Migration Of 90Sr Research Articles

Migration mechanisms of 90Sr and 137Cs on terraces

In order to investigate the impact of environmental conditions on the distribution and migration of 90Sr in the Longji terrace environment, the activity concentrations of 90Sr and 137Cs were determined. The activity concentration ranges of 90Sr and 137Cs in surface soil were 0.15–1.04 Bq/kg and 2.16–6.94 Bq/kg, respectively. These results showed that there was a similar trend between the activity concentration of 90Sr and 137Cs in the surface soil along the runoff path and their activity concentration were influenced by the slope of the terraced terrain. On the other hand, the activity ranges of 90Sr and 137Cs in soil cores were 0.01–2.74 Bq/kg and 0.43–7.19 Bq/kg, respectively. These results indicate that the migration mechanism of 90Sr is different from that of 137Cs. As compared with 137Cs, 90Sr is significantly influenced by the moisture content. In addition, high span of 137Cs/90Sr activity ratios were found in this study, which were attributed to the characteristics of cultivated land and frequent artificial disturbances that intensified the migration of 90Sr.

Analysing the behaviour of 90Sr and stable Sr in highly weathered soils: Soil to plant transfer factor and geochemical partitioning

Public concerns over environmental protection have increased after Fukushima accident. The soil-plant transfer factor (Fv) is a critical parameter for environmental risk assessment. 137Cs Fv values determined in acid Brazilian soils could be two orders of magnitude higher than Fv values measured in soils affected by the Chernobyl accident. This paper studied the behaviour of 90Sr in Brazilian soils where very few 90Sr Fv data is available. All classes of studied soils (Ferralsol, Acrisol and Nitisol) showed that more than 80% of total 90Sr in soils remains potentially mobile, mainly at the bioavailable phase, more than 2 years after soil contamination in an experiment conducted in lysimeters. Higher 90Sr Fv for maize and cabbage was observed in the acid soils with low content of exchangeable Ca, lower Fv values occurred at Nitisol, the subtropical soil type. It seems that the behaviour of 90Sr in these soils are mainly controlled by ionic competition mechanisms occurring for root uptake and sorption sites, with stable Sr and major nutrients (Ca, Mg and K). The mineralogy also seems to play a relevant role, since goethite rich clay soil presented 90Sr Fv values higher one or two orders of magnitude than 90Sr Fv values observed at clayed soil goethite rich with trace of vermiculite, for all studied crops. The high rate of 90Sr migration down the soil profiles observed for the studied soils during the 2 first years after contamination suggests a high rate of transfer to groundwater, even transfer to leafy crop group can be also a relevant pathway. In the present study, maize, among other plant species, presented the lowest Fv values, even when compared with maize cultivated in temperate soil. Our results suggest that stable Sr may not be a very good analogue of 90Sr for determining plant Fv values: geometric mean of stable Sr Fv for maize was Fvmaize = 6.3E-1 ± 2.1E0 (n = 8) and for 90Sr was Fvmaize = 1.8E-2 ± 2.5E0 (n = 16), geometric mean of stable Sr Fv for cabbage was Fvcabbage = 1.4E0 ± 3.9E0 (n = 17) and for 90Sr was Fvcabbage = 7.9E-1 ± 4.4E0 (n = 18).

Strontium transport modeling in high-concentrated nitrate solution in DEEP liquid radioactive waste repository

This article focuses on modeling 90Sr migration in strong nitrate solutions in aquifers used for radioactive waste disposal. This type of radioactive waste disposal is typical only for the Russian Federation and is a unique object of study. The calculations are based on the laboratory study of strontium sorption in nitrate solutions on sandy, loamy and clayey rocks under biotic (with natural microbial communities obtained from Seversky repository) and abiotic conditions. To obtain a strontium sorption model, first, an ion exchange model in PHREEQC software is fitted to the experimental data both manually and automatically (using MOUSE software). Since real nitrate-ion concentrations at radioactive waste injection sites can reach values of hundreds of grams per liter, strontium Kd values are predicted for high ionic strength (for which no experimental study of strontium sorption efficiency has been carried out) with PHREEQC-model. The strontium transport models accounting for sorption and the nitrate reduction processes have been developed using two numerical software packages: the GeRa 3D hydrogeological simulation code and the PHREEQC reactive transport code. Reactive transport modeling under different conditions shows a high sensitivity to dispersion. A significant effect of sorption of nitrate ion on Sr sorption is shown and a relatively small contribution of microbial processes to strontium transport is noted for liquid radioactive waste injection sites.

