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Journal of Environmental Radioactivity 114 (2012) 131e137
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Journal of Environmental Radioactivity
journal homepage: www.elsevier .com/locate/ jenvrad
Detection of Fukushima Daiichi nuclear power plant accident radioactivetraces in Monaco
M.K. Pham*, M. Eriksson, I. Levy, H. Nies, I. Osvath, M. BettiEnvironment Laboratories, International Atomic Energy Agency, 4 Quai Antoine 1er, MC 98000, Monaco
a r t i c l e i n f o
Article history:Received 10 August 2011Received in revised form4 January 2012Accepted 16 January 2012Available online 29 February 2012
Keywords:AtmosphereFukushima DaiichiAir massesScavengingRadionuclides
* Corresponding author. Tel.: þ377 97 97 72 27; faxE-mail address: [email protected] (M.K. Pham).
0265-931X/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.jenvrad.2012.01.010
a b s t r a c t
Daily air monitoring of radionuclides in the Principality of Monaco (43�730N, 7�430E) after the FukushimaDaiichi nuclear power plant accident showed that only Iodine-131 (131I) and Caesium isotopes (134Csand 137Cs) were detected. The peak of 131I varied and reached its maximum betweenMarch 29th and April5th, meanwhile both peaks of 134Cs and 137Cs arrived later and attained amaximum between April 1st and4th. Their maximum activity concentrations in air were 354, 30, and 37 mBq m�3 respectively. The 134Csto 137Cs activity ratio was close to 1, which is different from that one observed after the Chernobyl accident(around 0.54). Up to 95% of caesium isotopes were washed out by wet scavenging during 27e28th ofMarch, where the maximum deposition rates of 134Cs and 137Cs (13.7 and 19.1 mBq m�2 day�1, respec-tively) were observed. The significant input of 134Cs and 137Cs into the Mediterranean seawater column(30 m depth) was detected later, on the 24th of May. Radioisotopes of caesium and iodine were found farabove the applied detection limits, but still with no concern for harmful radiation exposure and publichealth. The contamination gradually decreased in air and activity concentrations returned to backgroundvalues after one or two months.
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1. Introduction
Radioactive releases to the atmosphere from the crippledFukushima Daiichi reactors started on March 12th, 2011. Morevolatile and/or particulate bound isotopes and radionuclides weretransported across the Pacific towards the North American conti-nent and around the northern hemisphere (CTBTO, 2011; Takemuraet al., 2011; Qiao et al., 2011). Traces of contaminated air masseswere detected in most of European countries despite dispersionandwashout along the trip of the contaminated air masses (Massonet al., 2011; Pittauerová et al., 2011). In Europe, the first signs of thereleases arrived in Iceland seven days after the release while thefirst peak of activity level was observed between March 28th and30th. The starting of plume was in the northwest and movedtowards southeast with a maximum observed in Central Europe. InMonaco (43�730N, 7�430E) sampling of aerosols and the rain or dryfallout collection were started daily on the 18th of March on theroof of NAEL-Monaco premises. It allowed determining the quan-tity of detectable radionuclides in aerosol samples as well as inprecipitation (dry or wet) samples, to follow the variation of theiractivity concentration and their deposition rates with time.
: þ377 97 97 72 73.
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2. Material and methods
The sampling station was located on the roof of the IAEA-NAELbuilding of the Principality of Monaco (43�500 N, 7�300 E), which is15 m above the ground level, north-western of Mediterranean Sea.The airfiltering systemusedwasmodel ISAP 2000 (Fully AutomatedHigh-Volume Aerosol Sampling Device, produced by INGENIEUR-ÜRO SCHULZE AUTOMATISIERUNGSTECHNIK, Germany). Thedeviceworked with a high precision volumetric flow rate controllerwith linear flow sensor, scaled by controlling temperature andpressure STP (standard temperature and pressure). The samplingwas done daily (starting from 9 am for one cycle of 24 h for eachfilter) from 18th March to 4th April and then every two-three daysuntil 7th May 2011. One filter magazine contained 30 filters. Quartzmicrofiber filters of 0.8 mm pore size and dimensions of 150 mmwere used. The typical air flow rate was 100 m3 per hour. The totalsampled air volumewas between 2000 and 6500m3. The ISAP 2000air filter system used was not equipped with charcoal trap, inconsequence only particulate radionuclides (especially hereparticulate 131I) was collected. The air sampler was protected witha locked cover to avoid direct input of rain. The filters were pressedand analysed for gammaemitting radionuclides bymeans of gammaspectrometry in calibrated geometry.
