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Analytical methods for the determination of 137Cs and 90Sr in ash of fuel pellets used in Italy
Microchemical Journal 103 (2012) 131–134
Contents lists available at SciVerse ScienceDirect
Microchemical Journal journal homepage: www.elsevier.com/locate/microc
Analytical methods for the determination of in Italy
137
Cs and
90
Sr in ash of fuel pellets used
Donatella Desideri a,⁎, Alba Rongoni b, Carla Roselli a, Daniela Saetta b, Laura Feduzi a a b
Department of Biomolecular Sciences, University of Urbino, P.zza Rinascimento 6, 61029 Urbino, Italy Department of Surgical and Radiological Science, Section of Medical Physics Environmental and Epidemiological, University of Perugia, Policlinico Monteluce, P.O. Box 1418, 06122 Perugia, Italy
a r t i c l e
i n f o
Article history: Received 18 January 2012 Accepted 12 February 2012 Available online 16 February 2012 Keywords: 137 Cs 90 Sr Wood fuel pellets Ash
a b s t r a c t In this study the radiological characterization of ashes of 22 different brands of wood pellets coming from different countries and used in the regions of central Italy was carried out. 137Cs and 90Sr, were found in the samples taken into account, 134Cs resulted always below the detection limit. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1 (the arithmetic mean resulted to 571 Bq kg− 1); 90Sr activity concentration ranges from 154.75 Bq kg− 1 to 1443.70 Bq kg− 1 (the arithmetic mean resulted to 684.80 Bq kg− 1). The ratio of 90Sr and 137 Cs activity concentration ranged from 0.22 to 40.79 showing a high variability. 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The concentration factors (activity concentration in ash/ activity concentration in wood pellets) resulted to 222.8 and 230.0 for 137Cs and 90Sr respectively; both radionuclides are found completely in the ashes. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Pellet are small particles (normally 6 mm diameter, sometimes 8 mm or larger) typically created by compressing an original material. Pelletizing is the industrial process used to create pellets, using a pellet mill or equipment for extrusion and spheronization. Wood pellets, corn pellets, and grass pellets are used as pellet stove fuel [1]. A report to the Massachusetts Department of Energy Resources estimates that the energy required to manufacture and transport pellets is less than 2% of the energy content of the pellets [2]. Pellets conforming to the norms commonly used in Europe have less than 10% water content, a good structural strength, a low dust and ash content and they are uniform in density. Because the wood fibres are broken down by the hammer mill, there is virtually no difference in the finished pellets between different wood types. Pellets can be made from nearly any wood variety, provided the pellet press is equipped with good instrumentation, the differences in feed material can be compensated for in the press regulation [3]. In June 2009, an Italian court has ordered the recall of 10,000 tonnes of wood fuel pellets imported over fears that they could have dangerous levels of radioactivity. The alarm was raised after someone in the northern Aosta Valley region, who had bought the pellets, sent them for analysis because they did not burn well. The results showed that wood pellets contained 137Cs with an activity concentration ranging from 10 to 320 Bq kg− 1, whereas an ash sample showed a concentration of
⁎ Corresponding author. Tel.: + 39 0722 303307; fax: + 39 0722 303306. E-mail address: [email protected] (D. Desideri). 0026-265X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2012.02.007
around 46000 Bq kg− 1; the ash, in fact, concentrates (25–200 times) the radionuclides initially present in wood pellet [4]. The pellets at the centre of the alert were imported from Lithuania in the autumn 2008 and were sold in 11 regions in the north and south of Italy. The names of the Lithuanian producer and the Italian importer and distributors are known. It is not yet clear if the wood used to produce the pellets actually came from Lithuania or from areas in non-EU countries with a higher contamination of caesium. The cause of the radioactivity was initially not specified, however it soon became very clear that the wood pellets contain radioactivity coming from the nuclear weapons fall-out and from the damaged nuclear reactor at Chernobyl (1986). The Chernobyl accident caused contamination of 134Cs and 137Cs in several European countries. When forest areas are contaminated with caesium, the radioactivity is absorbed by the vegetation, including trees [5–8]. The contaminated pellets themselves are not dangerous to humans: the dangers come a) from inhalation of the smoke produced when the pellets are burned; b) from inhalation of the ash during the polish operations of the domestic stoves and c) the use of ash as fertilizer for orchards and gardens. As far as the radioprotection legislation is concerned, Italy has implemented Council Directive 96/29/Euratom laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation [9] in its national legislation, including levels below which a practice may be exempted from the reporting requirements of the directive. While the exempt concentration value in the directive for 134Cs and 137Cs is 10,000 Bq kg− 1, the Italian legislation [10] has laid down a single lower value for all radionuclides of 1 Bq g− 1 (or 1000 Bq kg− 1). It should be noted that the activity concentrations detected by the Italian
132
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
Table 1 Ash samples, country of origin of wood fuel pellet and Italian region where it is used. Ash sample
Country of origin
Italian region of use
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Italy Lithuania Austria Italy Italy Spain Austria Austria Italy Unknown Unknown Slovenia Unknown Spain Austria Unknown Unknown Unknown Unknown Lituania Slovakia Austria
Umbria Umbria Marche Marche Marche Marche Marche Emilia Romagna Emilia Romagna Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Emilia Romagna Marche
authorities in the wood pellets are well below the national exemption level. However, the activity concentration in the ashes exceeds this value. It should be borne in mind that the exempt concentration values have been established for large quantities of material (of the order of 1 tonne). It is for the Italian authorities to assess the exposure pathways resulting from the higher concentrations in the ashes, for the relevant management options, and to decide whether further use of such pellets is permitted either without restrictions or subject to appropriate conditions. In this study ashes of 22 different brands of wood pellets coming from different countries and used in the regions of Central Italy were taken into account. The aim of this study was: 1) to determine the oncentration of 137Cs and that of 90Sr, another anthropogenic radionuclide; 2) to study the transfer of these two radionuclides from wood pellet to ashes; 3) to obtain a set of data to assess the dosimetric impact due to use of wood fuel pellets in the domestic stoves and of the ashes as fertilizers.
