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Kinetics of 3H, 90Sr and 137Cs content changes in hydrosphere in the Vltava River system (Czech Republic)
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Kinetics of 3H, 90Sr and 137Cs content changes in hydrosphere in the Vltava River system (Czech Republic) Eduard Hanslíka,∗, Diana Marešováa, Eva Juranováa,b, Barbora Sedlářováa a b
Department of Radiology, T. G. Masaryk Water Research Institute, p.r.i., Podbabská 30, 160 00 Prague, Czech Republic Faculty of Science, Institute for Environmental Studies, Charles University, Benátská 2, 128 01 Prague, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords: Tritium Strontium 90 Caesium 137 Effective ecological half-time Surface water Sediments
The paper presents results and interpretation of long-term monitoring of occurrence and behaviour of radioisotopes 3H, 90Sr, and 137Cs in the vicinity of the Temelín Nuclear Power Plant. 3H, 90Sr, and 137Cs originate predominantly from residual contamination due to atmospheric nuclear weapons tests and the Chernobyl disaster in the last century. Monitoring of radionuclides comprised surface waters, river sediments, aquatic plants, and fish. This enables an up-to-date appraisal of the Temelín Nuclear Power Plant impact on the hydrosphere in all indicators at standard power plant operation, as well as at critical situations. The time and spatial variability of these radionuclide concentrations were monitored in the hydrosphere at in- and out-flow of the Orlík Water Reservoir. The basic evaluated radioecological characteristics can be used in assessing the long-term kinetics of decline and behaviour of radionuclides and their potential release into the environment. A very slow decline in 3 H concentration at unaffected sites was observed. At sites downstream from the power plant the 3H concentrations were significantly higher, an evident impact of the power plant operation. A decline in 90Sr and 137Cs concentrations was observed in all the monitored indicators. Also, the characteristic effective and ecological half-lives were evaluated.
1. Introduction The usual operation of a nuclear power plant is associated with production of different radionuclides that can be released into the environment in very low concentrations. Operation of such facility is obviously accompanied with high requirements to keep radiation protection (Corner et al., 2011). Moreover, the past accidents at nuclear facilities had unquestionable impacts on environment: Fukushima accident (Konoplev et al., 2016), Chernobyl accident (Smith and Beresford, 2005) and accidents in the Southern Urals (Soyfer, 2002). Anthropogenic radionuclides in the territory of South Bohemia (Czech Republic) have been studied by T.G.M. Water research institute (TGM WRI) long because of the Temelín Nuclear Power Plant (Temelín NPP). Main technical parameters of the Temelín NPP are mentioned in Table 1. Pilot operation of the first reactor was launched in June 2002 and of the second one in April 2003. Since May 2003, the Temelín NPP has been in full operation. The plant releases its waste water into the Vltava River. The Orlík Water Reservoir, located on the Vltava River downstream of the waste water outflow, is presumed to play a major role in the radionuclides behaviour in the hydrosphere and its outflow from assessed area (Fig. 1).
∗
Usually, the wastewater from a NPP is discharged into a big river, e.g. as in (Pujol and Sanchez-Cabeza, 2000), however the wastewater from the Temelín NPP is discharged into a relatively small watercourse (see Table 2). Regarding the expected climate change impacts in the Czech Republic including the hydrological drought (e.g. Potop et al., 2012), the radionuclide activity concentrations has potential to increase due to lower dilution in the Vltava River affected directly by the Temelín NPP (Fig. 1). Anthropogenic radionuclides have been observed in the environment since atmospheric tests of nuclear weapons and following the accident at the Chernobyl nuclear reactor in the last century. During the atmospheric tests of nuclear weapons 186.103 PBq 3H, 622 PBq 90Sr and 948 PBq 137Cs was released (UNSCEAR, 2000). The estimated amount of released radionuclides during the Chernobyl disaster is 10 PBq 90Sr and 85 PBq 137Cs (UNSCEAR, 2000). According to Atlas (1998), the average surface deposition of 137Cs due to Chernobyl disaster in the Czech Republic was 7.6 kBq/m2. Estimates of the amount of 137Cs deposited on the territory of the Czech Republic are based predominantly on investigations carried out in June 1986 by the Centre of Radiation Hygiene of the Institute of Hygiene and Epidemiology (IHE CRH, 1987). These investigations were
Corresponding author. E-mail addresses: [email protected] (E. Hanslík), [email protected] (D. Marešová), [email protected] (E. Juranová), [email protected] (B. Sedlářová).
https://doi.org/10.1016/j.jenvrad.2017.11.029 Received 15 August 2017; Received in revised form 22 November 2017; Accepted 22 November 2017 0265-931X/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Hanslík, E., Journal of Environmental Radioactivity (2017), https://doi.org/10.1016/j.jenvrad.2017.11.029
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Table 1 Main technical parameters for the Temelín NPP (ČEZ, 2017). Number of reactor blocks Installed output Reactor Year of commissioning Radioactive discharges into the Vltava River Limit of 3H Annual average 3H dischargesa Limit of other activation and fission products (AaFP) Annual average discharges AaFPa
Table 2 Characteristics of sampling sites.
2 2 × 1055 MW pressurised water, VVER 1000 2002 Vltava Hluboká Vltava Hněvkovice Lužnice Koloděje Otava Topělec Vltava Solenice Vltava Štěchovice Vltava Prague Podolí Vltava Zelčín Elbe Hřensko
66 TBq/y 51 TBq/y 1 GBq/y 0.116 GBq/y
a Average in 2008–2016 when the 3H and other AaFP amount released from the Temelín NPP were stabilized.
Qa
TSS
K
Ca
m3/s
mg/l
mg/l
mg/l
9.4 ± 3.7 24.8 ± 8.5 11.5 ± 8.8 3.9 ± 1.8
3.6 7.0 3.9 4.2
30.0 30.6 23.6 23.3 84.3 85.6 143 152 319
± ± ± ±
Fig. 1. Map of the sampling sites.
2
1.0 2.3 1.3 1.2
16.2 26.6 19.1 21.0
± ± ± ±
5.3 6.4 4.2 4.4
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Fig. 2.
137
Cs surface activity in soil in the Czech Republic (kBq/m2) after the 1986 Chernobyl disaster, including
137
Cs fallout from nuclear weapon tests, according to Hanslík (1998).
The main objective of presented study is to assess the contribution of the Temelín NPP to overall radionuclide concentrations. It analyses the results of long-term monitoring and evaluates the development of radionuclide concentrations in surface water, sediments and fish in the vicinity of the Temelín NPP. Analysed radionuclides were tritium (3H), strontium 90 (90Sr) and caesium 137 (137Cs). Concentrations of radionuclides were evaluated in surface water, sediments, fish and aquatic flora both affected and unaffected by waste water discharges from the Temelín NPP before and during the operation of the plant. Main components of radionuclide background were quantified; they stem from natural (3H) and anthropogenic processes (3H, 90Sr, 137Cs; residual pollution from tests of nuclear weapons and Chernobyl disaster in the last century and the atmospheric transfer from nuclear facilities worldwide).
later completed by aerial surveys (Gnojek et al., 1997) and a map of contaminated areas was created (Hanslík, 1998) (Fig. 2). This map thus comprises even fallout from the atmospheric tests of nuclear weapons, estimated for 1986 by the UNSCEAR (2000) to be 1.9 kBq/m2 (cumulative deposition). The most seriously affected areas of the Czech Republic with surface deposition above 10 kBq/m2 are towards the northeast to north-west, which corresponds to the wind direction at the time of the first appearance of the contaminated plume. The second and third plumes reached our territory from the south-east to north-west. The recorded 137Cs volume activity in the Czech surface waters from May 1st to June 10th. 1986 ranged from 0.08 to 8.0 Bq/l (IHE CRH, 1987). The vicinity of the Temelín NPP ranks among regions afflicted by the first radioactive plume to arrive over our territory; according to IHE CRH (1987), fallout in this region reached 2.3–13 kBq/m2. A detailed aerial survey was carried out in 1992 by Dědáček and Plško (1992), subsequently amended by measurements in 1996 (Gnojek et al., 1997), and from both it follows that 137Cs surface contamination around the power plant in 1996 was 1–16 kBq/m2. These data would correspond with the 1986 fallout within 1.3–20.2 kBq/m2. However, 90Sr fallout data after the disaster are very scarce, and official data on the total 90Sr deposition had not been published. Due to a different character of the deposition, deposition estimates cannot be derived from the ratio of 90Sr and 137Cs in the reactor at the time of disaster, which was 0.12, as is the case of e.g. 134Cs (Smith and Beresford, 2005). For example, according to Outola et al. (2009), the recorded ratio of 90Sr and 137Cs in the fallout over Finland after the Chernobyl disaster ranged between 0.015 and 0.333. IHE CRH (1987) gives the 90Sr and 137Cs ratio in close-to-the-Earth atmospheric layer over Prague-Libuš in the range from 0.02 to 0.13. According to UNSCEAR (2000) estimates, 90Sr contribution in 1986, i.e. the cumulative 90Sr deposition from atmospheric tests of nuclear weapons, was 1.23 kBq/m2.
