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Long-range transport of gaseous 131I and other radionuclides from Fukushima accident to Southern Poland
Atmospheric Environment 91 (2014) 137e145
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Long-range transport of gaseous 131I and other radionuclides from Fukushima accident to Southern Poland Jerzy W. Mietelski a, *, Renata Kierepko a, Kamil Brudecki a, Pawe1 Janowski a, b, Krzysztof Kleszcz a, Ewa Tomankiewicz a a b
ski Institute of Nuclear Physics (IFJ PAN), Polish Academy of Sciences, 31-342 Kraków, Poland The Henryk Niewodniczan Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, A. Mickiewicza 30 Ave., 30-059 Kraków, Poland
h i g h l i g h t s Only volatile gamma emitters were found in Fukushima plume in Poland. Original method of measurements for gaseous 131I is presented. Results suggest Fukushima release below 10% of that from Chernobyl. The exchange between gaseous and aerosol fraction of 131I affects activity ratios.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 October 2013 Received in revised form 27 March 2014 Accepted 29 March 2014 Available online 30 March 2014
A serious accident at Fukushima Dai-Ichi NPP triggered radioactive emission to the atmosphere on 12 March 2011. The results of gamma spectrometric measurements of both gaseous and aerosol fraction of the air, collected in Krakow over the period from March 21 till the end of May 2011, as well as wet and dry deposition recorded from March till the end of October 2011, are presented in this paper. Krakow happened to be the first Polish location where radioactive isotopes characteristic for reactor releases, such as 131I, 132I, 129mTe, 132Te, 134Cs, 136Cs, and 137Cs, were detected. The maximum activity for aerosols equal to (5.73 0.35) mBq/m3, (0.461 0.041) mBq/m3 and (0.436 0.038) mBq/m3 for 131I, 134Cs and 137 Cs, respectively, was recorded for March 29, 2011. The data on the fallout are also given. The results of the radiochemical analysis of aerosol samples showed no traces of plutonium or americium isotopes associated with the disaster to be detected. The results of air activity concentration from Fukushima accident observed in Central Europe, Poland, in comparison to those of Chernobyl accident observed in Japan are presented and discussed. The comparison has revealed a discrepancy in the recognized relative scale of both accidents, and important difference in long distance transport of contamination, to exist. An attempt to explain the variation in the activity ratios between the aerosol fraction for 131I and 137Cs as resulting from exchange between the gaseous and aerosol fractions of 131I while the contamination had been propagating, is made. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Atmospheric radionuclides Fukushima accident Radiocesium Chernobyl Plutonium Radioactive fallout
1. Introduction A strong earthquake near Japan Islands, followed by enormous high tsunami on March 11, 2011 resulted in a serious overheating damage to have occurred in 3 reactors of the Fukushima Daiichi Nuclear Power Plant (Tanaka, 2012). Radioactive emission to the atmosphere began on March, 12 and lasted for over 2 weeks (IAEA, 2011). A radioactive plume migrated across the North Pacific,
* Corresponding author. E-mail address: [email protected] (J.W. Mietelski). http://dx.doi.org/10.1016/j.atmosenv.2014.03.065 1352-2310/Ó 2014 Elsevier Ltd. All rights reserved.
Northern America, Arctic and arrived over Europe from the northwestern direction (Masson et al., 2011, MacMullin et al., 2012). According to meteorological modelling available on the Internet, already on March 21e23 it was predicted for the cloud to be present over central Europe between March 24e27 (NOAA, 2011). Though at that time, the data on the release were scarce, from the spectra published in the open media one could expect only radioisotopes of volatile elements such as iodine, tellurium, and caesium to be detected. Among them iodine was the most interesting, as due to its complex chemistry, it can be transported both on aerosol and in gaseous fractions. A long-distance transportation, which is definitely the case for Japan release detectable in Central
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Table 1 Results of gamma spectrometric measurements of ground air activity concentration in Krakow following Fukushima accident for one day sampling cycle. Sampling start/stopa
V [m3]
Activity concentration [mBq/m3] 131
21/24.03 24/25.03 25/26.03 26/27.03 27/28.03 28/29.03 29/30.03 30/31.03 31.03/1.04 1/2.04 2/3.04 3/4.04 4/5.04 5/6.04 6/7.04 7/8.04 8/9.04 9/10.04 10/11.04 11/13.04 13/15.04 15/18.04 18/21.04 21/26.04 a
17 957 5975 6386 5256 7468 5385 5763 7264 6177 6396 6628 6230 8201 4261 6689 6554 6067 6788 6625 12 882 13 106 18 233 14 775 29 154
I aerosols
105 5 84 7 <12 840 37 1570 60 3600 200 5730 350 2910 120 908 42 668 33 718 35 2151 90 413 18 494 27 650 27 438 48 308 20 182 16 239 15 157 13 91 7 126 14 45 3 11 1
131
I gas
135 42 286 103 <48 604 170 2040 860 5200 1200 5220 340 3360 260 1120 110 1150 230 950 150 1520 410 625 95 510 220 930 250 680 320 775 90 940 190 1060 360 402 59 249 32 167 27 88 28 65 18
137
Cs
<9 <15 <9 <17 83 11 254 27 436 38 296 25 36 6 41 10 42 11 411 30 45 5 43 15 46 6 60 15 82 14 <24 42 5 40 8 <18 28 6 23 3 5.3 0.8
136
Cs
<7 <11 <7 <13 22 10 32 15 28 16 24 13 <11 <19 <18 27 5 <8 <28 <10 <20 <20 <18 <7 <10 <15 <11 2.4 1.1 <1
134
Cs
<5 <11 <36 16 8 105 20 206 35 461 41 307 28 35 8 75 22 54 17 420 50 56 7 44 13 45 8 67 27 64 21 25 10 45 16 37 11 18 5 32 6 14 2 6.5 0.8
132
Te/132I
<4 <8 <3 <9 45 10 109 17 124 39 <9 <8 <10 <10 41 10 <6 <15 <7 <10 <11 <9 <3 <5 <4 <8 11 7 32
7
Be
3810 4290 3800 3310 4680 4980 5690 6040 6330 5720 4340 7500 5220 3760 5490 4840 3960 2410 2740 3190 2420 2500 7650 6040
270 310 280 240 350 390 440 450 450 430 330 540 370 310 390 390 310 210 650 240 180 190 540 430
Year 2011.
Europe, i.e. over a 10 000 km distance, can result in a fractionation between gas and aerosol (ie. the ratio of the two fractions observed in Europe is not necessarily the same as was released in Japan). This ratio can be affected either by chemical reactions which may occur due to oxidation conditions in the air, sunlight, or exposition to UV radiation, also the physical removing of gasses and aerosols from radioactive cloud is different as well as their mutual exchange can happen. Thus it seems very interesting to study both aerosol and gaseous fractions of iodine isotopes in the nuclear accident cloud. Traces of all other nuclides in relation to iodine could also shed some light onto understanding differences in the air transport mechanism for different radionuclides. From the dosimetric point of view apart from measuring particular fraction of iodine from nuclear accidents, it is of vital importance to measure its gaseous fraction, since it can produce significant part of the dose from iodine. It is of greater importance for shorter transportation distances where higher iodine activity concentration in the air can be detected, so developing the method of gaseous iodine detection seems particularly important. 2. Material and methods 2.1. Sample collection Air sampling was carried out at one place, namely the Institute of Nuclear Physics in Krakow e IFJ PAN, 50.04 N, 19.58 E, 215 m a.s.l, with two aerosol samplers and one atmospheric precipitation collector. 2.1.1. Aerosol sampling The IFJ PAN operates two high volume aerosol samplers, namely the Aerosol Sampling Statione500 and MASS-500. The first one is a standard ASS-500 with the nominal airflow rate of 500 m3/h, designed and produced by CLOR (Central Laboratory for Radiation Protection, Warsaw). It works within the Polish Monitoring Network of Gamma-Ray Emitters in Ground-Level Air, coordinated by CLOR and Polish National Atomic Agency (PAA). The second one
is an older version of ASS-500 high volume sampler, extensively reconstructed and renamed as MASS-500 for Modified ASS-500, and it is IFJ property. All the aerosol samples were collected on Petryanov filters FPP-15-1.5 (polyvinyl chloride) displaying high good aerosol collecting properties (Bysiek et al., 2000). At the night of March 23, 2011 we received an informal communication that in Scandinavia iodine had been found (Masson et al., 2011), so in the morning of March 24, we changed the filters on MASS-500 and began an emergency mode operation; the filters were thus replaced every day till April 12. Then the sampling was run on a longer base, and ended with a whole week measurements at the end of April. The entire Polish network monitoring system consisting of 12 ASS-500 stations, turned from the week routine cycle to the emergency two-days-cycle on March 25 (Isajenko et al., 2011) and later, from April 1 till the end of the month, all the stations, including Krakow’s ASS-500, operated under a half-weekcycle. The measurements using MASS-500 produced 20 samples of aerosols deposited on the air filters from IFJ PAN (Table 1). 2.1.2. Gaseous sampling The gaseous fraction of the air was trapped in a double cartridge installed additionally inside the inlet of the MASS-500 station, behind the aerosol filter. This resulted in decreasing the flow rate from 500 m3/h to about 250 m3/h. The cartridge was tested with a , smaller aerosol sampler HVS-30 produced by Atmoservice, Poznan Poland, in an endocrinological hospital to measure 131I concentration in the air above septic tanks (Mietelski et al., 2005). The cartridge consists of two identical cassettes in a form of rectangular aluminium frames, filled with granular activated carbon impregnated with KI (IBJ-6, mesh size 2 mm, produced by Gryskand, Hajnówka, Poland). The carbon granulate is bordered both at the top and bottom of each cassette with fine stainless steel nets. Between the cassettes a rubber seal is inserted. The efficiency for gaseous iodine adsorption is calculated from the ratio of the activity found in the first and the second cassette under assumption that iodine was absorbed identically in both cassettes. Hence, with an infinite series of such cassettes, the absorbed activity would
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139
Table 2 Results of radiochemical analyses and alpha spectrometric measurements for transactinides in aerosol filters from Krakow (T e measurement time, Y e chemical yield). Set
Samplinga start/stop
Volume [m3]
T [s]
Y [%]
239þ240
1 2
21.03/2.04 2.04/11.04
74 027 58 043
605 042 487 595
80.5 3.6 86.5 3.6
5.1 1.5 13.8 1.9
<0.6 0.9 0.3
Sampling start/stop
Volume [m3]
T [s]
Y [%]
241
242
21.03/2.04 2.04/11.04
74 027 58 043
1149789 858 498
59.7 1.4 38.1 1.2
0.4 0.3 4.3 1.2
1 2 a
Pu [nBq/m3]
Am [nBq/m3]
238
Pu [nBq/m3]
Cm [nBq/m3]
<0.1 <0.3
Year 2011.
decrease in a geometrical progression. Thus, the total activity is obtained from the formula for the sum of an infinite geometrical series, as long as the results for the first and second cassette are considered as the first and second element of this series, respectively.
