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

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

• Caesium 137
• Strontium 90
• Tritium
• Effective Half-Time
• Ecological Half-Time
• Surface Water
• Sediments
• Concentration Factor
• Distribution Coefficient
• Radioecology

1. Introduction

The study focuses on an analysis of the results of long-term monitoring and assessment of radionuclide concentrations in hydrosphere in the vicinity of Temelín Nuclear Power Plant.

Pilot operation of the Temelín plant was launched in June 2002. Since September 2013, the Temelín plant installed capacity is 2 × 1055 MW. Construction and subsequently operation of the Temelín plant initiated implementation of a number of projects, which were focused on possible impacts of the plant on the environment. The length of the series of the data that were monitored during the implementation of the projects was more than 20 years.

During its operation, a nuclear power plant discharges waste waters that contain also radioactive substances, the most important of which is tritium. The waste waters include also other radionuclides, which originate mainly from surface water abstractions and inflows into the plant and minor quantities of these radionuclides originate from standard operation of the plant. The radionuclides that could originate from the plant operation include mainly caesium 137 and strontium 90. These radionuclides of artificial origin were detected in the components of the environment in the vicinity of the Temelín plant also before its operation. This fact is attributed to radionuclide contamination remaining in the environment components after tests of atmospheric nuclear weapons in the fifties and sixties of the 20th century and Chernobyl accident in 1986.

Caesium 137 and strontium 90 are radioecologically important radionuclides, which remain in the environment for a long period of time consequently to their long half-times (30.2 and 28.8 years, respectively). Main attention paid to caesium 137 in the research projects is associated with that fact that concentrations of this radionuclide can be determined from gammaspectrometric analysis, which requires relevant devices, but this determination is less time consuming as compared to radiochemical determination of the strontium 90 falling into beta emitters. This fact explains low availability of data and knowledge concerning concentrations of strontium 90 as compared to other radionuclides not only in the Czech Republic [1] . High attention was paid to tritium originates from the fact that its activities discharged into the environment highly exceed (by several orders of magnitude) those of the other radionuclides.

The main objective of the study was to analyze and integrate all of the knowledge on concentrations and behaviour of these radionuclides, which originated mainly from residual contamination, in order to assess the impacts of the Temelín plant on hydrosphere in these indicators during its standard operation and possible accidents. The analysis included standard radioecological characteristics, which were applicable for assessing long- term development and behaviour of radionuclides in the environment affected by their possible accidental releases on the territory of the Czech Republic or outside this territory.

The analysis of the results of the caesium 137 monitoring uses knowledge from publications of the project team [2] - [8] ). The paper also includes an assessment of strontium 90 and tritium concentrations in the Temelín locality, an assessment of outflows of caesium 137 and strontium 90 activities from this territory in relation to their concentrations accumulated consequently to Chernobyl accident, and an assessment of relationships between selected chemical and radioecological characteristics.

2. Methods

Concentrations of ¹³⁷Cs, ⁹⁰Sr and ³H were monitored in surface water (in all substances) and of ¹³⁷Cs and ⁹⁰Sr in sediments and complementarily in fish species and aquatic flora. Location of the sampling sites is shown in Figure 1.

The surface water monitoring was launched in 1990 in the Vltava River at Hněvkovice, the Lužnice at

Figure 1

Map of sampling sites

Koloděje and the Otava at Písek, which are river sites located outside possible impact of the Temelín plant (reference sites), and the Vltava River at Solenice located below the outflows from the plant. Since 1996, the monitoring was also carried out for the Vltava River at Hladná, the site located about 4 km downstream from the waste water outflow. Frequency of the sampling was 4 samples in a year. Volumes of the water samples were 50 l for ¹³⁷Cs and ⁹⁰Sr, 0.25 l for ³H and 1 l for suspended solids. The samples for ³H determination were stabilised by cooling while the large-volume samples were stabilised with nitric acid to pH below 2. The samples were dried by vaporization at temperature below boiling point and subsequently ignited (350˚C) and closed into the measuring containers. The determination of ¹³⁷Cs and ⁹⁰Sr therefore includes all of the substances.