The precipitation sample was collected using a 2 � 2 m2 stain-less steel funnel collector, which was installed 15 m above the
1 Tokyo Electric Power Company.2 Ministry of Education, Culture Sports, Science and Technology, Japan.
M.K. Pham et al. / Journal of Environmental Radioactivity 114 (2012) 131e137132
ground level with the wall height of the sampler as high as 2.5 m.This collector, designed to prevent evaporation of rainfall, consistedof 3 parallel polyethylene containers (capacity of 200 L each).During rain periods the acidified samples (20e40 L) were takenfrom homogenous bulk samples to determine the activityconcentration for the total (wet þ dry) deposition. If it was notraining during this period, the samplewas collected by cleaning thesurface of the collector system with diluted HCl (pH ¼ 2) todetermine the dry fallout deposition. In cases of low rain deposi-tion, the sample was collected by cleaning the surface of thecollector system with acidified distilled water, combined withwhatever rainfall was collected. The samples were then concen-trated by evaporation to 100 mL and analysed by gamma spec-trometry in well-defined and calibrated geometry.
Further investigation on the input of 134Cs and 137Cs to theseawater column was studied. The activity ratios, 134Cs/137Cs (i.e.the Fukushima contribution, assuming no 134Cs from other sources)were determined in large volume samples (up to 5000 m3) ofMediterranean Sea sampled near the Oceanographic Museum inMonaco at a water depth of 30 m (43�43.080N, 07�25.060E). Thewater sampling was performed in-situ by pumping filtered (1 mm)seawater through copper ferrocyanide-impregnated cotton-woundcartridge filters (Roos et al., 1994), i.e. in this case no Cs radio-chemical yield determination by 134Cs tracer was used. Thesesamples were taken twice a month, starting from mid-April. Inaddition to the in-situ seawater samples, a separate sample wastaken where the radiochemical yield determination with 134Cs wasadded for the determination of the 137Cs activity concentration. Thecotton-wound cartridge filters were ashed in the furnace (to 400 �Cmaximum) and analysed in the very low-background level anti-Compton underground gamma spectrometry.
2.1. Determination of the activity concentrations of gamma emitters
Activities of the samples collected were measured by gammaspectrometry using coaxial HPGe detectors (Canberra IndustriesInc. USA), which were located in the IAEA-NAEL undergroundlaboratory. Details of the low-background gamma-ray detectionsystem and calibration procedures are described elsewhere(Povinec et al., 2004, 2005). The uncertainties reported are propa-gated errors arising from the one sigma counting error due todetector efficiency calibration and background correction, using theformulae of uncertainty calculation previously described (Dovleteand Povinec, 2004). The calculated activities were corrected forradioactive decay to the mid-collection period. Typical propagateduncertainties were from 2 to 10%, depending on the activity levelsof different radionuclides detected. Meteorological data for thesampling station for each sampling period were obtained usingKIMO system (which contains software named KILOG which allowsquerying, retrieving and processing the data recorded by temper-ature, humidity and pressure recorders. Recorders and KILOG aredeveloped by the KIMO company, France) directly located at thesampling site.
3. Results and discussions
The analysis of gamma spectra of aerosol and precipitationsamples showed that only 131I, 134Cs and 137Cs were detected inMonaco air after the Fukushima Daiichi accident. The gamma linesfromnatural origin radionuclides such as 7Be, 40K, 210Pb and radiumdaughters (214Bi, 214Pb.) were of course also observed in thesegamma spectra. The temporal changes of 7Be, 137Cs and 210Pbactivity concentrations in surface air at Monaco for a long period(1997e2010) and their correlation with meteorological parametershave been discussed in a previous publication (Pham et al., 2011). In
this paper wewill treat only radionuclides issued from the accident,which were detected during the period 23rd of March until 8th ofMay 2011. Two different origin radionuclides 7Be (cosmic) and 210Pb(terrestrial) were used to interpret the data together with localmeteorological parameters.
The arrival and the diffusion of these radionuclides over allEuropean countries after Fukushima events as well as back-trackingtrajectory were described elsewhere (Masson et al., 2011, http://www.zamg.ac.at/; http://www.irsn.fr/FR/popup/Pages/irsn-meteo-france_Film-Global_8avril.aspx; http://www.kantei.go.jp/foreign/kan/topics/201106/iaea_houkokusho_e.html; http://www.nisa.meti.go.jp/english/files/en20110412-4.pdf, etc.).
