Behavior Of Radionuclides Research Articles

Hydrochemical behaviour of long-lived natural radionuclides in Spanish groundwaters

This research was focused on the analyses of the hydrochemical behaviour of long-lived natural radionuclides (210Po, 210Pb, 234,238U, 230,232Th, 226,228Ra) in groundwaters from Spanish aquifers with different geological characteristics and the evaluation of the dose by ingestion of these waters. The study was performed by the gross alpha-beta, alpha spectrometry and physicochemical analysis of a set of bottled drinking waters. Radionuclide activities in the investigated aquifers were highly variable. High concentration of 210Pb is associated with granitic bedrock and reducing conditions. On the other hand, the highest 238,234U concentrations were found in carbonate aquifers. Activities of 226Ra are largely controlled by ion exchange reactions due to the presence of relatively high concentration of chloride. Several waters exceeded the parametric value for gross alpha mainly due to 234U, 226Ra and/or 210Pb concentrations. Moreover, the content of 226Ra and 210Pb in the water contributed mainly to the indicative dose.

Separation of Uptake of Water and Ions in Porous Materials Using Energy Resolved Neutron Imaging

Migration of water and ions dissolved in water through concrete is of interest in civil engineering. In particular, the behavior of radionuclides dissolved in water is of great interest to the nuclear industry because significant numbers of nuclear structures contain large amounts of concrete, acting as a barrier to radionuclides against entering the environment. Study of the migration of water molecules and ions in concrete hitherto required destructive chemical analysis. In this work, we present a non-destructive probe to investigate the uptake of uranium, iodine and water into mortar in situ using a time-of-flight neutron imaging method that allows selecting different neutron energies, providing elemental sensitivity in the analysis of the absorption process. First results indicate that water molecules are the fastest migrating species while iodine is significantly slower, and uranium was not observed to migrate through the structure within the time frame of the experiment and furthermore blocks the migration of water.

Thermodynamic Analysis of the Oxidation of Radioactive Graphite in the CuO–NaCl–KCl–Na2CO3–K2CO3 Melt in Water Vapor

Graphite is widely used in the atomic industry and nuclear power engineering. In the next 10–15 years, the resource of most blocks in the uranium–graphite reactors in Russia will be exhausted with allowance for the elongation of the service life, as follows from the results of repair-and-renewal operations. High-activity graphite can be processed by flameless oxidation in molten salts. The purpose of this work is to study the behavior of radionuclides during the flameless oxidation of radioactive graphite in the CuO–NaCl–KCl–Na2CO3–K2CO3 melt in water vapor using a thermodynamic simulation and the Terra software package. A thermodynamic simulation is an effective and unique method used to investigate diverse high-temperature processes of thermal decomposition, reduction, and synthesis. The calculation is performed using a reference datable of the properties of individual substances. Graphite burns up at 573 K. The condensed compounds of cesium, chlorine, and uranium evaporate at 1673 K. An increase in the temperature to 1973 K leads to the vapor pressure of the condensed compounds of beryllium, calcium, and strontium. The condensed oxide of europium(III) and the condensed oxide of plutonium(IV) transform into a vapor state at 2173 K. The condensed oxide of nickel transforms into a vapor state at 2473 K. A further increase in the temperature to 2773 K leads to the transformation of the condensed oxide of americium(III) into a vapor state. Only a vapor–gas phase is present in the isolated system in the temperature range from 2773 to 3273 K.

Development and application of an advection-dispersion model for data analysis of electromigration experiments with intact rock cores

