Journal of Environmental Radioactivity 135 (2014) 128e134

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Characteristic of pollution with groundwater inflow 90Sr natural waters and terrestrial ecosystems near a radioactive waste storageq G.V. Lavrentyeva* Candidate of Biological Sciences, Department of Ecology, Obninsk Institute for Nuclear Power Engineering, Branch of the National Research Nuclear University MEPhI, Studgorodok, 1, 249040 Obninsk, Kaluga Region, Russian Federation

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 July 2013 Received in revised form 18 April 2014 Accepted 22 April 2014 Available online

The studies were conducted in the territory contaminated by 90Sr with groundwater inflow as a result of leakage from the near-surface trench-type radioactive waste storage. The vertical soil 90Sr distribution up to the depth of 2e3 m is analyzed. The area of radioactive contamination to be calculated with a value which exceeds the minimum significant activity 1 kBq/kg for the tested soil layers: the contaminated area for the 0e5 cm soil layer amounted to 1800  85 m2, for the 5e10 cm soil layer amounted to 300  12 m2, for the 10e15 cm soil layer amounted to 180  10 m2. It is found that 90Sr accumulation proceeds in a natural sorption geochemical barrier of the marshy terrace near flood plain. The exposure doses for terrestrial mollusks Bradybaena fruticum are presented. The excess 90Sr interference level was registered both in the ground and surface water during winter and summer low-water periods and autumn heavy rains. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Storage of radioactive waste 90 Sr Migration in soil Water Terrestrial molluscs

1. Introduction Now the emission of technogenic radionuclides into the environment is under a rigorous control of atomic power enterprises, however, the problem of ecological safety of radioactive waste (RAW) storage sites created in the second half of the last century is unsolved yet. It must be borne in mind that the RAW storage are in operation for 35e55 years and do not meet the current regulation requirements to a long-term radioactive waste storage (IAEA Safety Standards Series, 2011; SR, 2003). Proceeding from their forecasted conditions, the break of tightness and radionuclide ingress in the environment are expected and this may result in the additional exposure source for population and ecosystem as a whole. As a result of such emergency situations, practically all feasible measures aimed at security assurance are to be carried out, including those on the abatement of radionuclide migration in natural habitats. In turn, it is possible with regular monitoring of territories

q This research was conducted with financial support from Rosatom State Corporation (State Agreement No, 1054 This research was conducted with financial support from Rosatom State Corporation (State Agreement No. H.4b.43.9B.14.1054) and the Grant of the President of the Russian Federation (Agreement No.14.125.13. 368-MK). * Tel.: þ7 961 122 71 06. E-mail address: [email protected]. http://dx.doi.org/10.1016/j.jenvrad.2014.04.013 0265-931X/Ó 2014 Elsevier Ltd. All rights reserved.

polluted by technogenic radionuclides (IAEA Safety Standards Series, 2005). The article is aimed at the researching of characteristic of natural waters and terrestrial ecosystems pollution with groundwater inflow 90Sr. Despite a body of information on the features of technogenic radionuclide migration in natural habitats as a result of accidental releases from RAW storages (Roudak et al., 2011; Monastyrskaya et al., 2012; Simakov et al., 2008; Shandala et al., 2008; Sneve et al., 2007; Lavrentyeva et al., 2012a; Lavrentyeva, G.V., 2013), it should be considered that the radionuclide behavior will be highly dependent on the specific geomorphological, landscape, naturalclimatic and other characteristic of the ecosystem. Studies of radionuclide migration features depending on local conditions will allow the methodical basis of radioecological territory monitoring at a regional level to be expanded. The paper presents radioecological studies in the territory of a regional RAW storage. This object had been put into operation in the 50e70s of the last century. Now the object is a closure. There are 4 trench storage facility (N  1, 2, 3 and 4) (Fig. 1) for solid RAW in the object territory. The total waste volume is about 2500 m3. There is also a reinforced concrete container (N  5) of 330 m3 in volume for liquid RAW collection and storage (Vasiljeva et al., 2007). The territory under studies is situated in the middle of the river Protva basin in the terrace above flood- plain within the actual elevation 131e145 m. The distance to the river is 1000e1200 m. The