Table 2 Evaluation of the reproducibility of
2.1. Samples Analysis was carried out in 22 ash samples derived from the combustion of wood pellets of different brands obtained through normal
137
Cs (photopeak: 661.6 keV)
Fig. 1. γ spectrum of a sample of ash.
90
Sr method.
Sample 1
Yield %
Sr (Bq kg− 1)
Sample 2
Yield %
90 Sr (Bq kg− 1)
A B C Mean Stand. deviat. Stand. deviat. %
83.32 79.54 89.26 84.04 4.90 5.83
478.67 446.21 448.81 457.90 18.04 3.94
A B C Mean Stand. deviat. Stand. deviat. %
89.98 89.98 75.59 85.18 8.31 9.75
982.83 957.58 903.82 948.08 40.35 4.25
distribution channels. The samples came from of different countries and were used in the Umbria, Marche and Emilia Romagna, regions of Central Italy. Table 1 lists the ash samples analysed, the country of origin of the relevant wood pellets and the Italian region where they are used. 2.2. Radionuclides determination The activity concentration of radiocaesium was determined by γ-spectrometry. Samples were put and counted in Marinelli beakers. All the measurements were performed with a HPGe crystal of type “p” in coaxial geometry, with relative efficiency at 1.33 MeV equal to 25% (measured by placing a point source of 60Co, at 25 cm from the detector) ; the detectable energy ranges from 0.040 to 2.2 MeV; peak detection efficiencies were calculated automatically through a computer system interfaced with an multichannel analyser. 134Cs and 137Cs were determined by measuring the activity of their peaks at 569.32, 604.7, 795.84, 801.93 ( 134Cs) and 661.6 keV (137Cs) [7,8,11]. The detection limit was 0.2 Bq for 137Cs and 0.06 Bq for 134Cs. Fig. 1 reports the gamma spectrum of an ash pellet sample. The accuracy of the results is supported by the success of intercomparison exercises (IAEA). The 90Sr activity concentration was determined by applying a radiochemical method, a destructive technique, consisting in the separation of 90Y in radioactive equilibrium with parent 90Sr. The radioanalytical method used in this study, whose accuracy was regularly checked through participation in intercomparison exercises organized by the International Atomic Energy Agency (IAEA), was the following [12–14]. After addition of a known activity of Sr stable as carrier and Y stable as carrier and yield internal standard, the sample (0.25–0.50 g) was first Table 3 137 Cs and
2. Experimental
90
90
Sr activity concentration (Bq kg− 1) and their ratio.
Sample
137
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Mean Minimum Max
755 ± 72 3176 ± 292 65 ± 11 30 ± 5 815 ± 37 43 ± 2 92 ± 20 521 ± 47 90 ± 4 273 ± 26 73 ± 4 347 ± 15 537 ± 17 257 ± 14 981 ± 43 320 ± 30 400 ± 37 80 ± 8 58 ± 6 2788 ± 108 212 ± 10 645 ± 29 571 30 ± 5 3176 ± 292
Cs
90
Sr
458 ± 69 948 ± 142 1444 ± 217 1224 ± 184 1396 ± 209 255 ± 38 1150 ± 172 1065 ± 160 157 ± 24 410 ± 61 378 ± 57 762 ± 114 673 ± 101 399 ± 60 841 ± 126 599 ± 90 358 ± 54 164 ± 25 155 ± 23 627 ± 94 635 ± 95 966 ± 145 685 155 ± 23 1444 ± 217
90
Sr/137Cs
0.61 0.30 22.21 40.79 1.71 5.93 12.50 2.04 1.75 1.50 5.19 2.20 1.25 1.55 0.86 1.87 0.90 2.05 2.67 0.22 3.00 1.49 5.12 0.22 40.79
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
Table 4 90 Sr and 137Cs activity concentration (Bq kg− 1) in ash of pellets of the same brand but coming from different batches.