In this paper we will discuss only the activity concentrations ofthese radionuclides in aerosol and precipitation samples and theirevolution with time. More investigation of the fate of these radio-nuclides in soil after deposition will be done later for 134Cs and137Cs. The 131I was no longer detectable after one or two monthsdue to its short life time.
3.1. Radionuclides in aerosol samples
Following the Chernobyl accident on the 1ste3rd of May 1986,more than 28 radionuclides (long and short half-lives) mainlyfission products after the nuclear disaster were detected in Monacoair (Ballestra et al., 1987; Whitehead et al., 1988). This abundance ofradionuclides was due to the proximity of Monaco with the acci-dent site in Ukraine and to the occasional EasteWest air circulation.The gamma spectra of aerosol samples taken inMarch 2011 showedonly significantly peaks of 131I (364.5 keV, T1/2 ¼ 8.02 days), 134Cs(604, 795 keV, T1/2 ¼ 2.07 years) and 137Cs (661.5 keV, T1/2 ¼ 30years) that were attributable to Fukushima, and 7Be (477.6 keV),210Pb (46.5 keV) that were attributed to the cosmic and naturalterrestrial origin, respectively. The activity concentrations of theseradionuclides as well as 7Be and 210Pb are shown in the Table 1. Thevariations of 131I, 134Cs and 137Cs activity concentrations (and theiractivity ratios) with time are in Fig. 1 and Fig. 3, respectively. Theother significant peaks of 214Pb (352 keV) and 214Bi (609 keV)(radium daughters) were also observed but not subject to be dis-cussed in this paper.
Many more volatile or non-volatile radionuclides were releasedfrom Fukushima Daiichi. Japanese data from the near-field pub-lished by TEPCO1 and MEXT2 indicated high concentrations in theenvironment of Cs-isotopes and 131I, but significantly lower activ-ities for others such as 90Sr and plutonium isotopes. However only131I, 134Cs and 137Cs could be detected inmost of European countriesbecause of dispersion and washout along the trip of the contami-nated air masses (Masson et al., 2011).
There were several peaks of particulate 131I and it reached itsmaximum between March 29th and April 5th (Fig. 1, Table 1),meanwhile both peaks of 134Cs and 137Cs arrived later and attaineda maximum between April 1st and 4th (Fig. 3, Table 1). The fluc-tuation of particulate 131I with peaks of 290, 270 and 354 mBq m�3
on the 29th of March, 2nd and 5th of April, respectively and witha lower magnitude (87 mBq m�3) on the 19th of April allowed tosuggest that there were more than one wave/plume of radionu-clides that arrived over Monaco. It is interesting to notice that thesepeaks of 131I coincide with the maximum temperatures duringthese days (Fig. 1), when lower humidity and slightly higher pres-sure were observed (Table 1), although the variation of thesemeteorological parameters did not show much effect on the 7Beand 210Pb activity concentrations in air, as confirmed in our
Table 1Activity concentration of radionuclides in Monaco air between 23rd March and 7th May 2011.