S ¼
CA 1q
2.2. Gamma spectrometric measurements
(1)
where: S e gaseous 131I activity concentration in the air. q e the ratio between the activity found for 131I in the second (CB) and first (CA) cassette, namely:
q ¼ CB =CA
(2)
The total efficiency of gaseous iodine adsorption can be then defined as:
ε ¼
CA CB ¼ ¼ 1q S S CA
possibility of finding 131I in the fallout severely diminished, from the end of April we returned to evaporation under acidic conditions. The total number of atmospheric precipitation deposition samples was 9 (Table 3).
(3)
So, the total efficiency is known just by the ratio of activities found in two cassettes and there is no need to know if some iodine was lost. With 0.5 dm3 volume of carbon filling each cassette, a direct measurement of the exposed carbon in Marinelli beaker geometry is enabled. From March 21 till April 14, 2011 twenty samples of gaseous iodine were collected. The exposure time of the samples corresponds to the sampling time of the air filter on MASS-500 (Table 1). 2.1.3. Atmospheric precipitation sampling The fallout was collected over different periods, from a week to a month intervals with 2.2 m2 area collector made of stainless steel (Kierepko and Mietelski, 2010). Both, wet and dry deposition, were taken together in plastic barrels. In our typical procedure for fallout samples (rainwater, acidified with HNO3) a pre-concentration is done by evaporation to a small volume on a hot plate in a stainless steel pot to a small volume of about 0.5 L. The solution is then transferred to glass beaker. The containers are washed with HNO3 and wiped out with a paper filter, which are then ashed afterwards at 400 C. In the end, all the fractions are combined into one and evaporated in a polyethylene vial under an infrared lamp. As under such conditions losses of iodine isotopes would certainly take place, therefore the standard procedure was found inapplicable. To prevent such losses we initially tried to evaporate rainwater under basic conditions, i.e. without the acid added and the paper filter used. Three samples collected from March, 11th till April, 29th were treated that way. Unlike the case where evaporation follows acidification, the volume of the final solid sample, obtained with evaporation under basic conditions (pH w10, adjusted by adding ammonia), increased, most likely due to presence of carbonates. The higher volume raised the detection limits for activities measured with gamma spectrometry. As in second half of April the
Our laboratory has been accredited under Polish law for gamma spectrometric measurements (ISO 17025). All the filters, granulated carbon from gas iodine cassettes and evaporated precipitations were analysed by means of low background gamma spectrometer with HPGe detectors. Measurements were performed using three spectrometers, the majority of data were obtained using 11% relative efficiency Silena SpA (Italy) detector. Aerosol filters were measured once compressed to a 5 cm diameter, and about 4 mm high pellet. For such geometry the efficiency calibration was determined with a multi-gamma source SZN 40/10 by Polatom for all the spectrometers. Due to small detector efficiency the coincidence corrections for 134Cs activities were estimated to be below 5% (on the basis of the summing peak at 1.4 MeV) and were not introduced. The carbon from each cassette was transferred into a 0.5 dm3 plastic Marinelli beaker and measured. The activities were determined with a calibration performed for a standard mix gamma source SZM-3 by Polatom. For 364 keV 131I line this calibration was additionally verified by measurements of 131I liquid source obtained from the hospital. Evaporated rainwater was measured after at least 10 days from its collection due to time required to evaporate. Therefore, shortliving isotopes cannot be found. A special calibration for energies of 134Cs, 137Cs and 131I was applied. This calibration was carried out later, with diluted solutions of a certified liquid source. At each calibration the liquid solution was prepared for the final volume of the evaporated rainwater. The calibration for cosmogenic 7Be (477 keV) and 22Na (1275 keV) was performed with a linear approximation within the range 364 keVe1364 keV:
n o ln Eff ðEÞ ¼ a lnðEÞ þ b
(4)
where: Eff (E)e the detector efficiency for given gamma quantum energy E, a and b constants obtained from fit. All the results presented here are given for the day of measurement. 2.3. Radiochemical analysis At the time of Fukushima accident the disputable release of transactinides remained an open question, until tiny traces of some Fukushima origin Pu were reported recently to have been found in the environment (Zheng et al., 2012). In order to search for transactinides we made an effort to check whether any unusual actinides were present in the incoming air. The search, which followed gamma spectrometric measurements, for Pu, Am
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Table 3 Activity concentration decay corrected for the middle of the collection period for artificial and cosmogenic (for comparison) radionuclides found in rainwater (with dry deposition) in Kraków over MarcheOctober 2011. Collection time
Elapsed time sampling to meas. [days]
Rainwater volume [dm3]
131
11.03e28.03 28.03e5.04 5.04e29.04 29.04e30.05 30.05e4.07 4.07e1.08 1.08e6.09 6.09e3.10 3.10e31.10
127 15 56 103 77 106 105 100 95
30 10 160 190 155 270 140 30 18
<1480a 770 39 76 24 <3300 <390 <1500 <1700 <6300 <6000
I
7
134
Be
990 1518 1862 2550 2640 2100 1188 382 167
59 79 94 130 130 105 60 26 15
Cs [Bq/m3]
1.2 0.4 4.3 1.4 1.7 0.2 2.09 0.15 <0.4 <0.14 <0.20 <1.0 <1.5
137
Cs
<1.9 4.5 1.4 3.4 0.3 4.60 0.28 0.91 0.13 0.19 0.05 0.24 0.09 <1.1 <0.8
22
Na
<1.3 <2.6 0.58 0.21 0.31 0.25 0.14 <1.3 <1.7
0.16 0.07 0.09 0.05 0.06
a Only 131I result (presented limit) comes from direct measurement in 0.53 dm3 of rainwater in Marinelli beaker directly after end of collection, other results for this sample are obtained in measurement done after 127 days and full treatment (evaporation).
and Cm isotopes was performed for two sets of filters. The first set was combined from all the Petryanov filters from MASS-500 collected between March 21 and April 2. The second set consisted of filters collected between 2 and 11 of April, 2011. The combined samples were ashed at 600 C. Subjected later to wet mineralization with HF, HNO3, HCl and H3BO3 that followed adding the tracers 234Am and 242Pu (Mietelski et al., 1999; Kierepko et al., 2009). With plutonium adjusted as Puþ4 (LaRosa et al., 1992), it was separated from 8 M HNO3 on Dowex 1x8, followed with two co-precipitations, namely with oxalates and Fe(OH)3 and additional purification from thorium (TEVA resin). Americium and curium were separated from rare earths on Dowex-1 from acid-methanol solutions with ammonium thiocyanate added (Holm and Ballestra, 1989). Finally, from both americium/curium or plutonium fractions NdF3 sources were prepared (Sill, 1987) and measured by means of Silena AlphaQuattro spectrometer with Canberra PIPS detectors (450 mm2 area). The required quality of the analyses was verified with analyses of the reference material IAEA Soil 375. The determined activities of 266 27 mBq/kg and 55 4 mBq/kg, for 239þ240Pu and 238Pu, respectively, dropped within 95% confidential level. This material if of certified value for 1991 for 241Am, however, as Pu isotopic ratio reveals significant contribution of the Chernobyl fallout, one should assume additional increase of 241Am from 241Pu decay, hence the 1991 year value is no longer valid. For 241Am we obtained 0.30 0.03 Bq/kg, which with correction for ingrown of 241Am from 241Pu decay gives 0.15 0.02 Bq/kg. 3. Results 3.1. Gamma emitters in air samples We were the first laboratory in Poland to measure traces of 2011 Fukushima accident in the air in the morning of March 24, in the air filters exposed from 21 March 2011. The results for air samples are presented in Table 1. The presence of 131I, 132I, 129mTe, 132Te, 134Cs, 136 Cs and 137Cs in the air filters was established. These results were already partly published in a joint report from European air monitoring network (Masson et al., 2011). Measurable, i.e. above the detection limit, concentrations of caesium appeared two days later that those of iodine. The maximum activity for 131I, 134Cs and 137 Cs for aerosols of values of (5.73 0.35) mBq/m3, (0.461 0.041) mBq/m3 and (0.436 0.038) mBq/m3 for 131I, 134Cs and 137Cs, respectively, was observed on the 29th of March 2011. The average activity ratio for 134Cs to 137Cs was 1.11. The 131I time profile in the gaseous and aerosol fractions is presented in Fig. 1. The ratio between the activity in gas fraction 131I to aerosol fraction tended to change with time, reaching nearly 1 for the maximum activity, then
it increases to about 10 at mid-April. This ratio evolution with time is presented in Fig. 2. This can be understood this way: gas plume is subject of faster dispersion, so gas is detectable first, however due to faster dispersion the main part of plume is depleted in gas fraction. Eventually, the gas can stay in atmosphere for longer time then aerosols, therefore with time passing the gaseous component relatively rises up. Since the ASS-500 and MASS-500 were working under different cycles (modes) for changing samples the consistency of the results is not trivial to check. Thus in Fig. 3 the averages weighted by the value of total airflow calculated for 131I are displayed for 5 periods of 2011, namely March 21e25, March 25e28, March 28e30, March 30eApril 1, and April 1e4. The Pearson correlation factor R is equal to 0.98. However, the value of the straight line slope fit suggests about 9.7% on average systematic error resulting in higher values for MASS-500 in comparison to those for ASS-500. It is also important to note that MASS-500 and ASS-500 differ with regard to the method of air-flow measurement. While in the first one a vibration flow metre, adopted from the old version of ASS-500, is used, in the current version of ASS500 flow meter with Venturi nozzle is applied. Since it is hard to decide on the methods relative superiority, we do not provide any justification, apart from the comments on the systematic uncertainties level to be below 10%. The data obtained for the ratio q (Eq. (2)), which describes the efficiency of trapping the gaseous iodine in the carbon cartridge, were tested for any relation with such parameters as gaseous 131I activity concentration, total air volume and mean airflow rate. The results are presented in Figs. 4e6, respectively. As no correlation between the mentioned variables was manifested, it seems reasonable to conclude that method for gaseous iodine determination does not introduce systematic biases. 3.2. Search for alpha emitters in air filters The results of Pu and Am/Cm analysis are presented in Table 2. At the detection limit at a fraction of nBq/m3 neither the traces of 242 Cm were detected, nor unusual isotopic ratios for Pu isotopes, or between Pu and Am, were noticed. Activity concentration of 239þ240 Pu and 241Am were well within the typical level of few nBq/ 3 m (Mietelski et al., 1999, Kierepko and Mietelski, 2010). The second set revealed higher values, most likely due to strong western wind blowing at those days, which made the resuspension more effective. It may be thus concluded that in the traces of radioactive plume from Fukushima, measured in Krakow, we did not observed any measurable traces of transactinides of a fresh release, but solely resuspended remains of past (mostly global) fallouts. This suggests that the ratio between 137Cs and 239þ240Pu activity in Fukushima
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141
Fig. 1. Time sequence of 131I activity concentration for gaseous and aerosol fractions in Krakow, after the Fukushima accident. Each bar is located at the date when air sampling started, of different lengths: three days, two days, series of one day and again from two days to week. The ratio is presented in Fig. 2.