14
samples number
12 10 8 6
Sample
90
3 15 20 Naturkraft Premium (batch n. 286036)
1.444 ± 217 841 ± 126 – –
137
4 2 0
133
30-400
400-800 137
800-1000
>1000 -1
Cs concentration (Bq kg )
Fig. 2. Activity concentration classes of
137
Cs.
boiled with conc. HNO3 and H2O2, then the solution was evaporated to dryness and the residue boiled with conc. HCl and conc. HNO3 for two times. After the solution was evaporated to dryness and the residue was treated with conc. HCl and finally dissolved in 4–5 M HCl; then the solution was filtered. The solution was passed through a microporous polyethylene supporting tri-n-octylamine column (TNOA) to eliminate the natural 210 Bi; yttrium was retained into a microporous polyethylene supporting di (2ethyl-hexyl) phosphoric acid (HDEHP) chromatographic column at pH 1, eluted, precipitated as yttrium oxalate and measured by a low background (6.2 10− 3 s− 1) beta counter (Canberra-2404, USA) with a counting efficiency of 23%. The 90Y chemical yield resulted 85.83±6.29%. To verify the radioanalytical method reproducibility, for samples 1 and 2 the analyses were replicated three times obtaining the results shown in Table 2. The activity mean concentration was 457.90±18.04 and 948.08±40.35 Bq kg− 1 for sample 1 and sample 2 respectively; the relevant standard deviation resulted for both samples is b5% (3.94% and 4.25% for sample 1 and sample 2 respectively). 3. Results and discussion As far as gamma spectrometry is concerned, 134Cs resulted always below the detection limit; whereas, the determinations carried out by the researchers of Aosta Valley region showed the presence of 134Cs. The 137Cs activity concentrations are reported in Table 3. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1 ; the arithmetic mean resulted to 571 Bq kg − 1 . The activity concentration was
Sr
137
Cs
65 ± 11 981 ± 43 2788 ± 108 40,000
90
Sr/137Cs
22.21 0.86 – –
Cs (photopeak: 661.6 keV).
b400 Bq kg− 1 for 13 samples (59.09%); it ranged between 400 and 800 Bq kg− 1 for 5 samples (22.73%), between 800 and 1000 Bq kg− 1 for two samples (9.09%) and >1000 Bq kg− 1 for two samples (9.09%) (Fig. 2) coming from Lithuania. Table 3 reports also the 90Sr activity concentrations. The arithmetic mean of this radionuclide results to 684.80 Bq kg− 1 (minimum value 154.75 Bq kg− 1 and maximum value 1443.70 Bq kg− 1). The 90Sr activity concentration was b400 Bq kg− 1 for 7 samples (31.82%); it ranged between 400 and 800 Bq kg− 1 for 7 samples (31.82%), between 800 and 1000 Bq kg− 1 for 3 samples (13.63%) and >1000 Bq kg− 1 for 5 samples (22.73%) (Fig. 3). 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The ratio of 90Sr and 137Cs activity concentration ranged from 0.22 to 40.79 (Table 3) showing a high variability. Therefore the 137 Cs activity concentration, which can be easily determined by gamma spectrometry, cannot be used as indicator of the 90Sr activity concentration. Samples of the same brand but coming from different batches (samples 3 and 15) show different activity concentrations of 137Cs and 90Sr (Table 4). Also the sample 22 presents an 137Cs activity concentration very different than that reported by the media for the ashes of pellet of the same brand (Naturkraft Premium) recalled in Valle d'Aosta and at centre of alert but coming from a different batches (n. 286036) [4]. To evaluate the process of transferring from pellet to ashes, for the brand n. 22, 137Cs and 90Sr determination was carried out in wood pellets samples and in their relevant ashes. Taken into account the mean concentration obtained (2.93 Bq kg− 1 in wood pellets and 645.54 Bq kg− 1 in ashes for 137Cs, and 4.170 Bq kg− 1 in wood pellet and 965.66 Bq kg − 1 in ashes for 90Sr) the concentration factors (activity concentration in ash/activity concentration in wood pellets) resulted to 222.8 and 230.0 for 137Cs and 90Sr respectively (Fig. 4). If Cs and Sr completely transfer into ashes, the quantity of ashes would result 4.54‰, using the Cs experimental concentration factor, and 4.32‰, using the Sr experimental concentration factor. The mean value, 4.43‰, very close to values reported in literature [15] for ash of wood pellet (3–6‰), means that radiocaesium and radiostrontium completely remain in the ash. 4. Conclusion
8
samples number
7 6 5 4 3 2 1 0 100-400
400-800 90
800-1000
>1000 -1
Sr concentration (Bq kg )
Fig. 3. Activity concentration classes of
90
Sr.
