A model of radionuclide transfer by groundwater on the territory of the Russian Research Centre Kurchatov Institute

The convective transfer of ¹³⁷Cs and ⁹⁰Sr by groundwater on the territory of the Russian Research Centre Kurchatov Institute (RRCKI) was modeled. Geological data on the RRCKI site and possible sources of radionuclides show that the uppermost aquifer, composed of Quaternary sediments, is the most probable region of spreading of radioactive contamination. Since the lateral migration of radionuclides is predominant, a 2D horizontal model was used for the forecasting of spreading of radioactive contaminants in the subsurface medium. Transient or long-term repositories of radioactive materials at the RRCKI site (concentrated sources) and aquifer rocks contaminated in the course of removal of radionuclides from these repositories (distributed source) are responsible for groundwater pollution. The initial ¹³⁷Cs and ⁹⁰Sr distributions used in the forecasting of radionuclide migration were determined from their contents in core samples taken from wells drilled in contaminated areas of the RRCKI site. The zone of radionuclide migration is limited by poorly permeable moraine loam from below and by the water table from above. To determine the upper and lower boundaries, these surfaces were mapped in plan view. The data of meteorological observations over a long period were used to map the intensity of precipitation in the studied territory. The density of rocks in the uppermost aquifer and partition coefficients of radionuclides between rocks and groundwater were estimated from the data of laboratory examination of the core samples. The available data on the permeability of rock samples and the results of test pumping out of some wells were involved in the consideration. The results obtained and the data on the water table allowed us to define a gauge problem for determining the distribution of the filtration coefficient in the uppermost aquifer. This problem was solved taking the intensity of precipitation into account. The properties of the uppermost aquifer and the initial radionuclide distribution therein were used as initial data for modeling ¹³⁷Cs and ⁹⁰Sr migration on the territory of the RRCKI over 50 years.     

Results of Marine Radioecological Study of Fjords of Western Spitsbergen

The patterns of the distribution of technogenic radionuclides ¹³⁷Cs and ⁹⁰Sr in the water mass and bottom deposits of three fjords of Western Spitsbergen (Isfjorden and its arms Grønfjorden and Billefjorden) were studied. The hydrological processes affecting migration of radionuclides in these water bodies were described. It was shown that the ice sheet of the archipelago that accumulates atmospheric precipitation is a source of radioactive contamination of the marine environment of the coast. Technogenic isotopes were accumulated during nuclear weapon testing in the second half of the twentieth century. The current climatic changes strengthen the role of glaciers in the contamination of arctic seas. It was noted that extrema of the ¹³⁷Cs and ⁹⁰Sr specific activity is mainly concentrated in the areas of glacier runoff discharge.

     

Distribution and relationship of radionuclides to streambed gravels in a small watershed

In White Oak Creek watershed in eastern Tennessee, the radionuclides⁶⁰Co,⁹⁰Sr, and¹³⁷Cs were retained by streambed gravels on different sites:⁶⁰Co was associated with manganese in the hydrous oxide coatings on rocks and minerals;⁹⁰Sr occurred primarily as an exchangeable cation although small amounts were held in a nonexchangeable form; and¹³⁷Cs was held very selectively, presumably by illite in shale fragments composing the sediment. The distribution of radionuclides on sediments was size dependent: the 0.85–3.35 mm fine-gravel fraction was higher in radionuclide concentration than the sand fraction. An areal survey of radionuclide concentrations on streambed gravels from throughout the watershed, located numerous contamination sources. These radionuclide concentrations, when combined with both distribution coefficients of radionuclides between gravel and water and drainage area, were used to rank subsections of the watershed by their relative contribution to the overall contamination of the watershed. For⁹⁰Sr, this ranking procedure agreed with the measured discharges of subsections of the watershed which are routinely monitored. Research sponsored by the Oak Ridge National Laboratory (operated by U.S. Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation. Publication No. 2017, Environmental Sciences Division, ORNL.     