G.V. Lavrentyeva / Journal of Environmental Radioactivity 135 (2014) 128e134

129

oxide. Strontium carrier solution (50 mg of metal) and 5 M HNO3 of 200e300 cm3 in volume were added in a glass with annealed soil. The soil/solution mixture was boiled in a sand-bath during half an hour. A solution was separated from a solid phase by filtration. Solid soil was twice treated by boiling in 4e5 M HNO3 during half an hour. After filtration the solid soil sediment had been washed three times with distilled water in a filter. After filtration the solutions were combined and evaporated to 100 cm3. A version of oxalate precipitation was used to separate strontium from other radionuclides and chemical elements and to concentrate it. Ethanedioic acid solution (95 g/l H4C2O2) in the quantity of about 100 cm3 was added to the solution obtained after desalinization and evaporation. pH ¼ 4 in a solution was set by deacidification with an aqua ammonium solution. The solution with an oxalate precipitate was stayed for 4 h, further a precipitate was elutriated and washed twice with hot distilled water in a filter. A precipitate and a filter were dried and then annealed at 7500S in a muffle furnace during an hour. Hereafter a precipitate was put into a glass and dissolved in 3e4 M HNO3, the solution acidity was set at 3.0 M/l (the solution volume is preferably made up to 5e 10 cm3). When the accompanying components were separated, 90Sr was cleaned by extraction. Nitric-acid solution was put in a separating funnel of 50e100 cm3, poured with chloroform in a 2:1 ratio of the aqueous and organic phases, shaked up and phased. After phase separation, the aqueous solution was added by 5e10 cm3 dicyclohexane-18-crown-6 in 0.2 M of a chloroform solution and extracted by shaking up during 30 s. The organic phase was washed with two portions of 2M HNO3 solution in a 1:1 ratio; the aqueous phase was rejected. The extract (organic phase) or its aliquot part was put on a target and dried under an infrared lamp. Dry matter bactivity on the target was measured. Fig. 1. Diagram of sampling points at the RAW storage site and the adjacent territory.

2.2. Plant sample analysis storage facilities are put in well-drained, mainly sand deposits. The flood plain begins at a 100 m distance from the RAW storage. The soil is generally soddy-podzolic formed on deluvial and moraine loam. The soil texture is loamy and heavy clay loamy. In 1998e1999 the increased specific activity of 90Sr had been revealed in the surveying wells and in the following this was stipulated by surface water penetration in one of the facility (N  4). Storage facility N  4 has size: 21.5  10 m and a depth of 3 m. In reservoir overfilling, 90Sr and 137Cs radionuclide exposed water escaped outside. Multi-year studies allowed one to establish that 90Sr contributes much to radioactive contamination on the territory near the storage and in the adjacent territory (Vasiljeva et al., 2007; Lavrentyeva, 2013). 2. Materials and methods

Plant e great nettle (Urtíca dióica) e samples were collected at the same sites (Fig. 1). Before analysis, fresh crude plant samples were washed from dust and soil first with tap water, then with distilled water. Then the plant mass was dried up in desiccators at 80e850S. A dried plant sample was milled. The optimal size of plant fragments had to be about 1e5 mm. Plant mineralization was realized by dry ashing. After digestion a sample had undergone acid treatment according to the above procedure (Instruction, 1994). Analysis of radionuclide content in the studied soils was conducted by comparison with the regional background of radionuclide content in the soils within the 30-km radius of the Obninsk reactors, as well as levels of global fall-outs resulting from technogenic emissions and the disaster at the Chernobyl Nuclear Power Plant. The 90 Sr value amounted to 1.2e1.8 Bq/kg. (Vasiljeva et al., 2007; YB, 2011; Ivanov et al., 1999).

2.1. Soil sample analysis 2.3. Mollusk sample analysis Soil samples are collected by a special sampler with a set of Edelman hand soil drills (Eijkelkamp Firm, Netherlands). Layer-bylayer sampling had been carried out in a 5 cm increment to 50 cm and a 10 cm increment up to 2e3 m at controlled sites noted in the Fig. 1. Soil sample preparation for assessing 90Sr content had been realized according to the (Instruction, 1994). Soil mass of 1 kg was counter balance weighed and uniformly distributed on a stainless steel griddle in the layer of 20e30 mm in thickness. To dehumidify, the griddle with samples had been kept in a drying box at 110  C during 5e7 h. Dried samples were disintegrated and mixed in a mortar to the grain size of 2e3 mm. Then the mean average sample (mass 50e300 g) of air-dried soil was analytical balance weighed. The sample had been annealed in a muffle furnace at 700e750  C to transform the basic mass into