In this study the radiological characterization of ashes of different brands of wood pellets coming from different countries and used in the regions of Central Italy was carried out with the aim to obtain a set of data to assess the dosimetric impact due to use of wood fuel pellets in the domestic stoves and of the ashes as fertilizers. The samples showed the presence of 137Cs and 90Sr coming from the nuclear weapons fallout and from the damaged nuclear reactor at Chernobyl, but not that of 134 Cs. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1; 90Sr activity concentration ranges from 154.75 Bq kg− 1 to 1443.70 Bq kg− 1. 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The ratio of 90Sr and 137Cs activity concentration showed a high variability. Therefore the 137Cs activity concentration, which can be easily determined by gamma spectrometry, cannot be used as indicator of the 90Sr activity concentration. For a good assessment of the dosimetric impact, it is necessary to determine not only 137Cs but also 90Sr by expensive and time consuming
134
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
966.0
1000 900 ash
800 646.0
700
-1
Bq kg
600 ash
500 400
200 100
ash/pellet
Fig. 4.
Sr and
137
ash/pellet
2.9
4.2
pellet
pellet
0
90
230.0
222.8
300
Cs activity concentration (Bq kg
137
Cs
90
Sr
−1
) in wood pellet and in their relevant ash and concentration factor pellet/ashes for sample n. 22.
radiochemical separation procedures. The 90Sr determination method applied in this study presented a high reproducibility and a high radiochemical yield. References [1] "What are pellets". Pellet Fuels Institute. http://pelletheat.org/pellets/what-are-pellets/. Retrieved 7 November 2011. [2] Manomet Center for Conservation Science, Biomass Sustainability and Carbon Policy Study: Report to the Commonwealth of Massachusetts Department of Energy Resources, 2010. [3] Eija Alakangas, European Pellet Standards, http://www.eubia.org/uploads/media/ VTT_Eija_Alakangas-_01.pdf Retrieved 11 December 2011. [4] Claudio Operti, Il rinvenimento di pellet radioattivi e le azioni immediate di Arpa Valle d'Aosta. ARPA Rivista N.4, Luglio–Agosto 2009. [5] D. Lux, L. Kammerer, W. Ruhmand, E. Wirth, Cycling of Pu, Sr, Cs, and other longliving radionuclides in forest ecosystems of the 30-km zone around Chernobyl, Sci. Total Environ. 173 (1995) 375–384. [6] A.A. Odintsov, A.D. Sazhenyuk, V.A. Satsyuk, Association of 90Sr, 137Cs, 239,240Pu, 241Am, and 244Cm with soil adsorbing complex in soils typical of the vicinity of the Chernobyl NPP, Radiochemistry 46 (2004) 95–101. [7] G. Jia, D. Desideri, F. Guerra, M.A. Meli, C. Testa, Concentration and vertical distribution of plutonium and americium in Italian mosses and lichens, J. Radioanal. Nucl. Chem. 222 (1996) 3–9.
[8] K. Bunzl, W. Kracke, Cumulative deposition of 137Cs, 239(240)Pu e 241Am from global fallout in soils from forest, grassland and arable land in Bavaria (FRG), J. Environ. Radioact. 8 (1988) 1–14. [9] COUNCIL DIRECTIVE 96/29/Euratom of 13 May 1996. Laying down safety standards for the protection of the health of the workers and the general public against the dangers arising from ionising radiation (Official J.L. 159, 29.6.96). [10] Decreto Legislativo n.241 del 26/05/2000 “Attuazione della Direttiva 96/29/EURATOM in materia di protezione sanitaria della popolazione e dei lavoratori contro I rischi derivanti dalle radiazioni ionizzanti”. Supplemento Ordinario n.140/L alla Gazzetta Ufficiale n.203 del 31 agosto 2000. [11] D. Desideri, M.A. Meli, C. Roselli, Natural and artificial radioactivity determination of some medicinal plants, J. Environ. Radioact. 101 (2010) 751–756. [12] G. Jia, C. Testa, D. Desideri, F. Guerra, C. Roselli, Sequential separation and determination of plutonium, americium-241 and strontium-90 in soils and sediments, J. Radioanal. Nucl. Chem. 230s1 (1998) 21–27. [13] C. Testa, D. Desideri, F. Guerra, M.A. Meli, C. Roselli, G. Jia, The importance of separation chemistry for the determination of radionuclides in environmental samples, J. Radioanal. Nucl. Chem. 229/1 (1998) 23–31. [14] D. Desideri, C. Grimani, L. Monte, Migration processes of 137Cs and 90Sr in compartments of a lake ecosystem, J. Radioanal. Nucl. Chem. 266/1 (2005) 31–37. [15] http://www.enplus-pellets.de/downloads/ENplus_Manual_10-03.pdf.
