238Pu, 239,240Pu, 241Am, 90Sr and 137Cs in soils around nuclear research centre Řež, near Prague

Journal of Environmental Radioactivity 71 (2004) 115–125 www.elsevier.com/locate/jenvrad

238

Pu, 239,240Pu, 241Am, 90Sr and 137Cs in soils around nuclear research centre Rˇezˇ, near Prague Z. Ho¨lgye ∗, E. Schlesingerova´, J. Tecl, R. Filgas National Radiation Protection Institute, Sˇroba´rova 48, 100 00 Prague 10, Czech Republic Received 15 January 2003; received in revised form 15 May 2003; accepted 19 May 2003

Abstract Forty-four soil samples were taken around the nuclear research centre Rˇezˇ, near Prague. The mean activity concentrations of 238Pu, 239,240Pu, 241Am, 90Sr and 137Cs in uncultivated soil were 0.010, 0.26, 0.12, 2.7 and 23 Bq.kg⫺1, respectively. Contents of radionuclides in cultivated soil were lower and in forest soil higher than in uncultivated soil. The mean activity ratios of 238Pu/239,240Pu, 241Am/239,240Pu, 90Sr/239,240Pu and 239,240Pu/137Cs in uncultivated soil were 0.041, 0.47, 10.9 and 0.013, respectively. The mean activity ratios in cultivated and forest soils were close to the values given above. It follows from the results that the source of 239,240Pu, 90Sr and 137Cs in the studied area is deposition from atmospheric nuclear tests, in the case of 137Cs also deposition from Chernobyl accident. The contribution of the research centre effluents was not proved for these radionuclides. Increased activity ratio of 241 Am/239,240Pu indicates the presence of 241Am in the soils studied emanating from sources other than nuclear tests. Uniform distribution of the 241Am/239,240Pu activity ratio around the nuclear research centre and the absence of an area with evidently higher activity ratio, including at sites lying in the main wind direction, suggest that the additional activity of 241Am does not originate from the nuclear research centre. The additional source might be the deposition following the Chernobyl accident.  2003 Elsevier Ltd. All rights reserved. Keywords: Radionuclides; Soil;

∗

238

Pu;

239,240

Pu;

241

Am;

90

Sr;

137

Cs; Nuclear installation

Corresponding author. E-mail address: [email protected] (Z. Ho¨lgye).

0265-931X/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0265-931X(03)00162-0

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1. Introduction Nuclear research centre, Rˇ ezˇ (NRC) is situated 12 km northwest of the centre of Prague in a populated agricultural area. After its establishment in the late 1950s, the centre has had numerous physical and radiochemical laboratories at its disposal, as well as a light-water research reactor and a unit for the processing of radioactive waste. The last installation also served other organisations within the country. Monitoring of discharge of radionuclides from the NRC by airborne and liquid effluents has been performed by the staff at NRC. Furthermore, an independent scientific organisation has performed a radiation protection inspection. Nevertheless, neither NRC, nor the supervising organisation have investigated the impact of NRC on the content of biologically important radionuclides 238Pu, 239,240Pu, 241Am, and 90 Sr in the soils around the institute. The aim of this work was to determine the content of 238Pu, 239,240Pu, 241Am, 90Sr and also of radionuclides measurable by gamma-spectrometry in soils around NRC and evaluate the influence of approximately 40 years’ operation of NRC on the radionuclide content in soils.