Terrestrial mollusks Bradybaena fruticum were collected from plants (great nettle (Urtíca dióica)) and soil under plants at the tested sites (Fig. 1). At least 10 specimens were chosen in each mollusk sample. First soft tissues were removed from shells. Shells were grinded in a mortar, hereafter the direct 90Sr activity measurements were performed. Samples had been incinerated in a muffle furnace at 450  C during 6 h. Radiochemical separation and 90Sr content assessment were realized according to the above procedure. 2.4. Water sample analysis Well and hole water was sampled according to the state standard (SS, 2000). Water samples were collected from the following

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objects (Fig. 1): the surveying well C4 located near an emergency storage; the creek in the storage area on the marshy terrace near flood plain primarily supplied by groundwater (top water); the marshy territory appeared for a time after heavy rains and snow melting near site 7d. Water samples were acidified with nitric acid to pH ¼ 1e2 in the universal indicator paper. For that purpose the carriers in a form of nitric-acid solutions were added to the water solution: 10e20 mg strontium (in terms of metal) and 20 mg/l calcium. The carrier, i.e. alkaline-earth element (AEE) was precipitated as carbonates for strontium radionuclide concentration. The activity of 40K, 90Sr and 137Cs was measured in a scintillation b-spectrometer «BETA-01S» according to the standard procedure for assessing 90Sr concentration from b-radiation of its daughter 90Y radionuclide in environmental objects (Instruction, 1994). 2.5. Calculation of annual exposure doses for mollusks The annual doses of external b-exposure of mollusk tissues due to 90Sr and it daughter 90Y radionuclide contained in shells were calculated with software package ERICA Tool (Brown et al., 2008; Garnier-Laplace, Gilbin, 2006). 3. Results and discussion 3.1. Pattern of soil contamination with and the adjacent area

90

Sr at the RAW storage site

The analysis of long-term data (2004e2007) on the 90Sr radionuclide content in the soil of the studied site and the continued experimental work (2010e2013) allowed us to establish the following. A 1.5e2-fold reduction of the specific 90Sr activity in soil near the studied object had been observed from 2005 to 2012 (Fig. 2); this reduction may be stipulated by self-cleaning of ecosystem from radioactive contamination including radioactive decay, secondary dispersal, soil and plant radioisotope distribution, formed natural geochemical barriers and technogenic measures. We shall not forget about active horizontal displacement of radionuclides that occurs in flood plains, as a result of surface runoff after heavy rains or land loss during snowmelt runoff. The increase was observed of 90Sr concentration gradient from the contamination source (emergency storage) to the sampling sites 6a, 10e and 11 located beyond the object territory. In turn, it may be also was determined by lithological and geomorphological characteristic of the territory. The description of a lithological structure in the object territory shows that storage facility are put into well-drained, primarily