The sediments have been monitored since 1990 with frequency of one sample in a year in the Vltava River below Týn, the Lužnice at Koloděje and the Otava at Zvíkov (reference river sites), and in the Vltava at Doubrava, Chrást and Orlík Reservoir (affected sites). The sediments samples were taken from the top layer (0 - 10 cm).

The fish sampling was carried out by staff of Research Institute for Fishery and Hydrobiology in Vod?any, Vltava River Basin Company and T.G. Masaryk Water Research Institute. The analysis of the results included also those from the monitoring carried out by Faculty of Science of Charles University during the period 1986- 1990, in 1994 and annually since 1998.

The aquatic flora was sampled in the Vltava at Hněvkovice and the Lužnice at Koloděje (reference sites), and in the Vltava at Hladná, Solenice and Štechovice (affected sites) with annual frequency in the period 1989-2013. The sampling included littoral species, aquatic mosses, algae species and submerged species.

The solid samples were transported in polyethylene boxes or bags. For the analysis, the samples were dried at 105˚C. The samples of sediments were sieved and their fraction less than 2 mm was analyzed. The fish samples were disembowelled, weighted, pulped, dried and subsequently powderized and locked in measuring containers. The analyses were performed for dry matter and the results were recalculated for fresh weight. The flora samples were cut into pieces and located into measuring containers.

Gammaspectrometric analysis was applied to determine concentrations of ¹³⁷Cs by using methods specified in [9] and subsequently the ⁹⁰Sr concentrations were determined by using a method described in [10] . For determination of tritium activities, methods specified in [11] were used.

Trends in the concentrations of the radionuclides were analyzed by using regression equation in the form:

where C_t is radioactivity concentration, λ_eff is effective rate of decline in radioactivity concentration, calculated as the slope of decline line (1/y), t is time of the monitoring (y) and C₀ is natural logarithm of initial concentration.

Statistical significance of the regression line was verified by using Pearson coefficient.

3. Results and Discussion

3.1. Radionuclides in Surface Water

Concentrations of ¹³⁷Cs and ⁹⁰Sr were monitored in all components of surface waters and their trends were assessed by using data from the inflow and outflow into and from Orlík Reservoir. The analyses were performed for subsequent periods 1990-1994 and 1995-2013, and separately for 2001-2013. The analysis of ³H was performed for period 2000-2013.

The highest mean concentrations of ¹³⁷Cs and simultaneously also its highest activity decline were detected for the Otava River at Písek. In the period 2001-2013, the highest mean ¹³⁷Cs concentration was derived for the Lužnice River at Koloděje. In the whole period, the lowest ¹³⁷Cs concentrations were detected for the outflow from Orlík Reservoir (the Vltava River at Solenice). For the reservoir, the inflow and outflow ¹³⁷Cs concentrations are compared in Figure 2. Low variability among the river sites were derived for mean concentrations of ⁹⁰Sr. Its minimum values were observed in the Otava River at Písek, maximum values were observed in the Lužnice River at Koloděje. Figure 3 shows the ⁹⁰Sr concentrations at the inflow and outflow into and from Orlík Reservoir.

During the whole observation period, the concentrations of ¹³⁷Cs and ⁹⁰Sr in the tributaries of Orlík Reservoir were in harmony with values observed in other European countries that were affected by radioactive fallout from Chernobyl accident. The examples include data from Finland or ¹³⁷Cs concentrations in Lago Maggiore

Figure 2

Time changes in annual average 137 Cs concentrations at the inflow into and outflow from Orlík Reservoir

Figure 3

Time changes in annual average 90 Sr concentrations at the inflow into and outflow from Orlík Reservoir

Lake and its tributaries in Italy [12] .