Mechanisms Governing 90Sr Removal and Remobilisation in a VLLW Surface Disposal Concept

Flow-through columns were used to assess potential long-term trends in 90Sr biogeochemistry and transport in a Finnish near-surface very low-level waste (VLLW) repository concept. Experiments simulated the effects of water intrusion and flow through the repository barrier and backfill materials, examining impacts on 90Sr migration. Artificial rainwater containing 2.0 mg/L stable Sr (as a proxy for 90Sr) was pumped through column systems that had varying compositions from a matrix of rock flour (backfill material), bentonite (backfill/sealing material), and carbon steel (waste encapsulation material), for 295 days. Effluent geochemistry was monitored throughout. Sr retention behaviour in all column systems was broadly similar. Sr removal from influent rainwater was marked (~95% removed) at the beginning of the experiments, and this degree of removal was maintained for 20 days. Thereafter, Sr concentrations in the effluents began to rise, reaching ~2 mg/L by 295 days. Further, 56%–67% of added Sr was retained in the repository materials over the 295-day reaction period. Analysis of the effluents indicated that colloids did not form; as such, Sr output was likely to be aqueous Sr2+. Upon completion of the experiment, solid-associated Sr distribution and speciation in the columns were assessed through column sectioning and post-mortem analyses, which encompassed the following: total acid digests, sequential extractions, and XAS analysis. The total acid digests and sequential extractions showed that Sr was evenly distributed throughout the columns and that the majority (68%–87%) of solid-associated Sr was in the exchangeable fraction (MgCl2). This suggested that a major part of the solid-phase Sr was weakly bound to the column materials via outer-sphere sorption. Interestingly, a smaller amount of Sr (7%–23%) could only be extracted by aqua regia, suggesting that a proportion of Sr may bind more strongly to the barrier materials. XAS analysis of select samples confirmed that the dominant Sr phase was sorbed to the rock flour and bentonite, but not corroded carbon steel. Columns were also subject to remobilisation experiments using artificial rain- and seawater without added Sr. While rainwater remobilised Sr slowly, high-ionic strength seawater remobilised Sr at much higher rates in the systems containing bentonite. Interestingly, Sr was well retained in the rock flour-only system following rain and seawater intrusion. Overall, the results indicate that the column materials provide reactive surfaces for Sr removal should it be released from waste packages; however, the backfill and barrier materials have limited retention capacity, and the dominant sorption interaction is relatively weak. The safety case for the shallow disposal of radioactive waste should consider the possibility of seawater intrusion and that the bentonite-bound Sr was significantly more susceptible to remobilisation following seawater, despite retaining slightly more Sr during sorption experiments.

Вплив іонної сили розчину на формування підвищеної міграції 90Sr в підземних водах промислового майданчика Чорнобильської АЕС