An advection-dispersion model was developed for interpreting the experimental results of electromigration in granitic rock cores. The most important mechanisms governing the movement of the tracer ions, i.e. electromigration, electroosmosis and dispersion were taken into account by the advection-dispersion model, but the influence of aqueous chemistry was ignored. An analytical solution in the Laplace domain was derived and then applied to analyze the measured results of a series of experiments, performed in an updated experimental device using different applied voltages. The modelling results suggested that both studied tracers, i.e. iodide and selenite, are effectively non-sorbing in the intact rock investigated. The effective diffusivities and formation factors evaluated from the model were also found to be in good agreement with data reported in literature and the associated uncertainties are much smaller than those obtained from the classical ideal plug-flow model, which accounts only for the dominant effect of electromigration on ionic transport. To explore further how the quality of parameter identifications would be influenced by neglect of aqueous chemistry, a reactive transport model was also implemented, which may be regarded as a multi-component version of the advection-dispersion model. The analysis showed that the advection-dispersion model works equally well as the reactive transport model but requires much less computational demand. It can, therefore, be used with great confidence to interpret the experimental results of electromigration for studies of diffusion and sorption behavior of radionuclides in intact rock cores.

Does Salinity Affect the Distribution of the Artificial Radionuclides 90Sr and 137Cs in Water of the Saline Lakes? A Case of the Crimean Peninsula

In the framework of radioecological monitoring, the features of the distribution of the post-Chernobyl nuclear power plant (NPP) accident artificial radionuclides of 137Cs and 90Sr in the Crimean saline lakes were studied. Samples were collected from 12 Crimean lakes with a salinity range from 2 to 400 g/L in 2014–2017. Concentration of 90Sr varied from 5.9 to 313.6 Bq/m3, and 137Cs from 0.8 to 106.7 Bq/m3. Closing of the North Crimean Canal resulted in a decrease in radionuclide concentration in the lakes. About 61% of the total variability of 90Sr and 33% of 137Cs in lake water can be explained by salinity changes. The salinity affects the behavior of radionuclides in water, mainly influencing their solubility, on isotope exchange between the solution and bottom sediments, and also, probably, through its influence on accumulation of isotopes by aquatic organisms. Salinity is not the alone factor determining the behavior of radionuclides in the lakes, it only acts by interacting with other factors.

Influence of long-term aqueous leaching of irradiated graphite on surface properties and behavior of radionuclides

AbstractSamples of real irradiated (i-)graphite from bushings of RBMK reactor after several types of decontamination treatments were put in contact with aqueous solutions modelling underground water of Nizhnekansky massif (Russia) equilibrated with bentonite for periods up to 1.5 years. Leach rates of radionuclides and evolution of graphite surface morphology and oxidation state were monitored using nuclear spectroscopy, SEM and XPS. After the experiment, less than one third of surface carbons remains unoxidised. Extensive precipitation of secondary phases (alumosilicates, carbonates) was observed on some samples and is possibly correlated with surface oxidation extent. The leach rates of dose-forming 14C and 36Cl are comparable with the leach rates of radionuclides in glassy waste forms. According to the current study i-graphite could be regarded as a waste form, which is suitable for near-surface disposal.

Efficient sampling of shiitake-inoculated oak logs to determine the log-to-mushroom transfer factor of stable cesium.

BackgroundStable cesium (133Cs) naturally exists in the environment whereas recently deposited radionuclides (e.g., 137Cs) are not at equilibrium. Stable cesium has been used to understand the long-term behavior of radionuclides in plants, trees and mushrooms. We are interested in using 133Cs to predict the future transfer factor (TF) of radiocesium from contaminated logs to shiitake mushrooms in Eastern Japan. However, the current methodology to obtain a representative wood sample for 133Cs analysis involves mechanically breaking and milling the entire log (excluding bark) to a powder prior to analysis. In the current study, we investigated if sawdust obtained from cutting a log along its length at eight points is as robust but a faster alternative to provide a representative wood sample to determine the TF of 133Cs between logs and shiitake.MethodsOak logs with ready-to-harvest shiitake fruiting bodies were cut into nine 10-cm discs and each disc was separated into bark, sapwood and heartwood and the concentration of 133Cs was measured in the bark, sapwood, heartwood, sawdust (generated from cutting each disc) and fruiting bodies (collected separately from each disc), and the wood-to-shiitake TF was calculated.ResultsWe found that the sawdust-to-shiitake TF of 133Cs did not differ (P = 0.223) compared to either the sapwood-to-shiitake TF or heartwood-to-shiitake TF, but bark did have a higher concentration of 133Cs (P < 0.05) compared to sapwood and heartwood. Stable cesium concentration in sawdust and fruiting bodies collected along the length of the logs did not differ (P > 0.05).DiscussionSawdust can be used as an alternative to determine the log-to-shiitake TF of 133Cs. To satisfy the goals of different studies and professionals, we have described two sampling methodologies (Methods I and II) in this paper. In Method I, a composite of eight sawdust samples collected from a log can be used to provide a representative whole-log sample (i.e., wood and bark), whereas Method II allows for the simultaneous sampling of two sets of sawdust samples—one set representing the whole log and the other representing wood only. Both methodologies can greatly reduce the time required for sample collection and preparation.