2. Methods Concentrations of 3H, 90Sr and 137Cs were monitored in surface water (without filtration, i e. in both the dissolved and undissolved substances) and concentrations of 90Sr and 137Cs in sediments and complementarily in fish species and aquatic flora. Location of the sampling sites is shown in Fig. 1. Methods specified in Standards ČSN ISO 5667-1 (2007), ČSN ISO 5667-3 (2013), ČSN ISO 5667-4 (1994), ČSN ISO 5667-6 (2008) (national editions) were used for the sampling and sample processing. The surface water monitoring was launched in 1990 in the Vltava River at Hněvkovice, the Lužnice river at Koloděje and the Otava river at Písek, which are river sites located outside the impact of the Temelín NPP (reference sites), and in the Vltava River at Solenice located downstream of the outflows from the plant. Frequency of the sampling was 4 samples a year. Further, more detailed monitoring of 3H with the frequency of 12 samples a year was carried out at reference sites in the Vltava River at Hluboká and at the Elbe River at Lysá and at affected 3
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Fig. 3. Annual average 3H concentrations in surface water unaffected by waste water discharges from the Temelín NPP in the period of 1990–2016, without (A) and after correction (B) by subtracting the natural component and the activity originating from the atmospheric transfer from nuclear facilities worldwide.
significance of 0.05.3H in the analysed water samples from the reference sites has been pre-concentrated using electrolytic enrichment since 2012. The detection limit (DL) has been since then was 0.07 Bq/l. Gammaspectrometric analysis was implemented to determine concentrations of 137Cs by using methods specified in ČSN EN ISO 10703 (2008) and subsequently the 90Sr concentrations were determined by using the method described by Hanslík (1993). A Canberra device was used for the gamma spectrometry. The detection limit at the level of significance of 0.05 of 137Cs in water was 0.5 mBq/l, in the sediments 0.5 Bq/kg, in fish (wet weight) 0.1 Bq/kg. The 90Sr activity was detected from the residue after igniting via detection of yttrium 90 after radiochemical separation. Value of DL of 90Sr was 3 mBq/l. Trends in the concentrations of the radionuclides were analysed by using the following regression equation:
sites in the Vltava River at Podolí and at the Elbe River at Hřensko. Long-term average flow rates are displayed in Table 2. Data of total suspended solids (TSS), K and Ca are accompanied for sampling site where 90Sr and 137Cs analyses was performed. Volumes of the water samples were 0.25 l for 3H and 50 l for 90Sr and 137Cs. The samples for 3H determination were stabilized by cooling while the large-volume samples were stabilized 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 90Sr and 137Cs concentrations therefore includes both the dissolved and undissolved substances. Samples of water (1 l) for determination of TSS were taken with the same frequency (4 samples a year). The sediments, fish and aquatic flora have been monitored with frequency of one sample a year in both the reference and the affected sites. The sediment samples were taken from the top layer (0–10 cm) during the period of 1990–2016. Annual average activities of 90Sr and 134 Cs and 137Cs in dry weight from all sampling sites are presented. The fish sampling was carried out during the period of 1986–1990, in 1994 and 1995 and then annually since 1998, represented by omnivorous pelagic fish (mainly carp, bream). Three samples per year were analysed, annual average activities of 90Sr and 137Cs in wet weight are presented. The aquatic flora was sampled once a year at individual monitoring sites in the period of 1989–2016. The sampling included littoral species, aquatic mosses, algae species and submerged species. Since 2006 only reeds have been monitored. Annual average activities of 90Sr and 137Cs in dry weight from all sampling sites are presented. 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 the fraction of less than 2 mm was analysed. The fish samples were disembowelled, weighted, pulped, dried and subsequently pulverised and locked in measuring containers. The analyses were performed for dry weight and the results were recalculated for wet weight. The flora samples were cut into pieces and locked in measuring containers. For determination of 3H activities, methods specified in ČSN EN ISO 9698 (2011) were used. The 3H concentrations were determined by using Quantulus 1220 and TriCarb low-level liquid scintillation spectrometers. The relative efficiency of 3H measurement was 26%. The detection limit was set according to expected activities. For mixture of 8 ml of sample and 12 ml of scintillation solution and for counting time of 800 min (for samples not affected by the waste water discharges) or 300 min (for samples affected by the waste water discharges), the detection limit was 1.1 Bq/l and 2.1 Bq/l, respectively, at the level of
lnCj = −λ eff ⋅t + lnC0
(1)
where Cj is annual average radioactivity concentration in year j, λeff 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 initial concentration. Statistical significance of the regression line was verified by using the Pearson coefficient and t-test. Then the effective ecological half-lives (Teff) and the ecological halflives (Tecol) were calculated from the decrease in radionuclide activity according to the equation (Smith and Beresford, 2005):
ln 2 λ eff
(2)
1 1 1 = − Tecol Teff TP
(3)
Teff =
where TP is physical half-life (y). 3. Results and discussion 3.1. Radionuclides in surface water 3.1.1. Tritium 3 H concentrations in surface water were analysed separately at both the sites affected and the sites unaffected by the Temelín NPP. For data from unaffected sites in the period of 1990–2016 (see Fig. 3 A), Equation (1) gives effective ecological half-life of 16.3 ± 2.1 y. The trend of decrease was statistically significant, but the calculated effective ecological half-life was longer than the physical half-life of 3H 12.32 y (Rozanski and Gröning, 2004). The reason is that, apart from 4
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is shown in Fig. 5 for the Vltava River at Hněvkovice and the Vltava River at Solenice. In 2016, the average activity of 90Sr at both Hněvkovice (a reference site, source of technological water for the Temelín NPP) and Solenice (downstream of the Temelín waste water outflow) was 2.5 mBq/l. Temporal changes of the 137Cs concentrations in water samples taken from the Orlík Water Reservoir and its tributaries were studied for two separate periods, 1990–1994 and 1995–2016. The effective ecological half-lives (Teff) in individual tributaries and the outflow of the Orlík Water Reservoir were in the range of 1.4–2.2 y for the period of 1990–1994 and 8.4–15.4 y for the period of 1995–2016. The ecological half-lives (Tecol) were in the range of 1.5–2.4 y for the period of 1990–1994 and 11.5–31 y for the period of 1995–2016 (see Table 4). An example is shown in Fig. 6 for the Vltava River at Hněvkovice and the Vltava River at Solenice. In 2016, the average activity of 137Cs at both sites was less than 0.6 mBq/l. Our results showed that a decrease in the 90Sr and 137Cs concentrations, which was observed before the plant operation, also continued during the subsequent period. The results of monitoring 90Sr in the South Bohemia (Fig. 7 C2) obtained in connection with the Temelín NPP were compared with data measured by TGM WRI in the Vltava basin after the nuclear weapons tests (Fig. 7 A), results of the Danube River expedition in 1978 (Fig. 7 B) and further the results of the earlier monitoring in the Temelín NPP vicinity in the period of 1981–1984 (Fig. 7 C1). In the first evaluated period after the nuclear weapons tests and before the Chernobyl accident, the observed half-life was 6.9 ± 0.9 years; in the second period 1996–2016, after the Chernobyl disaster, it was 9.8 ± 0.9 years. It can be concluded that effective ecological half-lives of 90Sr observed after the nuclear weapons tests until the Chernobyl disaster and then after the Chernobyl are very similar. Results of our research focused on the vicinity of the Temelín NPP are in agreement with similar studies on changes in water contamination after the Chernobyl accident. For example, Zibold et al. (2001) showed a faster decrease of 137Cs concentration in the period of 1986–1988 and a slower phase in 1989–2000. Similarly, Smith and Beresford (2005) reported that the rate of decline of the 137Cs concentration in the Pripyat River was decreasing in recent years. The effective ecological half-lives of 1.2 years (dissolved phase) and 1.7 y (particulate phase) in the period of 1987–1991 increased to 3.4 y (dissolved phase) and 11.2 y (particulate phase) in the period of 1995–1998. This increase in Teff has also been observed in Belarus, Ukraine and Finland (Zibold et al., 2001). The concentrations of anthropogenic radionuclides 90Sr and 137Cs downstream of the waste water discharge from the Temelín NPP therefore originate mainly from the residual contamination from atmospheric tests of nuclear weapons and the Chernobyl accident. These activities show a decreasing trend in time. The detected activities concentrations in surface water are currently near the detection limits.