2. Experimental The soil sampling programme was prepared with respect to possible sources of radionuclides in the air from the NRC (there are two: a 70 m stack, through which the air from some buildings is discharged and pipes on roofs through which the air from isolated devices from other buildings is discharged), the prevailing wind as well as experience from outside the country. Soil samples were taken between June 1999 and August 2000 from 44 sites. Eight samples were taken near the NRC fence. Further samples were taken at distance of 750 (10 samples), 1500 (10), 3000 (8) and 5000 m (8), respectively from the centre of NRC (Fig. 1). At each site, a soil sample was taken from an area of 20 × 20 cm and depth of 20 cm. Depth of 20 cm was considered adequate as more than 90% activity of 239,240Pu, 241Am and 137Cs from atmospheric nuclear tests are still retained in the 0–20 cm soil layer (Jia et al., 1999; Ho¨ lgye and Maly´ , 2000). We attempted to take samples from areas with undisturbed soil. In the absence of such an area in the vicinity of the planned site, a sample of cultivated agricultural soil was taken. Two soil samples were taken under cliffs situated between Vltava fluvial plain and the adjacent plateau. The samples were dried at 105 °C (large stones and roots removed), crushed, sieved (1 mm), homogenised and weighed. For the analysis of plutonium and americium 25 g sieved soil was used, for 90Sr 150 g and for the gamma-spectrometry approximately 500 g. Plutonium and americium were extracted from the soil (using 242Pu and 243Am as tracers) first by boiling a soil sample with 200 ml 8 M HNO3, in a beaker covered by a glass watch, for 3 working days with occasional stirring. Evaporating liquid was replaced by concentrated HNO3. The insoluble residue was separated and plutonium and americium were leached from the insoluble residue for 2 h first by 100

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117

Fig. 1. Sampling sites. Distance from the centre of NRC: a, 750 m; b, 1500 m; c, 3000 m; d, 5000 m. W, prevailing wind direction.

ml 8 M HNO3 and then by 50 ml 8 M HNO3. The procedure was continued (Ho¨ lgye, 1991) by hydroxide precipitation, passing through strong basic anion exchanger (from HCl solution), coprecipitation by LaF3, extraction with 2-thenoyl-trifluoraceton in benzene and electrodeposition. The americium separation consists of coprecipitation with Ca oxalate, then with Fe(OH)3, passing thorough strong basic anion exchangers from hydrochloric acid solution, then from nitric acid solution, extraction chromatography (according to Ham, 1995) and electrodeposition. As leaching with nitric acid is not adequate for dissolution of high-fired plutonium oxide, plutonium in soil from five of the studied sites (site numbers 6, 9, 10, 11 and 14, Fig. 1) was also determined in soil samples treated by hydrofluoric acid before the acid leaching. This dissolution of plutonium oxide is comparable with fusion methods (Sill, 1975). 90 Sr in soil was determined using calcium oxalate method applied to soil (Volchok, 1984). Strontium from carbon free ash was leached using HCl and NaOH solutions. Repeated Ca oxalate precipitation, then coprecipitation with Fe(OH)3 and Ce(OH)3 were carried out. After the secular radioactive equilibrium between 90Sr and 90Y was

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reached, the 90Y was separated as Y(OH)3 and transferred to oxalate before activity measurement. Chemical yields of 90Sr and 90Y were determined by gamma measurement of 85Sr carrier and by titration method, respectively. Alpha activities of plutonium and americium radionuclides were measured by 1200 mm2 PIPS detector (Canberra). With knowledge of activity concentration of radionuclides at the site, the weight of the sieved soil and volume of the core, the cumulative deposition values of radionuclides at the sites were calculated. The data obtained were statistically evaluated using a program also applicable with censored values.