137Cs and 90Sr mobility in soils and transfer in soil–plant systems in the Novozybkov district affected by the Chernobyl accident

The Chernobyl radionuclides distribution and mobility in soils and uptake by plants have been studied in seminatural and agricultural moraine and in fluvioglacial landscapes typical for the areas of the Bryansk region affected by the accident.The major part of the Chernobyl ¹³⁷Cs accumulated in the topsoil is insoluble in water, 40 to 93% of this radionuclide is strongly fixed by soil, while 70 to 90% of the ⁹⁰Sr is present in water soluble, exchangeable and weak-acid soluble forms. Radionuclide vertical migration is most pronounced in local depressions with organic and gley soils in which both radionuclides are detected to the depth of 30–40 cm.In woodlands, most of the ¹³⁷Cs is still fixed in litter and the upper mineral soil layer. The concentration peak in litter has moved to the lower AOF layer. Concentration in topsoil leads to high radionuclide uptake by forest species with shallow root systems (bilberry, mushrooms, fern). Contaminated forest products may contribute considerably to the internal irradiation doses of the local population. On flood plain grasslands traditionally used by local populations for haycrops and grazing, radionuclides are more strongly fixed in soils with fine texture. Radioisotope uptake by plants decreases in the order: legumes>herbs>grasses. Transfer to grasses in local depressions is usually higher compared with the dry levees. Observed exclusions are assumed to be due to comparatively low mobility of ¹³⁷Cs and relatively high K content in soil. ¹³⁷Cs accumulation in potato tubers grown on sandy soddy podzolic watershed soils mainly corresponds to its total amount in soils; uptake of ⁹⁰Sr depends upon the percentage of its most mobile fraction.Pronounced relief is proved to cause different patterns in distribution and migration of radionuclides in soils and local food chains. The study showed it to be true for private farms situated in different landscape positions within the same settlement.The forest litter, topsoil and products, and flood plain pastures, especially localities in depressions are critical materials for the long-term radioecological monitoring of the contaminated landscapes of the study area and those of similar conditions. Population of the areas within the zone of contamination exceeding 15Ci/km² (555kBq/m²) should be recommended to exclude local forest products from their diets and to avoid cattle grazing on wet flood plain meadows without remediation.     

Assessment of 137Cs and 90Sr fluxes in the Barents Sea

The annual balance of radionuclides inflow/outflow was assessed for ¹³⁷Cs and ⁹⁰Sr isotopes in the Barents Sea, taking into account the atmospheric precipitation, inflow from the Norwegian and the White seas, as well as riverine discharge, liquid radioactive waste disposal (LRWD), and outflow to the adjacent seas. The original and published data for the period of 1950–2009 were analyzed. According to the multiyear dynamics (1960–2009), the inflow of ¹³⁷Cs and ⁹⁰Sr into the Barents Sea was significantly preconditioned by the Norwegian Sea currents; and precipitation played a major role in the 1950s, 1960s, and in 1986. Currently, the trans-border redeposition of ⁹⁰Sr prevails over ¹³⁷Cs redeposition in the Barents Sea, and constitutes about 99% of inflow of each element.     

A note on partition coefficient distributions

Much interest has been generated in assessing the possible risks of contamination for humans and marine life resulting from the dumping of nuclear waste in Arctic Seas by the former Soviet Union. Models are being used to predict the transport of radionuclides released from the dumping grounds. A key parameter in these models is the partition coefficient representing the uptake potential of marine sediments and seawater for radioactive contaminants. Partition coefficients are dependent upon the independent variables of sediment concentration and the sediment/water radionuclide distribution coefficients. Modelers must use estimated average values for the independent variables because data for these variables are lacking for the Arctic environment. In this note, we illustrate the differences between assuming that partition coefficients can be computed solely from the average values of the independent variables vs. exact probability distributions, and illustrate the technique for one of the radioactive contaminants,¹³⁷Cs. In general, errors in the sediment partition coefficient can be as high as 67% using average values; for¹³⁷Cs. the error is about 37%.     