H form the atmospheric nuclear weapons tests, there are fractions of H, which are considered to be steady, not changing with time. These are a relatively small 3H activities generated naturally by cosmic radiation and the atmospheric transfer of 3H from nuclear facilities worldwide, which is also considered constant in the analysed period. These stable 3H fractions were therefore eliminated in subsequent analysis (Fig. 3 B). The annual average 3H activities (c3HB,j) were corrected by subtracting its components originating from cosmic radiation (c3HCR) and the atmospheric transfer from nuclear facilities worldwide (c3HNF). The mean values were calculated by including 3H activities below the detection limit into the data set as values of the limit. After elimination of the constant components, which were appreciated 0.48 Bq/l according Hanslík et al. (1999), the effective ecological half-life (Teff) calculated for the period of 1990–2016 was 10.7 ± 1.3 y, which is shorter than that derived by using the first approach and is almost same as the physical half-life of 3H. The component of 3H concentration originating from tests of nuclear weapons will be further decreasing and thus it can be assumed that the effective half-life will increase. After decomposition of 3H from tests of nuclear weapons, its concentration will include a constant component originating from cosmic radiation and a slowly increasing component stemming from atmospheric transfer of 3H from gaseous and liquid releases from nuclear facilities in the Czech Republic and abroad. At sites (see above) unaffected by waste water discharges from the Temelín NPP, the mean 3H activity calculated by using the first approach (the alternative not involving elimination of the constant components) was 3.1 Bq/l at the beginning of the analysed period (1990) and less than 1.0 Bq/l at its end (2016). The 3H concentrations in surface waters in the vicinity of the Temelín NPP unaffected by waste water discharges are in accord with the results of observations performed abroad. Palomo et al. (2007) reported that 3H concentrations in samples taken in October 2005 and January 2006 in the vicinity of Asco Nuclear Power Plant (Spain) are between less than 0.6 and 0.93 Bq/l. The differences between the 3H concentrations in the vicinity of the Temelín and Asco NPPs are not significant. In contrast to the results derived for the unaffected sites, the trends in concentrations of 3H at the affected river sites were remarkably different. Since 2001, when the Temelín NPP was put in operation, 3H concentrations in the Vltava and Elbe Rivers downstream of the waste water outflow have been increasing. This is attributable to gradual increase in the output of the plant associated with increasing quantity of 3 H, since 2008 the 3H amount released from the Temelín NPP has been stabilized at about 51 TBq/year (average in 2008–2016). The concentrations in surface water correspond to the annual released 3H amount and the flow rate in the waste water recipient. The annual average concentration variability is caused by differences in released 3H amount (e.g. in 2015, the annual average flowrate in Solenice was 49.3 m3/s), annual flow rate fluctuation (in 2013, 63,8 TBq of 3H was released from the Temelín NPP) and also manipulation at the Orlík Reservoir, which can cause a significant retention of 3H. For the period of 2001–2016, annual average 3H concentrations in the Vltava and Elbe Rivers are shown in Fig. 4. Observed concentrations are comparable e.g. with annual average concentrations in Ems Geeste in Germany effected by the Emsland NPP (1 PWR reactor, 1400 MW (RWE, 2017), long term average flow rate 80 m3/s). GNIR (2017) reports in Ems Geeste 13.6–24.8 Bq/l in 2008–2012. 3
3.2. Radionuclides in sediments The sediment monitoring was focused on concentrations of 90Sr, Cs and 137Cs. Mean concentration of 90Sr in the whole observed period (1993–2016) was 1.6 Bq/kg and 1.4 Bq/kg in 2001–2016 when the Temelín NPP was in operation. The assessment of 134Cs was stopped in 1999 because starting this year, all observed values were below the DL. Mean concentration of 134Cs in the assessed period (1990–1999) was 5.6 Bq/kg. In 1990–2016, the mean concentration of 137Cs in sediments was 64.8 Bq/kg and in 2001–2016, it was 33.1 Bq/kg. For the whole territory of the Czech Republic, the mean 137Cs concentration in the period of 2000–2010 was 14.0 Bq/kg (Hanslík et al., 2014) which indicates that the sediments in the Orlík Water Reservoir and its tributaries fall into those highly contaminated by 137Cs in the Czech Republic. The activities of these radionuclides are decreasing in time (Fig. 8). 134
3.1.2. Strontium 90 and caesium 137 Temporal changes of the 90Sr concentrations in water samples taken from the Orlík Water Reservoir and its tributaries were studied for the period of 1993–2016. The trend of decrease of the 90Sr concentrations was observed over all of the assessed period. The effective ecological half-lives (Teff) in individual tributaries and the outflow of the Orlík Water Reservoir were in the range of 9.2–10.3 y and the ecological halflives (Tecol) were in the range of 13.4–15.9 y (see Table 3). An example 5
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Fig. 4. Annual average 3H concentrations (c3H) and longterm average flow rates (Qa) in the Vltava and Elbe Rivers upstream (Hluboká) and downstream (the other sites) of the outflow of waste water from the Temelín NPP.
Table 3 Evaluated effective ecological and ecological half-lives of strontium 90 for individual tributaries and the outflow of the Orlík Water Reservoir (Vltava Solenice) in the period 1993–2016. Vltava Hněvkovice Teff
Lužnice Koloděje Tecol
Teff
Otava Topělec Tecol
Vltava Solenice
Teff
Tecol
Teff
Tecol
10.3 ± 1.2
15.9 ± 2.7
10.1 ± 1.2
15.6 ± 2.6
(y) 9.9 ± 1.1
15.1 ± 2.5
9.2 ± 1.0
13.4 ± 2.1
Fig. 5. Temporal changes of 90Sr concentration (c90Sr) in the Vltava River at Hněvkovice (reference site, source of technological water) and the Vltava River at Solenice (downstream of the Temelín waste water outflow) in the period of 1993–2016.
Table 4 Evaluated effective ecological and ecological half-lives of caesium 137 for individual tributaries and the outflow of the Orlík Water Reservoir in the period 1990–1994 and 1995–2016. Period
Vltava Hněvkovice Teff
Lužnice Koloděje Tecol
Teff
Otava Topělec Tecol
Vltava Solenice
Teff
Tecol
Teff
Tecol
1.4 ± 0.6 10.8 ± 2.6
1.5 ± 0.7 16.9 ± 6.9
1.5 ± 0.3 11.5 ± 2.0
1.5 ± 0.3 18.5 ± 5.5
(y) 1990–1994 1995–2016
1.5 ± 0.4 8.4 ± 0.9
1.6 ± 0.5 11.7 ± 1.8
2.2 ± 0.8 15.4 ± 10.6
2.4 ± 0.9 31 ± 25
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Fig. 6. Temporal changes of 137Cs concentration (c137Cs) in the Vltava River at Hněvkovice and the Vltava River at Solenice in the periods of 1990–1994 and 1995–2016.
Fig. 7. Time changes of 90Sr concentration in the surface water in the periods 1963–1986 and 1993–2016, A - Vltava Prague-Podolí site, B - Donau Expedition 1978, C - Temelín NPP vicinity.
Fig. 8. Temporal changes of annual average concentrations of 90Sr (a90Sr), 134Cs (a134Cs), and 137Cs (a137Cs) in sediments (dry weight) in the Orlík Water Reservoir and its main tributaries in the periods of 1993–2016 (90Sr), 1990–1999 (134Cs) and 1990–2016 (137Cs).