sampling site 1

Specific Sr-90 acƟvity, Bq/kg

55

sampling site 2c 45

sandy deposits (Table 1). The moraine loam depth is low and it can not be a reliable barrier under emergency situations. The first reliable aquitard represented by almost a 20-meter continuous clay soil is found at the depth from 23 m in the storage top to about 18 m in its lower part. The characteristic of a geomorphological territory structure also contribute to the surface and internal soil radionuclide migration (Vasiljeva et al., 2007). In this case the surface runoff 90Sr migration is stipulated by the following factors. Surface slopes of about 10-150 promotes to surface erosion. The low-thickness (not more than 1 m at the bottom of the slope) deluvial formation is the redeposited clay loam. The presence of almost rectilinear hollows along the maximum gradient lines is indicative of the low erosion soil stability. The flushing water conditions in the aeration zone, light soil texture, significant slope of territory are reason of the active internal soil migration of 90Sr. At the depth of 6 m in the centre of the terrace slope and at about 3 m in its lower part the sand is underlain by loam which serves a confining layer for top water; in the lower slope part it crops out and groundwater is discharged here. We must note that texture of the soil (silt, clay) of the adjacent territory contribute to minimization of the 90Sr migration processes (Table 2). It offers the expected formation of a natural geochemical barrier at the sites 6a, 10e and 11 where this radionuclide is accumulated. During eight years, the 90Sr specific activity at the sampling points of that area has increased on average by 1.7e2 times. The 90Sr maximum specific activity in soil exceeding 1 kBq/kg was recorded in 2012 at the sampling points 6a (1,7  0,3 kBq/kg), 10f (1,1  0,2 kBq/kg) and 11 (1,6  0,2 kBq/kg) outside the storage site (Fig. 1). Due to significant irregularity of contamination of the studied site with 90Sr, we took separate measurements of the radionuclide specific activity from various soil sublayers in the sampling points. The data analysis of radionuclide vertical distribution in the soil behind the site allowed us to establish the following characteristics. Relatively similar dependence of radionuclide specific activity at depths was discovered for soddy glay soil of back marsh (points 6a, 10f and 11) (Fig. 3). The 90Sr maximum specific activity of 1.7 kBq/ kg was recorded in the upper 2-cm layer, which may be caused by few factors. First, the soil samples collected in the upper layer that concentrate 90Sr represent clay loam, which contributes to reduction of radionuclide migration processes due to its active sorption. Second, a drift of silt from contaminated areas may occur during flood, as well as runoff from a contaminated RAW storage site. Third, active fixation of 90Sr by soil organic fraction may occur. In spite of the fact that, in the next soil layers, we can observe a trend of drastic decrease of radionuclide activity (3e8 times), which may be related to predominance of sand deposits, 90Sr migrates to the deeper layers; even at the 2-meter depth, it reaches a value that exceeds value (1.2e1.8 Bq/kg) by 80e100 times. A slightly different picture of radionuclide distribution in soils is observed at the RAW storage site (Fig. 3). A relatively uniform 90Sr distribution through immature soddy soil profile may be caused by biogeochemical and technogenic factors. First, the processes of

35 Table 1 Description of the lithological basis of the territory of the RAW storage (Vasiljeva et al., 2007).

25 15 5 2005

2010

2011

2012

Year Fig. 2. Change in the specific activity of (error is a confidence interval).

90

Sr in soils of the territory of the RAW storage

Depth, meter

Soil characteristics

0e0.5 0.5e8.8 8.8e11.7 11.7e13.5 13.5e15.7 15.7e16.8

Backfill soil Alluvial consertal sandstone Alluvial fine low-loamy sand Moraine loam with a high gravel and pebble concentration Fluvioglacial consertal sandstone with gravel and pebble Gravel-pebble and sandy fluvioglacial deposites

G.V. Lavrentyeva / Journal of Environmental Radioactivity 135 (2014) 128e134

131

Table 2 Dose rate of terrestrial mollusc external exposure to the b e particles and characteristic of sampling points. Sampling points

Characteristic of sampling points

Dose rate on mGy/year

1b 1 2a 2c 2b

Fluvioglacial and alluvial sandy sediments, disturbed soil. Herb-grass vegetation.

84.0 76.0 346.0 46.0 653.0

3 4 6 6a 7b 7d 10 10a 10b 10c 10d 10e

Fluvioglacial and alluvial sandy sediments, disturbed soil. Buried diluvial loam soil (redeposited covering loam) closed 40 cm thick layer of sand deposits. Herb-grass vegetation. The surface is not swamped, covered with diluvial loam. Reclaimed turf medium loamy soils. Raspberry, filbert, in a grassy nettle tier dominates. The surface is not swamped, covered with diluvial loam. Reclaimed turf with signs podzolization medium loamy soils. Raspberries in a grassy tier dominates nettle, hops. Swampy surface, covered with silt (depht of 2e10 cm) with the inclusion of weakly decomposed plant residues. Alder, aspen, nettle. Swampy surface, covered with silt (depht of 2e10 cm) with the inclusion of weakly decomposed plant residues and sand. Alder, aspen, nettle, hops. Swampy surface, covered with silt (depht of 2e5 cm) with the inclusion of weakly decomposed plant residues, sand. Alder, willow, aspen, bulrush. Swampy surface, covered with silt (depht of 2e5 cm) with the inclusion of weakly decomposed plant residues and sand. Alder, aspen, nettle. Swampy surface, covered with (depht of 2e5 cm) with the inclusion of weakly decomposed plant residues and sand. Alder, aspen, nettle, hops. Swampy surface, covered with (depht of 2e5 cm) with the inclusion of weakly decomposed plant residues and sand. Alder, aspen, nettle.