3. Results and discussion 3.1. Obtained data The activity concentrations of 238Pu, 239,240Pu, 241Am, 90Sr and 137Cs in soil at individual sites around NRC are presented in Table 1. The frequency distribution of values of concentrations of individual radionuclides at all studied sites (except two sites under the cliffs) are log-normal. The log-normal distribution also exists for values of concentrations of individual radionuclides pertaining to cultivated, uncultivated or forest soils. In Table 2, arithmetical mean and its 95% confidence limit of concentration of studied radionuclides in uncultivated, cultivated, forest soil and soils at all sites (except the two sites under rocky walls) around NRC are presented. The same values for cumulative deposition of studied radionuclides around NRC are presented in Table 3. In Table 4 the activity ratios of 238Pu/239,240Pu, 241Am/239,240Pu, 90 Sr/239,240Pu and 239,240Pu/137Cs in soil at the individual studied sites are presented. In Table 5, the arithmetical mean and its 95% confidence limit of activity ratios of 238Pu/239,240Pu, 241Am/239,240Pu, 90Sr/239,240Pu and 239,240Pu/137Cs in uncultivated, cultivated, forest soil and in soils from all sites (except two sites under the cliffs) are presented. 3.2. Evaluation of the obtained data It follows from Table 2 that the mean concentrations of 239,240Pu, 241Am and in most cases also the mean concentrations of 90Sr and 137Cs in soil around NRC increase in the order: cultivated soil ⬍ uncultivated soil ⬍ forest soil. The order is similar to this pertaining to radionuclides originating from atmospheric nuclear tests as observed earlier (Bunzl and Kracke, 1988). The lower level of fallout radionuclides in cultivated soils compared to uncultivated ones is explained by overturning of soil at tillage. The higher level of fallout radionuclides in forest soil is explained by interceptive function of woodland canopy (Bunzl and Kracke, 1988). The highest content of radionuclides in soil near rock faces (Table 1) can be explained by collection of rain by large surface of rock and capture of radionuclides from water by soil components. Hereafter we evaluate the obtained data for individual radionuclides.

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Table 1 Activity concentrations of radionuclides in soils around NRC Site

Soil

238

Pu (Bq.kg–1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

C U U U U C U C U U U C U F R C C C F C C U C U C U F R F U C C F C C C F F C C F C C C

⬍0.01 0.007 ± 0.007 ± 0.006 ± 0.015 ± 0.008 ± 0.017 ± 0.008 ± 0.012 ± 0.012 ± 0.010 ± ⬍0.008 0.011 ± ⬍0.008 0.061 ± ⬍0.016 ⬍0.012 ⬍0.012 0.024 ± ⬍0.008 ⬍0.013 0.009 ± ⬍0.004 0.011 ± ⬍0.006 0.009 ± 0.018 ± 0.040 ± 0.034 ± 0.008 ± ⬍0.004 ⬍0.004 0.012 ± ⬍0.004 ⬍0.008

0.001 0.002 0.002 0.003 0.002 0.004 0.002 0.002 0.002 0.002 0.003 0.008

0.004

0.003 0.002 0.002 0.002 0.003 0.003 0.002

0.003

0.008 ± 0.002 0.030 ± 0.003 ⬍0.004 ⬍0.005 ⬍0.006 0.005 ± 0.001 0.007±0.002 ⬍0.004

239,.240

Pu (Bq.kg–1)

0.091 0.163 0.191 0.114 0.253 0.221 0.292 0.167 0.306 0.356 0.404 0.140 0.342 0.242 2.010 0.168 0.160 0.188 0.744 0.176 0.172 0.219 0.147 0.310 0.091 0.201 0.696 1.700 0.742 0.227 0.107 0.132 0.363 0.096 0.118 0.064 0.243 0.998 0.076 0.098 0.180 0.173 0.136 0.100

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.005 0.003 0.006 0.008 0.008 0.006 0.012 0.006 0.009 0.017 0.012 0.008 0.018 0.024 0.083 0.016 0.012 0.012 0.036 0.016 0.020 0.015 0.005 0.017 0.004 0.006 0.017 0.030 0.019 0.013 0.005 0.012 0.014 0.004 0.007 0.007 0.008 0.041 0.004 0.003 0.010 0.006 0.007 0.008

241

Am (Bq.kg–1)

0.060 ± 0.091 ± 0.081 ± 0.063 ± 0.131 ± 0.094 ± 0.126 ± 0.059 ± 0.074 ± 0.186 ± 0.179 ± 0.063 ± 0.129 ± 0.075 ± 0.936 ± 0.063 ± 0.082 ± 0.066 ± 0.337 ± 0.056 ± 0.072 ± 0.104 ± 0.070 ± 0.123 ± ⬍0.060 0.101 ± 0.354 ± 0.718 ± 0.380 ± 0.149 ±