The concentrations of ¹³⁷Cs and ⁹⁰Sr at the inflow into and outflow from Orlík Reservoir were permanently decreasing during the whole observation period. Between the two analyzedperiods, the rate of the decline expressed by effective half-time of ¹³⁷Cs decreased from 1.5 - 2.2 years in the period 1990-1994 to 8.2 - 15.4 years in 1995-2013. The decrease continued also during operation of the Temelín plant. The concentrations of ⁹⁰Sr, which have been monitored since 1993, did not exhibit any change in the activity decline. During the whole observation period (1993-2013), the effective half-times were in the range from 8.0 to 11.5 years.

The difference in concentration decline between ¹³⁷Cs and ⁹⁰Sr was reported for a number of European rivers. Concentrations of ¹³⁷Cs in global fallout from Chernobyl accident after the tests of nuclear weapons in the atmosphere exceeded highly those of ⁹⁰Sr. The activities of both radionuclides were rapidly declining in the initial period and this trend continued during the following years for ¹³⁷Cs while the rate of the ⁹⁰Sr decline was decreasing. This fact is reflected in lengthening of effective half-time [13] . However, the activities of the radionuclides were decreasing at all river sites also during the operation of the Temelín plant (2001-2013). During this period, the effective half-times of ¹³⁷Cs ranged between 8.0 and 15.3 years (when the decreasing trend was statistically significant) in the individual river sites, including those affected by the plant. The half-times derived for ¹³⁷Cs exhibited therefore low spatial variability. The effective half-times of ⁹⁰Sr ranged in this period between 7.4 and 14.0 years and their mean value for the tributaries of Orlík Reservoir (reference sites) was 10.6 years.

In the whole period, the lowest ¹³⁷Cs concentrations were derived for the outflow from Orlík Reservoir (the Vltava River at Solenice), which is attributable to its biding with suspended solids and their sedimentation in the reservoir. It was derived that 86% of suspended solids and 62% of ¹³⁷Cs inflowing into Orlík Reservoir accumulates in the reservoir. The activities of ¹³⁷Cs accumulated in Orlík Reservoir were also declining with effective half-time of 9.0 years. Similar ¹³⁷Cs accumulation was reported for cascade of reservoirs constructed on the Dnepr River [14] or for lakes Lago di Lugano and Lago di Maggiore in Switzerland and Italy. The ¹³⁷Cs concentrations in the upper lake (Lago di Lugano) exceed permanently those in the lower lake (Lago di Maggiore) by one or two orders of magnitude [12] . Accumulation of ⁹⁰Sr in reservoirs was not substantiated [14] . During some periods, the ⁹⁰Sr concentrations in reservoirs can even remobilize and outflow from a reservoir, which was substantiated also for Orlík Reservoir, whose mean ratio between the inflow and outflow of ⁹⁰Sr activities was 0.9.

Outflows of ¹³⁷Cs and ⁹⁰Sr activities were assessed in relation to their concentrations that were accumulated in individual basins until 1986 consequently to Chernobyl accident and tests of atmospheric nuclear weapons. During the period 1990-2013, the annual outflow of ¹³⁷Cs activity from the individual basins did not exceed 1% of the total activity accumulated in the basin. At the end of this period, the annual outflows in the tributaries of Orlík Reservoir and at the outflow from the reservoir were in the range from 0.002% to 0.02%. Similarly, [15] reported that in 2005 the outflows from small basins in Austrian Alps ranged between 0.0008% and 0.0031% with average of 0.002%. For the whole basin area of the Vltava, Lužnice and Otava Rivers upstream from the Vltava River at Solenice, the total outflow of ¹³⁷Cs in the period 1986-2013 was 0.49% of the ¹³⁷Cs activity accumulated in the basin, which substantiates that the contribution of the ¹³⁷Cs outflow to the total ¹³⁷Cs reduction in the basin is very small.