90

Sr,

Dose rate on mGy/year

137

Cs,

Dose rate on mGy/year

40

K,

14.0  2.0 28.0  3.0 57.0  5.0 1$102  1$103 12.0  2.0

1.0  1$101 94$102  8$102 99$102  7$102 83$102  9$102 2.0  1.0

35.0  3.0

1$102  1$103

94$102  7$102

56.0  5.0

2$102  1$103

82$102  9$102

    

6.0 8.0 5.0 7.0 13.0

134.0 281.0 62.0 89.0 537.0

    

24.0 31.0 12.0 17.0 37.0

e 5$102  3$103 2$102  1$103 e 3$102  1$103

e 69$102  8$102 1.0  1$101 e 1.0  8$101

182.0 74.0 50.0 47.0

   

27.0 4.0 13.0 7.0

1$102  2$103 12.0  3.0 17.0  4.0 27$102  2$102

1.0 1.0 1.0 1.0

28.0  5.0

1.0  8$102

77.0  7.0

   

9$101 7$101 7$102 5$102

 Confidence interval.

subsoil inflow of radionuclides and their penetration into upper layers mostly occur due to filtration and capillary rise of contaminated waters. Second, the absence of scrub and tree vegetation at the site near the sampling point leads to minimization of radionuclide fixation in the upper layer. The third factor is technogenic e performance of overburden work after intake of radionuclides in groundwater, and mixing the soil layers with various activity. At

that, the 90Sr specific activity at different depths exceeds the background value by 50e120 times. The obtained data allowed the area of radioactive contamination to be calculated with a value which exceeds the minimum significant activity 1 kBq/kg for the tested soil layers: the contaminated area for the 0e5 cm soil layer amounted to 1800  85 m2, for the 5e 10 cm soil layer amounted to 300  12 m2, for the 10e15 cm soil

Fig. 3. Vertical distribution of 90Sr in soils inside (sampling points 2a, 2c and 2d) and outside (sampling points 6a, 10e and 11) the RAW storage site (error is a confidence interval).

132

G.V. Lavrentyeva / Journal of Environmental Radioactivity 135 (2014) 128e134

layer amounted to 180  10 m2 (SR, 2002). These data may be of service in developing the program of 90Sr contaminated soil rehabilitation at the stage of RAW storage decommissioning. 3.2. Biota exposure dose in the RAW storage area Terrestrial mollusks Bradybaena fruticum have been chosen as reference species most properly reflecting the ecosystem 90Sr effect. Some papers (Khmeleva et al., 1993; Frantsevich et al., 1995; Gudkov et al., 2009) have stated that practically the whole amount of radioactive strontium is concentrated in a mollusk shell. In addition, the content of 90Sr in mollusk shells is primarily governed by the ground contamination level and undergoes insignificant seasonal and taxonomic variations. In view of ICRP recommendations on a step-by-step approach to the radioecological situation analysis, this paper presents results of the first stage which involves the screening analysis to reveal obvious situations not requiring further consideration (ICRP, 2009). The screening value meant for the initial biota safety assessment is taken equal to 10 mGy/h. It should be noted that this value is taken as a safe biota exposure limit within the European PROTECT project (Kryshev, Sazykina, 2013). Taking the foregoing into account, further studies of radioecological conditions are not efficient at the local sites, where the is not target of exceeding. Hence, the next stage of these radioecological studies intended for a more detailed analysis in view of local ecosystem contamination conditions should be carried out at the sites with consideration of the safe biota exposure limit (Table 2). 3.3. 90Sr content in surface and underground waters at the RAW storage site and the adjacent area In 2010, the 90Sr volumetric activity was measured in water samples collected each season from inspection wells and controlled water bodies where the highest radionuclide activity was recorded earlier (Lavrentyeva et al., 2012b): in the surveying well; in the creek; and in the marsh (Fig. 1). In the context of hydrology, the year 2010 had no significant deviations from the average many-year characteristics. The steady negative winter temperature in 2009e2010 had begun from 6 December, 2009 and lasted until 20 March, 2010. Snow had fallen on the thawed ground and did not melt in winter months. About 121  15 mm of snow had precipitated during this period. Thus, snow melting in 2010 took place under the conditions of the active snow water discharge through the thawed ground into the underground horizons. Spring flood under such conditions was characterized by low water and weak inversion feed of surface water into the underground water-bearing layers. The transition to stable positive temperature was registered on the 20th of March. This date is the end of a winter low-water period

Table 3 Activity concentration of

90

Sr in groundwater surface water near the RAW storage.