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assessed for the periods of 1986–1990 and 1994–2016. Between the two periods, the 137Cs concentrations decreased from 2.45 to 47.9 Bq/ kg (1986–1990) to less than 0.05–2.35 Bq/kg (1994–2016). The results of the monitoring and assessment of the 90Sr and 137Cs concentrations in fish are illustrated in Fig. 10. The concentrations in the Czech Republic are substantially lower than those in the areas most affected by the Chernobyl accident. Those activities were at levels of hundreds of kBq/kg shortly after the accident and in the early 1990's remained at levels of dozens of kBq/kg (Smith et al., 2000). The activities of several kBq/kg were reported from Switzerland, England or Germany in this period (Smith et al., 2000). In accord with the results derived for surface water (and sediments), the concentrations of 90Sr and 137Cs in fish exhibited a decreasing trend. The evaluated effective ecological half-life (Teff) for 90Sr was 10.5 y and the ecological half-life (Tecol) was 16.5 y for the period of 1990–2016 (Table 6). The effective ecological half-lives derived for several fish species in Finnish lakes were between 7 and 30 y (Outola et al., 2009). For 137Cs the evaluated half-lives were shorter than for 90Sr. Identical results were reported by Franić and Marović (2007) from observation in Croatia in the period of 1987–1992, while this decrease exceeded that derived by Smith et al. (2000) for identical period. The reported half-lives are between 2 and 3 y. In accord with the results from the Czech Republic, the literature shows that the decrease in the following period was significantly declining towards that expressed by physical half-life. The effective ecological half-lives in Finnish lakes were between 3 and 6 y (Outola et al., 2009). Franić and Marović (2007) reported 5 y for the period of 1993–2005. The 137Cs half-lives that were derived for fish correspond to those derived for water. The decreasing trend also continued during the operation of the Temelín NPP. Concentrations of 90Sr and 137Cs were also monitored in aquatic flora. Concentrations of 137Cs were monitored for several aquatic flora species (dry weight). The results substantiated an assumption that the highest 137Cs concentrations were accumulated in a group of aquatic mosses (21.8 Bq/kg in 1996) and algae (17.9 Bq/kg in 1996). Comparison of the results from both the river sites unaffected and the ones affected by the outflow from the Temelín NPP was complicated by different plants growing at the individual sites, with the 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 show that concentrations of 137Cs in the reed species decreased with the effective ecological half-life of 10.7 y and the ecological half-life of 16.5 y for the period of 1996–2016. The decreasing
Table 5 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 134 and 137 in sediments. Period
Tecol
Teff y
90
Sr Cs Cs
134 137
1993–2016 1990–1999 1990–2016
14.0 ± 3.9 1.7 ± 0.2 8.9 ± 0.9
27.1 ± 11.6 11.0 ± 6.7 12.6 ± 2.2
The rates of decline are similar for the reference sites and the affected sites and therefore the trends of decline were evaluated for average annual activities from all observed sites (Table 5). Fig. 9 shows comparison of 137Cs and 134Cs concentrations ratio calculated from observed data and theoretical trend of 137Cs and 134Cs concentrations ratio, which was derived from released activities during the Chernobyl accident (85 PBq 137Cs and 54 PBq 134Cs, according UNSCEAR, 2000). We can conclude that dominant part of radiocaesium contamination comes from Chernobyl disaster and minor part from atmospheric tests of nuclear weapons. Apart from 90Sr, 134Cs (until 1999), and 137Cs, the results of the monitoring did not substantiate sediment contamination by any other activation and fission products detectable by gamma-ray spectrometry or 90Sr determination.
3.3. Radionuclides in fish and aquatic flora The monitoring of fish and aquatic flora focused on concentrations Sr and 137Cs. The concentrations of 90Sr in fish were assessed for the entire observation period of 1990–2016. For this period, the mean 90Sr concentration in fish was 0.6 Bq/kg. Relatively rare data and information on 90Sr concentrations in fish include (Outola et al., 2009), where it was reported that in the period of 1978–1997 the concentrations in the analysed river species were in the range of 10–17 Bq/kg, which exceeded the 90Sr concentrations in fish from the Orlík Water Reservoir by approximately one order of magnitude. The concentration 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 (Outola et al., 2009). The concentrations of 137Cs in fish (related to wet weight) were of
90
Fig. 9. Time changes in annual average concentration of 137 Cs (A1) and 134Cs (A2) in the bottom sediments in the Orlik Reservoir and their ratio, calculated from observed data and from the ratio during Chernobyl accident.
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Fig. 10. Temporal changes in 90Sr and 137Cs concentrations (a90Sr, a137Cs) in fish (wet weight) in the Orlík Water Reservoir in the periods of 1990–2016 (a90Sr) and 1986–1990, 1994–2016 (a137Cs).
second monitoring period were different (1990–1994 and 1995–2016). Concentrations of 3H at sites unaffected by the Temelín NPP decreased slowly and their values were substantially below those from the sites affected by the plant. The effective ecological half-life calculated for the period of 1990–2016 was 16.3 years or 10.7 years after subtraction of the natural 3H component and the 3H originating from the atmospheric transfer from nuclear facilities worldwide.
Table 6 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 137 in fish. Period
Teff
Tecol y
90
Sr Cs
137
1990–2016 1986–1990 1994–2016
10.5 ± 2.4 1.0 ± 0.1 8.3 ± 3.1
16.5 ± 5.2 1.0 ± 0.1 11.5 ± 6.6
Acknowledgment This work was supported by the CEZ Group and the Czech Ministry of Environment (project no. MPZ0002071101).
Table 7 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 137 in reed species. Period
Teff
Appendix A. Supplementary data
Tecol
Supplementary data related to this article can be found at http://dx. doi.org/10.1016/j.jenvrad.2017.11.029.
y 90
Sr Cs
137
1990–2016 1996–2016
6.7 ± 0.6 10.7 ± 2.2
8.7 ± 1.0 16.5 ± 5.6
References Atlas of caesium deposition on Europe after the Chernobyl accident, 1998. Office for official publications of the Europe communities, luxemburg. Corner, A., Venables, D., Spence, A., Poortinga, W., Demski, C., Pidgeon, N., 2011. Nuclear power, climate change and energy security: exploring British public attitudes. Energy Policy 39 (9), 4823–4833. ČEZ, 2017. https://www.cez.cz/en/power-plants-and-environment/nuclear-powerplants/temelin.html, Accessed date: 24 October 2017. ČSN EN ISO 5667–1, 2007. Water Quality - Sampling - Part 1: Guidance on the Design of Sampling Programmes and Sampling Techniques (ISO 5667-1:2006). Czech Standard Institute. ČSN EN ISO 5667–3, 2013. Water Quality – Sampling – Part 3: Preservation and Handling of Water Samples (ISO 5667-3:2012). Czech Office for Standards, Metrology and Testing. ČSN EN ISO 10703, 2008. Water Quality – Determination of the Activity Concentration of Radionuclides by High Resolution Gamma-ray Spectrometry (ISO 10703:2007). (Czech Standard). ČSN ISO 5667–4, 1994. Water Quality - Sampling - Part 4: Guidance on Sampling from Lakes, Natural and Man-made (ISO 5667-4:1987). Czech Standard Institute. ČSN ISO 5667–6, 2008. Water Quality - Sampling - Part 6: Guidance on Sampling of Rivers and Streams (ISO 5667-6:2005). Czech Standard Institute. ČSN EN ISO 9698, 2011. Water Quality – Determination of Tritium Activity Concentration – Liquid Scintillation Counting Method (ISO 9698:2010). Czech Office for Standards, Metrology and Testing. Dědáček, K., Plško, J., 1992. Aerial Geological Survey of the Vicinity of NPP Temelín. Geofyzika, Brno (In Czech). Franić, Z., Marović, G., 2007. Long-term investigations of radiocaesium activity concentrations in carp in North Croatia after the Chernobyl accident. J. Environ. Radioact. 94, 75–85. Global Network of Isotopes in Rivers. The GNIR Database. http://www-naweb.iaea.org/ napc/ih/IHS_resources_gnir.html. Accessed 24.10.2017.
trend was identified for the unaffected as well as for the affected river sites and continued in the period when the Temelín NPP was in the operation. 90Sr concentration in reed species was in the range of less than 0.4 and 6.1 Bq/kg (dry weight) and this concentration decreased with the effective ecological half-life of 6.7 y and the ecological half-life of 8.7 y (Table 7).
4. Conclusions Concentrations of anthropogenic radionuclides downstream of the wastewater outflow from the Temelín NPP are mainly due to the residual contamination from global fallout and the Chernobyl accident. The influence of the Temelín NPP on concentration of the activation and fission products in the hydrosphere (except 3H) has been negligible. Downstream of the plant, significantly higher 3H activity concentrations were detected, corresponding to the 3H discharged from the Temelín NPP. For all of the components of the environment, concentrations of 90Sr and 137Cs, which were used for calculation of their effective and ecological half-lives, decreased. The rate of decrease in 90Sr concentration was invariable during the whole assessed period of 1993–2016. For 137 Cs in surface water and fish, the rates of decrease in the first and 9
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1048–1056. Potop, V., Možný, M., Soukup, J., 2012. Drought evolution at various time scales in the lowland regions and their impact on vegetable crops in the Czech Republic. Agric. For. Meteorology 156, 121–133. Pujol, L., Sanchez-Cabeza, J., 2000. Use of tritium to predict soluble pollutants transport in Ebro river waters (Spain). Environ. Pollut. 108 (2), 257–269. Rozanski, K., Gröning, M., 2004. Tritium assay in water samples using electrolytic enrichment and liquid scintillation spectrometry. Quantifying Uncertain. Nucl. Anal. Meas. 195–217 IAEA-TECDOC-1401. RWE, 2017. http://www.rwe.com/web/cms/en/16646/rwe-power-ag/fuels/nuclearpower/emsland-nuclear-power-station/. Accessed 24.10.2017. Smith, J.T., Kudelsky, A.V., Ryabov, I.N., Hadderingh, R.H., 2000. Radiocaesium concentration factors of Chernobyl-contaminated fish: study of the influence of potassium, and „blind“ testing of a previously developed model. J. Environ. Radioact. 48, 359–369. Smith, J.T., Beresford, N.A., 2005. Chernobyl – Catastrophe and Consequences. Praxis Publishing Ltd, Chichester, UK, pp. 310 ISBN 3-540-23866-2. Soyfer, V.N., 2002. Radiation accidents in the Southern Urals (1949-1967) and human genome damage. Comp. Biochem. Physiology Part A Mol. Integr. Physiology 133 (3), 715–731. UNSCEAR, 2000. Report to the General Assembly: Sources and Effects of Ionizing Radiation, vol. I Sources. Available from: www.unscear.org. Zibold, G., Kaminski, S., Klemt, E., Smith, J.T., 2001. Time-dependency of the 137Cs activity concentration in fresh lakes, measurement and prediction, Radioprotection. In: Proceeding of the International Congress ECORAD 2001, Aix-en-Provence, France, vol. 37. pp. 75–80 C1, 2002.