Date I-131 mBq m�3 Cs-134 mBq m�3 Cs-137 mBq m�3 Be-7 mBq m�3 Pb-210 mBq m�3 T �C H % P mBar
23-Mar-11 7.8 � 4.6 2.7 � 1.2 3.9 � 3.2 3390 � 260 780 � 50 17.5 35 96024-Mar-11 8.3 � 1.4 0.4 � 0.2 0.7 � 0.5 3520 � 260 790 � 50 16.8 55 102825-Mar-11 8.5 � 1.5 0.9 � 0.4 1.4 � 0.5 3220 � 240 780 � 50 15.6 64 102026-Mar-11 28 � 3 0.4 � 0.2 1.5 � 0.5 3160 � 240 910 � 50 16.0 65 101427-Mar-11 33 � 4 0.6 � 0.3 1.1 � 0.3 3200 � 240 740 � 40 13.8 83 101229-Mar-11 290 � 20 9.9 � 2.6 13 � 3 2440 � 190 410 � 40 17.1 66 101230-Mar-11 215 � 17 7.5 � 1.6 7.6 � 2.3 1660 � 130 620 � 40 15.1 74 101431-Mar-11 190 � 15 7.6 � 1.9 8.2 � 2.6 1800 � 140 750 � 40 17.5 67 101801-Apr-11 270 � 20 23 � 2 23 � 2 2070 � 160 580 � 40 17.8 72 102002-Apr-11 200 � 15 30 � 2 32 � 2 3420 � 260 815 � 50 17.4 72 101704-Apr-11 220 � 20 30 � 3 37 � 4 3920 � 300 830 � 50 17.1 73 101205-Apr-11 354 � 27 21 � 2 23 � 2 6590 � 490 580 � 40 19.7 52 101907-Apr-11 156 � 12 20 � 1 19 � 1.4 6600 � 490 870 � 50 19.4 63 100009-Apr-11 99 � 8 20 � 1 22 � 1 6140 � 460 1008 � 55 18.5 72 101811-Apr-11 48 � 4 9 � 1 12 � 1 5970 � 450 1266 � 70 21.1 63 101814-Apr-11 76 � 6 12 � 1 14 � 1 5690 � 420 320 � 20 20.0 65 101416-Apr-11 87 � 7 5.6 � 0.7 8.5 � 0.8 4650 � 350 540 � 30 21.6 35 101819-Apr-11 48 � 4 9.8 � 0.6 11.5 � 0.7 5400 � 400 740 � 40 20.7 41 100021-Apr-11 38 � 4 6.5 � 0.8 7.7 � 0.8 5740 � 430 905 � 60 19.9 43 101524-Apr-11 8.2 � 0.8 2.4 � 0.2 3.4 � 0.3 5020 � 370 624 � 30 18.1 69 101327-Apr-11 7.4 � 0.9 2.3 � 0.2 3.4 � 0.3 4920 � 370 860 � 50 20.6 57 100705-May-11 3.7 � 1.3 0.6 � 0.5 0.7 � 0.5 7620 � 570 835 � 50 20.9 49 101707-May-11 5 � 1 1.5 � 0.2 2.1 � 0.2 9790 � 730 940 � 60 21.5 40 1020
M.K. Pham et al. / Journal of Environmental Radioactivity 114 (2012) 131e137 133
previous observation (Pham et al., 2011). However, the variation of210Pb issued from radon emanation from the terrestrial crust seemsto coincidence with some peaks of 131I with a day or two delay(Fig. 2), showing that the radon emanationwas probably influencedby higher temperatures during these days as well as this particulate131I, but the radon daughter (210Pb), which is not volatile, attainedits maximum activity concentration later.
From the study of other groups in Europe, the average gaseous/total 131I ratio was 77.2% (Masson et al., 2011). This is the sameaverage value as the one found after Chernobyl (Cambray et al.,1987). According to the measurements taken on the FukushimaDaiichi NPP site from March 22nd to April 4th, the average partic-ulate/gaseous 131I ratio was 0.46 � 0.17, i.e. a gaseous/total ratio of71% � 11%. This is roughly the same as the one observed in Europe,leading to the assumption that 131I remains mainly in its gaseousform during transport. A rough estimate of the total 131I inventory
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Fig. 1. Activity concentration of 131I in aerosol samples collected in Monaco (blue line) and thfigure legend, the reader is referred to the web version of this article.)
(around 1 PBq) that passed over Europe during this period is<1% ofthe released amount (150 PBq, NISA Japanese Agency http://www.nisa.meti.go.jp/english/files/en20110412-4.pdf).
The 134Cs and 137Cs activity concentration maxima (30,37 mBq m�3, respectively) were detected in Monaco air on the 1stand 4th of April, whereas some other smaller contaminated airmasses arrived later on the 9th, 14th and 19th of April (Fig. 3),meanwhile the time and spatial average values from 20th of Marchto 12th of April in Europe were about 76 and 72 mBq m�3, for 137Csand 134Cs respectively with a maximum value of 750 mBq m�3 inLodz, Poland between 28th and 30th of March (Masson et al., 2011).It would be relevant to notice that 134Cs and 137Cs activityconcentrations in Monaco in a normal situation (before theFukushima event) are not detectable for 134Cs (with the detectionlimit at 604 keV of less than 0.1 mBq m�3) and around0.1e0.5 mBq m�3 for 137Cs, respectively (Pham et al., 2011). And also
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Fig. 2. Activity concentration of 131I (blue line), 7Be (red line) and 210Pb (green line) in aerosol samples collected in Monaco.