Thermodynamic modeling of 90Sr migration was performed based on data from monitoring studies on well 4-G, which, before its liquidation in 2008, was located on the industrial site of the Chornobyl nuclear power plant. The study of the 90Sr migration forms was carried out using a set of software tools “Geochemist’s Workbench Community Edition”. In order to confirm and understand the migration processes, modeling of the spread of various complex 90Sr compounds such as SrCO3, SrHCO3, SrSO4, SrOH+ and SrNO3 + with groundwater was carried out. With the help of SpecE8, the calculation of various forms of 90Sr was performed, and the ionic strength of the groundwater solution (ISS) was also calculated. In the range of pH 9.5–12.4, there is an increase in the Sr2+ concentration in groundwater by 200–500 times to 550 Bq/l. In the same pH interval, according to thermodynamic modeling, an increase in the concentration of strontium in the form of SrOH+ and a decrease in the form of Sr2+ is observed in groundwater. At the same time, the dominance of strontium concentrations in the form of SrOH+ over Sr2+ does not occur. The reason for the sharp increase in the volume activities of 90Sr in strongly alkaline groundwater was the increase in the ISS > 5 mmol/l. An increase in the ISS of strongly alkaline groundwater leads to a decrease in the sorption properties of soils, and to the remobilization of adsorbed 90Sr back to groundwater through cation exchange. Probably, in the pH range of 9.5–12.4 and the ISS > 5 mmol/l, there is a change in the surface charge of soil particles, usually from negative to positive, in which cations cannot be sorbed, but, on the contrary, must to remobilize from the soil surface to groundwater. At the same time, pH = 9.5 is probably the point of zero charge (pzc). To assess the possibility of a relationship between the concentrations of 90Sr and ISS, a correlation analysis using the geochemical statistics method was carried out. At the same time, the correlation coefficient K = 0.87, which proves the existence of a close relationship.

Migration of 90Sr in the Soils of the East Ural Radioactive Trace (EURT)

Migration of 90Sr in the Soils of the East Ural Radioactive Trace (EURT)

Effect of Various Salts on the Vertical Migration of 90Sr in Gray Forest Soil

Effect of Various Salts on the Vertical Migration of 90Sr in Gray Forest Soil

Удельная активность и особенности вертикальной миграции стронция-90 в торфянике Мурманской области

The peatlands of the Arctic territories are repositories of radioactive contaminations. The physicochemical properties, specific activity and features of vertical migration of 90Sr in the peat profile of the Murmansk region have been studied. A correlation matrix was compiled according to the studied indicators. The factor that determines the localization of 90Sr in peat has been established. The sources of isotope for the region were determined.
 The reaction of the peat medium is acidic (4.2 ≤ pHwater ≤ 4.9; 3.6 ≤ pHsalt ≤ 4.1). The ash content of peat is medium and high (5.2 % ≤ Ash ≤ 28 %). The share of organic matter in the peat profile is more than 70 %. The upper part of the profile is saline (soluble salts>0.3%). The share of carbonates in the peat profile is insignificant (0.42–0.83 %).
 90Sr activity (0.55–7.7 Bq/kg) was recorded in each peat sample. The activity of the technogenic radionuclide is below the established permissible norm and within the range typical for all Russian soils. The 90Sr isotope is localized in the upper layers of the profile and at a depth of more than 16 cm. The localization of 90Sr in peat layers is due to the content of water-soluble salts (r = 0.85). The main sources of the isotope for the Murmansk region are past global fallout from nuclear tests, the Chernobyl accident and current local fallout from nuclear fuel facilities.

РЕТРОСПЕКТИВНАЯ ОЦЕНКА И МОДЕЛИРОВАНИЕ РАДИОАКТИВНОГО ЗАГРЯЗНЕНИЯ ТЕРРИТОРИИ РЕСПУБЛИКИ БЕЛАРУСЬ В РЕЗУЛЬТАТЕ КАТАСТРОФЫ НА ЧЕРНОБЫЛЬСКОЙ АЭС