Determining the porosity and water impregnation in irradiated graphite

Impurities in nuclear graphite can become neutron-activated during operation, generating radionuclides and leading to modifications in the microstructure of the graphite due to fast neutrons. The long-term disposal of nuclear graphite waste requires collecting data on the behaviour of long-lived radionuclides in disposal conditions (water-saturated). The release of radionuclides in solution depends on a number of physicochemical processes such as water ingress into the graphite structure (radionuclides sites), as well as the solubilisation and transport of radionuclides in solution through the graphite pores. Analysis of the impregnation (impregnation speed, impregnation rate) of water in the porous graphite environment represents one of the main parameters that will greatly influence the physicochemical processes controlling the release of radionuclides in solution. For this reason, the impregnation of irradiated samples from the G2 and St Laurent A2 (SLA2) gas-cooled graphite-moderated reactors was studied, as was the distribution of the porosity. Results show that the geometric density of the samples decreases after irradiation, which is expressed as an increase in the total porosity or more precisely in the open porosity mainly due to CO2 radiolytic corrosion. This means that irradiated graphite is mainly a macroporous solid. Nuclear graphite becomes a hydrophilic material with its open porosity filled by water in just a few days. This is due to the presence of functional groups on the pore surface.

Long term decrease of 137Cs bioavailability in French pastures: Results from 25 years of monitoring

Long term radioactivity monitoring programs contribute to the understanding of the behavior of radionuclides in the environment. This work aims to investigate the long term behavior of Cesium-137 in pasture ecosystem (root soil, grass and cow's milk) by using of more than twenty five years monitoring data collected at ten of French pasture sites contaminated by atmospheric fallouts from Chernobyl and nuclear atmospheric tests. We estimated with a simple exponential model the long term effective half-lives of radiocesium in root soil, grass vegetation and cow's milk along with their associated uncertainties. The average values of the effective half-lives over all the investigated sites were determined as 17, 11 and 9 years for soil, grass and milk respectively. Those values compare favorably to those estimated in previous studies in literature. These findings further enable us to quantify the decrease of 137Cs bioavailability which ranges from 0.008 to 0.044 year−1 with an average value of 0.026 year−1 (i.e. effective half lives ranging from 16 to 87 years with an average value of 26 years in soil).

Radiological assessment of the bauxite residue valorization chain

The behavior of radionuclides in the bauxite residue valorization chain has been analyzed, and accumulation ratios have been measured for secondary residues produced after recovery of valuable metals. Key analysis outcomes are valid specifically for the processes and raw materials in use at the Aluminium of Greece plant and are as follows: the processing of bauxite residue is unlikely to create secondary residues that would be hazardous from the radiological perspective, even if bauxite residue is processed successively multiple times to recover different metals. From a radiological perspective, there are no considerable limitations for the exploitation of specific BR for metal recovery. As some conclusions may be raw material or process dependent, future research could assess the possibility of applying these outcomes to other bauxite plants.

Plutonium and other radionuclides persist across marine-to-terrestrial ecotopes in the Montebello Islands sixty years after nuclear tests.