M.K. Pham et al. / Journal of Environmental Radioactivity 114 (2012) 131e137134
it would be relevant to notice that a slightly higher concentration of137Cs in comparison with 134Cs is due to the contribution of re-suspension of 137Cs from soil surface. This contribution is esti-mated around 20% if considering that 134Cs/137Cs ratio is equal to 1in aerosol sample. A rough estimate of the 137Cs inventory (around0.2 PBq) that passed over Europe during this period is around 1e3%of the released amount (6e12 PBq of 137Cs, NISA Japanese Agencyhttp://www.nisa.meti.go.jp/english/files/en20110412-4.pdf).
In contrast to iodine behaviour, which was mainly found ingaseous form which then disappeared due to a short half-life (8.02days), caesium was rapidly bound to aerosols and thus highlysubject to washout removal by dry or wet deposition. Here we cansee the decrease of caesium isotope activities in air mainly due tothe heavy rain in 27e28th of March (Fig. 3) (see more detail below
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Fig. 3. Activity concentration of 134Cs and 137Cs and their a
for wet and dry deposition). Meteorological local conditions such astemperature, humidity and pressure seemed to have no effect onthe variation of caesium concentrations, confirming our previousstudy (Pham et al., 2011).
3.2. Comparison of 137Cs activity concentration with other events
The comparison of 137Cs activity concentration with otherevents such as Chernobyl in 1986 and Algeciras in 1998 are shownin the Fig. 4. The peak of 137Cs observed in Monaco after theFukushima incident was much lower than the maximum observedfollowing the Chernobyl accident (2500 times lower) (Ballestraet al., 1987) or Algeciras accident (3 times) (Pham et al., 1999,2011). It is notable that the 134Cs to 137Cs activity ratio was about
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Fig. 4. Comparison of 137Cs concentration in the Monaco air from the Fukushima accident with the Chernobyl (note: 137Cs values of Algeciras and Fukushima events are on the rightvertical axis).
M.K. Pham et al. / Journal of Environmental Radioactivity 114 (2012) 131e137 135
0.54 after the Chernobyl accident (Whitehead et al., 1988), indi-cating a much longer burn-up of the nuclear fuel at Fukushimareactors. The Chernobyl accident occurred in connection witha long lasting graphite fire with high temperatures, resulting in farreaching contamination also from less volatile radionuclides and intransport to higher atmosphere.
3.3. Radionuclides in the precipitation or dry fallout samples
The activity concentration of 134Cs and 137Cs in the washoutsamples (by dry and/or wet deposition) and their deposition rates,including the precipitation rates during period studied are in theTable 2 and Fig. 5. Some data of sample collection for January andFebruary andMay before and after Fukushima accident were addedto allow the determination of the important washout of theseradionuclides by precipitation scavenging. The activity concentra-tion is expressed in mBq L�1 in precipitation case and the depositionrate of radionuclides is expressed in mBq m�2 day�1.
The activity concentration of 134Cs was around its detection limit(10 mBq L�1) in January, Februaryanduntil 26th ofMarch,meanwhilethe 137Cs activity concentration was observed at 200e590 mBq L�1,which is equivalent with 480e2350 mBq m�2 day�1 (the conver-sion factor, figured in the last column in the Table 2, is done by takinginto account the precipitation rate). This 137Cs was due to local re-suspension as found in a previous study (Pham et al., Submitted forpublication). The 134Cs activity concentration in precipitationduring weekend 27e28th March reached 980 mBq L�1 (100 times
Table 2Activity concentration of caesium and their deposition rates in the precipitation of Mona
Date Cs-134 mBq L�1 Cs-134 mBq m�2 day�1 C
January LLD LLDFebruary LLD LLD01e26-March LLD LLD27e28-March 980 � 60 13,740 � 790 128 Marche8 April 620 � 309 Aprile4 May 1220 � 50 730 � 30 104e31 May 570 � 100 270 � 50 1
LLD: Lower Limit Detection.