Fig. 2. Time sequence of the ratio of the gas to aerosol fraction of air activity of
131
I observed in Krakow (presented in Fig. 1). Each bar is located at the date the sampling began.
aerosol can be considered higher than 106, which is close to the data published recently for environmental studies in Japan (Zheng et al., 2012). 3.3. Results for gamma emitters in dry and wet precipitation The results for the fallout are presented in Tables 3 and 4. All activity concentration and deposition data are calculated for the middle date of the considered sampling period. The activity concentration of precipitation presented in Table 3 is expressed in Bq/ m3; Table 4 presents basically the same results but calculated as deposition in Bq/m2. The results for cosmogenic nuclides, i.e. 22Na and 7Be, are also given in both Tables for comparison. The data covers period from 2011, March 11 till the end of October. The majority of samples were collected roughly over one month. The
samples differ significantly in volume of water from precipitation, i.e. from 10 dm3 for March, 28 till April 5, 2011, to 270 dm3 from July, 4 till August, 1 in 2011. The 131I was present in measurable amounts for samples collected before the 5th of April 2011. The 131I maximum activity concentration in atmospheric precipitation, i.e. rainwater with dry deposition dissolved taken together, reached 770 39 Bq/m3 in samples collected between March 28 and April 5, 2011. This data can be compared with results for USA given in the report of US Geological Survey and US Department of the Interior (Wetherbee et al., 2012). The maximal values for radionuclides activity concentration in wet precipitation in US compared with those for Poland are 50, 290 and 120 times higher (in US) for 131I, 137 Cs and 134Cs, respectively. For total maximum deposition those numbers are 580, 340 and 125, for 131I (for Wayoming), and 137Cs, 134 Cs (for California), respectively.
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though recorded at the level of fractions of mSv, still remained small. This can be compared to the estimated dose for inhabitants of Japan. 4.1. Impact of Chernobyl accident in Japan vs. Fukushima accident in Europe (Poland)
Fig. 3. The consistency test for results obtained with two independent aerosol sampling stations (ASS-500 and MASS-500) for results on activity concentration of aerosol fraction of 131I .
4. Discussion Isotopic composition of Fukushima plume in Kraków was the same as determined for other European countries (Masson et al., 2011). A Lithuanian report (Lujaniené et al., 2012) was the only one where plutonium with unusual isotopic ratio was claimed, hence fresh Fukushima release was concluded there. Nevertheless, it has neither been accompanied by other transactinides, nor confirmed elsewhere in Europe so far. Our constrain is two order of magnitude lower (106 compare to 104 reported there). One can notice that maximum for 131I activity concentration in the air from Fukushima accident in Kraków was about 6 mBq/m3, whereas in the Chernobyl cloud it was about 60 Bq/m3 (Mietelski et al., 1988), thus a factor of 104 between those numbers is recorded. The present results showed that the doses obtained by humans exposed to the Fukushima cloud in such a remote location as Poland are completely negligible, as they remain within the range of single nSv. The doses for Poles from Chernobyl accident
Traces of activity released at the Chernobyl accident were observed even in Japan. Detecting a European release in Japan, and a Japanese one in Europe, provide a kind of symmetry. Thus it seems interesting to compare the Chernobyl fallout in Japan with that from Fukushima detected in a Central European country such as Poland. For example, the deposition of 131I in May 1986 in Akita (Japan) was reported as nearly equal to 19 kBq/m2, while for 137Cs it was 414 Bq/m2 (Aoyama et al., 1987). These numbers for iodine and radiocesium are ca. 200 to ca. 50 times, respectively, bigger than those of Fukishima fallout reported presently for Poland (so they are at range of Fukushima fallout in US, reported in Wetherbee et al., 2012). A poorer enhancement of Chernobyl in Japan over Fukushima in Europe ratios can be noticed for the maximum gaseous and aerosol 131I activity concentration in the air. Such ratios found in 1986 in Tokaimura, Japan, were at the maximum close to 100 mBq/m3 and 300 mBq/m3 for aerosol and gaseous 131I , respectively (Ishida et al., 1988), which is from 16 to 50 times higher than the results for Fukushima cloud in Poland. However, the 131I maximum activity concentration in Chernobyl cloud over Japan was reported to have reached 0.8 Bq/m3 on the 5th of May 1986 (Imanaka and Koide, 1986), i.e. over 100 times more than the maximum for Fukushima plume observed in Krakow. The difference proves to be a bit bigger than expected from the estimated releases, as Fukushima release is believed to have been about 10% of the activity release from Chernobyl and rather not support the estimation of 43% for 137Cs release given in paper by Stohl et al. (2012). This is much closer to Chernobyl-Fukushima comparison from paper of Draxler and Rolph (2012). The other likely explanation is severe elimination of radioactive aerosol in Fukushima cloud over its way to Central Europe (Poland), which seems rather unlikely as the results for Central Europe are the maximum values reported for Europe (Masson et al., 2011).
Fig. 4. The lack of correlation between the ratio q (Eq. (2)) and activity concentration for the gaseous fraction of
131
I.
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Fig. 5. Correlation plot between the ratio q (Eq. (2)) for activity concentration of the gaseous fraction of sampler. No relation observed.
131
I trapped in a carbon cartridge and air volume passing through the air
Fig. 6. The lack of correlation between the ratio q (Eq. (1)) for activity concentration of the gaseous fraction of
4.2. Dynamic equilibrium between aerosol and gaseous fractions of 131 I Another suggestion can be made by analysing the aerosol part of the 131I activity ratio to any other aerosol-transported radionuclide, for example 137Cs. Fig. 7 presents the ratio of 131I to 137Cs activity recorded for filters, i.e. for the aerosol fraction. All activity results were divided into two populations one for days of relatively high and other for days of relatively low activity concentration, in relation to the general profile of activity changes over the specific period. The trivial part of changes in this ratio is due to radioactive decay. The presented solid curve (Fig. 7) depicts a radioactive decay evolution of this ratio for the population of high activity, starting from the initial values. The uncertainties for the experimental
143
131
I and the mean airflow rate trough the carbon cartridge.
values used to obtain the fit presented by the solid curve are small since the activity concentration for those points were relatively high, when compared to the others. The dashed curve fits the exponential decay to the value of 131I to 137Cs activity ratio for lower activity samples. Such a split in the activity ratio for the two populations can originate from various factors such as subsequent releases, having different ratios as suggested before (Masson et al., 2011), or different transport properties. Conceivably the high activity samples may originate from undisturbed transport trajectories, i.e. the plume not meeting rain or snow on its way, whereas the others of relatively low activities, from air masses disturbed with precipitations. But how is the ratio affected? In addition, interestingly enough, the fitted half life time of the presented exponential decay yields a half life time not of 131I (8.03 days) but
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Table 4 Activity deposition (dry and wet) for artificial and cosmogenic radionuclides during MarcheOctober 2011 (all results decay corrected for the middle of collection time). Collection time
Rain precipitation [mm]
131
7
134
11.03e28.03 28.03e5.04 5.04e29.04 29.04e30.05 30.05e4.07 4.07e1.08 1.08e6.09 6.09e3.10 3.10e31.10
13 4 71 84 69 120 62 13 8
<840 3.37 0.17 5.4 1.7 <270 <26 <180 <106 <83 <47
13.0 0.8 6.67 0.35 130.7 6.6 212.3 11 179.3 9.0 248.7 12.5 72.9 3.7 5.0 0.3 2.2 0.2
TOTAL Mar.eOct.