Environmental evaluation of elemental cesium and strontium contents and their isotopic activity concentrations in different soils of La Mancha (Central Spain)

Cesium and Strontium concentrations were analyzed in eight pedogenetic soil profiles developed on different rocks from a semiarid mediterranean region: La Mancha (Central Spain). Concentration activities of ¹³⁷Cs and ⁹⁰Sr, as for some soil properties, were also measured. The results are presented in this document: Cs concentrations range between 0.4 and 18.3 mg kg⁻¹ and Sr varies widely between 11.0 and 3,384 mg kg⁻¹. Therefore, it is clear that there is a broad range of concentrations and there are also values significantly higher than the average values stated by several authors. Concentrations of long-life artificial radionuclides (¹³⁷Cs, ⁹⁰Sr) were determined in some of the same soils. The activity concentration mean values (Bq kg⁻¹) were ranging between 0.82 and 21.76 for ¹³⁷Cs and ⁹⁰Sr variations range between 6.73 and 0.35. There were no significant correlations between radionuclides and stable trace elements. The data indicate that the soils do not show significant radioactivity of these elements and therefore they do not pose a danger. By the same token, no risk of contamination by this activity was detected. Finally, spatial patterns seem to be affected by the soil type and some soil properties.     

Some geochemical and environmental aspects of the Chernobyl nuclear accident

The Chernobyl nuclear accident took place on 1986-04-26, and resulted in radionuclide pollution of vast regions of Byelorussia. This has raised several geochemical problems: (1) investigation of the distribution and behaviour of radionuclides in the natural and technogenic landscapes (which were examined as a result of a 5-a study); (2) modes of occurence of radioactive elements in the environment; and (3) preliminary estimation of radionuclide migration in the future. As background information, geochemical studies carried out within Byelorussia, as well as landscape investigations in the period 1953–1987 made under the guidance of K.I. Lukashev were very important for solving the above questions. According to the results of these investigations, the lithogeochemical and hydrogeochemical zoning of Byelorussia is understood and the radioactive background of the republic was studied in the 1960s, as well as the distribution and peculiarities of clay minerals, carbonates, FeMn oxides, organic matter, pH-Eh, and the contents of many elements in the surficial deposits of Byelorussia. All these factors are of great importance for understanding the behaviour of radionuclides.Radionuclide fallout on Byelorussia in the first days after the accident was mainly dependent on the mass movement of air and rain. In cities, fallout was confined to regions with intensive industrial dust emissions, as well as to river valleys, where degassing of deep-seated zones through faults occurred side by side with evaporation. Radionuclide washout from upland territories can be related to secondary processes.After 5 a, the radioactive emission near the surface of the Earth decreased due to the decay of short-lived isotopes and penetration of radionuclides deeper into the soil, although the major part still occurs at a depth of 1–5 cm. Bogs, peat-bog soils, aquifers with fluctuating groundwater levels, variable pH-Eh conditions and a igh biological activity are all factors contributing to radionuclide migration in the Byelorussian landscape. A part of the radionuclides is gradually removed from eluvial landscape and accumulated in subareal landscape (e.g. lakes, oxbow-lakes, water-storage basins).The Chernobyl debris are represented by the following substances: “hot” particles, pseudocolloids, aerosols and gaseous compounds. Study of the modes of occurrence of radionuclides by different methods (e.g. extracts, sorbents) made it possible to estimate the migration capacity of some radionuclides (Cs, Sr, Ce, Ru), and to distinguish two zones around the reactor—the nearest and remote ones—differing in the ratio of “hot” particles and condensate fallout, which causes a different migration capcity of radionuclides.A very important part is assigned to biological processes and organic matter, which cause the destruction of “hot” paricles, the formation of organomethallic complexes, and water migration of nuclides.In the future (within 300 and more years), the redistribution of radionuclides in the landscape involves processes of weathering, erosion and sedimentation which will strongly depend on climatic conditions, Side by side with a gradual decay of Cs and Sr, an appreciable accumulation of²⁴¹Am, which is very mobile in landscape, should be expected due to decaying²⁴¹Pu.A considerable development of scientific and applied exploration should also be expected in the future and this will help in solving problems of radioactive pollution of landscapes.     