Contents lists available at SciVerse ScienceDirect
Microchemical Journal journal homepage: www.elsevier.com/locate/microc
Analytical methods for the determination of in Italy
137
Cs and
90
Sr in ash of fuel pellets used
Donatella Desideri a,⁎, Alba Rongoni b, Carla Roselli a, Daniela Saetta b, Laura Feduzi a a b
Department of Biomolecular Sciences, University of Urbino, P.zza Rinascimento 6, 61029 Urbino, Italy Department of Surgical and Radiological Science, Section of Medical Physics Environmental and Epidemiological, University of Perugia, Policlinico Monteluce, P.O. Box 1418, 06122 Perugia, Italy
a r t i c l e
i n f o
Article history: Received 18 January 2012 Accepted 12 February 2012 Available online 16 February 2012 Keywords: 137 Cs 90 Sr Wood fuel pellets Ash
a b s t r a c t In this study the radiological characterization of ashes of 22 different brands of wood pellets coming from different countries and used in the regions of central Italy was carried out. 137Cs and 90Sr, were found in the samples taken into account, 134Cs resulted always below the detection limit. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1 (the arithmetic mean resulted to 571 Bq kg− 1); 90Sr activity concentration ranges from 154.75 Bq kg− 1 to 1443.70 Bq kg− 1 (the arithmetic mean resulted to 684.80 Bq kg− 1). The ratio of 90Sr and 137 Cs activity concentration ranged from 0.22 to 40.79 showing a high variability. 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The concentration factors (activity concentration in ash/ activity concentration in wood pellets) resulted to 222.8 and 230.0 for 137Cs and 90Sr respectively; both radionuclides are found completely in the ashes. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Pellet are small particles (normally 6 mm diameter, sometimes 8 mm or larger) typically created by compressing an original material. Pelletizing is the industrial process used to create pellets, using a pellet mill or equipment for extrusion and spheronization. Wood pellets, corn pellets, and grass pellets are used as pellet stove fuel [1]. A report to the Massachusetts Department of Energy Resources estimates that the energy required to manufacture and transport pellets is less than 2% of the energy content of the pellets [2]. Pellets conforming to the norms commonly used in Europe have less than 10% water content, a good structural strength, a low dust and ash content and they are uniform in density. Because the wood fibres are broken down by the hammer mill, there is virtually no difference in the finished pellets between different wood types. Pellets can be made from nearly any wood variety, provided the pellet press is equipped with good instrumentation, the differences in feed material can be compensated for in the press regulation [3]. In June 2009, an Italian court has ordered the recall of 10,000 tonnes of wood fuel pellets imported over fears that they could have dangerous levels of radioactivity. The alarm was raised after someone in the northern Aosta Valley region, who had bought the pellets, sent them for analysis because they did not burn well. The results showed that wood pellets contained 137Cs with an activity concentration ranging from 10 to 320 Bq kg− 1, whereas an ash sample showed a concentration of
⁎ Corresponding author. Tel.: + 39 0722 303307; fax: + 39 0722 303306. E-mail address: [email protected] (D. Desideri). 0026-265X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2012.02.007
around 46000 Bq kg− 1; the ash, in fact, concentrates (25–200 times) the radionuclides initially present in wood pellet [4]. The pellets at the centre of the alert were imported from Lithuania in the autumn 2008 and were sold in 11 regions in the north and south of Italy. The names of the Lithuanian producer and the Italian importer and distributors are known. It is not yet clear if the wood used to produce the pellets actually came from Lithuania or from areas in non-EU countries with a higher contamination of caesium. The cause of the radioactivity was initially not specified, however it soon became very clear that the wood pellets contain radioactivity coming from the nuclear weapons fall-out and from the damaged nuclear reactor at Chernobyl (1986). The Chernobyl accident caused contamination of 134Cs and 137Cs in several European countries. When forest areas are contaminated with caesium, the radioactivity is absorbed by the vegetation, including trees [5–8]. The contaminated pellets themselves are not dangerous to humans: the dangers come a) from inhalation of the smoke produced when the pellets are burned; b) from inhalation of the ash during the polish operations of the domestic stoves and c) the use of ash as fertilizer for orchards and gardens. As far as the radioprotection legislation is concerned, Italy has implemented Council Directive 96/29/Euratom laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation [9] in its national legislation, including levels below which a practice may be exempted from the reporting requirements of the directive. While the exempt concentration value in the directive for 134Cs and 137Cs is 10,000 Bq kg− 1, the Italian legislation [10] has laid down a single lower value for all radionuclides of 1 Bq g− 1 (or 1000 Bq kg− 1). It should be noted that the activity concentrations detected by the Italian
132
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
Table 1 Ash samples, country of origin of wood fuel pellet and Italian region where it is used. Ash sample
Country of origin
Italian region of use
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Italy Lithuania Austria Italy Italy Spain Austria Austria Italy Unknown Unknown Slovenia Unknown Spain Austria Unknown Unknown Unknown Unknown Lituania Slovakia Austria
Umbria Umbria Marche Marche Marche Marche Marche Emilia Romagna Emilia Romagna Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Umbria Emilia Romagna Marche
authorities in the wood pellets are well below the national exemption level. However, the activity concentration in the ashes exceeds this value. It should be borne in mind that the exempt concentration values have been established for large quantities of material (of the order of 1 tonne). It is for the Italian authorities to assess the exposure pathways resulting from the higher concentrations in the ashes, for the relevant management options, and to decide whether further use of such pellets is permitted either without restrictions or subject to appropriate conditions. In this study ashes of 22 different brands of wood pellets coming from different countries and used in the regions of Central Italy were taken into account. The aim of this study was: 1) to determine the oncentration of 137Cs and that of 90Sr, another anthropogenic radionuclide; 2) to study the transfer of these two radionuclides from wood pellet to ashes; 3) to obtain a set of data to assess the dosimetric impact due to use of wood fuel pellets in the domestic stoves and of the ashes as fertilizers.