The contribution of the ⁹⁰Sr outflow to its total reduction in the basin exceeds that of ¹³⁷Cs by approximately one order of magnitude. During the period 1986-2013, the outflow of ⁹⁰Sr represented 3.6% of its total accumulation in the basin of the Vltava River at Solenice. This is in harmony with results reported by [16] , who concluded that the contribution of the ⁹⁰Sr outflow exceeds that of the outflow of ¹³⁷Cs because immobilisation of ⁹⁰Sr into sediments is much smaller as compared to ¹³⁷Cs fixation.

In contrast to the results derived for ¹³⁷Cs and⁹⁰Sr, the trends in the concentrations of ³H at unaffected (reference) and affected river sites were greatly different. In the period 2000-2013, the mean ³H concentration at the reference sites was 1.1 Bq/l. Great differences were derived also between the ³H activities at the effected river sites, the Vltava River at Hladná and the Vltava River at Solenice. In addition, both river sites exhibit great difference between values of mean and median calculated from the individual measurements (for the Vltava at Hladná: mean 19.6 Bq/l, median 2.4 Bq/l, for the Vltava at Solenice: mean 14.3 Bq/l, median 11.7 Bq/l). This fact can be explained by high variability in the waste water discharges from the Temelín plant. For the reference sites, the rate of the decline in the ³H concentration was small and below that relevant to the physical half-time, which indicates that significant additional ³H activities originate also from its natural background and tritium produced by nuclear facilities located outside of the territory of the Czech Republic. After subtracting this contamination, statistically significant decreasing trend with effective half time 4.7 years was found only for the profile Vltava at Hluboká.

For all of the assessed radionuclides except for tritium at affected river sites, frequency of values below the minimum detectable activities greatly increased during the last years of the monitored period. The concentrations of these radionuclides are therefore close to measurement limits of the existing methods and analytical devices.

The data on annual discharges of ¹³⁷Cs, ⁹⁰Sr and ³H at unaffected (reference) and affected river sites were compared with the data provided by Czech Power Works, Temelín Power Plant on discharges of ³H and other activation and fission products (AAFP). The results of a balance assessment of the radionuclides discharged in the Vltava River at Hněvkovice and the Lužnice River at Koloděje in the period 1990-2013 showed that the background activities were relevant to 2.50 GBq/y for ¹³⁷Cs, 8.03 GBq/y for ⁹⁰Sr and 1.84 TBq/y for ³H. In the period 2002-2013, the Temelín plant discharged annually 38.8 TBq/y of tritium while maximum annual discharges of other AAFP did not exceed 0.5 GBq/y [17] [18] ). The background activities of ¹³⁷Cs and ⁹⁰Sr presently exceed substantially other AAFP discharged from the temelín plant. in the period 2002-2013, the quantity of ³h discharged in the vltava river at hladná was 7.12 - 229 tbq/y, in average 35.5 tbq/y. in terms of ³h, the impact of the waste water discharges from the temelín plant was therefore substantiated.

3.2. Radionuclides in Sediments

The sediment monitoring was focused on concentrations of ¹³⁷Cs and ⁹⁰Sr. In the whole period, the mean concentration of ¹³⁷Cs in sediments was 69.2 Bq/kg and in 2001-2013, it was 31.3 Bq/kg. For the whole territory of the Czech Republic, the mean ¹³⁷Cs concentration in the period 2000-2010 was 14.0 Bq/kg [19] , which indicates that the sediments in Orlík Reservoir and its tributaries fall into those highly contaminated by ¹³⁷Cs in the Czech Republic. Mean concentration of ⁹⁰Sr in the observation period (1993-2013) of 2 Bq/kg was substantially below that of ¹³⁷Cs.