0.007 0.019 0.020 0.010 0.008 0.005 0.008 0.006 0.009 0.026 0.009 0.010 0.010 0.006 0.024 0.006 0.007 0.006 0.024 0.011 0.012 0.018 0.010 0.014 0.018 0.061 0.051 0.042 0.020

0.110 ± 0.024 0.161 ± 0.034

0.210 ± 0.023 0.501 ± 0.056 0.109 ± 0.014 0.106 ± 0.016

90

Sr (Bq.kg–1)

1.02 2.47 3.22 1.07 3.40 1.41 0.46 1.00 3.39 2.96 3.95 1.92 3.80 1.76 2.93 0.80 1.08 2.17 1.26 1.91 1.63 2.33 1.39 2.77 1.27 1.39 6.52 1.73 1.72 2.53 2.63 2.02 1.11 1.42 1.39 1.66 2.70 3.33 1.43 0.80 1.87 1.36 1.52 1.40

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.09 0.63 0.65 0.01 0.79 0.11 0.02 0.05 0.22 0.25 0.27 0.11 0.34 0.19 0.27 0.03 0.03 0.19 0.10 0.13 0.13 0.16 0.09 0.20 0.10 0.09 0.41 0.16 0.11 0.17 0.25 0.05 0.13 0.10 0.09 0.16 0.19 0.35 0.14 0.08 0.16 0.11 0.15 0.11

137

Cs (Bq.kg–1) 9.8 ± 1 11 ± 1 13 ± 1 11 ± 1 15 ± 1 17 ± 2 17 ± 2 13 ± 1 21 ± 2 31 ± 3 27 ± 3 9.7 ± 1 25 ± 2 20 ± 2 117 ± 10 3.3 ± 0.2 6.6 ± 0.8 9.5 ± 0.9 43 ± 4 7.6 ± 0.7 7.5 ± 0.4 70 ± 5 9.7 ± 0.6 18 ± 2 5.6 ± 0.4 26 ± 1 44 ± 3 63 ± 6 70 ± 6 22 ± 1 5.7 ± 0.6 9±1 29 ± 2 9.1 ± 0.9 7.7 ± 0.8 5.9 ± 0.5 44 ± 4 59 ± 3 5.1 ± 0.3 7 ± 0.5 22 ± 1 5.9 ± 0.3 14 ± 1 8.8 ± 0.8

C, cultivated soil; U, uncultivated soil; F, forest soil; R, soil under cliffs.The errors quoted are ±1 sigma counting error.

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Table 2 Mean activity concentrations of radionuclides in soils around NRC Radionuclide

Soil

Number of values

Arithmetic mean (Bq.kg⫺1)

95% confidence interval (Bq.kg⫺1)

238

F U C Altogether F U C Altogether F U C Altogether F U C Altogether F U C Altogether

8 13 20 41 8 13 21 42 8 13 13 34 8 13 21 42 8 13 21 42

0.018 0.010 0.004 0.009 0.53 0.26 0.14 0.24 0.27 0.12 0.073 0.13 2.5 2.7 1.5 2.0 42 23 10 20

0.0095 0.0088 0.0027 0.0068 0.34 0.22 0.12 0.20 0.17 0.099 0.064 0.11 1.7 1.9 1.3 1.7 31 18 8 16

Pu

239,240

Pu

241

Am

90

Sr

137

Cs

0.033 0.012 0.010 0.012 0.85 0.32 0.16 0.30 0.44 0.14 0.083 0.16 3.7 3.8 1.7 2.4 56 31 13 26

F, forest soil; U, uncultivated soil; C, cultivated soil.

3.3.