higher than detection limit), or equivalent of 13,700 mBq m�2 day�1,meanwhile the 137Cs activity concentration attained 1370 mBq L�1, orequivalent of 19,100 mBq m�2 day�1. The difference of activityconcentrations between 134Cs and 137Cs is due to the contribution of137Cs re-suspension, which is estimated around 28% (i.e. the differ-ence between two values 980 and 1370 mBq L�1 of 134Cs and 137Cs,respectively, divided by the 137Cs value of 1370 mBq L�1). Thiscontributionfitswellwith that found in the aerosol samples of above20%. From28thMarch to 8thApril therewas no precipitation and thedeposition rates of 134Cs and 137C were due to dry deposition andwere 620 and680 mBqm�2 day�1, respectively. Theseweremuch less(44e56 times) than the deposition rates due to the precipitationduring 27e28th of March. The deposition rates of 134Cs and 137Cswere rather constant from 9th of April to 11th of May(620e680 mBq m�2 day�1 for 134Cs and 730e940 mBq m�2 day�1 for137Cs, respectively) and became significantly lower for 134Cs(270 mBq m�2 day�1) during the rest of May, where still littleprecipitation occurred. The important peak of 134Cs and 137Cs activityconcentrations or their important deposition rates during 27e28thof March shows that almost 90e95% of caesium radionuclideswere washed out by the precipitation (Fig. 5). The smaller peaks(5e10%) of both 134Cs and 137Cs deposition in the following days (28Marche08 April and 09 Aprile04 May, Fig. 5) would probably fit tothe next received wave/plume of radionuclides (see above in the“Radionuclides in aerosol samples” section) or the re-suspension inaerosol samples, and theywere progressivelywashed out by dry andwet scavenging (08e31 May, Fig. 5).
co.
s-137 mBq L�1 Cs-137 mBq m�2 day�1 Precipitation
mm mm day�1
330 � 80 1130 � 280 95 3.4200 � 80 480 � 200 91 2.4590 � 150 2350 � 600 104 4370 � 50 19,100 � 700 28 14
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Fig. 5. Deposition rate of 134Cs and 137Cs in Monaco air following Fukushima accident.
M.K. Pham et al. / Journal of Environmental Radioactivity 114 (2012) 131e137136
3.4. Radionuclides in the seawater at 30 m depth
Radio-caesium originated from the Fukushima NPP accidentwas first detected in these seawater samples on the 24th of May2011, i.e. 54 days after the main plume passed Monaco. The reasonof the delay can be explained because the samples were taken fromthe 30m depth meaning that a lag time can be expected for verticalmixing. The seawater concentration of 137Cs was about1.8 � 0.1 mBq L�1, of which 0.26% (�0.06%) originating from theFukushima accident assuming a 134Cs/137Cs ratio is 1 in theFukushima fallout.
4. Conclusion
The daily air monitoring of radionuclides originated from theFukushima Daiichi nuclear power plants accident in Monaco(43�500N, 7�350E) showed that only 131I, 134Cs and 137Cs weredetected. There were several peaks of 131I and reached itsmaximum between March 29th and April 5th, whereas the highestconcentration of 134Cs and 137Cs in air was between April 1st and4th. There might have been more than one plume of radioactivityreleased (at different concentrations level). Most of caesiumisotopes (up to 95%) were washed out by wet scavenging during27e28th of March, where the maximum deposition rates of 134Csand 137Cs were observed. On the 24th of May the seawaterconcentration of 137Cs was about 1.8 � 0.1 mBq L�1, of which 0.26%(�0.06%) originating from the Fukushima accident.
A rough estimate of the total 131I inventory (around 1 PBq) thathad passed over Europe during this period was <1% of the releasedamount (150 PBq). Concerning the caesium, the total inventoryover Europe (around 0.2 PBq) was of 1e3% of the released amount(6e12 PBq of 137Cs). Within the Fukushima event, the 134Cs to 137Csactivity ratio was close to 1, which is different from that observedafter the Chernobyl accident (around 0.54) and this activity ratiowas quite constant over time. The maximum activities observedin Monaco were 2e3 orders of magnitude lower than after theChernobyl accident in 1986. This most likely will lead to fallouton the level of only few Bq m�2. Radioisotopes of caesium andiodine were above (about 100 times in the maximum case) theirdetection limits, but still with no concern for harmful radiation
exposure and public health. The contamination was graduallydeclining and activity concentrations returned to backgroundvalues after one or two months.
Acknowledgements
The authors are indebted to colleagues F. Avaullee, F. Camallongaand J.-F. Comanducci for the maintenance service of air samplerISAP 2000 and the rain water collector system in NAEL premises,which allow running smoothly the system during emergencysituation. Special acknowledgement is to the Editor-in-chief ofJENVRAD and three anonymous reviewers for their comments inthis paper. The International Atomic Energy Agency is grateful tothe Government of the Principality of Monaco for the supportprovided to its Environment Laboratories.
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