Since the 1956 completion of nuclear testing at the Montebello Islands, Western Australia, this remote uninhabited island group has been relatively undisturbed (no major remediations) and currently functions as high-value marine and terrestrial habitat within the Montebello/Barrow Islands Marine Conservation Reserves. The former weapons testing sites, therefore, provide a unique opportunity for assessing the fate and behaviour of Anthropocene radionuclides subjected to natural processes across a range of shallow-marine to island-terrestrial ecological units (ecotopes). We collected soil, sediment and biota samples and analysed their radionuclide content using gamma and alpha spectrometry, photostimulated luminescence autoradiography and accelerator mass spectrometry. We found the activity levels of the fission and neutron-activation products have decreased by ~hundred-fold near the ground zero locations. However, Pu concentrations remain elevated, some of which are high relative to most other Australian and international sites (up to 25,050 Bq kg-1 of 239+240+241Pu). Across ecotopes, Pu ranked from highest to lowest in the following order: island soils > dunes > foredunes > marine sediments > and beach intertidal zone. Low values of Pu and other radionuclides were detected in all local wildlife tested including endangered species. Activity concentrations ranked (highest to lowest) terrestrial arthropods > terrestrial mammal and reptile bones > algae > oyster flesh > whole crab > sea turtle bone > stingray and teleost fish livers > sea cucumber flesh > sea turtle skin > teleost fish muscle. The three detonations (one from within a ship and two from 30 m towers) resulted in differing contaminant forms, with the ship detonation producing the highest activity concentrations and finer more inhalable particulate forms. The three sites are distinct in their 240/239Pu and 241/239Pu atom ratios, including the Pu transported by natural process or within migratory living organisms.

Construction of Aquatic Environmental Database Near Wolsong Nuclear Power Plant

Radioactive materials are released into the air and deposited on the surface soil after a nuclear accident. Radionuclides deposited in soil are transported by precipitation to nearby environments and contaminate the surface water system. Basic data on surface watershed and soil erosion models have been collected and analyzed to evaluate the behavior of radionuclides deposited on surface soil after a nuclear accident. Data acquisition and analysis in aquatic environment were performed to investigate the physical characteristics and variation of biota in rivers and lakes of the Nakdong river area near the Wolsong nuclear power plant. For these purposes, a digital map, and hydrological, water quality and biota data were gathered and a systematic database (DB) was constructed in connection with them. Constructed aquatic DB will be supplied and used in surface watershed and soil erosion models for investigation of long-term movement of radionuclides in adsorptive form in surface soil. Finally, basic data and established models will be utilized for general radiological impact assessment in aquatic environment.

Investigation on the radiolytic stability of polybenzimidazole-based polymeric resins for the recovery of lanthanides, actinides, palladium from aqueous medium

Radiolytic stability of polymeric resins is an important aspects in nuclear materials processing. The different dosage of gamma radiation was subjected to meta-polybenzimidazole (m-PBI), para-polybenzimidazole (p-PBI) and pyridine-m-PBI based polymeric resins, which was taken for the present radiolytic stability investigation. Irradiated polymers were characterized by FT-IR, SEM and TGA analysis. Extraction of U(IV) and Pd(II) as a function of nitric acid concentration using 50, 100 and 150 kGy gamma irradiated polymeric resins was carried out and static capacity was also investigated for the gamma irradiated polymeric resins and compared with their unirradiated ones. In addition, the extraction behaviour of radionuclides, namely, plutonium, americium and europium as a function of HNO3 concentration utilizing both unirradiated and 150 kGy gamma irradiated polymeric resins was studied for the first time. Results indicated that FT-IR spectra of both unirradiated and 150 kGy irradiated resins are similar. TGA analysis revealed 50% and 20% weight loss for pyridine-m-PBI, m-PBI, respectively. The distribution ratio values decreases with increase in gamma irradiation. The uranium and palladium static capacities were found to be 30 and 182 mg/g resin, respectively. The overall results indicated that p-PBI resin has higher extraction efficiency and exhibits better radiation resistant behaviour as compared to pyridine-m-PBI and m-PBI.