Table 2 Evaluation of the reproducibility of
2.1. Samples Analysis was carried out in 22 ash samples derived from the combustion of wood pellets of different brands obtained through normal
137
Cs (photopeak: 661.6 keV)
Fig. 1. γ spectrum of a sample of ash.
90
Sr method.
Sample 1
Yield %
Sr (Bq kg− 1)
Sample 2
Yield %
90 Sr (Bq kg− 1)
A B C Mean Stand. deviat. Stand. deviat. %
83.32 79.54 89.26 84.04 4.90 5.83
478.67 446.21 448.81 457.90 18.04 3.94
A B C Mean Stand. deviat. Stand. deviat. %
89.98 89.98 75.59 85.18 8.31 9.75
982.83 957.58 903.82 948.08 40.35 4.25
distribution channels. The samples came from of different countries and were used in the Umbria, Marche and Emilia Romagna, regions of Central Italy. Table 1 lists the ash samples analysed, the country of origin of the relevant wood pellets and the Italian region where they are used. 2.2. Radionuclides determination The activity concentration of radiocaesium was determined by γ-spectrometry. Samples were put and counted in Marinelli beakers. All the measurements were performed with a HPGe crystal of type “p” in coaxial geometry, with relative efficiency at 1.33 MeV equal to 25% (measured by placing a point source of 60Co, at 25 cm from the detector) ; the detectable energy ranges from 0.040 to 2.2 MeV; peak detection efficiencies were calculated automatically through a computer system interfaced with an multichannel analyser. 134Cs and 137Cs were determined by measuring the activity of their peaks at 569.32, 604.7, 795.84, 801.93 ( 134Cs) and 661.6 keV (137Cs) [7,8,11]. The detection limit was 0.2 Bq for 137Cs and 0.06 Bq for 134Cs. Fig. 1 reports the gamma spectrum of an ash pellet sample. The accuracy of the results is supported by the success of intercomparison exercises (IAEA). The 90Sr activity concentration was determined by applying a radiochemical method, a destructive technique, consisting in the separation of 90Y in radioactive equilibrium with parent 90Sr. The radioanalytical method used in this study, whose accuracy was regularly checked through participation in intercomparison exercises organized by the International Atomic Energy Agency (IAEA), was the following [12–14]. After addition of a known activity of Sr stable as carrier and Y stable as carrier and yield internal standard, the sample (0.25–0.50 g) was first Table 3 137 Cs and
2. Experimental
90
90
Sr activity concentration (Bq kg− 1) and their ratio.
Sample
137
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Mean Minimum Max
755 ± 72 3176 ± 292 65 ± 11 30 ± 5 815 ± 37 43 ± 2 92 ± 20 521 ± 47 90 ± 4 273 ± 26 73 ± 4 347 ± 15 537 ± 17 257 ± 14 981 ± 43 320 ± 30 400 ± 37 80 ± 8 58 ± 6 2788 ± 108 212 ± 10 645 ± 29 571 30 ± 5 3176 ± 292
Cs
90
Sr
458 ± 69 948 ± 142 1444 ± 217 1224 ± 184 1396 ± 209 255 ± 38 1150 ± 172 1065 ± 160 157 ± 24 410 ± 61 378 ± 57 762 ± 114 673 ± 101 399 ± 60 841 ± 126 599 ± 90 358 ± 54 164 ± 25 155 ± 23 627 ± 94 635 ± 95 966 ± 145 685 155 ± 23 1444 ± 217
90
Sr/137Cs
0.61 0.30 22.21 40.79 1.71 5.93 12.50 2.04 1.75 1.50 5.19 2.20 1.25 1.55 0.86 1.87 0.90 2.05 2.67 0.22 3.00 1.49 5.12 0.22 40.79
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
Table 4 90 Sr and 137Cs activity concentration (Bq kg− 1) in ash of pellets of the same brand but coming from different batches.