238

Pu,

239,240

Pu

Mean activity concentrations of 238Pu and 239,240Pu in uncultivated soil around NRC 0.010 and 0.260 Bq.kg⫺1, respectively, were found (Table 2). These values are very close to the mean values 0.010 and 0.273 Bq.kg⫺1, respectively, determined by analysis of soil samples taken at 50 different sites of grassland soil (the mean annual precipitation at the sites ranging from 480 to 990 mm) in the former Czechoslovakia in 1990 (Ho¨ lgye and Filgas, 1995). Mean cumulative deposition values of 238Pu and 239,240Pu in uncultivated soil (Table 3) around NRC are also close to values 1.7 and 49.3 Bq.m⫺2, respectively, obtained in the mentioned study. According to UNSCEAR (1982), the deposition of 238 Pu and 239,240Pu on 40–50° north latitude from atmospheric nuclear tests (in the case of 238Pu also from SNAP-9A satellite burn-up) amounted to 1.5 and 58 Bq.m⫺2, respectively, up to 1980. Lower deposition on the area studied from global fallout could be expected with respect to lower value of annual precipitation on this area (510 mm). The activity ratios of 238Pu/239,240Pu in these soils give the main evidence of the fact that the emission from NRC could contribute only very little to the content of plutonium in the studied soils. The mean activity ratio of 238Pu/239,240Pu in soils around NRC (Table 5) and also activity ratios of these radionuclides at individual sites (Table 4) are similar to the values reported for global fallout: 0.037 (Bunzl and

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121

Table 3 Mean cumulative deposition of radionuclides around NRC Radionuclide

Soil

Number of values

Arithmetic mean (Bq.m⫺2)

95% confidence interval (Bq.m⫺2)

238

F U C Altogether F U C Altogether F U C Altogether F U C Altogether F U C Altogether

8 13 20 41 8 13 21 42 8 13 13 34 8 13 21 42 8 13 21 42

2.2 2.0 0.9 1.6 66 49 29 42 33 23 16 22 310 510 320 380 5300 4400 1800 3300

1.4 1.7 0.6 1.3 47 42 25 36 24 19 14 19 230 370 280 320 4300 3400 1600 2700

Pu

239,240

Pu

241

Am

90

Sr

137

Cs

3.4 2.3 1.2 1.9 91 56 34 49 46 26 18 26 420 710 370 440 6600 5800 2100 4010

F, forest soil; U, uncultivated soil; C, cultivated soil.

Kracke, 1988), 0.034 (Ho¨ lgye and Filgas, 1995), 0.034 (Jia et al., 1999), 0.038 (Kim et al., 1998), 0.034 (Mitchell et al., 1990). Concentrations of plutonium isotopes found in soils, which were treated with hydrofluoric acid before acid leaching, were close to those obtained without the HF treatment (Table 1). The results indicate absence of plutonium in the form of hardly soluble plutonium oxide at these sites (and supposedly at all the studied sites). 3.4.

241

Am

Mean activity concentrations of 241Am in cultivated and uncultivated soils around NRC 0.073 and 0.12 Bq.kg⫺1, respectively, were found (Table 2). The values are close to mean values 0.047 and 0.241 Bq.kg⫺1, respectively, as found in such soils in central Italy (Jia et al., 1999). The concentrations of 241Am in soil around most of nuclear installations in England and Wales were in the range 0.03–0.4 Bq.kg⫺1 (Sanchez et al., 1996). Mean cumulative deposition values of 241Am in cultivated, uncultivated and forest soils around NRC (Table 3) are also close to the reported data: 34.7 (Jia et al., 1999) 25 Bq.m⫺2 (UNSCEAR, 1982). According to Jia et al. (1999) 241Am content in soil increases by 0.6 Bq.m⫺2 per year as a result of decay of 241Pu. For example, the value of 25 Bq.m⫺2 (UNSCEAR, 1982) gives 37 Bq.m⫺2 at our sampling time.