Americium biodistribution in rats after wound contamination with different physicochemical forms in the presence or absence of plutonium: analyses using STATBIODIS

Americium (Am) biodistribution data obtained after wound contamination in rats were analysed to evaluate and quantify the influence of different physicochemical forms of Am in the presence or absence of plutonium (Pu). The biodistribution data were individual Am daily urinary excretion and tissue retention. The data were analysed with STATBIODIS, a statistical tool developed in the laboratory and based on the R language. Non-parametric methods were selected to comply with the data characteristics. Am systemic tissue retention and urinary excretion data were much greater for contamination with soluble physicochemical forms than insoluble forms. Meanwhile, Am relative biodistribution between the main retention tissues (skeleton, liver and kidney) remained the same. Hence, after absorption into blood the radionuclide behaviour was independent of the physicochemical form. The presence of Pu did not change the Am biodistribution. Comparisons of the biodistribution data from the laboratory with mean values published by other laboratories showed that soluble to moderately soluble forms of Am resulted in similar urine excretion after contamination, whether it was intravenous, intramuscular, subcutaneous injection or incision. Findings from this work will contribute to improve the understanding and interpretation of wound contamination cases with different physicochemical forms and mixtures of actinides including Am.

Calcium carbonate precipitation in compacted bentonite using electromigration reaction method and its application to estimate the ion activity coefficient in the porewater

ABSTRACT In the safety assessment of radioactive waste disposal, it is critical to understand the porewater chemistry in compacted bentonite in order to predict long-term migration behavior of radionuclides in the engineered barrier. This study estimates the activity coefficients of dissolved ions in the porewater of compacted bentonite from the concentrations of ions at which CaCO3 precipitation occurred. Solutions containing CaCl2 and NaHCO3 were introduced under electrical potential gradient from the opposite sides of the compacted Na-bentonite packed at the dry density of 1.0kg/dm3. After the electromigration, the spatial distribution of ions along the compacted bentonite sample was determined. Sequential extraction method was developed to distinctly determine the concentrations of free ions in the porewater and in solid phase in bentonite. The results show that the exchangeable Na+ ions were progressively replaced by the incoming Ca2+ ions, and the compacted bentonite sample can be divided into three zones: Ca-, Ca-/Na-, and Na-bentonite zones. Precipitates of CaCO3 were observed both in Ca- and Ca/Na-bentonite zones. The experimentally determined activity coefficients were at least smaller by a factor of 3 compared to the theoretical approximation calculated using PHREEQC code assuming dilute-solution conditions with no electrostatic interactions between ions and bentonite surface.

Assessment of temporal variations of natural radionuclides Beryllium-7 and Lead-212 in surface air in Tanay, Philippines

Detection of radionuclides in surface air allows researchers to gain further insight on the behavior of radionuclides that may affect human radiation exposure especially in the event of a nuclear emergency. In this study, activity concentrations of naturally-occurring radionuclides Beryllium-7 (7Be) and Lead-212 (212Pb) in surface air and meteorological data collected in Tanay, Philippines from January 2012 to December 2017 were evaluated to determine the impact of atmospheric conditions and processes to airborne radioactivity. Surface air concentrations of 7Be and 212Pb were found to range from 0.00779 ± 0.00188 to 11.2 ± 0.116 mBq/m3 and from 1.371 ± 0.036 to 106.6 ± 1.075 mBq/m3, respectively. 7Be and 212Pb show distinct annual trends, suggesting that atmospheric conditions affect both radionuclides differently and independently. 7Be shows two peak concentrations annually, with the first peak occurring between January to April and the second lower peak occurring between October and November. 212Pb, on the other hand, shows annual peak concentrations occurring between April and June. Ambient temperature showed strong positive correlation with 212Pb concentration in surface air and a weak negative correlation with 7Be; relative humidity and precipitation showed varying degrees of negative correlation with radionuclide concentrations in surface air. Source locations for the unusually high 212Pb activity concentrations detected on 11–13 May 2013 and 19–31 May 2015 determined using WEB-GRAPE and HYSPLIT atmospheric transport models are presented as a case study. The data and findings of this study shall serve as basis for further studies on local and regional atmospheric transport and radiological impact assessment for the implementation of an effective nuclear and radiological emergency preparedness and response system in the country.