14
samples number
12 10 8 6
Sample
90
3 15 20 Naturkraft Premium (batch n. 286036)
1.444 ± 217 841 ± 126 – –
137
4 2 0
133
30-400
400-800 137
800-1000
>1000 -1
Cs concentration (Bq kg )
Fig. 2. Activity concentration classes of
137
Cs.
boiled with conc. HNO3 and H2O2, then the solution was evaporated to dryness and the residue boiled with conc. HCl and conc. HNO3 for two times. After the solution was evaporated to dryness and the residue was treated with conc. HCl and finally dissolved in 4–5 M HCl; then the solution was filtered. The solution was passed through a microporous polyethylene supporting tri-n-octylamine column (TNOA) to eliminate the natural 210 Bi; yttrium was retained into a microporous polyethylene supporting di (2ethyl-hexyl) phosphoric acid (HDEHP) chromatographic column at pH 1, eluted, precipitated as yttrium oxalate and measured by a low background (6.2 10− 3 s− 1) beta counter (Canberra-2404, USA) with a counting efficiency of 23%. The 90Y chemical yield resulted 85.83±6.29%. To verify the radioanalytical method reproducibility, for samples 1 and 2 the analyses were replicated three times obtaining the results shown in Table 2. The activity mean concentration was 457.90±18.04 and 948.08±40.35 Bq kg− 1 for sample 1 and sample 2 respectively; the relevant standard deviation resulted for both samples is b5% (3.94% and 4.25% for sample 1 and sample 2 respectively). 3. Results and discussion As far as gamma spectrometry is concerned, 134Cs resulted always below the detection limit; whereas, the determinations carried out by the researchers of Aosta Valley region showed the presence of 134Cs. The 137Cs activity concentrations are reported in Table 3. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1 ; the arithmetic mean resulted to 571 Bq kg − 1 . The activity concentration was
Sr
137
Cs
65 ± 11 981 ± 43 2788 ± 108 40,000
90
Sr/137Cs
22.21 0.86 – –
Cs (photopeak: 661.6 keV).
b400 Bq kg− 1 for 13 samples (59.09%); it ranged between 400 and 800 Bq kg− 1 for 5 samples (22.73%), between 800 and 1000 Bq kg− 1 for two samples (9.09%) and >1000 Bq kg− 1 for two samples (9.09%) (Fig. 2) coming from Lithuania. Table 3 reports also the 90Sr activity concentrations. The arithmetic mean of this radionuclide results to 684.80 Bq kg− 1 (minimum value 154.75 Bq kg− 1 and maximum value 1443.70 Bq kg− 1). The 90Sr activity concentration was b400 Bq kg− 1 for 7 samples (31.82%); it ranged between 400 and 800 Bq kg− 1 for 7 samples (31.82%), between 800 and 1000 Bq kg− 1 for 3 samples (13.63%) and >1000 Bq kg− 1 for 5 samples (22.73%) (Fig. 3). 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The ratio of 90Sr and 137Cs activity concentration ranged from 0.22 to 40.79 (Table 3) showing a high variability. Therefore the 137 Cs activity concentration, which can be easily determined by gamma spectrometry, cannot be used as indicator of the 90Sr activity concentration. Samples of the same brand but coming from different batches (samples 3 and 15) show different activity concentrations of 137Cs and 90Sr (Table 4). Also the sample 22 presents an 137Cs activity concentration very different than that reported by the media for the ashes of pellet of the same brand (Naturkraft Premium) recalled in Valle d'Aosta and at centre of alert but coming from a different batches (n. 286036) [4]. To evaluate the process of transferring from pellet to ashes, for the brand n. 22, 137Cs and 90Sr determination was carried out in wood pellets samples and in their relevant ashes. Taken into account the mean concentration obtained (2.93 Bq kg− 1 in wood pellets and 645.54 Bq kg− 1 in ashes for 137Cs, and 4.170 Bq kg− 1 in wood pellet and 965.66 Bq kg − 1 in ashes for 90Sr) the concentration factors (activity concentration in ash/activity concentration in wood pellets) resulted to 222.8 and 230.0 for 137Cs and 90Sr respectively (Fig. 4). If Cs and Sr completely transfer into ashes, the quantity of ashes would result 4.54‰, using the Cs experimental concentration factor, and 4.32‰, using the Sr experimental concentration factor. The mean value, 4.43‰, very close to values reported in literature [15] for ash of wood pellet (3–6‰), means that radiocaesium and radiostrontium completely remain in the ash. 4. Conclusion
8
samples number
7 6 5 4 3 2 1 0 100-400
400-800 90
800-1000
>1000 -1
Sr concentration (Bq kg )
Fig. 3. Activity concentration classes of
90
Sr.