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Table 4 Activity ratios of radionuclides in soils around NRC Site

Soil

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

C U U U U C U C U U U C U F R C C C F C C U C U C U F R F U C C F C C C F F C C F C C C

238

Pu/239,240Pu

241

Am/239,240Pu

0.035 ± 0.006

0.66 0.56 0.42 0.55 0.52 0.43 0.43 0.35 0.24 0.52 0.44 0.45 0.38 0.31 0.47 0.38 0.51 0.35 0.45 0.32 0.42 0.47 0.48 0.40

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.09 0.12 0.11 0.09 0.04 0.03 0.03 0.03 0.03 0.08 0.03 0.08 0.03 0.04 0.02 0.05 0.06 0.04 0.04 0.07 0.08 0.09 0.07 0.05

± ± ± ± ±

0.50 0.51 0.42 0.51 0.66

± ± ± ± ±

0.09 0.10 0.03 0.06 0.10

0.043 0.037 0.053 0.059 0.036 0.058 0.048 0.039 0.034 0.025

± ± ± ± ± ± ± ± ± ±

0.006 0.010 0.017 0.012 0.009 0.014 0.012 0.007 0.006 0.005

0.032 ± 0.009 0.030 ± 0.004

0.032 ± 0.005 0.041 ± 0.013

0.045 0.026 0.024 0.046 0.035

0.010 0.003 0.002 0.004 0.009

0.033 ± 0.008

0.83 ± 0.20 0.44 ± 0.09

0.033 ± 0.008 0.030 ± 0.003

0.86 ± 0.10 0.50 ± 0.06

0.029 ± 0.006 0.051 ± 0.015

0.61 ± 0.08 0.61 ± 0.09

90

Sr/239,240Pu

11.2 15.2 16.9 9.39 13.4 6.38 1.58 5.99 11.1 8.31 9.78 13.7 11.1 7.27 1.46 4.76 6.75 11.5 1.69 10.9 9.48 10.6 9.46 8.94 14.0 6.92 9.37 1.02 2.32 11.2 24.6 15.3 3.06 14.8 11.8 25.9 11.1 3.36 18.8 8.16 10.4 7.86 11.2 14.0

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

C, cultivated soil; U, uncultivated soil; F, forest soil; R, soil under cliffs.

1.2 3.9 3.4 0.66 3.1 0.53 0.09 0.37 0.79 0.81 0.73 1.1 1.2 1.1 0.15 0.49 0.54 1.3 0.16 1.2 1.3 1.0 0.69 0.81 1.3 0.49 0.63 0.10 0.16 0.98 2.6 1.4 0.38 1.2 1.0 3.8 0.86 0.38 2.1 0.85 1.1 0.69 1.2 1.6

239,240

Pu/137Cs

0.009 0.015 0.015 0.010 0.017 0.013 0.017 0.013 0.015 0.012 0.015 0.014 0.014 0.012 0.017 0.051 0.024 0.020 0.017 0.023 0.023 0.003 0.015 0.017 0.016 0.008 0.016 0.027 0.011 0.010 0.019 0.015 0.013 0.011 0.015 0.011 0.006 0.017 0.015 0.014 0.008 0.030 0.010 0.011

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.005 0.003 0.002 0.001 0.003 0.003 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.002 0.001 0.001

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Table 5 Mean activity ratios of radionuclides in soils around NRC Ratio of activities

Soil

Number of values

Arithmetic mean

95% confidence interval

238

Pu/239,240Pu

241

Am/239,240Pu

F U C Altogether F U C Altogether F U C Altogether F U C Altogether

6 13 4 23 8 13 12 33 8 13 21 42 8 13 21 42

0.033 0.041 0.041 0.039 0.52 0.47 0.48 0.49 6.2 10.9 12 11 0.013 0.013 0.018 0.015

0.029 0.036 0.033 0.035 0.43 0.41 0.41 0.44 3.6 7.8 10.1 8.9 0.0098 0.01 0.015 0.013

90

Sr/239,240Pu

239,240

Pu/137Cs

0.038 0.047 0.051 0.043 0.63 0.54 0.56 0.53 10.6 15 15 13 0.016 0.017 0.021 0.018

F, forest soil; U, uncultivated soil; C, cultivated soil.