450
8.8a
871
a
I
Be
Cs [Bq/m2]
137
22
0.016 0.005 0.03 0.01 0.14 0.02 0.18 0.01 <0.02 <0.02 <0.015 <0.013 <0.013
<0.020 0.03 0.01 0.17 0.02 0.38 0.02 0.06 0.01 0.023 0.015 0.015 0.006 <0.014 <0.011
<0.015 <0.012 0.04 0.01 0.018 0.006 0.021 0.006 0.029 0.006 <0.012 <0.018 <0.013
0.37
0.68
0.11
Cs
Na
For 28 Marche29 April only.
both fitted curves give half life time of about 5 days, precisely 4.34 0.66 and 5.00 0.86 days (using GraphPad Prism v.4.0), for the solid and dashed curve, respectively. To reassume, the ratio of 131 I to 137Cs diminished with the half-life time two times shorter than the physical half-life time of 131I and two populations can be distinguished in the results (Fig. 7). Seeking the explanation to it, we suggest that might be attributed to two processes. Firstly, a transversal distribution of the radioactive cloud must be wider for gaseous substances then for aerosol ones. Secondly, the exchange between gaseous and aerosol components for radioiodine isotope occurs within the plume. The experimental points of the dashed curve, with relatively low activities, apparently represent the sides of the plume, whereas the solid line shows its central parts, with relatively high activities. Within the entire plume iodine from gaseous fraction turns into the aerosol fraction and vice versa, the gaseous turns into the aerosol. A dynamic exchange between those two phases seems very likely. These two effects combined together allow to provide an explanation for properties of the observed 131I to 137Cs activity ratios. The effective decay of 131I occurs faster than the physical half-life time, by the factor of two, because within the travelling plume approximately half of the iodine turns effectively into the gaseous form. Still, the low activity samples show higher aerosol iodine component, in comparison to 137Cs, with gaseous iodine turning back to the aerosol form, which is pronouncedly manifested for low active, side parts of the radioactive plum. Fig. 8
Fig. 7. The 131I/137Cs activity ratio recorded in Krakow in the aerosol fraction (air filters), the decay corrected for the middle date of sample acquisition over the period between March 27 and April 12 of 2011. Two populations of results are distinguished, one from relatively high activity samples, most likely from the main plume e squares and solid line fit; and the second from relatively low active samples, most likely from the sides of the main plume e triangles and dashed line fit. Both fits show the half-life time two times shorter than expected.
shows the activity ratios 131I/137Cs for aerosol samples as a function of the activity ratio of 131I aerosol to gaseous fraction. The samples with relatively low activities, i.e. the ones thought to have originated from the plume sides and represented with the dashed line fit in Fig. 7, seem to have higher content of the gaseous iodine in comparison to the aerosol iodine, which supports our hypothesis. Our results for rain compared with Korean results published recently (Lee et al., 2013) reveal strikingly surprising features. Despite huge difference in distance from Fukushima, we observed similar concentration of 131I at the maximum, whereas for radiocaesium our results are lower by an order of magnitude. We find this result very interesting and confirming the hypothesis of exchange between the gaseous and aerosol fractions of 131I , enabling a prolonged suspension of 131I in the air.
5. Conclusions The aerosol fraction of the air collected between March 21 and the end of May 2011 in Krakow revealed traces of 131I, 132I, 129mTe, 132 Te, 134Cs, 136Cs and 137Cs with the maximum observed on the 29th of March 2011. Even at the maximum the observed 131I activity concentrations were at the level of few mBq/m3, while for other radionuclides at a fraction of mBq/m3. Such amounts produce negligible doses at the level below 1 mSv. No traces of freshly released actinides were detected. The observed resulting fallout was at the level of a few Bq/m2. Beside the aerosol, also the gaseous fraction of 131I was detected within the similar period. The applied
Fig. 8. Activity ratios 131I (aerosol)/137Cs versus 131I aerosol/gaseous. Samples with relatively low activities, suggested to have originated from the plume sides e dashed line fit in Fig. 7 e seem to have higher content of the gaseous iodine in comparison to the aerosol iodine.
J.W. Mietelski et al. / Atmospheric Environment 91 (2014) 137e145
method for determining the gaseous 131I in a modified high volume aerosol sampler seems to work properly. The presented results were compared to the data on the Chernobyl plume data for Japan. The comparison shows the values for Chernobyl in Japan are higher by roughly two orders of magnitude over similar results during Fukushima accident observed in Central Europe. It may suggest that the real ratio of releases was higher by only 1 order of magnitude than the one calculated from the official reports. Finally, the great variability of activity concentration ratios between the aerosol fraction of 131I and other nuclides suggests an exchange between the gaseous and aerosol fractions of 131I to have occurred while contamination had been propagating, establishing a kind of dynamic equilibrium. We suggest that while propagating in the air the aerosol iodine is converted to gaseous with the effective half-life time similar to the physical half life time of 131I, i.e. about 8 days, reducing the observed 131I to 137Cs activity ratio in the aerosol by a factor of two, regarding its physical decay. On the other hand, the gaseous iodine is partially converted back into the more reactive forms, which then attracted the aerosol, hence they were detected in the aerosol fraction. Such an effect was noticeable in relatively low activity samples, most likely originating from the sides of the radioactive plume. Acknowledgements Parts of the presented research were carried out under the strategic research project “Technologies supporting the development of safe nuclear power” financed by the National Centre for Research and Development (NCBiR). Research Task “Development of methods to assure nuclear safety and radiation protection for current and future needs of nuclear power plants”, contract No. SP/ J/6/143339/11. References Aoyama, M., Hirose, K., Sugimura, Y., 1987. Deposition of gamma-emitting nuclides in Japan after the reactor-IV accident at Chernobyl. Journal of Radioanalytical and Nuclear Chemistry, Articles 116 (2), 291e306. Bysiek, M., Biernacka, M., Lipinski, P., September 2000. 3rd International Meeting on Low-Level Air Radioactivity Monitoring, Dabrowo Poland. Draxler, R.R., Rolph, G.G., 2012. Evaluation of the Transfer Coefficient Matrix (TCM) approach to model the atmospheric radionuclide air concentrations from Fukushima. Journal of Geophysical Research, Atmospheres 117. http:// dx.doi.org/10.1029/2011JD017205. Holm, E., Ballestra, S., 1989. Methods for Radiochemical Analyses of Plutonium, Americium and Curium, within the “Measurements of Radionuclides in Food and the Environment e a Guidebook”. In: IAEA Technical Report Series No. 295. IAEA Press. IAEA http://www.iaea.org/newscenter/news/2011/fukushima110311.html. Imanaka, T., Koide, H., 1986. Fallout in Japan from Chernobyl. Journal of Environmental Radioactivity 4, 149e153. Isajenko, K.A., Piotrowska, B., Stawarz, O., Kwiatkowska, I., 2011. “Japanese” cloud over Poland. Poste˛ py Techniki Ja˛ drowej 54 (3), 4e10 (in Polish). Ishida, J., Miyagawa, N., Watanabe, H., Asano, T., Kitahara, Y., 1988. Environmental radioactivity around Tokai-Works after the reactor accident at Chernobyl. Journal of Environmental Radioactivity 7, 17e27. Kierepko, R., Mietelski, J.W., 2010. Activity concentration of Plutonium in atmospheric precipitation. Nukleonika 55 (2), 201e204.
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_ S., Kapa1a, J., 2009. Kierepko, R., Mietelski, J.W., Borowiec, W., Tarasiewicz, S., B1azej, Plutonium traces in atmospheric precipitation and in aerosols from Krakow and Bialystok. Radiochimica Acta 97 (4e5), 253e255. LaRosa, J.J., Cooper, E., Ghods-Esphahani, A., Jansta, V., Makarewicz, M., Shawky, S., Vajda, N., 1992. Radiochemical methods used by the IAEA’s Laboratories at Seibersdorf for the determination of 90Sr, 144Ce and Pu radionuclides in the environment samples collected for the International Chernobyl Project. Journal of Environmental Radioactivity 17, 183e209. Lee, Sang-Han, Heo, Dong-Hye, Kang, Han-Byeol, Oh, Pil-Jae, Lee, Jong-Man, Park, Tae-Soon, Lee, K.B., Oh, J.S., Suh, Jung-Ki, 2013. Distribution of 131I, 134Cs, 137 Cs and 239,240Pu concentrations in Korean rainwater after the Fukushima nuclear power plant accident. Journal of Radioanalytical and Nuclear Chemistry 296, 727e731. Lujaniené, G., Bycenkiene, S., Povinec, P.P., Gera, M., 2012. Radionuclides from the Fukushima accident in the air over Lithuania: measurements and modelling approaches. Journal of Environmental Radioactivity 114, 71e80. MacMullin, S., Giovanetti, G.K., Green, M.P., Henning, R., Holmes, R., Vorren, K., Wilkerson, J.F., 2012. Measurement of airborne fission products in Chapel Hill, NC, USA from the Fukushima Dai-ichi reactor accident. Journal of Environmental Radioactivity 112, 165e170. Masson, O., Baeza, A., Bieringer, J., Brudecki, K., Bucci, S., Cappai, M., Carvalho, F.P., Connan, O., Cosma, C., Dalheimer, A., Didier, D., Depuydt, G., De Geer, L.E., De Vismes, A., Gini, L., Groppi, F., Gudnason, K., Gurriaran, R., Hainz, D., Halldorsson, O., Hammond, D., Hanley, O., Holey, K., Homoki, Zs, Ioannidou, A., Isajenko, K., Jankovick, M., Katzlberger, C., Kettunen, M., Kierepko, R., Kontro, R., Kwakman, P.J.M., Lecomte, M., Leon Vintro, L., Leppänen, A.