In this study the radiological characterization of ashes of different brands of wood pellets coming from different countries and used in the regions of Central Italy was carried out with the aim to obtain a set of data to assess the dosimetric impact due to use of wood fuel pellets in the domestic stoves and of the ashes as fertilizers. The samples showed the presence of 137Cs and 90Sr coming from the nuclear weapons fallout and from the damaged nuclear reactor at Chernobyl, but not that of 134 Cs. 137Cs activity concentration ranges from 30 to 3176 Bq kg− 1; 90Sr activity concentration ranges from 154.75 Bq kg− 1 to 1443.70 Bq kg− 1. 77.2% of the samples show a 90Sr activity concentration higher than that of 137Cs. The ratio of 90Sr and 137Cs activity concentration showed a high variability. Therefore the 137Cs activity concentration, which can be easily determined by gamma spectrometry, cannot be used as indicator of the 90Sr activity concentration. For a good assessment of the dosimetric impact, it is necessary to determine not only 137Cs but also 90Sr by expensive and time consuming
134
D. Desideri et al. / Microchemical Journal 103 (2012) 131–134
966.0
1000 900 ash
800 646.0
700
-1
Bq kg
600 ash
500 400
200 100
ash/pellet
Fig. 4.
Sr and
137
ash/pellet
2.9
4.2
pellet
pellet
0
90
230.0
222.8
300
Cs activity concentration (Bq kg
137
Cs
90
Sr
−1
) in wood pellet and in their relevant ash and concentration factor pellet/ashes for sample n. 22.
radiochemical separation procedures. The 90Sr determination method applied in this study presented a high reproducibility and a high radiochemical yield. References [1] "What are pellets". Pellet Fuels Institute. http://pelletheat.org/pellets/what-are-pellets/. Retrieved 7 November 2011. [2] Manomet Center for Conservation Science, Biomass Sustainability and Carbon Policy Study: Report to the Commonwealth of Massachusetts Department of Energy Resources, 2010. [3] Eija Alakangas, European Pellet Standards, http://www.eubia.org/uploads/media/ VTT_Eija_Alakangas-_01.pdf Retrieved 11 December 2011. [4] Claudio Operti, Il rinvenimento di pellet radioattivi e le azioni immediate di Arpa Valle d'Aosta. ARPA Rivista N.4, Luglio–Agosto 2009. [5] D. Lux, L. Kammerer, W. Ruhmand, E. Wirth, Cycling of Pu, Sr, Cs, and other longliving radionuclides in forest ecosystems of the 30-km zone around Chernobyl, Sci. Total Environ. 173 (1995) 375–384. [6] A.A. Odintsov, A.D. Sazhenyuk, V.A. Satsyuk, Association of 90Sr, 137Cs, 239,240Pu, 241Am, and 244Cm with soil adsorbing complex in soils typical of the vicinity of the Chernobyl NPP, Radiochemistry 46 (2004) 95–101. [7] G. Jia, D. Desideri, F. Guerra, M.A. Meli, C. Testa, Concentration and vertical distribution of plutonium and americium in Italian mosses and lichens, J. Radioanal. Nucl. Chem. 222 (1996) 3–9.
[8] K. Bunzl, W. Kracke, Cumulative deposition of 137Cs, 239(240)Pu e 241Am from global fallout in soils from forest, grassland and arable land in Bavaria (FRG), J. Environ. Radioact. 8 (1988) 1–14. [9] COUNCIL DIRECTIVE 96/29/Euratom of 13 May 1996. Laying down safety standards for the protection of the health of the workers and the general public against the dangers arising from ionising radiation (Official J.L. 159, 29.6.96). [10] Decreto Legislativo n.241 del 26/05/2000 “Attuazione della Direttiva 96/29/EURATOM in materia di protezione sanitaria della popolazione e dei lavoratori contro I rischi derivanti dalle radiazioni ionizzanti”. Supplemento Ordinario n.140/L alla Gazzetta Ufficiale n.203 del 31 agosto 2000. [11] D. Desideri, M.A. Meli, C. Roselli, Natural and artificial radioactivity determination of some medicinal plants, J. Environ. Radioact. 101 (2010) 751–756. [12] G. Jia, C. Testa, D. Desideri, F. Guerra, C. Roselli, Sequential separation and determination of plutonium, americium-241 and strontium-90 in soils and sediments, J. Radioanal. Nucl. Chem. 230s1 (1998) 21–27. [13] C. Testa, D. Desideri, F. Guerra, M.A. Meli, C. Roselli, G. Jia, The importance of separation chemistry for the determination of radionuclides in environmental samples, J. Radioanal. Nucl. Chem. 229/1 (1998) 23–31. [14] D. Desideri, C. Grimani, L. Monte, Migration processes of 137Cs and 90Sr in compartments of a lake ecosystem, J. Radioanal. Nucl. Chem. 266/1 (2005) 31–37. [15] http://www.enplus-pellets.de/downloads/ENplus_Manual_10-03.pdf.