The article presents conceptual approaches to retrospective assessment and predictive modeling of radioactive contamination of the territory of the Republic of Belarus as a result of the Chernobyl accident. The work was carried out within the framework of project 3.01 «Investigation of the effect of ionizing radiation in a wide range of doses and with the variability of radiation characteristics at different levels of organization of a living organism», GPNI «Natural resources and the envi-ronment» of the subprogram «Radiation and biological systems» for 2021-2025. We determined the most significant radionuclide composition (for assessing the consequences of the release of radionuclides into the environment for biota) and the levels of radioactive contamination of ecosystem components in the observation zone of the Gomel, Vitebsk and Grodno regions of the Republic of Belarus. The radiation situation was considered at different time stages, namely as a result of atmospheric nuclear weapons testing and after an emergency release at the Chernobyl nuclear power plant [1; 2]. At present time, according to our data, in the observation zone of the Gomel, Vitebsk and Grodno regions of the Republic of Belarus, the radiation situation is caused by 23Cs and 90Sr radionuclides. The migration of 90Sr in the soil and through the food chain significantly increases as a result of the destruction of fuel particles and, as a consequence, 90Sr enters the soil solutions, after which it migrates deep into the soil. In addition, in the Gomel region, 241Am accumulates due to the decay of 241Pu. The maximum contamination level of 241Am will be established by 2060 and will exceed 239 + 240Pu by a factor of 2.7, while territories with a contamination level of 238 + 239 + 240Pu + 241Am up to 1000 Bq / m2 may possibly go outside the 30-km zone. The results of scientific research were introduced into the educational process within the framework of lectures and practical classes at the Faculty of Environmental Monitoring of the International Sakharov Environmental Institute of Belarusian State University.

Correlation between chemical composition and 90Sr concentrations in groundwater of the Chornobyl NPP industrial site

The volumetric activity of the divalent 90Sr ion in groundwater at the Chornobyl NPP industrial site ranges from 1 to 2 to 400–3800 Bq/l. The increase in groundwater radionuclides concentrations is associated with the reduced sorption properties of local sediments, which affect the migration capacity of radionuclides in the environment. The decrease of the 90Sr sorption properties of sediments is caused by changes in the chemical composition of groundwater. A new statistical method has been performed. Method based on the Monte Carlo method in order to evaluate the correlations between the 90Sr volumetric activity and the groundwater chemical composition components. Simulation results using this method suggest a correlation between the volumetric activity of 90Sr, the concentrations cations, the pH, and the oxidation index (organic contents). A direct correlation was established between the volumetric activity of 90Sr, Ca2+ concentrations and the pH of groundwater in the range from 7 to 12.4. It was revealed that the concentrations of Na+ and K+ do not affect the conditions of 90Sr migration with groundwater. There is an inverse correlation between the concentration of 90Sr and the oxidation index, which is an indirect indicator of the organic substances content in water. Thus, the presence of organic substances in the groundwater effectively promotes sorption of 90Sr. The proposed method of geochemical statistics enables a quantitative assessment of groundwater monitoring results.

Adaptive Capability of the VERT_MIG Algorithm to Simulate Vertical Migration of Radionuclides in Soils

The possibility of using the VERT_MIG algorithm in simulation models of the vertical migration of radionuclides in soil is discussed. The algorithm was successfully used to develop models of 137Cs and 90Sr migration for radioactive contamination of different soils as a result of the accidents at the Chernobyl and Fukushima-1 nuclear power plants. The modeling results are given. Prospects for further use of this algorithm and some aspects of using imitation modeling in this area are discussed.

Assessment of strontium transport in clay medium by using a reactive transport modelling approach – an HP1 case study model

Modelling of radionuclide transport in the geosphere is a key issue of the evaluation of safety of low- and intermediate-level radioactive waste (LILW) repositories. In Bulgaria, due to the operation of Kozloduy Nuclear Power Plant (NPP), a building of such facility is ongoing. The migration of 90Sr was evaluated by simulation of flow and chemical modelling, performed with coupled numerical code HP1. The adsorption properties of the clays were implemented in the code by surface complexation reactions between strontium and iron oxides. The results were compared with another model performed with computer code HYDRUS 1-D, in which the adsorption properties of the medium were evaluated with the relevant for strontium distribution coefficient, Kd.