The mean activity ratio of 241Am/239,240Pu in soils (Table 5) and also the activity ratio of 241Am/239,240Pu at most sites (Table 4) around NCR are, however, higher then the mean activity ratio of these radionuclides originating from atmospheric nuclear tests in soils and sediments presented in different studies: 0.32, 0.35 (Jia et al., 1999), 0.30 (Bunzl and Kracke, 1988), 0.30 (Bunzl et al., 1995), 0.34, 0.37, 0.39, 0.42 (mean in layers in sediment cores (Mitchell et al., 1992)), 0.43 (Sha et al., 1991). In soils around NRC, 241Am is probably present from sources other than deposition of atmospheric nuclear tests. If the source of additional 241Am were the emission from NRC, in the soils around this installation the area(s) with evidently higher activity ratio of 241Am/239,240Pu (for example on sites lying downwind) could be expected. Such an area does not exist and we suppose that a possible origin of additional activity of 241Am in soils around NRC is deposition from the Chernobyl accident. Only little attention has so far been paid to contribution of the Chernobyl accident to 241Am content in soil (except soil in some states of the former USSR). 3.5.

90

Sr

Mean concentrations of 90Sr in cultivated and uncultivated soils (Table 2) around NRC are close to the mean values found in other studies: 1.53, 5.40 (Jia et al., 1999), 2.82 (Aarkrog et al., 1991), 4.5 Bq.kg⫺1 (Juzˇ nicˇ , 1990). Around most of the nuclear installations in England and Wales, the 90Sr content in soil was less than 5 Bq.kg⫺1 (Sanchez et al., 1996). The mean cumulative deposition values of 90Sr in the soils studied (Table 3) are

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less than the UNSCEAR value 3.23 × 103 Bq.m⫺2 of deposition of this radionuclide on 40–50° N latitude up to 1980 (at our sampling time the value decreased due to radioactive decay to 1.5 × 103 Bq.m⫺2). The mean activity ratios of 90Sr/239,240Pu in the soils studied (Table 5) are close to the activity ratios of these radionuclides originating from atmospheric nuclear tests in soil reported in the last years: 11.2, 8.0 (Jia et al., 1999), 4.9 (Kim et al., 1998). Comparison of the data obtained with those reported shows no evidence of the presence of 90Sr originating from NRC in the studied soils. 3.6.

137

Cs

Mean cumulative deposition values of 137Cs in cultivated, uncultivated and forest soils around NRC were 1800, 4400 and 5300 Bq.m⫺2, respectively (Table 3). The mean cumulative deposition values of 137Cs originating from atmospheric nuclear tests in arable (cultivated), grassland (uncultivated) and forest soils in Bavaria (0– 20 cm layer, mean annual precipitation at sites studied being 600–1200 mm) in 1984 were 2680, 2820 and 3580 Bq.m⫺2, respectively (Bunzl and Kracke, 1988). At our sampling time, the activities decreased to 1850, 1950 and 2470 Bq.m⫺2, respectively, due to radioactive decay. It is evident that mean cumulative deposition of 137Cs in uncultivated and forest soils around NRC is higher (even at lower mean annual precipitation on the studied area) than could be expected from global fallout. The same result follows from the comparison of activity ratios of 239,240Pu/137Cs at individual sites (Table 4) with expected ratios of these radionuclides originating from atmospheric nuclear tests 0.026 (the published value 0.023 (Mitchell et al., 1990) was normalized to our sampling data) in soil. However, the deposition of 137Cs from the Chernobyl accident on the studied area was between 1–30 kBq.m⫺2 (IHE Report, 1986). At none of our sampling sites around NRC was cumulative deposition exceeding 30 kBq.m⫺2 found. We can state that the 137Cs found in soils around NRC originated from the nuclear tests and from the Chernobyl accident and that no contribution from NRC was demonstrated. In soils around NRC, natural radionuclides measurable by gamma-spectrometry are present. Apart from 137Cs no artificial gamma emitters (activation, fission products) were found in these soils.