Object

Date

Activity concentration, Bq/l

The surveying well C4

15.03.10 15.06.10 22.07.10 20.10.10 15.06.10 22.07.10 20.10.10 15.06.10 22.07.10 20.10.10

34 29 34 38 5 34 38 2 1 5$101

The creek

The marsh

 Confidence interval.

and the start-up of spring snow melting and heavy rains. The period of spring heavy rains and active snow melting was observed from 20 March to 18 June. During this period the main bulk of the slope runoff (288  17 mm), consisting of melt-water (121  15 mm) and spring heavy rain (167  14 mm) enters subterraneous horizons and the river valley. The summer drought period, i.e. dry hot summer with rare short rains, had come from 18 June. The groundwater recharge and surface runoff had practically ceased. The amount of precipitations during two summer months was as little as 20  4 mm. The summer drought period had completed on the 20th of August. Heavy rains had started and persisted practically continuously till 4 September, then interruptedly up to frosts. The amount of precipitations compared with the summer months had doubled and 20 October (the last date of activity measurements) it corresponded to 39  12 mm. Groundwater contamination near the old RAW storage from monitoring results of 2010 is illustrated by the calendar data of Table 3. The water activity concentration in a sample taken from the well N  4 changes slightly with hydrological seasons. The groundwater 90 Sr activity value of 34 Bq/l was registered in the late winter lowwater period and the early period of snow melting and spring rains. The water sample, collected on the 15th of June, characterizes the end of spring snow melting. The analyzed water had demonstrated a positive reducing trend of this radionuclide activity concentration apparently due to the residual groundwater dilution by rain precipitations. The value of 90Sr activity in groundwater during the dry hot summer period is similar to 90Sr content in the sample collected in the winter low-water period. The a slight increase in activity of 90 Sr to 38 Bq/l in a well was observed in the early autumn heavy rain period as a result of the winter runoff front registered. In addition, the groundwater radionuclide concentration in different hydrological seasons exceeded the pollution standard (5 Bq/l) by a factor of 6e8 (RSS, 2009). Surface water contamination near the RAW storage based on the results of monitoring in 2010 is illustrated in Table 3. The activity concentration of 90Sr in the creek water after flooding was 5 Bq/l. This very day the activity concentration in the marsh located in this brook valley was 1.5 Bq/l. In the summer lowwater period of a drought season the activity of 90Sr in a brook sample had increased up to 34 Bq/l and in a marsh sample it dropped to 0.75 Bq/l. It is clear that rain precipitations had diluted the initial 90Sr concentration in June. Autumn rains which enriched the surface runoff of 90Sr accumulated in trench stagnant water during the drought summer period began on the 19th of 2010. Strontium-90 concentration in brook water was 7e8 times higher than the standard of water pollution (4.9 Bq/l) during summer drought low-water and autumn heavy rains, respectively. The analysis of the results of long-term monitoring of 90Sr in surface and underground waters allows us to note that, within

         

5 3 6 7 1 5 7 1 8$101 3$101

Precipitation mm 1 7 0 5 7 0 5 7 0 5

 5$101 4 1 4 2 4 2

Air temperature, 0C 7 14 29 3 14 29 3 14 29 3

         

5$101 1 2 1 1 2 1 2 1 6$101

Hydrological season Winter low-water period After flooding Summer drought period Autumn heavy rains After flooding Summer drought period Autumn heavy rains After flooding Summer drought period Autumn heavy rains

G.V. Lavrentyeva / Journal of Environmental Radioactivity 135 (2014) 128e134 250

The surveying well

A

PrecipitaƟons

120

200 100

150

80

60

100

40 50 20 0

PrecipitaƟons/month, mm

Volumetric acƟvity of Sr-90, Bq/l

140

133

07.2010

03.2010

08.2006

11.2005

07.2005

10.2003

03.2005

05.2003

02.2003

04.2002

07.2002

12.2001

07.2001

03.2001

08.2000

06.2000

02.2000

04.2000

08.1999

12.1999

06.1999

04.1999

02.1999

10.1998

12.1998

0

12

B

The marsh

250

PrecipitaƟons 10

200

The creek

8 150 6 100 4 50

2

PrecipitaƟons/month, mm

Volumetric acƟvity of Sr-90, Bq/l

Sampling Ɵme (month.year)

0

0

Sampling Ɵme (month. year) Fig. 4. Results of

90

Sr monitoring in underground (A) and surface (B) waters in the area of the RAW storage.