In harmony with the results derived for surface water, the concentrations of ¹³⁷Cs and ⁹⁰Sr in sediments were decreasing at all monitored sites during the whole observation period, including the years when the Temelín- plant was in the operation. The ¹³⁷Cs effective half-time was 7.5 years or 15.8 years in the period 2001-2013 (Figure 4), which is shorter as compared to that of 23.8 years reported for the period 2000-2010 in [19] as a mean for the sediments on the territory of the Czech Republic. The effective half-time of ⁹⁰Sr derived from the decreasing trends in the ⁹⁰Sr concentrations in sediments was 14.7 years. The results show that the effective half-time is gradually increasing similarly to that derived for surface water.

The results of an analysis of ¹³⁷Cs and ⁹⁰Sr distribution coefficients between water and sediments showed that the values of K_d137Cs and K_d90Sr do not exhibit any trends in the observation periods, 1990-2013 (¹³⁷Cs) and 1993- 2013 (⁹⁰Sr).

Figure 4

Time changes in annual average concentrations of 137 Cs and 90 Sr in bottom sediments (dry matter)

The values of the K_d137Cs coefficients calculated for the individual river sites are in the range from 2.7 × 10² to 1.27 × 10⁵ l/kg and their mean value is 2.53 × 10⁴ l/kg. These results are in harmony with those reported in literature. Reference [20] reported that the best estimate of K_d137Cs is 8 × 10⁴ l/kg and the value of 2.9 × 10⁴ l/kg is specified in [21] . The fact that the K_d137Cs distribution coefficients of sediments in Orlík Reservoir and its tributaries are moderately below those reported can be attributed to different methods that are used for determination of the concentrations of the radionuclides. For this study, the concentrations were determined from all of the water components (both dissolved substances and suspended solids) while the results reported in the literature relate mostly to the concentrations derived from dissolved substances only.

The analysis of the K_d90Sr coefficients was focused on their integrated assessment for all of the monitored sites. These coefficients calculated for the whole observation period were in the range from 190 to 1770 l/kg with mean value of 440 l/kg. The K_d90Sr coefficients are substantially below those that were derived for ¹³⁷Cs (K_d137Cs), which is in harmony with the results reported in literature [20] [21] . They are again smaller as compared to the mean values but still in the range of the individual values reported in the literature. The fact that the ⁹⁰Sr concentrations were determined from all of the water components in this study plays less important role as compared to that in the ¹³⁷Cs assessment.

3.3. Radionuclides in Aquatic Fauna and Flora

The monitoring of aquatic flora and fish was focused on concentrations of ¹³⁷Cs and ⁹⁰Sr. The concentrations of ¹³⁷Cs in fish (related to fresh weight) were assessed for the periods 1986-1990, 1994-2013 and separately for 2001-2013. Between the two periods, the ¹³⁷Cs concentrations decreased from 2.0 - 47.9 Bq/kg (1986-1990) to 0.05 - 2.35 Bq/kg (1994-2013). With respect to less data availability, the concentrations of ⁹⁰Sr in fish were assessed for the whole observation period 1990-2013. For this period the mean ⁹⁰Sr concentration in fish was 0.6 Bq/kg. The results of the monitoring and assessment of the ¹³⁷Cs and ⁹⁰Sr concentrations in fish are illustrated in Figure 5. The concentrations in the Czech Republic are substantially below those in areas affected by the first radioactive cloud. In the most affected areas in the vicinity of Chernobyl, these activities shortly after the accident were at levels of hundreds of kBq/kg and at early nineties still at levels of tens kBq/kg. The activities of several kBq/kg in this period were reported from Switzerland, England or Germany [22] .

Relatively rare data and information on ⁹⁰Sr concentrations in fish include those by [1] , who reported that in the period 1978-1997 the concentrations in the analyzed river species were in the range of 10 - 17 Bq/kg, which exceeded the ⁹⁰Sr concentrations in fish from Orlík Reservoir by approximately one order of magnitude. The concentration levels of ⁹⁰Sr were however smaller by several orders of magnitude as compared to those of ¹³⁷Cs. Most of the ⁹⁰Sr activity is accumulated in bones and thus ⁹⁰Sr is less dangerous than ¹³⁷Cs in terms of radioactive doses originating from food chain [1] .