References Aarkrog, A., Bøtter-Jensen, L., Jiang, C.Q., Dahlgaard, H., Hansen, H., Holm, E., Lauridsen, B., Nielsen, S.P., Søgaard-Hansen, J., 1991. Environmental radioactivity in Denmark in 1988 and 1989, Risø-R570. Risø National Laboratory, Roskilde, Denmark. Bunzl, K., Kracke, W., 1988. Cumulative deposition of 137Cs, 238Pu, 239,240Pu and 241Am from global fallout in soils from forest, grassland and arable land in Bavaria (FRG). Journal of Environmental Radioactivity 8, 1–14. Bunzl, K., Kracke, W., Schimmack, W., Auerswald, K., 1995. Migration of fallout 239,240Pu, 241Am and 137 Cs in the various horizons of a forest soil under pine. Journal of Environmental Radioactivity 28, 17–34.

Z. Ho¨ lgye et al. / J. Environ. Radioactivity 71 (2004) 115–125

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Ham, G.J., 1995. Determination of actinides in environmental materials using extraction chromatography. The Science of the Total Environment 173/174, 19–22. Ho¨ lgye, Z., 1991. Analysis of plutonium in biological and environmental materials. Journal of Radioanalytical and Nuclear Chemistry, Letters 149, 275–280. Ho¨ lgye, Z., Filgas, R., 1995. Inventory of 238Pu and 239,240Pu in the soil of Czechoslovakia in 1990. Journal of Environmental Radioactivity 199, 181–189. Ho¨ lgye, Z., Maly´ , M., 2000. Sources, vertical distribution, and migration rates of 239,240Pu, 238Pu, and 137 Cs in grassland soil in three localities of central Bohemia. Journal of Environmental Radioactivity 47, 135–147. IHE report. 1986. Report on radiation situation in CSSR after the Chernobyl accident. IHE-CRH Institute of hygiene and epidemiology, Centre of radiation hygiene, Prague, Czech Republic. Jia, G., Testa, C., Desideri, D., Guerra, F., Meli, M.A., Roselli, C., Belli, M.E., 1999. Soil concentration, vertical distribution and inventory of plutonium, 241Am, 90Sr and 137Cs in the Marche region of central Italy. Health Physics 77, 52–61. Juzˇ nicˇ , K., 1990. Recent levels of 90Sr activity in the environment of the Krsˇ ko nuclear power plant. Journal of Environmental Radioactivity 11, 169. Kim, C.S., Lee, M.H., Kim, C.K., Kim, K.H., 1998. 90Sr, 137Cs, 239,240Pu and 238Pu concentrations in surface soils of Korea. Journal of Environmental Radioactivity 40, 75–88. Mitchell, P.I., Sanchez-Cabeza, J.A., Ryan, T.P., McGarry, A.T., Vidal-Quatras, A., 1990. Preliminary estimates of cumulative caesium and plutonium deposition in the Irish terrestrial environment. Journal Radioanalytical and Nuclear Chemisry, Articles 138, 241–256. Mitchell, P.I., Schell, W.R., McGarry, A., Ryan, T.P., Sanchez-Cabeza, J.A., Vidal-Quatras, A., 1992. Studies of the vertical distribution of 134Cs, 137Cs, 238Pu, 239,240Pu, 241Pu, 241Am and 210Pb in ombrogenous mires at mid-latitudes. Journal Radioanalytical and Nuclear Chemistry, Articles 156, 361–387. Sanchez, A.L., Horrill, A.D., Singleton, D.L., Leonard, D.R.P., 1996. Radionuclides around nuclear sites in England and Wales. The Science of the Total Environment 181, 51–63. Sha, L., Yamamoto, M., Kumura, K., Ueno, K., 1991. 239,240Pu, 241Am and 137Cs in soils from several areas in China. Journal of Radioanalytical and Nuclear Chemistry, Letters 155, 45. Sill, C.W., 1975. Some problems in measuring plutonium in the environment. Health Physics 29, 619. UNSCEAR, 1982. Ionizing Radiation: Sources and Biological Effects. United Nations, New York, USA. Volchok, H.L., 1984. EML Procedures Manual, HASL-300. Environmental Measurements Laboratory, US Department of Energy, New York, USA.