Gnojek, I., Hanák, J., Dědáček, K., 1997. Distribution of Cs-137 Fallout in Terms of Possible Contamination of Water Streams in the Czech Republic. Geofyzika, Brno (In Czech). Hanslík, E., 1993. Determination of Sr-90 and Yt-90. In: Čapková, A. (Ed.), Guide for Determination Water Quality Indicators. Ministry of the Environment of the Czech Republic. Hanslík, E., 1998. The Environment Contamination as a Consequence of the Chernobyl Accident at the Level of the Year 1996 and Impact on Surface Water Contamination and River Bottom Sediments. WRI TGM, Praha (In Czech). Hanslík, E., Budská, E., Sedlářová, B., Šimonek, P., 1999. Trends in changes in radionuclide content in the hydrosphere in the vicinity of the NPP Temelín. In: Proceedings of XVI. Conference Radionuclides and Ionizing Radiation in Water Management. ČVTVHS, Praha (In Czech). Hanslík, E., Marešová, D., Juranová, E., 2014. Natural and artificial radionuclides in river bottom sediments and suspended matter in the Czech Republic in the period 20002010. J. Environ. Prot. 5 (2), 114–119. IHE CRH, 1987. Report on the State of Radiation on the Territory of the Czechoslovak Republic after the Chernobyl Accident. Centre of Radiation Hygiene of the Institute of Hygiene and Epidemiology, Praha (in Czech). Available from: www.suro.cz. Konoplev, A., Golosov, V., Laptev, G., Nanba, K., Onda, Y., Takase, T., Yoshimura, K., 2016. Behavior of accidentally released radiocesium in soil-water environment: looking at fukushima from a chernobyl perspective. J. Environ. Radioact. 151, 568–578. Outola, I., Saxén, R., Heinävaara, L., 2009. Transfer of 90Sr into fish in Finnish lakes. J. Environ. Radioact. 100, 657–664. Palomo, M., Penalver, A., Aguilar, C., Borrull, F., 2007. Tritium activity levels in environmental water samples from different origins. Appl. Radiat. isotopes 65,
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Kinetics of 3H, 90Sr and 137Cs content changes in hydrosphere in the Vltava River system (Czech Republic) Eduard Hanslíka,∗, Diana Marešováa, Eva Juranováa,b, Barbora Sedlářováa a b
Department of Radiology, T. G. Masaryk Water Research Institute, p.r.i., Podbabská 30, 160 00 Prague, Czech Republic Faculty of Science, Institute for Environmental Studies, Charles University, Benátská 2, 128 01 Prague, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords: Tritium Strontium 90 Caesium 137 Effective ecological half-time Surface water Sediments
The paper presents results and interpretation of long-term monitoring of occurrence and behaviour of radioisotopes 3H, 90Sr, and 137Cs in the vicinity of the Temelín Nuclear Power Plant. 3H, 90Sr, and 137Cs originate predominantly from residual contamination due to atmospheric nuclear weapons tests and the Chernobyl disaster in the last century. Monitoring of radionuclides comprised surface waters, river sediments, aquatic plants, and fish. This enables an up-to-date appraisal of the Temelín Nuclear Power Plant impact on the hydrosphere in all indicators at standard power plant operation, as well as at critical situations. The time and spatial variability of these radionuclide concentrations were monitored in the hydrosphere at in- and out-flow of the Orlík Water Reservoir. The basic evaluated radioecological characteristics can be used in assessing the long-term kinetics of decline and behaviour of radionuclides and their potential release into the environment. A very slow decline in 3 H concentration at unaffected sites was observed. At sites downstream from the power plant the 3H concentrations were significantly higher, an evident impact of the power plant operation. A decline in 90Sr and 137Cs concentrations was observed in all the monitored indicators. Also, the characteristic effective and ecological half-lives were evaluated.
1. Introduction The usual operation of a nuclear power plant is associated with production of different radionuclides that can be released into the environment in very low concentrations. Operation of such facility is obviously accompanied with high requirements to keep radiation protection (Corner et al., 2011). Moreover, the past accidents at nuclear facilities had unquestionable impacts on environment: Fukushima accident (Konoplev et al., 2016), Chernobyl accident (Smith and Beresford, 2005) and accidents in the Southern Urals (Soyfer, 2002). Anthropogenic radionuclides in the territory of South Bohemia (Czech Republic) have been studied by T.G.M. Water research institute (TGM WRI) long because of the Temelín Nuclear Power Plant (Temelín NPP). Main technical parameters of the Temelín NPP are mentioned in Table 1. Pilot operation of the first reactor was launched in June 2002 and of the second one in April 2003. Since May 2003, the Temelín NPP has been in full operation. The plant releases its waste water into the Vltava River. The Orlík Water Reservoir, located on the Vltava River downstream of the waste water outflow, is presumed to play a major role in the radionuclides behaviour in the hydrosphere and its outflow from assessed area (Fig. 1).
∗
Usually, the wastewater from a NPP is discharged into a big river, e.g. as in (Pujol and Sanchez-Cabeza, 2000), however the wastewater from the Temelín NPP is discharged into a relatively small watercourse (see Table 2). Regarding the expected climate change impacts in the Czech Republic including the hydrological drought (e.g. Potop et al., 2012), the radionuclide activity concentrations has potential to increase due to lower dilution in the Vltava River affected directly by the Temelín NPP (Fig. 1). Anthropogenic radionuclides have been observed in the environment since atmospheric tests of nuclear weapons and following the accident at the Chernobyl nuclear reactor in the last century. During the atmospheric tests of nuclear weapons 186.103 PBq 3H, 622 PBq 90Sr and 948 PBq 137Cs was released (UNSCEAR, 2000). The estimated amount of released radionuclides during the Chernobyl disaster is 10 PBq 90Sr and 85 PBq 137Cs (UNSCEAR, 2000). According to Atlas (1998), the average surface deposition of 137Cs due to Chernobyl disaster in the Czech Republic was 7.6 kBq/m2. Estimates of the amount of 137Cs deposited on the territory of the Czech Republic are based predominantly on investigations carried out in June 1986 by the Centre of Radiation Hygiene of the Institute of Hygiene and Epidemiology (IHE CRH, 1987). These investigations were
Corresponding author. E-mail addresses: [email protected] (E. Hanslík), [email protected] (D. Marešová), [email protected] (E. Juranová), [email protected] (B. Sedlářová).
https://doi.org/10.1016/j.jenvrad.2017.11.029 Received 15 August 2017; Received in revised form 22 November 2017; Accepted 22 November 2017 0265-931X/ © 2017 Published by Elsevier Ltd.
Please cite this article as: Hanslík, E., Journal of Environmental Radioactivity (2017), https://doi.org/10.1016/j.jenvrad.2017.11.029
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Table 1 Main technical parameters for the Temelín NPP (ČEZ, 2017). Number of reactor blocks Installed output Reactor Year of commissioning Radioactive discharges into the Vltava River Limit of 3H Annual average 3H dischargesa Limit of other activation and fission products (AaFP) Annual average discharges AaFPa
Table 2 Characteristics of sampling sites.
2 2 × 1055 MW pressurised water, VVER 1000 2002 Vltava Hluboká Vltava Hněvkovice Lužnice Koloděje Otava Topělec Vltava Solenice Vltava Štěchovice Vltava Prague Podolí Vltava Zelčín Elbe Hřensko
66 TBq/y 51 TBq/y 1 GBq/y 0.116 GBq/y
a Average in 2008–2016 when the 3H and other AaFP amount released from the Temelín NPP were stabilized.