Компьютерное моделирование термических процессов с участием радионуклидов U, Cl, Pu, Be, Ni, Am при нагревании радиоактивного графита в атмосфере углекислого газа

Компьютерное моделирование термических процессов с участием радионуклидов U, Cl, Pu, Be, Ni, Am при нагревании радиоактивного графита в атмосфере углекислого газа

Corrosion Performance of Engineered Barrier System in Deep Horizontal Drillholes

The disposal of spent nuclear fuel and other high-level radioactive waste in deep horizontal drillholes is an innovative system. Canisters of highly corrosion-resistant nickel-chromium-molybdenum (Ni-Cr-Mo) alloys are specified for the disposal of this nuclear waste. The canisters are emplaced along a steel casing in a horizontal drillhole that is one to three kilometers deep into or below a low-permeability geologic formation. The drillhole is in fully saturated rock with anoxic and reducing pore waters. A time-interval analysis method was used to track the evolution of the environment and to analyze corrosion performance of a representative engineered barrier system (EBS) configuration. In this analysis, the canisters remained perforation-free for tens of thousands of years. The amounts of hydrogen and metal oxides formed as by-products of the metal corrosion process were determined. These by-products are of interest, because both hydrogen and metal oxides can affect the chemical composition of the environment and the transport and sorption behavior of radionuclides and other species. Beneficial attributes that contribute to the extraordinarily long life of the canisters were identified. Several inherent characteristics of the horizontal drillhole disposal system reduced the complexities and uncertainties of the analysis.

Adsorption behaviors of Eu(III) on granite: batch, electron probe micro-analysis and modeling studies

Although granite has been widely considered as the host rock of the high-level radioactive waste (HLRW) repository in the world, the adsorption behaviors of radionuclides on granite are quite complicated and still unclear, especially at molecular scales. In this study, the adsorption behaviors of europium(III) on Beishan granite (BSG), a preliminary selection of host rock for the HLRW repository in China, were explored under environmental conditions combining batch, electron probe micro-analyzer (EPMA), and modeling approaches. X-ray diffraction (XRD) pattern confirmed that albite, quartz and biotite were the main mineralogical components for the BSG grains. Eu(III) species on BSG grains are predominant as the ion exchange (≡X3Eu0) and the inner sphere complexes of ≡SwOEu(OH)20, ≡SsOEu(OH)2,0 ≡SsOEu2+, and ≡SwOEu2+. EPMA showed that the distribution of Eu(III) on BSG grains was strongly correlated to the biotite, which suggested that biotite is the host phase for retarding trivalent actinides in the BSG grains. The presence of soil humic and fulvic acids could enhance Eu(III) adsorption on BSG grains under low-pH conditions, and inhibit the adsorption under higher pH range.

Study of Soil Erosion for Evaluation of Long-term Behavior of Radionuclides Deposited on Land

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) resulted in the deposition of large quantities of radionuclides over parts of eastern Japan. Radioactive contaminants have been observed over a large area including forests, cities, rivers and lakes. Due to the strong adsorption of radioactive cesium by soil particles, radioactive cesium migrates with the eroded soil, follows the surface flow paths, and is delivered downstream of population-rich regions and eventually to coastal areas. In this study, we developed a model to simulate the transport of contaminated sediment in a watershed hydrological system and this model was compared with observation data from eroded soil observation instruments located at the Korea Atomic Energy Research Institute. Two methods were applied to analyze the soil particle size distribution of the collected soil samples, including standardized sieve analysis and image analysis methods. Numerical models were developed to simulate the movement of soil along with actual rainfall considering initial saturation, rainfall infiltration, multilayer and rain splash. In the 2019 study, a numerical model will be used to add rainfall shield effect by trees, evaporation effect and shield effects of surface water. An eroded soil observation instrument has been installed near the Wolsong nuclear power plant since 2018 and observation data are being continuously collected. Based on these observations data, we will develop the numerical model to analyze long-term behavior of radionuclides on land as they move from land to rivers, lakes and coastal areas.