Conceptual Model to Determine Maximum Activity of Radioactive Waste in Near-Surface Disposal Facilities

For development of the management strategy for radioactive waste to be placed in near-surface disposal facilities (NSDF), it is necessary to justify long-term safety of such facilities. Use of mathematical modelling methods for long-term forecasts of radwaste radiation impacts and assessment of radiation risks from radionuclides migration can help to resolve this issue. The purpose of the research was to develop the conceptual model for determining the maximum activity of radwaste to be safely disposed in the NSDF and to test it in the case of Lot 3 Vector NSDF (Chornobyl exclusion zone). This paper describes an approach to the development of such a model. The conceptual model of 90Sr migration from Lot 3 through aeration zone and aquifer soils was developed. The results of modelling are shown. The proposals on further steps for the model improvement were developed.

Cherenkov counting of 90Sr and 90Y in bark and leaf samples collected around Fukushima Daiichi Nuclear Power Plant

The radioactivity of 90Sr and 137Cs in environmental samples, bark and leaf, collected around the Fukushima Daiichi Nuclear Power Plant in May 2013 was determined with the aim of investigating the migration of both nuclides using their radioactivity ratio. The radioactivity of 90Sr was determined by using Cherenkov counting of 90Y after purification using Sr resin and that of 137Cs was determined by γ-spectrometry. Quench correction in Cherenkov counting was investigated by measurements of samples spiked with purified 90Y revealed that the radioactivity could be evaluated without quench correction. The radioactivity ratio of 90Sr to 137Cs in bark samples of 4.2 × 10−3 and 1.2 × 10−2 was compared with the results from soil samples collected in July 2011 to show that the migration of 90Sr was slower than 137Cs in bark and tree.

Studies of strontium(II) sorption on soil samples in the presence of phosphate ions

Studies of 90Sr migration in soil systems require determination of some factors affecting this process. One of the most important factors is sorption of strontium cation in the presence of other ions. The paper presents the õstudies on Sr (II) sorption in the presence of phosphate ions in the solution. It was found that under the study cations at pH (3–10) in the presence of phosphate cation sorption increases depending on the soil type. The isotherms can be described by Freundlich equation.

Migration of 90Sr in the solid phase of the soil-soil solution-plant systems and ways to reduce it

A model of 90Sr migration in soil-soil solution-plant system was developed, and an expression was obtained for estimating the strontium migration. In accordance with the model, the 90Sr migration in the soil-plant system can be reduced by liming of acidic soils only to a certain limit determined by the cation-exchange capacity of the soil. According to the estimations, for the 90Sr migration into plants on limed soil to be efficiently reduced by a factor of 2, taking into account the economically acceptable level of 1–4 wt % for sorbent introduction into soil, it is necessary that the ratio of the sorption potentials of the sorbent and soil should be no less than 25.

Distribution and migration of 90Sr in components of the Dnieper River basin and the Black Sea ecosystems after the Chernobyl NPP accident

The change in 90Sr concentrations in hydrobionts, water and bottom sediments of the Chernobyl NPP pond-cooler, the Kievskoe and Kakhovskoe reservoirs, the Northern-Crimean canal and the Black Sea after the Chernobyl NPP accident was studied. The environmental half-times for the decrease of 90Sr concentrations were determined: in water – 4.1–24.3 years; algae and flowering water plants – 3.6–7.7 years, in molluscs – 2.4–6.7 years, and in fish – 7.8–12.9 years. The time for 90Sr concentrations to decrease to pre-accident levels were estimated: in freshwater reservoirs and the northwest part of the Black Sea this was 32–44 years, and in freshwater hydrobionts this was 25–73 years. The contribution of dose from 90Sr to the hydrobionts, sampled from the Kakhovskoe reservoir, the Northern-Crimean canal and the Black Sea, has not reached values which could impact them during the entire post-accident period. This complex of comparative studies was carried out for the first time.