In harmony with the results derived for surface water, the concentrations of ¹³⁷Cs and ⁹⁰Sr in fish exhibited a decreasing trend. In the period 1986-1990, the rapid decrease in ¹³⁷Cs activities was characterized by effective

Figure 5

Time changes in annual concentrations of 137 Cs and 90 Sr in fish (fresh weight)

time-life of 1 year and ecological half-time of 1.1 years. Identical results were reported in [23] from observation in Croatia in the period 1987-1992 while this decrease exceeded that derived by [22] for identical period. The reported half-times are in the range between 2 and 3 years. In harmony with the results from the Czech Republic, the literature sources show that the decrease in the following period was significantly declining towards that expressed by physical half-time. The effective half-times in the Finland lakes were between 3 and 6 years [1] , reference [23] reported 5 years for the period 1993-2005, and in Orlík Reservoir, the effective and ecological half-times were 5.1 and 6.1 years, respectively, in the period 1994-2013. The ¹³⁷Cs half-times that were derived for fish correspond to those derived for water. The decreasing trend continued also during the operation of the Temelín plant.

The half-times reported for ⁹⁰Sr are substantially longer. The effective half-times derived for several fish species in the Finland lakes were between 7 and 30 years [1] . For fish species in Orlík Reservoir the effective half- time was (9.4 years).The results of ¹³⁷Cs and ⁹⁰Sr monitoring of surface water and fish (fresh weight) were used for determination of concentration factors CF_137Cs and CF_90Sr. It was concluded in [1] that concentration factor can be calculated under steady conditions, which occur 8 to 10 years after an accident. For Orlík Reservoir, the CF_137Cs values calculated from the period 1986-1990 did not differ significantly from those derived for the period after 1995 and therefore the mean CF_137Cs was calculated by using all of the calculated values. Its resulting value was 217 l/kg. The mean CF_137Cs value specified in [21] is 3.0 × 10³ l/kg (the range of the values is 4.5 × 10¹ - 2.4 × 10⁴) while the ¹³⁷Cs mean factor calculated for fish species in Orlík Reservoir is smaller by one order of magnitude. All of the calculated values were however in the range reported in [21] . The smaller values of CF_137Cs can be explained by several factors, which include small size of the statistical sample, uneven proportion between predatory and unpredatory fish species, the use of both dissolved solids and suspended solidsin surface water for determination of the ¹³⁷Cs concentration, and also small ¹³⁷Cs concentrations because the values reported in literature are frequently derived from localities, whose ¹³⁷Cs activities are higher.

For ⁹⁰Sr, the mean value of the concentration factor (CF_90Sr) was 130 l/kg, which is in approximate harmony with the mean of 1.9 × 10² l/kg (range of 2.2 × 10¹ - 7.1 × 10² l/kg) reported in [19] . Similar results were reported in [18] for lakes in the vicinity Chernobyl (46 - 452) while [1] reported 550 - 1300 l/kg for lakes in Finland.

Concentrations of ¹³⁷Cs were monitored also for several aquatic flora species (in dried matter). The results substantiated an assumption that the highest ¹³⁷Cs concentrations are accumulated in a group of aquatic mosses (21.8 Bq/kg in 1996) and algae (17.9 Bq/kg in 1996). A comparison of the results between the river sites unaffected and affected by the outflows from the Temelín plant was complicated by different plants growing at the individual sites with exception of reed species. Since 2006, the monitoring was therefore focused on these species, which were also used for the assessment. The results of the assessment showed, that the concentrations of ¹³⁷Cs in the reed species were decreasing with effective half-time of 13.4 years. The decreasing trend was identified for unaffected as well as for affected river sites and continued also in the period when the Temelín plant was in the operation.

The ⁹⁰Sr concentrations in reed species were in the range between <0.4 and 6.1 Bq/l (in dried matter) and these concentrations were decreasing with effective half-time of 6.5 years. The results are for ¹³⁷Cs and ⁹⁰Sr illustrated in Figure 6.