Qa
TSS
K
Ca
m3/s
mg/l
mg/l
mg/l
9.4 ± 3.7 24.8 ± 8.5 11.5 ± 8.8 3.9 ± 1.8
3.6 7.0 3.9 4.2
30.0 30.6 23.6 23.3 84.3 85.6 143 152 319
± ± ± ±
Fig. 1. Map of the sampling sites.
2
1.0 2.3 1.3 1.2
16.2 26.6 19.1 21.0
± ± ± ±
5.3 6.4 4.2 4.4
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Fig. 2.
137
Cs surface activity in soil in the Czech Republic (kBq/m2) after the 1986 Chernobyl disaster, including
137
Cs fallout from nuclear weapon tests, according to Hanslík (1998).
The main objective of presented study is to assess the contribution of the Temelín NPP to overall radionuclide concentrations. It analyses the results of long-term monitoring and evaluates the development of radionuclide concentrations in surface water, sediments and fish in the vicinity of the Temelín NPP. Analysed radionuclides were tritium (3H), strontium 90 (90Sr) and caesium 137 (137Cs). Concentrations of radionuclides were evaluated in surface water, sediments, fish and aquatic flora both affected and unaffected by waste water discharges from the Temelín NPP before and during the operation of the plant. Main components of radionuclide background were quantified; they stem from natural (3H) and anthropogenic processes (3H, 90Sr, 137Cs; residual pollution from tests of nuclear weapons and Chernobyl disaster in the last century and the atmospheric transfer from nuclear facilities worldwide).
later completed by aerial surveys (Gnojek et al., 1997) and a map of contaminated areas was created (Hanslík, 1998) (Fig. 2). This map thus comprises even fallout from the atmospheric tests of nuclear weapons, estimated for 1986 by the UNSCEAR (2000) to be 1.9 kBq/m2 (cumulative deposition). The most seriously affected areas of the Czech Republic with surface deposition above 10 kBq/m2 are towards the northeast to north-west, which corresponds to the wind direction at the time of the first appearance of the contaminated plume. The second and third plumes reached our territory from the south-east to north-west. The recorded 137Cs volume activity in the Czech surface waters from May 1st to June 10th. 1986 ranged from 0.08 to 8.0 Bq/l (IHE CRH, 1987). The vicinity of the Temelín NPP ranks among regions afflicted by the first radioactive plume to arrive over our territory; according to IHE CRH (1987), fallout in this region reached 2.3–13 kBq/m2. A detailed aerial survey was carried out in 1992 by Dědáček and Plško (1992), subsequently amended by measurements in 1996 (Gnojek et al., 1997), and from both it follows that 137Cs surface contamination around the power plant in 1996 was 1–16 kBq/m2. These data would correspond with the 1986 fallout within 1.3–20.2 kBq/m2. However, 90Sr fallout data after the disaster are very scarce, and official data on the total 90Sr deposition had not been published. Due to a different character of the deposition, deposition estimates cannot be derived from the ratio of 90Sr and 137Cs in the reactor at the time of disaster, which was 0.12, as is the case of e.g. 134Cs (Smith and Beresford, 2005). For example, according to Outola et al. (2009), the recorded ratio of 90Sr and 137Cs in the fallout over Finland after the Chernobyl disaster ranged between 0.015 and 0.333. IHE CRH (1987) gives the 90Sr and 137Cs ratio in close-to-the-Earth atmospheric layer over Prague-Libuš in the range from 0.02 to 0.13. According to UNSCEAR (2000) estimates, 90Sr contribution in 1986, i.e. the cumulative 90Sr deposition from atmospheric tests of nuclear weapons, was 1.23 kBq/m2.
2. Methods Concentrations of 3H, 90Sr and 137Cs were monitored in surface water (without filtration, i e. in both the dissolved and undissolved substances) and concentrations of 90Sr and 137Cs in sediments and complementarily in fish species and aquatic flora. Location of the sampling sites is shown in Fig. 1. Methods specified in Standards ČSN ISO 5667-1 (2007), ČSN ISO 5667-3 (2013), ČSN ISO 5667-4 (1994), ČSN ISO 5667-6 (2008) (national editions) were used for the sampling and sample processing. The surface water monitoring was launched in 1990 in the Vltava River at Hněvkovice, the Lužnice river at Koloděje and the Otava river at Písek, which are river sites located outside the impact of the Temelín NPP (reference sites), and in the Vltava River at Solenice located downstream of the outflows from the plant. Frequency of the sampling was 4 samples a year. Further, more detailed monitoring of 3H with the frequency of 12 samples a year was carried out at reference sites in the Vltava River at Hluboká and at the Elbe River at Lysá and at affected 3
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Fig. 3. Annual average 3H concentrations in surface water unaffected by waste water discharges from the Temelín NPP in the period of 1990–2016, without (A) and after correction (B) by subtracting the natural component and the activity originating from the atmospheric transfer from nuclear facilities worldwide.
significance of 0.05.3H in the analysed water samples from the reference sites has been pre-concentrated using electrolytic enrichment since 2012. The detection limit (DL) has been since then was 0.07 Bq/l. Gammaspectrometric analysis was implemented to determine concentrations of 137Cs by using methods specified in ČSN EN ISO 10703 (2008) and subsequently the 90Sr concentrations were determined by using the method described by Hanslík (1993). A Canberra device was used for the gamma spectrometry. The detection limit at the level of significance of 0.05 of 137Cs in water was 0.5 mBq/l, in the sediments 0.5 Bq/kg, in fish (wet weight) 0.1 Bq/kg. The 90Sr activity was detected from the residue after igniting via detection of yttrium 90 after radiochemical separation. Value of DL of 90Sr was 3 mBq/l. Trends in the concentrations of the radionuclides were analysed by using the following regression equation:
sites in the Vltava River at Podolí and at the Elbe River at Hřensko. Long-term average flow rates are displayed in Table 2. Data of total suspended solids (TSS), K and Ca are accompanied for sampling site where 90Sr and 137Cs analyses was performed. Volumes of the water samples were 0.25 l for 3H and 50 l for 90Sr and 137Cs. The samples for 3H determination were stabilized by cooling while the large-volume samples were stabilized 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 90Sr and 137Cs concentrations therefore includes both the dissolved and undissolved substances. Samples of water (1 l) for determination of TSS were taken with the same frequency (4 samples a year). The sediments, fish and aquatic flora have been monitored with frequency of one sample a year in both the reference and the affected sites. The sediment samples were taken from the top layer (0–10 cm) during the period of 1990–2016. Annual average activities of 90Sr and 134 Cs and 137Cs in dry weight from all sampling sites are presented. The fish sampling was carried out during the period of 1986–1990, in 1994 and 1995 and then annually since 1998, represented by omnivorous pelagic fish (mainly carp, bream). Three samples per year were analysed, annual average activities of 90Sr and 137Cs in wet weight are presented. The aquatic flora was sampled once a year at individual monitoring sites in the period of 1989–2016. The sampling included littoral species, aquatic mosses, algae species and submerged species. Since 2006 only reeds have been monitored. Annual average activities of 90Sr and 137Cs in dry weight from all sampling sites are presented. 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 the fraction of less than 2 mm was analysed. The fish samples were disembowelled, weighted, pulped, dried and subsequently pulverised and locked in measuring containers. The analyses were performed for dry weight and the results were recalculated for wet weight. The flora samples were cut into pieces and locked in measuring containers. For determination of 3H activities, methods specified in ČSN EN ISO 9698 (2011) were used. The 3H concentrations were determined by using Quantulus 1220 and TriCarb low-level liquid scintillation spectrometers. The relative efficiency of 3H measurement was 26%. The detection limit was set according to expected activities. For mixture of 8 ml of sample and 12 ml of scintillation solution and for counting time of 800 min (for samples not affected by the waste water discharges) or 300 min (for samples affected by the waste water discharges), the detection limit was 1.1 Bq/l and 2.1 Bq/l, respectively, at the level of
lnCj = −λ eff ⋅t + lnC0
(1)
where Cj is annual average radioactivity concentration in year j, λeff 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 initial concentration. Statistical significance of the regression line was verified by using the Pearson coefficient and t-test. Then the effective ecological half-lives (Teff) and the ecological halflives (Tecol) were calculated from the decrease in radionuclide activity according to the equation (Smith and Beresford, 2005):
ln 2 λ eff
(2)
1 1 1 = − Tecol Teff TP
(3)
Teff =
where TP is physical half-life (y). 3. Results and discussion 3.1. Radionuclides in surface water 3.1.1. Tritium 3 H concentrations in surface water were analysed separately at both the sites affected and the sites unaffected by the Temelín NPP. For data from unaffected sites in the period of 1990–2016 (see Fig. 3 A), Equation (1) gives effective ecological half-life of 16.3 ± 2.1 y. The trend of decrease was statistically significant, but the calculated effective ecological half-life was longer than the physical half-life of 3H 12.32 y (Rozanski and Gröning, 2004). The reason is that, apart from 4