Radionuclide migration at experimental polygon at Red Forest waste site in Chernobyl zone. Part 2: Hydrogeological characterization and groundwater transport modeling

Abstract This article represents the second of two articles, which review the main results of the international radioecological projects: Chernobyl Pilot Site Project (1999–2003) and Experimental Platform in Chernobyl (2004–2008). These projects studied radionuclide migration from the near-surface radioactive waste trench at the Red Forest waste dump in the Chernobyl zone, which contained nuclear fuel particles. This article presents results from the comprehensive hydrogeological site characterization program including the following issues: geological structure of the study site, hydraulic properties of the deposits, tracer tests in the aquifer, results of groundwater monitoring and unsaturated zone regime studies, as well as data on the 90Sr distribution in the unsaturated zone and aquifer, and analyses of 90Sr sorption behavior. The derived parameters were used to develop and calibrate 1D (flow tube) and 2D (cross-section) models describing the migration of 90Sr from the studied waste trench to the unsaturated zone and aquifer over a 16-a period (1986–2002). The models involved the following sub-models: (1) the geostatistical (structural) model for radioactivity distribution in the trench (using GSLIB); and (2) the radionuclide source term model (STERM1D) describing dissolution of fuel particles and a 1D of radionuclide redistribution in the trench body and unsaturated zone. The MODFLOW – MT3D codes were used to model the 2D 90Sr transport in the aquifer cross-section. Calibration of the 1D model with respect to Kds and dispersivities allowed quite accurate reproduction of 90Sr migration behavior for the early period (1995–1998). The less perfect fit between the 1D and 2D modeling results and monitoring data for the later period (1999–2002) suggests the need to improve the conceptual radionuclide migration model (i.e. to account for transient hydraulic and geochemical regimes of the waste site).

Geochemical influence of waste trench no. 22T at Chernobyl Pilot Site at the aquifer: Long-term trends, governing processes, and implications for radionuclide migration

This article discusses and analyzes data for geochemical monitoring of groundwater, collected in 1998–2008 at the international experimental radioecological study site (Chernobyl Pilot Site) located in the Red Forest radioactive waste dump site in the Chernobyl exclusion zone. Groundwater in the zone of influence of the studied waste trench no. 22T was characterized by a specific geochemistry. Along with a high content of 90Sr (of an order of n × 1000–n × 10,000 Bq/L) groundwater showed elevated concentrations of Ca, K, NO3-, SO42- and of some trace elements (in particular stable Sr), and had more acidic pH values compared to “background” aquifer conditions. The observed water quality changes are apparently related to degradation of organic matter (pine forest remnants, litter, humus containing topsoil layer) buried inside trench no. 22T, which have lead to acidification of groundwater and leaching of cations adsorbed on the exchange complex of soils buried inside the trench. Regime monitoring data for the project period of 1998–2008 shows a progressive decrease of concentrations of the leached ions accompanied by an increase of pH in the chemical plume emerging from the trench. This can be explained by a combined effect of a gradual decrease of the inventory, humification of the original organic matter inside the trench, and of nutrient element uptake by roots of the newly planted pine forest on top of the trench. The identified trends of evolution of geochemical regime favor attenuation of subsurface migration of 90Sr from Red Forest waste dumps due to an increase of the 90Sr distribution coefficients, and stabilization of plumes of contaminated groundwater.

Inventory and vertical migration of 90Sr fallout and 137Cs/ 90Sr ratio in Spanish mainland soils

In this paper the inventory of 90Sr in 34 points distributed along the Spanish peninsular territory is presented. Obtained values range between 173 Bq/m 2 and 2047 Bq/m 2. From these data set and those 137Cs data obtained in a previous work the 137Cs/ 90Sr activity ratio has been established, laying this value between 0.9 and 3.6. Also the migration depth of both radionuclides has been analysed obtaining for 137Cs an average value 57% lower than that obtained for 90Sr. Additionally, this paper presents the results obtained in 11 sampling points in which the activity vertical profile has been measured. These profiles have been analysed to state the behaviour of strontium in soils and after, by using a convective–diffusive model, the parameters of the model which governs the vertical migration of 90Sr in the soil, v (apparent convection velocity) and D (apparent diffusion coefficient) have been evaluated. Mean values obtained are 0.20 cm/year and 3.67 cm 2/year, respectively.