuclides. The four issues are as follows: A) "Identification of alteration rate acceleration mechanism and conditions", B) "Investigation into the protective nature of glass alteration layers", C) "Model development for potential disposal environments", and D) "Investigation into the effective surface area".

Radionuclides in wastewater treatment plants: monitoring of Sicilian plants.

Three Sicilian wastewater treatment plants were monitored to assess the occurrence and the behaviour of radionuclides. Two sampling campaigns (screening and long-term) were carried out during which liquid and solid samples have been analysed. It was found that ¹³¹I mostly occurred in the samples analysed during the screening campaign (43% of the analysed samples contained ¹³¹I). High ¹³¹I specific activity was found in the mixed liquor, recycled sludge and dehydrated sludge samples. This finding was mainly due to the tendency of (131)I to be associated with solid particles. During the long-term sampling campaign an influence of the sludge retention time (SRT) on the ¹³¹I behaviour was found. Increasing the SRT and consequently decreasing the fraction of active organic biomass inside the system, the specific activity of ¹³¹I decreases.

Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal.

The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10-13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2-252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5-1.8 nm nanoparticles with a proportion forming 20-60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium-uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.

Behavior of radionuclides induced in cooling water for electromagnets at the 12 GeV proton accelerator facility

The behavior of radionuclides in the cooling water for the electromagnets at the 12 GeV proton accelerator facility was studied by measuring γ-ray spectra of the cooling water and the ion-exchange unit in the water circulation system. These measurements indicated that the major photon radiations originating from the cooling-water were annihilation radiation from the positron emitters 11C, 13N and 15O during the accelerator’s operation, while γ-ray emission from 7Be became dominant several hours after the beam operation had stopped. Spatial distribution and behavior of 11C and 7Be in the cooling-water system were discussed based on their existing states in water.

Determination of sorption characteristics for artificial radionuclides in the hydrosphere

Adsorption onto solid particles plays an important role in the transport of radioactive contaminants in the hydrosphere. Sorption is usually described with a distribution coefficient: a ratio of radioactivity fixed on solid phase and dissolved in water in equilibrium. In this study, we developed, optimised and verified a method that uses a series of batch experiments for determination of the distribution coefficients of radionuclides in sediment–water and suspended solids–water systems. This can be further used for describing radionuclide behaviour in river courses. This work was funded by the Czech Ministry of Interior, as a part of Safety research project.

The application and development of geochemical modeling in high-level radioactive waste disposal

With the development of nuclear industry, the treatment and disposal of radioactive wastes are becoming increasingly urgent and challenging. Investigation of the migration behavior of radionuclides in the environment is the most important and direct way to obtain the basic parameters used to assess the influence of radionuclides on the surrounding environment and peoples health. In recent years, geochemical models based on numerical method, using the experimental data, thermodynamic and kinetic data of radionuclides has been established to analysis the continuous and long-term change of radionuclides in geological media. Up to now, there are more than ten geochemical codes commonly used in the world. In this paper, a brief introduction of geochemical models in terms of thermodynamic equilibrium principles, speciation distribution calculation methods and surface complexation assumptions are presented. Case study in the application and development of geochemical models with respect to the speciation calculation and surface complexation is disscussed. Furthermore, an example of Ca-U-CO3 complex is used to elucidate the importance of the integrality of the thermodynamic database, in order to propagate the application and development of geochemical models in China.

Uranium and technetium interactions with wüstite [Fe1–xO] and portlandite [Ca(OH)2] surfaces under geological disposal facility conditions

AbstractIron oxides resulting from the corrosion of large quantities of steel that are planned to be installed throughout a deep geological disposal facility (GDF) are expected to be one of the key surfaces of interest for controlling radionuclide behaviour under disposal conditions. Over the lengthy timescales associated with a GDF, the system is expected to become anoxic so that reduced Fe(II) phases will dominate. Batch experiments have therefore been completed in order to investigate how a model reduced Fe-oxide surface (wüstite, Fe1–xO) alters as a function of exposure to aqueous solutions with compositions representative of conditions expected within a GDF. Additional experiments were performed to constrain the effect that highly alkaline solutions (up to pH 13) have on the adsorption behaviour of the uranyl (UO22+) ion onto the surfaces of both wüstite and portlandite [Ca(OH)2; representative of the expected cementitious phases]. Surface co-ordination chemistry and speciation were determined byex situX-ray absorption spectroscopy measurements (both X-ray absorption near-edge structure analysis (XANES) and extended X-ray absorption fine structure analysis (EXAFS)). Diffraction, elemental analysis and XANES showed that the bulk solid composition and Fe oxidation state remained relatively unaltered over the time frame of these experiments (120 h), although under alkaline conditions possible surface hydroxylation is observed, due presumably to the formation of surface hydroxyl complexes. The surface morphology, however, is altered significantly with a large degree of roughening and an observed decrease in the average particle size. Reduction of U(VI) to U(IV) occurs during adsorption in almost all cases and this is interpreted to indicate that wüstite may be an effective reductant of U during surface adsorption. This work also shows that increasing the carbonate concentration in reactant solutions dramatically decreases the adsorption coefficients for U on both wüstite and portlandite, consistent with U speciation and surface reactivity determined in other studies. Finally, the EXAFS results include new details about exactly how U bonds to this metal oxide surface.