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is shown in Fig. 5 for the Vltava River at Hněvkovice and the Vltava River at Solenice. In 2016, the average activity of 90Sr at both Hněvkovice (a reference site, source of technological water for the Temelín NPP) and Solenice (downstream of the Temelín waste water outflow) was 2.5 mBq/l. Temporal changes of the 137Cs concentrations in water samples taken from the Orlík Water Reservoir and its tributaries were studied for two separate periods, 1990–1994 and 1995–2016. The effective ecological half-lives (Teff) in individual tributaries and the outflow of the Orlík Water Reservoir were in the range of 1.4–2.2 y for the period of 1990–1994 and 8.4–15.4 y for the period of 1995–2016. The ecological half-lives (Tecol) were in the range of 1.5–2.4 y for the period of 1990–1994 and 11.5–31 y for the period of 1995–2016 (see Table 4). An example is shown in Fig. 6 for the Vltava River at Hněvkovice and the Vltava River at Solenice. In 2016, the average activity of 137Cs at both sites was less than 0.6 mBq/l. Our results showed that a decrease in the 90Sr and 137Cs concentrations, which was observed before the plant operation, also continued during the subsequent period. The results of monitoring 90Sr in the South Bohemia (Fig. 7 C2) obtained in connection with the Temelín NPP were compared with data measured by TGM WRI in the Vltava basin after the nuclear weapons tests (Fig. 7 A), results of the Danube River expedition in 1978 (Fig. 7 B) and further the results of the earlier monitoring in the Temelín NPP vicinity in the period of 1981–1984 (Fig. 7 C1). In the first evaluated period after the nuclear weapons tests and before the Chernobyl accident, the observed half-life was 6.9 ± 0.9 years; in the second period 1996–2016, after the Chernobyl disaster, it was 9.8 ± 0.9 years. It can be concluded that effective ecological half-lives of 90Sr observed after the nuclear weapons tests until the Chernobyl disaster and then after the Chernobyl are very similar. Results of our research focused on the vicinity of the Temelín NPP are in agreement with similar studies on changes in water contamination after the Chernobyl accident. For example, Zibold et al. (2001) showed a faster decrease of 137Cs concentration in the period of 1986–1988 and a slower phase in 1989–2000. Similarly, Smith and Beresford (2005) reported that the rate of decline of the 137Cs concentration in the Pripyat River was decreasing in recent years. The effective ecological half-lives of 1.2 years (dissolved phase) and 1.7 y (particulate phase) in the period of 1987–1991 increased to 3.4 y (dissolved phase) and 11.2 y (particulate phase) in the period of 1995–1998. This increase in Teff has also been observed in Belarus, Ukraine and Finland (Zibold et al., 2001). The concentrations of anthropogenic radionuclides 90Sr and 137Cs downstream of the waste water discharge from the Temelín NPP therefore originate mainly from the residual contamination from atmospheric tests of nuclear weapons and the Chernobyl accident. These activities show a decreasing trend in time. The detected activities concentrations in surface water are currently near the detection limits.
H form the atmospheric nuclear weapons tests, there are fractions of H, which are considered to be steady, not changing with time. These are a relatively small 3H activities generated naturally by cosmic radiation and the atmospheric transfer of 3H from nuclear facilities worldwide, which is also considered constant in the analysed period. These stable 3H fractions were therefore eliminated in subsequent analysis (Fig. 3 B). The annual average 3H activities (c3HB,j) were corrected by subtracting its components originating from cosmic radiation (c3HCR) and the atmospheric transfer from nuclear facilities worldwide (c3HNF). The mean values were calculated by including 3H activities below the detection limit into the data set as values of the limit. After elimination of the constant components, which were appreciated 0.48 Bq/l according Hanslík et al. (1999), the effective ecological half-life (Teff) calculated for the period of 1990–2016 was 10.7 ± 1.3 y, which is shorter than that derived by using the first approach and is almost same as the physical half-life of 3H. The component of 3H concentration originating from tests of nuclear weapons will be further decreasing and thus it can be assumed that the effective half-life will increase. After decomposition of 3H from tests of nuclear weapons, its concentration will include a constant component originating from cosmic radiation and a slowly increasing component stemming from atmospheric transfer of 3H from gaseous and liquid releases from nuclear facilities in the Czech Republic and abroad. At sites (see above) unaffected by waste water discharges from the Temelín NPP, the mean 3H activity calculated by using the first approach (the alternative not involving elimination of the constant components) was 3.1 Bq/l at the beginning of the analysed period (1990) and less than 1.0 Bq/l at its end (2016). The 3H concentrations in surface waters in the vicinity of the Temelín NPP unaffected by waste water discharges are in accord with the results of observations performed abroad. Palomo et al. (2007) reported that 3H concentrations in samples taken in October 2005 and January 2006 in the vicinity of Asco Nuclear Power Plant (Spain) are between less than 0.6 and 0.93 Bq/l. The differences between the 3H concentrations in the vicinity of the Temelín and Asco NPPs are not significant. In contrast to the results derived for the unaffected sites, the trends in concentrations of 3H at the affected river sites were remarkably different. Since 2001, when the Temelín NPP was put in operation, 3H concentrations in the Vltava and Elbe Rivers downstream of the waste water outflow have been increasing. This is attributable to gradual increase in the output of the plant associated with increasing quantity of 3 H, since 2008 the 3H amount released from the Temelín NPP has been stabilized at about 51 TBq/year (average in 2008–2016). The concentrations in surface water correspond to the annual released 3H amount and the flow rate in the waste water recipient. The annual average concentration variability is caused by differences in released 3H amount (e.g. in 2015, the annual average flowrate in Solenice was 49.3 m3/s), annual flow rate fluctuation (in 2013, 63,8 TBq of 3H was released from the Temelín NPP) and also manipulation at the Orlík Reservoir, which can cause a significant retention of 3H. For the period of 2001–2016, annual average 3H concentrations in the Vltava and Elbe Rivers are shown in Fig. 4. Observed concentrations are comparable e.g. with annual average concentrations in Ems Geeste in Germany effected by the Emsland NPP (1 PWR reactor, 1400 MW (RWE, 2017), long term average flow rate 80 m3/s). GNIR (2017) reports in Ems Geeste 13.6–24.8 Bq/l in 2008–2012. 3
3.2. Radionuclides in sediments The sediment monitoring was focused on concentrations of 90Sr, Cs and 137Cs. Mean concentration of 90Sr in the whole observed period (1993–2016) was 1.6 Bq/kg and 1.4 Bq/kg in 2001–2016 when the Temelín NPP was in operation. The assessment of 134Cs was stopped in 1999 because starting this year, all observed values were below the DL. Mean concentration of 134Cs in the assessed period (1990–1999) was 5.6 Bq/kg. In 1990–2016, the mean concentration of 137Cs in sediments was 64.8 Bq/kg and in 2001–2016, it was 33.1 Bq/kg. For the whole territory of the Czech Republic, the mean 137Cs concentration in the period of 2000–2010 was 14.0 Bq/kg (Hanslík et al., 2014) which indicates that the sediments in the Orlík Water Reservoir and its tributaries fall into those highly contaminated by 137Cs in the Czech Republic. The activities of these radionuclides are decreasing in time (Fig. 8). 134
3.1.2. Strontium 90 and caesium 137 Temporal changes of the 90Sr concentrations in water samples taken from the Orlík Water Reservoir and its tributaries were studied for the period of 1993–2016. The trend of decrease of the 90Sr concentrations was observed over all of the assessed period. The effective ecological half-lives (Teff) in individual tributaries and the outflow of the Orlík Water Reservoir were in the range of 9.2–10.3 y and the ecological halflives (Tecol) were in the range of 13.4–15.9 y (see Table 3). An example 5
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Fig. 4. Annual average 3H concentrations (c3H) and longterm average flow rates (Qa) in the Vltava and Elbe Rivers upstream (Hluboká) and downstream (the other sites) of the outflow of waste water from the Temelín NPP.
Table 3 Evaluated effective ecological and ecological half-lives of strontium 90 for individual tributaries and the outflow of the Orlík Water Reservoir (Vltava Solenice) in the period 1993–2016. Vltava Hněvkovice Teff
Lužnice Koloděje Tecol
Teff
Otava Topělec Tecol
Vltava Solenice
Teff
Tecol
Teff
Tecol
10.3 ± 1.2
15.9 ± 2.7
10.1 ± 1.2
15.6 ± 2.6
(y) 9.9 ± 1.1
15.1 ± 2.5
9.2 ± 1.0
13.4 ± 2.1
Fig. 5. Temporal changes of 90Sr concentration (c90Sr) in the Vltava River at Hněvkovice (reference site, source of technological water) and the Vltava River at Solenice (downstream of the Temelín waste water outflow) in the period of 1993–2016.