环境生态系统散落核素示踪研究新进展

环境生态系统中的放射性核素既具有生态毒性,对生物和人体健康产生重要影响,又具有稳定的衰变函数和输入通量,对环境生态系统具有重要示踪价值。人类可利用放射性核素来认识环境生态系统:①环境生态系统中放射性核素的基准:放射性强度与环境生态系统之间的平衡关系;②环境生态系统中放射性核素的行为:在环境生态系统不同宿体和组分间的运移关系。考察放射性核素在生态系统不同环节中比活度的变化有助于认识环境生态过程生物地球化学作用的影响。       

Strontium-90 in surface and groundwater of the reclamation systems at the Chernobyl exclusion zone

The left bank of the Pripiat' river, opposite of the Chernobyl Nuclear Power Plant (ChNPP) is covered with a developed network of drainage canals, built for the reclamation of the swampy floodplain. This area is highly contaminated after the disaster in 1986. Concentrations of the most mobile radionuclide, ⁹⁰Sr, are comparable with ¹³⁷Cs, and reach many MBq m^-2. Their ratio in the upper 10 cm of soil is about 1. The high surface contamination as well as precipitation and flooding have been responsible for the water pollution in this area. Some specifics of ⁹⁰Sr behaviour in surface and groundwater, controlled by the hydrological regime, are described.     

Erosion rate in badlands of central Italy: estimation by radiocaesium isotope ratio from Chernobyl nuclear accident

The input of¹³⁷Cs into the troposphere from the Chernobyl nuclear accident made intriguing the use of fallout¹³⁷Cs as a tool for estimating the rate of soil erosion over Europe. The present paper reports on the adoption of¹³⁷Cs/¹³⁴Cs activity ratio to differentiate the vertical distribution of¹³⁷Cs prioir to and following the Chernobyl accident. The¹³⁷Cs/¹³⁴Cs activity ration in the radioactive clouds is required to calculate pre and post- 1986¹³⁷Cs amounts, considering that the whole¹³⁴Cs was actually derived from Chernobyl. By using this procedure, the erosion rates could be evaluated for the badland area, the Paglia River basin (central Italy), before and after the Chernobyl accident. Nine sites from two areas of this basin were sampled and analyzed. Erosion rates, ranging from 1.5 to 8.4 mm/a were measured, the values depending both on the basin lithology and site slope. These first results are consistent with those yielded by quantitative geomorphologic methods.     

Estimate of the density of global fallout of cesium-137 according to the data of its content in closed geochemical arenas of southwestern Siberia

The density of global radioactive contamination was the most reliable estimated in marine regions and less accurate for intracontinental areas with semi-arid and arid climatic conditions. This work presents the results of using a new method developed for estimating the density of global radioactive contamination based on the calculation of ¹³⁷Cs concentration in closed lake catchments. An average density of of ¹³⁷Cs contamination in the model closed lake catchments of southwestern Siberian steppe landscapes is 0.80 ± 0.24 kBq m^–2 that is 2–3 times lower than the levels calculated on the basis of the published data.     

Migration of transuranic elements in groundwater from the near-surface radioactive waste site

Field experiments and laboratory studies were performed to investigate migration processes of plutonium isotopes from a near-surface radioactive waste trench to the underlying sandy aquifer at the Red Forest waste dump in the Chernobyl zone. The objectives of these experiments were to characterize the spatial distribution and possible migration mechanisms of plutonium in the aquifer. During 2002–2007 experimental investigations were carried out and spatial distributions of plutonium isotopes (^239,240Pu, ²³⁸Pu), ⁹⁰Sr and major ions in the aquifer in the direction of the groundwater flow were obtained. Specific activities of radionuclides in groundwater depended on the location of the piezometer and varied in the range of 1–360 mBq kg⁻¹ for ^239,240Pu, 0.5–180 mBq kg⁻¹ for ²³⁸Pu and n–n·10⁴ Bq kg⁻¹ for ⁹⁰Sr. It was found that the spatial features of the distributions of plutonium and strontium specific activities in the upper eolian aquifer were similar, i.e. there was a correlation between the positions of the activity maxima of the radionuclides. The Pu isotopes plume in the aquifer spreads about 15 m downstream of the radionuclides source. Characterization of the initial radionuclide composition of the waste showed that all plutonium in the aquifer originated from the trench. The ratio of plutonium isotopes (^239,240Pu/²³⁸Pu) at the sampling time was the same in waste material and in groundwater samples. In situ ultrafiltration of several groundwater samples was carried out. The size fractionation data obtained suggest that a significant part of plutonium (50–98%) in the groundwater sampled close to the source from the upper part of the aquifer is associated with a very low molecular weight fraction (<1 kDa).     