twelve years of monitoring the RAW storage, the 90Sr concentration in water bodies repeatedly changed (Fig. 4). The most drastic changes in strontium radioactivity can be seen in water samples collected from the well C4 (Fig. 4 A). During the period from December 1998 to August 1999, we recorded stable high radionuclide content practically independent of the precipitation amount. A sudden decrease in 90Sr activity in subterranean waters of the well occurred in summer 1999. Starting from this period and until August 2010, the graphs of strontium activity and amount of precipitation are synchronous. During the period from December 1999 to July 2002, a relative shift in maximum values in graphs was observed. After that, until November 2005, we see graph synchronism once again; in 2006 and 2010, complete divergence between graphs. Despite uneven changes in the 90Sr activity, we can note a slight decrease in water radioactivity. The analysis of long-term dynamics of the 90Sr emission from the RAW storage allows us to state that the first of the abovementioned periods is defined by transit carryover of radionuclide under conditions of sealing failure in the trenches with radioactive waste. Radioactive subterranean waters that filled the trench evenly discharged into the aquifer, which was recorded after water sampling from the C4 well. Change in activity in the aquifer occurred in summer 1999, when waterproofing of trenches has undergone repairs (Vasiljeva et al., 2007). Supposedly, after repair, the strontium discharge from the trench temporarily stopped, and the soil of trench bunds where significant amount of radionuclide has collected became the main source of 90Sr.

The repeated spike of radioactivity in subterranean waters was recorded in the 2000 year. In the period required for radionuclide to migrate from the trench to the well, the increase of water radioactivity in the inspection well was delayed from the date of precipitation. The water activity level in this period slightly decreased regardless the amount of precipitation, which can be explained by partial sorption of 90Sr by a bergmeal shield. Upon saturation of bergmeal barrier, the water activity level began to gradually increase, and the activity once again became synchronous with rain precipitation. It should be noted that the observations of activity in the date range of October 1999 to November 2005 showed a good correlation with rainfall. The correlation coefficient is 0.53. Activity is directly proportional to the amount of precipitation with aspect ratio 0.706. The reliability of this factor (p-value) is equal to 1.5e7. In the last interval of the graph that covers years 2005e2010, radioactivity of subterranean waters has decreased, and its relation to meteorological conditions became uncertain. 4. Conclusions The review of previous studies of radionuclide migration in the natural environment has shown that these problems are thoroughly understood, however, practically all efforts are aimed at investigating the radionuclide behavior in a soil-plant cover and aquatic ecosystems in aerial contamination. In this case radioactive substances enter into the soil-plant cover surface, often together with hardly soluble particles and stay in the upper soil profile for

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G.V. Lavrentyeva / Journal of Environmental Radioactivity 135 (2014) 128e134

years. The radionuclide behavior and characteristic of their vertical and lateral migration, their impact on biota with groundwater inflow are studied poorly. Our research considers just this way of radioactive contamination and it is very important for assessing the radioactive waste storage impact on adjacent territory in case of the multi-barrier protection fault. It is found that 90Sr accumulation proceeds in a natural sorption geochemical barrier of the marshy terrace near flood plain. The data analyzed on the vertical soil radionuclide distribution in the object and adjacent territories allowed one to establish the following. The maximum specific activity of 90Sr was recorded in the upper horizon of 2 cm in depth and amounted to 1.7 kBq/kg in the object territory. There is a relatively uniform radionuclide distribution over a soil profile in the RAW storage territory and it does not exceed 250 Bq/kg. Screening analysis of biota conditions during radioecological studies has shown that this contamination is local in character. Therefore further studies in the territory should be conducted in accordance with local contamination conditions at certain sites. Results of natural water monitoring near the RAW storage enabled to establish the most dynamic periods of 90Sr activity concentration variations to which greater attention is to be paid. The excess 90Sr interference level was registered in ground water as well as surface water during winter and summer low-water periods and autumn heavy rains. In view of the foregoing, it may be concluded that acute radioecological problems in the RAW storage territory have not been revealed for the present. However, the places of 90Sr accumulation can act as a secondary source of radioactive contamination and this requires continued radioecological studies of the territory.

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Characteristic of pollution with groundwater inflow (90)Sr natural waters and terrestrial ecosystems near a radioactive waste storage.

The studies were conducted in the territory contaminated by (90)Sr with groundwater inflow as a result of leakage from the near-surface trench-type ra...
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