Table 4 Evaluated effective ecological and ecological half-lives of caesium 137 for individual tributaries and the outflow of the Orlík Water Reservoir in the period 1990–1994 and 1995–2016. Period
Vltava Hněvkovice Teff
Lužnice Koloděje Tecol
Teff
Otava Topělec Tecol
Vltava Solenice
Teff
Tecol
Teff
Tecol
1.4 ± 0.6 10.8 ± 2.6
1.5 ± 0.7 16.9 ± 6.9
1.5 ± 0.3 11.5 ± 2.0
1.5 ± 0.3 18.5 ± 5.5
(y) 1990–1994 1995–2016
1.5 ± 0.4 8.4 ± 0.9
1.6 ± 0.5 11.7 ± 1.8
2.2 ± 0.8 15.4 ± 10.6
2.4 ± 0.9 31 ± 25
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Fig. 6. Temporal changes of 137Cs concentration (c137Cs) in the Vltava River at Hněvkovice and the Vltava River at Solenice in the periods of 1990–1994 and 1995–2016.
Fig. 7. Time changes of 90Sr concentration in the surface water in the periods 1963–1986 and 1993–2016, A - Vltava Prague-Podolí site, B - Donau Expedition 1978, C - Temelín NPP vicinity.
Fig. 8. Temporal changes of annual average concentrations of 90Sr (a90Sr), 134Cs (a134Cs), and 137Cs (a137Cs) in sediments (dry weight) in the Orlík Water Reservoir and its main tributaries in the periods of 1993–2016 (90Sr), 1990–1999 (134Cs) and 1990–2016 (137Cs).
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assessed for the periods of 1986–1990 and 1994–2016. Between the two periods, the 137Cs concentrations decreased from 2.45 to 47.9 Bq/ kg (1986–1990) to less than 0.05–2.35 Bq/kg (1994–2016). The results of the monitoring and assessment of the 90Sr and 137Cs concentrations in fish are illustrated in Fig. 10. The concentrations in the Czech Republic are substantially lower than those in the areas most affected by the Chernobyl accident. Those activities were at levels of hundreds of kBq/kg shortly after the accident and in the early 1990's remained at levels of dozens of kBq/kg (Smith et al., 2000). The activities of several kBq/kg were reported from Switzerland, England or Germany in this period (Smith et al., 2000). In accord with the results derived for surface water (and sediments), the concentrations of 90Sr and 137Cs in fish exhibited a decreasing trend. The evaluated effective ecological half-life (Teff) for 90Sr was 10.5 y and the ecological half-life (Tecol) was 16.5 y for the period of 1990–2016 (Table 6). The effective ecological half-lives derived for several fish species in Finnish lakes were between 7 and 30 y (Outola et al., 2009). For 137Cs the evaluated half-lives were shorter than for 90Sr. Identical results were reported by Franić and Marović (2007) from observation in Croatia in the period of 1987–1992, while this decrease exceeded that derived by Smith et al. (2000) for identical period. The reported half-lives are between 2 and 3 y. In accord with the results from the Czech Republic, the literature shows that the decrease in the following period was significantly declining towards that expressed by physical half-life. The effective ecological half-lives in Finnish lakes were between 3 and 6 y (Outola et al., 2009). Franić and Marović (2007) reported 5 y for the period of 1993–2005. The 137Cs half-lives that were derived for fish correspond to those derived for water. The decreasing trend also continued during the operation of the Temelín NPP. Concentrations of 90Sr and 137Cs were also monitored in aquatic flora. Concentrations of 137Cs were monitored for several aquatic flora species (dry weight). The results substantiated an assumption that the highest 137Cs concentrations were accumulated in a group of aquatic mosses (21.8 Bq/kg in 1996) and algae (17.9 Bq/kg in 1996). Comparison of the results from both the river sites unaffected and the ones affected by the outflow from the Temelín NPP was complicated by different plants growing at the individual sites, with the 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 show that concentrations of 137Cs in the reed species decreased with the effective ecological half-life of 10.7 y and the ecological half-life of 16.5 y for the period of 1996–2016. The decreasing
Table 5 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 134 and 137 in sediments. Period
Tecol
Teff y
90
Sr Cs Cs
134 137
1993–2016 1990–1999 1990–2016
14.0 ± 3.9 1.7 ± 0.2 8.9 ± 0.9
27.1 ± 11.6 11.0 ± 6.7 12.6 ± 2.2
The rates of decline are similar for the reference sites and the affected sites and therefore the trends of decline were evaluated for average annual activities from all observed sites (Table 5). Fig. 9 shows comparison of 137Cs and 134Cs concentrations ratio calculated from observed data and theoretical trend of 137Cs and 134Cs concentrations ratio, which was derived from released activities during the Chernobyl accident (85 PBq 137Cs and 54 PBq 134Cs, according UNSCEAR, 2000). We can conclude that dominant part of radiocaesium contamination comes from Chernobyl disaster and minor part from atmospheric tests of nuclear weapons. Apart from 90Sr, 134Cs (until 1999), and 137Cs, the results of the monitoring did not substantiate sediment contamination by any other activation and fission products detectable by gamma-ray spectrometry or 90Sr determination.
3.3. Radionuclides in fish and aquatic flora The monitoring of fish and aquatic flora focused on concentrations Sr and 137Cs. The concentrations of 90Sr in fish were assessed for the entire observation period of 1990–2016. For this period, the mean 90Sr concentration in fish was 0.6 Bq/kg. Relatively rare data and information on 90Sr concentrations in fish include (Outola et al., 2009), where it was reported that in the period of 1978–1997 the concentrations in the analysed river species were in the range of 10–17 Bq/kg, which exceeded the 90Sr concentrations in fish from the Orlík Water Reservoir by approximately one order of magnitude. The concentration 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 (Outola et al., 2009). The concentrations of 137Cs in fish (related to wet weight) were of
90
Fig. 9. Time changes in annual average concentration of 137 Cs (A1) and 134Cs (A2) in the bottom sediments in the Orlik Reservoir and their ratio, calculated from observed data and from the ratio during Chernobyl accident.
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Fig. 10. Temporal changes in 90Sr and 137Cs concentrations (a90Sr, a137Cs) in fish (wet weight) in the Orlík Water Reservoir in the periods of 1990–2016 (a90Sr) and 1986–1990, 1994–2016 (a137Cs).
second monitoring period were different (1990–1994 and 1995–2016). Concentrations of 3H at sites unaffected by the Temelín NPP decreased slowly and their values were substantially below those from the sites affected by the plant. The effective ecological half-life calculated for the period of 1990–2016 was 16.3 years or 10.7 years after subtraction of the natural 3H component and the 3H originating from the atmospheric transfer from nuclear facilities worldwide.
Table 6 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 137 in fish. Period
Teff
Tecol y
90
Sr Cs
137
1990–2016 1986–1990 1994–2016
10.5 ± 2.4 1.0 ± 0.1 8.3 ± 3.1
16.5 ± 5.2 1.0 ± 0.1 11.5 ± 6.6
Acknowledgment This work was supported by the CEZ Group and the Czech Ministry of Environment (project no. MPZ0002071101).
Table 7 Evaluated effective ecological and ecological half-lives of strontium 90 and caesium 137 in reed species. Period
Teff
Appendix A. Supplementary data
Tecol
Supplementary data related to this article can be found at http://dx. doi.org/10.1016/j.jenvrad.2017.11.029.
y 90
Sr Cs
137
1990–2016 1996–2016
6.7 ± 0.6 10.7 ± 2.2
8.7 ± 1.0 16.5 ± 5.6
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trend was identified for the unaffected as well as for the affected river sites and continued in the period when the Temelín NPP was in the operation. 90Sr concentration in reed species was in the range of less than 0.4 and 6.1 Bq/kg (dry weight) and this concentration decreased with the effective ecological half-life of 6.7 y and the ecological half-life of 8.7 y (Table 7).
4. Conclusions Concentrations of anthropogenic radionuclides downstream of the wastewater outflow from the Temelín NPP are mainly due to the residual contamination from global fallout and the Chernobyl accident. The influence of the Temelín NPP on concentration of the activation and fission products in the hydrosphere (except 3H) has been negligible. Downstream of the plant, significantly higher 3H activity concentrations were detected, corresponding to the 3H discharged from the Temelín NPP. For all of the components of the environment, concentrations of 90Sr and 137Cs, which were used for calculation of their effective and ecological half-lives, decreased. The rate of decrease in 90Sr concentration was invariable during the whole assessed period of 1993–2016. For 137 Cs in surface water and fish, the rates of decrease in the first and 9
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