Estimation of radioactive leakages into the Pacific Ocean due to Fukushima nuclear accident

High concentrations of several radionuclides were reported in the sea near the Fukushima Daiichi Nuclear Power Station (FDNPS) in Japan due to the nuclear accident that occurred on 11 March 2011. The main source of these concentrations was leakage of highly radioactive liquid effluent from a pit in the turbine building near the intake canal of Unit-2 of FDNPS through a crack in the concrete wall. In the immediate vicinity of the plant, seawater concentrations reached 68 MBq m^?3 for ¹³⁴Cs and ¹³⁷Cs, and exceeded 100 MBq m^?3 for ¹³¹I in early April 2011. These concentrations began to fall as of 11 April 2011 and, at the end of April, had reached a value close to 0.1 MBq m^?3 for ¹³⁷Cs. Following the nuclear accident, the Tokyo Electric Power Company (TEPCO) had initiated intense monitoring of the environment including the Pacific Ocean. Seawater samples were collected and the concentrations of few radionuclides were measured on a wide spatial and temporal scale. In this study, the measured concentrations of different radionuclides near the south discharge canal of the FDNPS were used to estimate their leakages into the Pacific Ocean. The method is based on estimating the release rates that reproduce the concentration of radionuclides in seawater at a chosen location using a two-dimensional advection–dispersion model in an iterative manner. The radioactive leakages were estimated as 5.68 PBq for ¹³¹I, 2.24 PBq for ¹³⁴Cs and 2.25 PBq for ¹³⁷Cs. Leakages were also estimated for ^99mTc, ¹³⁶Cs, ¹⁴⁰Ba and ¹⁴⁰La and they range between 0.02 PBq (^99mTc) and 0.53 PBq (¹⁴⁰Ba). It was estimated that about 11.28 PBq of radioactivity in total was leaked into the Pacific Ocean from the damaged FDNPS. Out of this, ¹³¹I constitutes 50.3 %; ¹³⁴Cs 20 %; ¹³⁷Cs 20 %; ¹⁴⁰Ba 4.6 %; ¹³⁶Cs 2.6 %; ¹⁴⁰La 2.3 % and ^99mTc 0.2 % of the total radioactive leakage. Such quantitative estimates of radioactive leakages are essential prerequisites for short-term and local-scale as well as long-term and large-scale radiological impact assessment of the nuclear accident.     

Permeable reactive barriers based on natural zeolites from Kazakhstan in solving ecological problems: Mathematical model and simulation

In view of ecological problems stemming from the leakage of reservoirs with liquid radioactive wastes (LRW) and groundwater contamination with radioactive Cs⁺ and Sr²⁺, we have estimated the physicochemical (including sorption) characteristics of clinoptilolite-bearing tuff (CBT) from the Chankanai deposit in Kazakhstan. Data were obtained on the chemical and phase composition of CBT, its total cationexchange capacity, and equilibrium (exchange isotherms) and kinetic (diffusion coefficients) characteristics in sorbing radioactive Cs⁺ and Sr²⁺ from 0.07 n CaCl₂ solution (model solutions of groundwaters). We proved that CBT efficiently sorbs Cs from this solution and practically does not sorb Sr and elucidated the reasons for the low selectivity with respect to Sr²⁺. Based on the equilibrium and kinetic characteristics of the process, a mathematical model is suggested for Cs sorption under dynamic conditions. The protection lifetime of the clinoptilolite-based geochemical barrier is evaluated.     

Flocculation improves uptake of Sr and Cs from radioactive effluents

This paper presents the results of investigation on uptake of radioactive species ⁹⁰Sr and ¹³⁷Cs present in the liquid effluents from nuclear processing plants. Chemical precipitation process is adopted to remove radioactivity from the effluents with low and intermediate level of activity. In this process, radioactive ⁹⁰Sr and ¹³⁷Cs are co-precipitated along with copper ferrocyanide, ferric hydroxide and either calcium phosphate or barium sulphate. These precipitates being fine in size require flocculation for enhanced settling rate in clarifier/thickener. The flocculation by some selected high molecular weight polyacrylamide based polymers has improved the uptake of radioactive metal ions. The adsorption of these radioactive species has been found to increase in the presence of these flocculants thereby improving the decontamination factor (DF). While flocculating the precipitates, there may be some complex formation with Sr²⁺/Cs⁺, flocculant and the substrate. This has enhanced the uptake of the radioactive metal ions from the liquid component. The plant trials have indicated the improvement of DF value due to flocculation by cationic flocculant.     