-P., Lind, B., Lujaniene, G., Mc Ginnity, P., Mc Mahon, C., Mala, H., Manenti, S., Manolopoulou, M., Mattila, A., Mauring, A., Mietelski, J.W., Møller, B.S., Nielsen, P., Nikolick, J., Overwater, R.M.W., Palsson, S.E., Papastefanou, C., Penev, I., Pham, M.K., Povinec, P.P., Ramebäck, H., Reis, M.C., Ringer, W., Rodriguez, A., Rulík, P., Saey, P.R.J., Samsonov, V., Schlosser, C., Sgorbati, G., Silobritiene, B.V., Söderström, C., Sogni, R., Solier, L., Sonck, M., Steinhauser, G., Steinkopff, T., Steinmann, P., Stoulos, S., Sykora, I., Todorovic, D., Tooloutalaie, N., Tositti, L., Tschiersch, J., Ugron, A., Vagena, E., Vargas, A., Wershofen,a, H., Zhukova, O., 2011. Tracking of airborne radionuclides from the damaged Fukushima Dai-Ichi nuclear reactors by European networks. Environmental Science & Technology 45, 7670e7677. Mietelski, J.W., Broda, R., Sieniawski, J., 1988. Long lived isotopes in the Chernobyl radioactive cloud at Krakow. Journal of Radioanalytical and Nuclear Chemistry Letters 127 (5), 367e378. ska, M., Krupa, J.O., 1999. Plutonium isotopes Mietelski, J.W., Kozak, K., Wa˛ s, B., Jasin concentration in the ground level air and rain samples from krakow, Proceedings of 13-th radiochemical Conference; 19-24-th April 1998, Marianskie Laznie-Jachymov, Czech Republic. Czechoslovak Journal of Physics 49 (Suppl. 1), 115e117. Mietelski, J.W., Grabowska, S., Nowak, T., Bogacz, J., Gaca, P., Bartyzel, M., Budzanowski, M., 2005. Inhalation dose due to presence of I-131 in air above septic tank system of an endocrinology hospital. Radiation Protection Dosimetry 117, 395e401. NOAA, web page: http://www.sos.noaa.gov/Datasets/dataset.php?id¼332. Sill, C.W., 1987. Precipitation of actinides as fluorides or hydroxides for high resolution alpha spectrometry. Nuclear and Chemical Waste Management 7, 201e 215. Stohl, A., Seibert, P., Wotawa, G., Arnold, D., Bukhart, J.F., Eckhardt, S., Tapia, C., Vargas, A., Yasunari, T.J., 2012. Xenon-133 and caesium-137 releases into the atmosphere from the Fukushima Dai-ichi nuclear power plant, determination of the source term, atmospheric dispersion, and deposition. Atmospheric Chemistry and Physics 12, 2313e2343. Tanaka, Shun-ichi, 2012. Accident at the Fukushima Dai-ichi nuclear power stations of TEPCO e outline & lessons learned. Proceedings of the Japan Academy Series B Physical and Biological Sciences 88 (9), 471e484. http://dx.doi.org/10.2183/ pjab.88.47. Wetherbee, G.A., Debey, T.M., Nilles, M.A., Lehmann, C.M.B., Gay, D.A., 2012. Fission Products in National Atmospheric Deposition ProgramdWet Deposition Samples PRIOR to and Following the Fukushima Dai-Ichi Nuclear Power Plant Incident, March 8eApril 5, 2011. In: U.S. Geological Survey Open-File Report 2011e1277, p. 27. Zheng, J., Tagami, K., Watanabe, Y., Uchida, Sh, Aono, T., Ishii, N., Yoshida, S., Kubota, Y., Fuma, Sh, Ihara, S., 2012. Isotopic evidence of plutonium release into environment from Fukushima DNPP accident. Nature Scientific Reports 2 (304). http://dx.doi.org/10.1038/srep00304.
Contents lists available at ScienceDirect
Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv
Long-range transport of gaseous 131I and other radionuclides from Fukushima accident to Southern Poland Jerzy W. Mietelski a, *, Renata Kierepko a, Kamil Brudecki a, Pawe1 Janowski a, b, Krzysztof Kleszcz a, Ewa Tomankiewicz a a b
ski Institute of Nuclear Physics (IFJ PAN), Polish Academy of Sciences, 31-342 Kraków, Poland The Henryk Niewodniczan Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, A. Mickiewicza 30 Ave., 30-059 Kraków, Poland
h i g h l i g h t s Only volatile gamma emitters were found in Fukushima plume in Poland. Original method of measurements for gaseous 131I is presented. Results suggest Fukushima release below 10% of that from Chernobyl. The exchange between gaseous and aerosol fraction of 131I affects activity ratios.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 October 2013 Received in revised form 27 March 2014 Accepted 29 March 2014 Available online 30 March 2014
A serious accident at Fukushima Dai-Ichi NPP triggered radioactive emission to the atmosphere on 12 March 2011. The results of gamma spectrometric measurements of both gaseous and aerosol fraction of the air, collected in Krakow over the period from March 21 till the end of May 2011, as well as wet and dry deposition recorded from March till the end of October 2011, are presented in this paper. Krakow happened to be the first Polish location where radioactive isotopes characteristic for reactor releases, such as 131I, 132I, 129mTe, 132Te, 134Cs, 136Cs, and 137Cs, were detected. The maximum activity for aerosols equal to (5.73 0.35) mBq/m3, (0.461 0.041) mBq/m3 and (0.436 0.038) mBq/m3 for 131I, 134Cs and 137 Cs, respectively, was recorded for March 29, 2011. The data on the fallout are also given. The results of the radiochemical analysis of aerosol samples showed no traces of plutonium or americium isotopes associated with the disaster to be detected. The results of air activity concentration from Fukushima accident observed in Central Europe, Poland, in comparison to those of Chernobyl accident observed in Japan are presented and discussed. The comparison has revealed a discrepancy in the recognized relative scale of both accidents, and important difference in long distance transport of contamination, to exist. An attempt to explain the variation in the activity ratios between the aerosol fraction for 131I and 137Cs as resulting from exchange between the gaseous and aerosol fractions of 131I while the contamination had been propagating, is made. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Atmospheric radionuclides Fukushima accident Radiocesium Chernobyl Plutonium Radioactive fallout
1. Introduction A strong earthquake near Japan Islands, followed by enormous high tsunami on March 11, 2011 resulted in a serious overheating damage to have occurred in 3 reactors of the Fukushima Daiichi Nuclear Power Plant (Tanaka, 2012). Radioactive emission to the atmosphere began on March, 12 and lasted for over 2 weeks (IAEA, 2011). A radioactive plume migrated across the North Pacific,
* Corresponding author. E-mail address: [email protected] (J.W. Mietelski). http://dx.doi.org/10.1016/j.atmosenv.2014.03.065 1352-2310/Ó 2014 Elsevier Ltd. All rights reserved.
Northern America, Arctic and arrived over Europe from the northwestern direction (Masson et al., 2011, MacMullin et al., 2012). According to meteorological modelling available on the Internet, already on March 21e23 it was predicted for the cloud to be present over central Europe between March 24e27 (NOAA, 2011). Though at that time, the data on the release were scarce, from the spectra published in the open media one could expect only radioisotopes of volatile elements such as iodine, tellurium, and caesium to be detected. Among them iodine was the most interesting, as due to its complex chemistry, it can be transported both on aerosol and in gaseous fractions. A long-distance transportation, which is definitely the case for Japan release detectable in Central
138
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Table 1 Results of gamma spectrometric measurements of ground air activity concentration in Krakow following Fukushima accident for one day sampling cycle. Sampling start/stopa
V [m3]
Activity concentration [mBq/m3] 131
21/24.03 24/25.03 25/26.03 26/27.03 27/28.03 28/29.03 29/30.03 30/31.03 31.03/1.04 1/2.04 2/3.04 3/4.04 4/5.04 5/6.04 6/7.04 7/8.04 8/9.04 9/10.04 10/11.04 11/13.04 13/15.04 15/18.04 18/21.04 21/26.04 a
17 957 5975 6386 5256 7468 5385 5763 7264 6177 6396 6628 6230 8201 4261 6689 6554 6067 6788 6625 12 882 13 106 18 233 14 775 29 154
I aerosols
105 5 84 7 <12 840 37 1570 60 3600 200 5730 350 2910 120 908 42 668 33 718 35 2151 90 413 18 494 27 650 27 438 48 308 20 182 16 239 15 157 13 91 7 126 14 45 3 11 1
131
I gas
135 42 286 103 <48 604 170 2040 860 5200 1200 5220 340 3360 260 1120 110 1150 230 950 150 1520 410 625 95 510 220 930 250 680 320 775 90 940 190 1060 360 402 59 249 32 167 27 88 28 65 18
137
Cs
<9 <15 <9 <17 83 11 254 27 436 38 296 25 36 6 41 10 42 11 411 30 45 5 43 15 46 6 60 15 82 14 <24 42 5 40 8 <18 28 6 23 3 5.3 0.8
136
Cs
<7 <11 <7 <13 22 10 32 15 28 16 24 13 <11 <19 <18 27 5 <8 <28 <10 <20 <20 <18 <7 <10 <15 <11 2.4 1.1 <1
134
Cs
<5 <11 <36 16 8 105 20 206 35 461 41 307 28 35 8 75 22 54 17 420 50 56 7 44 13 45 8 67 27 64 21 25 10 45 16 37 11 18 5 32 6 14 2 6.5 0.8
132
Te/132I
<4 <8 <3 <9 45 10 109 17 124 39 <9 <8 <10 <10 41 10 <6 <15 <7 <10 <11 <9 <3 <5 <4 <8 11 7 32
7
Be
3810 4290 3800 3310 4680 4980 5690 6040 6330 5720 4340 7500 5220 3760 5490 4840 3960 2410 2740 3190 2420 2500 7650 6040
270 310 280 240 350 390 440 450 450 430 330 540 370 310 390 390 310 210 650 240 180 190 540 430
Year 2011.