CF_137Cs concentration factors were assessed for the reed species and knotgrass (Polygonumhydropiper) and CF_90Sr factors for the reed species. The mean values of CF_137Cs (recalculated for fresh weight) were 60.7 l/kg for reed species and 276 l/kg for the knotgrass, which is in the limits of 1.9 × 10⁰ - 3.3 × 10⁴ l/kg, 9.7 × 10¹ l/kg in average, reported in [21] .

The mean CF_90Sr value of 17.7 l/kg (fresh weight) for reed species is in the range (5 - 551 l/kg) specified in [20] while [21] ) reported higher values (3.9 × 10¹ - 1.9 × 10³ l/kg, 4.1 × 10² l/kg in average). It can be concluded that ¹³⁷Cs and ⁹⁰Sr bioaccumulation in aquatic flora depends on a number of factors (plant species, seasonality, etc.) and its lower levels as compared to aquatic fauna are attributable to a feeding level [20] .

4. Summary

For all of the components of the environment, the concentrations of ¹³⁷Cs and ⁹⁰Sr, which were used for calculation of their effective and ecological half-times, were decreasing. For ¹³⁷Cs in surface water and fish, the rates of the decrease in the first and second monitoring period were different. The rate of the decrease in ⁹⁰Sr concentration was invariable. The results of the monitoring showed that 86% of suspended solids and 62% of ¹³⁷Cs inflowing into Orlík Reservoir accumulated in the reservoir while accumulation of ⁹⁰Sr was not substantiated. Outflows of ¹³⁷Cs and ⁹⁰Sr activities were assessed in relation to their concentrations that were accumulated in individual basins until 1986 consequently to Chernobyl accident and tests of atmospheric nuclear weapons. The results for the whole area of the Vltava, Lužnice and Otava River basins upstream from the Vltava River at Solenice showed that during the period 1986-2013 only 0.49% of ¹³⁷Cs activity and 3.6% of ⁹⁰Sr activity that accumulated in the basins were washed and flowed out from the area. Distribution coefficients derived from summary analysis of sediments were 2.5 × 10⁴ l/kg for K_d137Cs and 4.4 × 10² l/kg for K_d90Sr. Mean values of the concentration factor in fish were 217 l/kg for CF_137Cs and 130 l/kg for CF_90Sr, and in reed 60.7 l/kg for CF_137Cs and 17.7 l/kg for CF_90Sr. Concentrations of ³H in river sites not affected by Temelín plant were slowly decreasing and their values were substantially below those from the sites affected by the plant.

The data on annual discharges of ¹³⁷Cs, ⁹⁰Sr and ³H at unaffected (reference) and affected river sites were compared with the data provided by Czech Power Works, Temelín Power Plant on discharges of ³H and other AAFP. The results of a balance assessment of the radionuclides discharged in the Vltava River at Hněvkovice- and the Lužnice River at Koloděje in the period 1990-2013 showed that the background activities were relevant to 2.50 GBq/y for ¹³⁷Cs, 8.03 GBq/y for ⁹⁰Sr and 1.84 TBq/y for ³H. In the period 2002-2013, the Temelín plant discharged annually 39 TBq/y of tritium while maximum annual discharges of other AAFP did not exceed 0.5 GBq/y. The background activities of ¹³⁷Cs and ⁹⁰Sr presently exceed substantially other AAFP discharged from the Temelín plant. In the period 2002-2013, the quantity of ³H discharged in the Vltava River at Hladná was in average 35.5 TBq/y. In terms of ³H, the impact of the waste water discharges from the Temelín plant was there-

Figure 6

Time changes in annual average concentrations of 137 Cs and 90 Sr in aquatic plants (dry matter)

fore substantiated.

Acknowledgements

This paper was prepared with the support of the project Czech Electric Company No. 90002551.

References

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