Annual cycle of radionuclide contamination on tide-washed pasture in the Mersey Estuary, NW England

The radionuclide burden of vegetation comprising a tide-washed pasture at Ince Marsh in the Mersey Estuary, U.K., derives mainly from adhered external particulates originating as suspended sediments in estuarine water. Radionuclide concentrations are dominated by the growth cycle of the vegetation, with the highest winter levels of contamination activity an order of magnitude greater than the lowest levels in mid-summer. A secondary effect due to sediment transfer during periods of severe flooding produces subsidiary features on this dominant seasonal profile. Radionuclide concentrations on vegetation are in the range¹³⁷Cs=8–191,¹³⁴Cs=0.3–0.9,²⁴¹Am=0.6–46,²³⁸Pu=0.1–1.5, and^239/240Pu=0.8–44 Bq kg⁻¹. These ranges reflect the relative concentrations of radionuclides in estuarine sediment (¹³⁷Cs=615,²⁴¹Am=202, and^239/240Pu=104 Bq kg⁻¹) rather than the values in filtered estuary water (¹³⁷Cs=0.4,²⁴¹Am=0.001, and^239/240Pu=0.001 Bq 1⁻¹). Median K_d values for these radionuclide species are Cs=1,400, Am=200,000, and Pu=80,000 1 kg⁻¹).     

Ice accumulation rate in Changme-Khangpu glacier,Sikkim

Vertical profiles of¹³⁷Cs and²¹⁰Pb have been determined in a 9 m column of ice from accumulation zone of Changme-Khangpu glacier in north Sikkim valley.¹³⁷Cs activity varies from 4 to 22 dpm/ L. In many samples²¹⁰Pb occurs at a level of 20 to 65 dpm/ L which is much higher than the expected fallout value.¹³⁷Cs and²¹⁰Pb activities correlate well with each other but not with the dust content. Possibility of²¹⁰Pb production in the nuclear explosions is discussed. Several peaks appear in the depth profile of¹³⁷Cs and²¹⁰Pb which can be matched with Chinese atmospheric nuclear explosions with some phase difference if a uniform ice accumulation rate of 0.7 m per year is assumed since 1969.     

Chernobyl radiocaesium in a karst system,Marble Cave,Crimea

 Surface contamination with radioactive caesium introduced into the environment after the accident at the Chernobyl nuclear plant was high enough in the Crimean Mountains to allow using radiocaesium as an indicator of penetration of radioactive contamination into a karst system. Caesium concentrations have been studied in soils above Marble Cave, Tchatyrdag Plateau, in percolation waters and in sediments transported by percolation waters within the cave. Contamination of the daylight surface with ¹³⁷Cs is about 30 kqB m^–2 which is approximately 13 times higher than the density of global fallouts. Besides ¹³⁷Cs, almost all samples showed presence of ¹³⁴Cs with the ¹³⁷Cs/¹³⁴Cs ratio close to that of Chernobyl contaminations. Concentrations of ¹³⁷Cs range from 9 to 15 mBq l^–1 in the present percolation waters in the cave. In sediments related to percolation waters ¹³⁴Cs is detected in some samples besides ¹³⁷Cs, although the effect of ²²⁸Ac is not ruled out. Surprisingly, the highest concentrations of radiocaesium were measured in "old" sediments in the cave's lower series. These sediments are not associated with modern percolation and are represented by a clay/moonmilk alternating sequence deposited in an old dried cave lake. Moonmilk layers have higher caesium content than clay. It is assumed that Chernobyl caesium was transported into the cave with aerosols which were then deposited mainly in areas where condensation occurs. The sampling site is located just in the boundary between two microclimatic zones with a temperature gradient of 0.5  °C. Active condensation processes occur in this area. Caesium was not detected in another similar sampling site (old lake deposits) located within homogeneous microclimatic conditions. If the above interpretation is correct, these results show the geochemical significance of the aerosol-condensation mechanism of mass transport and localisation. Received: 1 June 1995 · Accepted: 4 December 1995