Europe, i.e. over a 10 000 km distance, can result in a fractionation between gas and aerosol (ie. the ratio of the two fractions observed in Europe is not necessarily the same as was released in Japan). This ratio can be affected either by chemical reactions which may occur due to oxidation conditions in the air, sunlight, or exposition to UV radiation, also the physical removing of gasses and aerosols from radioactive cloud is different as well as their mutual exchange can happen. Thus it seems very interesting to study both aerosol and gaseous fractions of iodine isotopes in the nuclear accident cloud. Traces of all other nuclides in relation to iodine could also shed some light onto understanding differences in the air transport mechanism for different radionuclides. From the dosimetric point of view apart from measuring particular fraction of iodine from nuclear accidents, it is of vital importance to measure its gaseous fraction, since it can produce significant part of the dose from iodine. It is of greater importance for shorter transportation distances where higher iodine activity concentration in the air can be detected, so developing the method of gaseous iodine detection seems particularly important. 2. Material and methods 2.1. Sample collection Air sampling was carried out at one place, namely the Institute of Nuclear Physics in Krakow e IFJ PAN, 50.04 N, 19.58 E, 215 m a.s.l, with two aerosol samplers and one atmospheric precipitation collector. 2.1.1. Aerosol sampling The IFJ PAN operates two high volume aerosol samplers, namely the Aerosol Sampling Statione500 and MASS-500. The first one is a standard ASS-500 with the nominal airflow rate of 500 m3/h, designed and produced by CLOR (Central Laboratory for Radiation Protection, Warsaw). It works within the Polish Monitoring Network of Gamma-Ray Emitters in Ground-Level Air, coordinated by CLOR and Polish National Atomic Agency (PAA). The second one
is an older version of ASS-500 high volume sampler, extensively reconstructed and renamed as MASS-500 for Modified ASS-500, and it is IFJ property. All the aerosol samples were collected on Petryanov filters FPP-15-1.5 (polyvinyl chloride) displaying high good aerosol collecting properties (Bysiek et al., 2000). At the night of March 23, 2011 we received an informal communication that in Scandinavia iodine had been found (Masson et al., 2011), so in the morning of March 24, we changed the filters on MASS-500 and began an emergency mode operation; the filters were thus replaced every day till April 12. Then the sampling was run on a longer base, and ended with a whole week measurements at the end of April. The entire Polish network monitoring system consisting of 12 ASS-500 stations, turned from the week routine cycle to the emergency two-days-cycle on March 25 (Isajenko et al., 2011) and later, from April 1 till the end of the month, all the stations, including Krakow’s ASS-500, operated under a half-weekcycle. The measurements using MASS-500 produced 20 samples of aerosols deposited on the air filters from IFJ PAN (Table 1). 2.1.2. Gaseous sampling The gaseous fraction of the air was trapped in a double cartridge installed additionally inside the inlet of the MASS-500 station, behind the aerosol filter. This resulted in decreasing the flow rate from 500 m3/h to about 250 m3/h. The cartridge was tested with a , smaller aerosol sampler HVS-30 produced by Atmoservice, Poznan Poland, in an endocrinological hospital to measure 131I concentration in the air above septic tanks (Mietelski et al., 2005). The cartridge consists of two identical cassettes in a form of rectangular aluminium frames, filled with granular activated carbon impregnated with KI (IBJ-6, mesh size 2 mm, produced by Gryskand, Hajnówka, Poland). The carbon granulate is bordered both at the top and bottom of each cassette with fine stainless steel nets. Between the cassettes a rubber seal is inserted. The efficiency for gaseous iodine adsorption is calculated from the ratio of the activity found in the first and the second cassette under assumption that iodine was absorbed identically in both cassettes. Hence, with an infinite series of such cassettes, the absorbed activity would
J.W. Mietelski et al. / Atmospheric Environment 91 (2014) 137e145
139
Table 2 Results of radiochemical analyses and alpha spectrometric measurements for transactinides in aerosol filters from Krakow (T e measurement time, Y e chemical yield). Set
Samplinga start/stop
Volume [m3]
T [s]
Y [%]
239þ240
1 2
21.03/2.04 2.04/11.04
74 027 58 043
605 042 487 595
80.5 3.6 86.5 3.6
5.1 1.5 13.8 1.9
<0.6 0.9 0.3
Sampling start/stop
Volume [m3]
T [s]
Y [%]
241
242
21.03/2.04 2.04/11.04
74 027 58 043
1149789 858 498
59.7 1.4 38.1 1.2
0.4 0.3 4.3 1.2
1 2 a
Pu [nBq/m3]
Am [nBq/m3]
238
Pu [nBq/m3]
Cm [nBq/m3]
<0.1 <0.3
Year 2011.
decrease in a geometrical progression. Thus, the total activity is obtained from the formula for the sum of an infinite geometrical series, as long as the results for the first and second cassette are considered as the first and second element of this series, respectively.
S ¼
CA 1q
2.2. Gamma spectrometric measurements
(1)
where: S e gaseous 131I activity concentration in the air. q e the ratio between the activity found for 131I in the second (CB) and first (CA) cassette, namely:
q ¼ CB =CA
(2)
The total efficiency of gaseous iodine adsorption can be then defined as:
ε ¼
CA CB ¼ ¼ 1q S S CA
possibility of finding 131I in the fallout severely diminished, from the end of April we returned to evaporation under acidic conditions. The total number of atmospheric precipitation deposition samples was 9 (Table 3).
(3)
So, the total efficiency is known just by the ratio of activities found in two cassettes and there is no need to know if some iodine was lost. With 0.5 dm3 volume of carbon filling each cassette, a direct measurement of the exposed carbon in Marinelli beaker geometry is enabled. From March 21 till April 14, 2011 twenty samples of gaseous iodine were collected. The exposure time of the samples corresponds to the sampling time of the air filter on MASS-500 (Table 1). 2.1.3. Atmospheric precipitation sampling The fallout was collected over different periods, from a week to a month intervals with 2.2 m2 area collector made of stainless steel (Kierepko and Mietelski, 2010). Both, wet and dry deposition, were taken together in plastic barrels. In our typical procedure for fallout samples (rainwater, acidified with HNO3) a pre-concentration is done by evaporation to a small volume on a hot plate in a stainless steel pot to a small volume of about 0.5 L. The solution is then transferred to glass beaker. The containers are washed with HNO3 and wiped out with a paper filter, which are then ashed afterwards at 400 C. In the end, all the fractions are combined into one and evaporated in a polyethylene vial under an infrared lamp. As under such conditions losses of iodine isotopes would certainly take place, therefore the standard procedure was found inapplicable. To prevent such losses we initially tried to evaporate rainwater under basic conditions, i.e. without the acid added and the paper filter used. Three samples collected from March, 11th till April, 29th were treated that way. Unlike the case where evaporation follows acidification, the volume of the final solid sample, obtained with evaporation under basic conditions (pH w10, adjusted by adding ammonia), increased, most likely due to presence of carbonates. The higher volume raised the detection limits for activities measured with gamma spectrometry. As in second half of April the
Our laboratory has been accredited under Polish law for gamma spectrometric measurements (ISO 17025). All the filters, granulated carbon from gas iodine cassettes and evaporated precipitations were analysed by means of low background gamma spectrometer with HPGe detectors. Measurements were performed using three spectrometers, the majority of data were obtained using 11% relative efficiency Silena SpA (Italy) detector. Aerosol filters were measured once compressed to a 5 cm diameter, and about 4 mm high pellet. For such geometry the efficiency calibration was determined with a multi-gamma source SZN 40/10 by Polatom for all the spectrometers. Due to small detector efficiency the coincidence corrections for 134Cs activities were estimated to be below 5% (on the basis of the summing peak at 1.4 MeV) and were not introduced. The carbon from each cassette was transferred into a 0.5 dm3 plastic Marinelli beaker and measured. The activities were determined with a calibration performed for a standard mix gamma source SZM-3 by Polatom. For 364 keV 131I line this calibration was additionally verified by measurements of 131I liquid source obtained from the hospital. Evaporated rainwater was measured after at least 10 days from its collection due to time required to evaporate. Therefore, shortliving isotopes cannot be found. A special calibration for energies of 134Cs, 137Cs and 131I was applied. This calibration was carried out later, with diluted solutions of a certified liquid source. At each calibration the liquid solution was prepared for the final volume of the evaporated rainwater. The calibration for cosmogenic 7Be (477 keV) and 22Na (1275 keV) was performed with a linear approximation within the range 364 keVe1364 keV:
n o ln Eff ðEÞ ¼ a lnðEÞ þ b
(4)
where: Eff (E)e the detector efficiency for given gamma quantum energy E, a and b constants obtained from fit. All the results presented here are given for the day of measurement. 2.3. Radiochemical analysis At the time of Fukushima accident the disputable release of transactinides remained an open question, until tiny traces of some Fukushima origin Pu were reported recently to have been found in the environment (Zheng et al., 2012). In order to search for transactinides we made an effort to check whether any unusual actinides were present in the incoming air. The search, which followed gamma spectrometric measurements, for Pu, Am
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Table 3 Activity concentration decay corrected for the middle of the collection period for artificial and cosmogenic (for comparison) radionuclides found in rainwater (with dry deposition) in Kraków over MarcheOctober 2011. Collection time
Elapsed time sampling to meas. [days]
Rainwater volume [dm3]
131
11.03e28.03 28.03e5.04 5.04e29.04 29.04e30.05 30.05e4.07 4.07e1.08 1.08e6.09 6.09e3.10 3.10e31.10
127 15 56 103 77 106 105 100 95
30 10 160 190 155 270 140 30 18
<1480a 770 39 76 24 <3300 <390 <1500 <1700 <6300 <6000
I
7
134
Be
990 1518 1862 2550 2640 2100 1188 382 167
59 79 94 130 130 105 60 26 15
Cs [Bq/m3]
1.2 0.4 4.3 1.4 1.7 0.2 2.09 0.15 <0.4 <0.14 <0.20 <1.0 <1.5
137
Cs
<1.9 4.5 1.4 3.4 0.3 4.60 0.28 0.91 0.13 0.19 0.05 0.24 0.09 <1.1 <0.8
22
Na
<1.3 <2.6 0.58 0.21 0.31 0.25 0.14 <1.3 <1.7
0.16 0.07 0.09 0.05 0.06
a Only 131I result (presented limit) comes from direct measurement in 0.53 dm3 of rainwater in Marinelli beaker directly after end of collection, other results for this sample are obtained in measurement done after 127 days and full treatment (evaporation).
and Cm isotopes was performed for two sets of filters. The first set was combined from all the Petryanov filters from MASS-500 collected between March 21 and April 2. The second set consisted of filters collected between 2 and 11 of April, 2011. The combined samples were ashed at 600 C. Subjected later to wet mineralization with HF, HNO3, HCl and H3BO3 that followed adding the tracers 234Am and 242Pu (Mietelski et al., 1999; Kierepko et al., 2009). With plutonium adjusted as Puþ4 (LaRosa et al., 1992), it was separated from 8 M HNO3 on Dowex 1x8, followed with two co-precipitations, namely with oxalates and Fe(OH)3 and additional purification from thorium (TEVA resin). Americium and curium were separated from rare earths on Dowex-1 from acid-methanol solutions with ammonium thiocyanate added (Holm and Ballestra, 1989). Finally, from both americium/curium or plutonium fractions NdF3 sources were prepared (Sill, 1987) and measured by means of Silena AlphaQuattro spectrometer with Canberra PIPS detectors (450 mm2 area). The required quality of the analyses was verified with analyses of the reference material IAEA Soil 375. The determined activities of 266 27 mBq/kg and 55 4 mBq/kg, for 239þ240Pu and 238Pu, respectively, dropped within 95% confidential level. This material if of certified value for 1991 for 241Am, however, as Pu isotopic ratio reveals significant contribution of the Chernobyl fallout, one should assume additional increase of 241Am from 241Pu decay, hence the 1991 year value is no longer valid. For 241Am we obtained 0.30 0.03 Bq/kg, which with correction for ingrown of 241Am from 241Pu decay gives 0.15 0.02 Bq/kg. 3. Results 3.1. Gamma emitters in air samples We were the first laboratory in Poland to measure traces of 2011 Fukushima accident in the air in the morning of March 24, in the air filters exposed from 21 March 2011. The results for air samples are presented in Table 1. The presence of 131I, 132I, 129mTe, 132Te, 134Cs, 136 Cs and 137Cs in the air filters was established. These results were already partly published in a joint report from European air monitoring network (Masson et al., 2011). Measurable, i.e. above the detection limit, concentrations of caesium appeared two days later that those of iodine. The maximum activity for 131I, 134Cs and 137 Cs for aerosols of values of (5.73 0.35) mBq/m3, (0.461 0.041) mBq/m3 and (0.436 0.038) mBq/m3 for 131I, 134Cs and 137Cs, respectively, was observed on the 29th of March 2011. The average activity ratio for 134Cs to 137Cs was 1.11. The 131I time profile in the gaseous and aerosol fractions is presented in Fig. 1. The ratio between the activity in gas fraction 131I to aerosol fraction tended to change with time, reaching nearly 1 for the maximum activity, then
it increases to about 10 at mid-April. This ratio evolution with time is presented in Fig. 2. This can be understood this way: gas plume is subject of faster dispersion, so gas is detectable first, however due to faster dispersion the main part of plume is depleted in gas fraction. Eventually, the gas can stay in atmosphere for longer time then aerosols, therefore with time passing the gaseous component relatively rises up. Since the ASS-500 and MASS-500 were working under different cycles (modes) for changing samples the consistency of the results is not trivial to check. Thus in Fig. 3 the averages weighted by the value of total airflow calculated for 131I are displayed for 5 periods of 2011, namely March 21e25, March 25e28, March 28e30, March 30eApril 1, and April 1e4. The Pearson correlation factor R is equal to 0.98. However, the value of the straight line slope fit suggests about 9.7% on average systematic error resulting in higher values for MASS-500 in comparison to those for ASS-500. It is also important to note that MASS-500 and ASS-500 differ with regard to the method of air-flow measurement. While in the first one a vibration flow metre, adopted from the old version of ASS-500, is used, in the current version of ASS500 flow meter with Venturi nozzle is applied. Since it is hard to decide on the methods relative superiority, we do not provide any justification, apart from the comments on the systematic uncertainties level to be below 10%. The data obtained for the ratio q (Eq. (2)), which describes the efficiency of trapping the gaseous iodine in the carbon cartridge, were tested for any relation with such parameters as gaseous 131I activity concentration, total air volume and mean airflow rate. The results are presented in Figs. 4e6, respectively. As no correlation between the mentioned variables was manifested, it seems reasonable to conclude that method for gaseous iodine determination does not introduce systematic biases. 3.2. Search for alpha emitters in air filters The results of Pu and Am/Cm analysis are presented in Table 2. At the detection limit at a fraction of nBq/m3 neither the traces of 242 Cm were detected, nor unusual isotopic ratios for Pu isotopes, or between Pu and Am, were noticed. Activity concentration of 239þ240 Pu and 241Am were well within the typical level of few nBq/ 3 m (Mietelski et al., 1999, Kierepko and Mietelski, 2010). The second set revealed higher values, most likely due to strong western wind blowing at those days, which made the resuspension more effective. It may be thus concluded that in the traces of radioactive plume from Fukushima, measured in Krakow, we did not observed any measurable traces of transactinides of a fresh release, but solely resuspended remains of past (mostly global) fallouts. This suggests that the ratio between 137Cs and 239þ240Pu activity in Fukushima
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141
Fig. 1. Time sequence of 131I activity concentration for gaseous and aerosol fractions in Krakow, after the Fukushima accident. Each bar is located at the date when air sampling started, of different lengths: three days, two days, series of one day and again from two days to week. The ratio is presented in Fig. 2.
Fig. 2. Time sequence of the ratio of the gas to aerosol fraction of air activity of
131
I observed in Krakow (presented in Fig. 1). Each bar is located at the date the sampling began.
aerosol can be considered higher than 106, which is close to the data published recently for environmental studies in Japan (Zheng et al., 2012). 3.3. Results for gamma emitters in dry and wet precipitation The results for the fallout are presented in Tables 3 and 4. All activity concentration and deposition data are calculated for the middle date of the considered sampling period. The activity concentration of precipitation presented in Table 3 is expressed in Bq/ m3; Table 4 presents basically the same results but calculated as deposition in Bq/m2. The results for cosmogenic nuclides, i.e. 22Na and 7Be, are also given in both Tables for comparison. The data covers period from 2011, March 11 till the end of October. The majority of samples were collected roughly over one month. The
samples differ significantly in volume of water from precipitation, i.e. from 10 dm3 for March, 28 till April 5, 2011, to 270 dm3 from July, 4 till August, 1 in 2011. The 131I was present in measurable amounts for samples collected before the 5th of April 2011. The 131I maximum activity concentration in atmospheric precipitation, i.e. rainwater with dry deposition dissolved taken together, reached 770 39 Bq/m3 in samples collected between March 28 and April 5, 2011. This data can be compared with results for USA given in the report of US Geological Survey and US Department of the Interior (Wetherbee et al., 2012). The maximal values for radionuclides activity concentration in wet precipitation in US compared with those for Poland are 50, 290 and 120 times higher (in US) for 131I, 137 Cs and 134Cs, respectively. For total maximum deposition those numbers are 580, 340 and 125, for 131I (for Wayoming), and 137Cs, 134 Cs (for California), respectively.
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though recorded at the level of fractions of mSv, still remained small. This can be compared to the estimated dose for inhabitants of Japan. 4.1. Impact of Chernobyl accident in Japan vs. Fukushima accident in Europe (Poland)
Fig. 3. The consistency test for results obtained with two independent aerosol sampling stations (ASS-500 and MASS-500) for results on activity concentration of aerosol fraction of 131I .
4. Discussion Isotopic composition of Fukushima plume in Kraków was the same as determined for other European countries (Masson et al., 2011). A Lithuanian report (Lujaniené et al., 2012) was the only one where plutonium with unusual isotopic ratio was claimed, hence fresh Fukushima release was concluded there. Nevertheless, it has neither been accompanied by other transactinides, nor confirmed elsewhere in Europe so far. Our constrain is two order of magnitude lower (106 compare to 104 reported there). One can notice that maximum for 131I activity concentration in the air from Fukushima accident in Kraków was about 6 mBq/m3, whereas in the Chernobyl cloud it was about 60 Bq/m3 (Mietelski et al., 1988), thus a factor of 104 between those numbers is recorded. The present results showed that the doses obtained by humans exposed to the Fukushima cloud in such a remote location as Poland are completely negligible, as they remain within the range of single nSv. The doses for Poles from Chernobyl accident
Traces of activity released at the Chernobyl accident were observed even in Japan. Detecting a European release in Japan, and a Japanese one in Europe, provide a kind of symmetry. Thus it seems interesting to compare the Chernobyl fallout in Japan with that from Fukushima detected in a Central European country such as Poland. For example, the deposition of 131I in May 1986 in Akita (Japan) was reported as nearly equal to 19 kBq/m2, while for 137Cs it was 414 Bq/m2 (Aoyama et al., 1987). These numbers for iodine and radiocesium are ca. 200 to ca. 50 times, respectively, bigger than those of Fukishima fallout reported presently for Poland (so they are at range of Fukushima fallout in US, reported in Wetherbee et al., 2012). A poorer enhancement of Chernobyl in Japan over Fukushima in Europe ratios can be noticed for the maximum gaseous and aerosol 131I activity concentration in the air. Such ratios found in 1986 in Tokaimura, Japan, were at the maximum close to 100 mBq/m3 and 300 mBq/m3 for aerosol and gaseous 131I , respectively (Ishida et al., 1988), which is from 16 to 50 times higher than the results for Fukushima cloud in Poland. However, the 131I maximum activity concentration in Chernobyl cloud over Japan was reported to have reached 0.8 Bq/m3 on the 5th of May 1986 (Imanaka and Koide, 1986), i.e. over 100 times more than the maximum for Fukushima plume observed in Krakow. The difference proves to be a bit bigger than expected from the estimated releases, as Fukushima release is believed to have been about 10% of the activity release from Chernobyl and rather not support the estimation of 43% for 137Cs release given in paper by Stohl et al. (2012). This is much closer to Chernobyl-Fukushima comparison from paper of Draxler and Rolph (2012). The other likely explanation is severe elimination of radioactive aerosol in Fukushima cloud over its way to Central Europe (Poland), which seems rather unlikely as the results for Central Europe are the maximum values reported for Europe (Masson et al., 2011).
Fig. 4. The lack of correlation between the ratio q (Eq. (2)) and activity concentration for the gaseous fraction of
131
I.
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Fig. 5. Correlation plot between the ratio q (Eq. (2)) for activity concentration of the gaseous fraction of sampler. No relation observed.
131
I trapped in a carbon cartridge and air volume passing through the air
Fig. 6. The lack of correlation between the ratio q (Eq. (1)) for activity concentration of the gaseous fraction of
4.2. Dynamic equilibrium between aerosol and gaseous fractions of 131 I Another suggestion can be made by analysing the aerosol part of the 131I activity ratio to any other aerosol-transported radionuclide, for example 137Cs. Fig. 7 presents the ratio of 131I to 137Cs activity recorded for filters, i.e. for the aerosol fraction. All activity results were divided into two populations one for days of relatively high and other for days of relatively low activity concentration, in relation to the general profile of activity changes over the specific period. The trivial part of changes in this ratio is due to radioactive decay. The presented solid curve (Fig. 7) depicts a radioactive decay evolution of this ratio for the population of high activity, starting from the initial values. The uncertainties for the experimental
143
131
I and the mean airflow rate trough the carbon cartridge.
values used to obtain the fit presented by the solid curve are small since the activity concentration for those points were relatively high, when compared to the others. The dashed curve fits the exponential decay to the value of 131I to 137Cs activity ratio for lower activity samples. Such a split in the activity ratio for the two populations can originate from various factors such as subsequent releases, having different ratios as suggested before (Masson et al., 2011), or different transport properties. Conceivably the high activity samples may originate from undisturbed transport trajectories, i.e. the plume not meeting rain or snow on its way, whereas the others of relatively low activities, from air masses disturbed with precipitations. But how is the ratio affected? In addition, interestingly enough, the fitted half life time of the presented exponential decay yields a half life time not of 131I (8.03 days) but
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Table 4 Activity deposition (dry and wet) for artificial and cosmogenic radionuclides during MarcheOctober 2011 (all results decay corrected for the middle of collection time). Collection time
Rain precipitation [mm]
131
7
134
11.03e28.03 28.03e5.04 5.04e29.04 29.04e30.05 30.05e4.07 4.07e1.08 1.08e6.09 6.09e3.10 3.10e31.10
13 4 71 84 69 120 62 13 8
<840 3.37 0.17 5.4 1.7 <270 <26 <180 <106 <83 <47
13.0 0.8 6.67 0.35 130.7 6.6 212.3 11 179.3 9.0 248.7 12.5 72.9 3.7 5.0 0.3 2.2 0.2
TOTAL Mar.eOct.
450
8.8a
871
a
I
Be
Cs [Bq/m2]
137
22
0.016 0.005 0.03 0.01 0.14 0.02 0.18 0.01 <0.02 <0.02 <0.015 <0.013 <0.013
<0.020 0.03 0.01 0.17 0.02 0.38 0.02 0.06 0.01 0.023 0.015 0.015 0.006 <0.014 <0.011
<0.015 <0.012 0.04 0.01 0.018 0.006 0.021 0.006 0.029 0.006 <0.012 <0.018 <0.013
0.37
0.68
0.11
Cs
Na
For 28 Marche29 April only.
both fitted curves give half life time of about 5 days, precisely 4.34 0.66 and 5.00 0.86 days (using GraphPad Prism v.4.0), for the solid and dashed curve, respectively. To reassume, the ratio of 131 I to 137Cs diminished with the half-life time two times shorter than the physical half-life time of 131I and two populations can be distinguished in the results (Fig. 7). Seeking the explanation to it, we suggest that might be attributed to two processes. Firstly, a transversal distribution of the radioactive cloud must be wider for gaseous substances then for aerosol ones. Secondly, the exchange between gaseous and aerosol components for radioiodine isotope occurs within the plume. The experimental points of the dashed curve, with relatively low activities, apparently represent the sides of the plume, whereas the solid line shows its central parts, with relatively high activities. Within the entire plume iodine from gaseous fraction turns into the aerosol fraction and vice versa, the gaseous turns into the aerosol. A dynamic exchange between those two phases seems very likely. These two effects combined together allow to provide an explanation for properties of the observed 131I to 137Cs activity ratios. The effective decay of 131I occurs faster than the physical half-life time, by the factor of two, because within the travelling plume approximately half of the iodine turns effectively into the gaseous form. Still, the low activity samples show higher aerosol iodine component, in comparison to 137Cs, with gaseous iodine turning back to the aerosol form, which is pronouncedly manifested for low active, side parts of the radioactive plum. Fig. 8
Fig. 7. The 131I/137Cs activity ratio recorded in Krakow in the aerosol fraction (air filters), the decay corrected for the middle date of sample acquisition over the period between March 27 and April 12 of 2011. Two populations of results are distinguished, one from relatively high activity samples, most likely from the main plume e squares and solid line fit; and the second from relatively low active samples, most likely from the sides of the main plume e triangles and dashed line fit. Both fits show the half-life time two times shorter than expected.
shows the activity ratios 131I/137Cs for aerosol samples as a function of the activity ratio of 131I aerosol to gaseous fraction. The samples with relatively low activities, i.e. the ones thought to have originated from the plume sides and represented with the dashed line fit in Fig. 7, seem to have higher content of the gaseous iodine in comparison to the aerosol iodine, which supports our hypothesis. Our results for rain compared with Korean results published recently (Lee et al., 2013) reveal strikingly surprising features. Despite huge difference in distance from Fukushima, we observed similar concentration of 131I at the maximum, whereas for radiocaesium our results are lower by an order of magnitude. We find this result very interesting and confirming the hypothesis of exchange between the gaseous and aerosol fractions of 131I , enabling a prolonged suspension of 131I in the air.
5. Conclusions The aerosol fraction of the air collected between March 21 and the end of May 2011 in Krakow revealed traces of 131I, 132I, 129mTe, 132 Te, 134Cs, 136Cs and 137Cs with the maximum observed on the 29th of March 2011. Even at the maximum the observed 131I activity concentrations were at the level of few mBq/m3, while for other radionuclides at a fraction of mBq/m3. Such amounts produce negligible doses at the level below 1 mSv. No traces of freshly released actinides were detected. The observed resulting fallout was at the level of a few Bq/m2. Beside the aerosol, also the gaseous fraction of 131I was detected within the similar period. The applied
Fig. 8. Activity ratios 131I (aerosol)/137Cs versus 131I aerosol/gaseous. Samples with relatively low activities, suggested to have originated from the plume sides e dashed line fit in Fig. 7 e seem to have higher content of the gaseous iodine in comparison to the aerosol iodine.
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method for determining the gaseous 131I in a modified high volume aerosol sampler seems to work properly. The presented results were compared to the data on the Chernobyl plume data for Japan. The comparison shows the values for Chernobyl in Japan are higher by roughly two orders of magnitude over similar results during Fukushima accident observed in Central Europe. It may suggest that the real ratio of releases was higher by only 1 order of magnitude than the one calculated from the official reports. Finally, the great variability of activity concentration ratios between the aerosol fraction of 131I and other nuclides suggests an exchange between the gaseous and aerosol fractions of 131I to have occurred while contamination had been propagating, establishing a kind of dynamic equilibrium. We suggest that while propagating in the air the aerosol iodine is converted to gaseous with the effective half-life time similar to the physical half life time of 131I, i.e. about 8 days, reducing the observed 131I to 137Cs activity ratio in the aerosol by a factor of two, regarding its physical decay. On the other hand, the gaseous iodine is partially converted back into the more reactive forms, which then attracted the aerosol, hence they were detected in the aerosol fraction. Such an effect was noticeable in relatively low activity samples, most likely originating from the sides of the radioactive plume. Acknowledgements Parts of the presented research were carried out under the strategic research project “Technologies supporting the development of safe nuclear power” financed by the National Centre for Research and Development (NCBiR). Research Task “Development of methods to assure nuclear safety and radiation protection for current and future needs of nuclear power plants”, contract No. SP/ J/6/143339/11. References Aoyama, M., Hirose, K., Sugimura, Y., 1987. Deposition of gamma-emitting nuclides in Japan after the reactor-IV accident at Chernobyl. Journal of Radioanalytical and Nuclear Chemistry, Articles 116 (2), 291e306. Bysiek, M., Biernacka, M., Lipinski, P., September 2000. 3rd International Meeting on Low-Level Air Radioactivity Monitoring, Dabrowo Poland. Draxler, R.R., Rolph, G.G., 2012. Evaluation of the Transfer Coefficient Matrix (TCM) approach to model the atmospheric radionuclide air concentrations from Fukushima. Journal of Geophysical Research, Atmospheres 117. http:// dx.doi.org/10.1029/2011JD017205. Holm, E., Ballestra, S., 1989. Methods for Radiochemical Analyses of Plutonium, Americium and Curium, within the “Measurements of Radionuclides in Food and the Environment e a Guidebook”. In: IAEA Technical Report Series No. 295. IAEA Press. IAEA http://www.iaea.org/newscenter/news/2011/fukushima110311.html. Imanaka, T., Koide, H., 1986. Fallout in Japan from Chernobyl. Journal of Environmental Radioactivity 4, 149e153. Isajenko, K.A., Piotrowska, B., Stawarz, O., Kwiatkowska, I., 2011. “Japanese” cloud over Poland. Poste˛ py Techniki Ja˛ drowej 54 (3), 4e10 (in Polish). Ishida, J., Miyagawa, N., Watanabe, H., Asano, T., Kitahara, Y., 1988. Environmental radioactivity around Tokai-Works after the reactor accident at Chernobyl. Journal of Environmental Radioactivity 7, 17e27. Kierepko, R., Mietelski, J.W., 2010. Activity concentration of Plutonium in atmospheric precipitation. Nukleonika 55 (2), 201e204.
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