Actinides measurements on environmental samples of the Garigliano Nuclear Power Plant (Italy) during the decommissioning phase
Antonio Petraglia, Carmina Sirignano, Raffaele Buompane, Antonio D'Onofrio, Carlo Sabbarese, Alfonso Maria Esposito, Filippo Terrasi
AActinides measurements on environmental samples of the Garigliano Nuclear Power Plant (Italy) during the decommissioning phase
A. Petraglia , C. Sirignano , R. Buompane , A. D'Onofrio , C. Sabbarese , A. M. Esposito , F. Terrasi CIRCE, Dipartimento di Matematica e Fisica, Università degli Studi della Campania “L. Vanvitelli” Caserta, Italy SoGIN, Garigliano NPP, Sessa Aurunca (Caserta)
An environmental survey was carried out in orderto provide an adequate and updated assessment ofthe radiological impact that the decommissioningoperations of the Garigliano NNP may haveprocured to the environment of the surroundingarea. Some isotopes of uranium ( U, U, U) andplutonium (
Pu,
Pu) and some γ-emitterradionuclides ( Co,
Cs and K,) were measuredto quantify the possible contamination and identifythe origin source. Actinides isotopes were measuredwith the AMS technique that is able to detectelements in traces and reach sensitivity that cannotbe obtained with other methods. The results showthat the anthropogenic component is essentiallydue to the atmospheric fallout and nocontamination can be charged to the NPP. Dataare represented in geo-referenced maps to highlightthe distribution area and some particular aspects ofeach measured radionuclide. IntroductionThe study of the radiological impact of a NuclearPower Plant (NPP) decommissioning activities isimportant for the population and the environmentof the area surrounding the plant, for the workersoperating inside the plant and for characterisationand classification of the structural materials to beremoved. Hence, a radiological characterization ofenvironmental and structural materials is necessary.The Garigliano Nuclear Power Plant (GNPP),located in central Italy, about halfway betweenRome and Naples, is in the decommissioning phasefrom 90s. The Centre for Isotopic Research onCultural and Environmental Heritage (CIRCE,Caserta, Italy), in collaboration with SoGIN(Nuclear Plant Management Company), is carryingon a research program to provide a set ofcharacteristic isotopic markers to assess the possibleradiological impact that decommissioningoperations at the GNNP (Figure 1) could haveprovided to the surrounding area. Previous surveys(Sabbarese et al., 2005; Petraglia et al., 2012) havebeen carried to assess the contamination levels overthe years in order to safeguard the health of peopleand the environment and, also, to lower the level of risk perception among the population by meansobjective and verifiable scientific data. In the above campaigns we did, natural andartificial gamma emitter radionuclides weremeasured. Since the amount of the Uraniumisotopes ( U, U, U) and Plutonium isotopes(
Pu,
Pu) and their abundance ratios canprovide a signature of the contamination origin, inthe actual campaign also these radionuclides weremeasured to obtain a very sensitive survey tool.These measurements require a method with highsensitivity. The Accelerator Mass Spectrometry(AMS) technique is the most sensitive available forthe detection of long-lived radioisotopes at ultra-trace levels. At the CIRCE laboratory the AMStechnique was extended to some long-livedradioisotopes and was applied for measuring theconcentration and isotopic ratios of U and Puisotopes in environmental and structural samples(De Cesare et al., 2011). The analysis of the radionuclide quantity and theirratios could give much information. The U/ Uratio provides information on neutrons exposure. Infact, the
U is generated by neutron activation of
U. Its presence in nature is minimal and its ratiowith respect to
U is between 10 -8 and 10 -11 . Highervalues give us information about the presence ofanthropogenic contamination (Steier et al., 2008).Figure 1. The Garigliano Nuclear Power Plant,Sessa Aurunca CE – Italy.nother, the analysis of Co, originating fromneutron activation of Co, gives us information onthe degree of contamination of the matrix from thereactor material, or it could also be an indicator ofexposure to the neutron flow. The fission product
Cs is an indicator of the degree of the samplecontamination with radioactive anthropogenicmaterial. With the advancement of dismantling activities anew and comprehensive measurement campaign hasbecome necessary in the years 2015-2017. It hasbeen involved both structural materials and theenvironment around the plant. The first purposehas been to define the radiological signature(footprint) of the buildings and structures of theGNPP, so to guide future decommissioningoperations and to monitor the different phases ofthe activities. The other purpose is an update andan in-depth study of the environmental matrixmeasurements in the area around the plant. Here,only the results of environmental samples are shownand discussed, while the results of structuralmaterials are reported in a future work (Terrasi etal. 2017).Sampling area and methodThe entire plain of Garigliano hosting the GNPP,from the sea at the foot of the surrounding hills,was chosen as survey area. Samples taken inside theGNPP area and from the surroundings were subjectto different types of measurements for thequantitative determination of radionuclides withdifferent characteristics, but all effective markers ofthe GNPP influence. The environmental sampling points are shown onthe map of the Figure 2. Soil samples (pink) wereFigure 2. Location of the 191 environmentalsamples collected in the surroundings of the GNPP(in red).
Figure 3. Montage of some of the 49 collectedvegetal samples. Figure 4: U and Pu chemical purification for AMS measurements.ollected in points arranged according to a uniformsquare grid covering the Garigliano plain: thepoints were chosen approximately on each 1,5 kmmesh. Some samples were also collected on thesurrounding hills in easily accessible points. Sevenother sampling points were selected in the Seleplain, approximately 130 km away from the GNPP,in order to have a background reference. Overall,no. 100 soil samples in the Garigliano plain and no.7 samples in the Sele plain have been collected. Thesampling was made by digging a 20x20x20 cm holein soil, whose surface is previously cleaned by anyorganic surface layer (usually herbaceous). Plant samples (green labels in Figure 2) were takenfrom the native plants of the area, both wild andcultivated plants, leaves and fruits, depending onavailability. In total the number of plant specimensis 49: tomatoes, ferns, ivies, figs, olive trees,peaches, lemons, pomegranates, potatoes, greenbeans and others. Along the river, no. 10 sedimentsand no. 7 water samples were taken; and anotherno. 11 groundwater samples were acquired fromwells in the area immediately surrounding theGNPP. Finally, other different environmentalsamples were taken: fishes, mussels, milk, springwaters, etc. Altogether no. 191 environmentalsamples were collected; among them, no. 80randomly selected soil samples were chosen toFigure 5. Synoptical comparison of the specific activity values of the three γ-emitter radionuclides and twoactinides. Figures 6a,b,c,d. False colour maps of specificactivities of some radionuclides under study.erform uranium and plutonium AMSmeasurements.Sample preparation and measurementsThe γ measurements were carried out using a high-resolution germanium hyper-pure γ-ray detector(1.9 keV resolution at 1.332 MeV and 70%efficiency) properly shielded; spectra were acquired,displayed and analysed on computer running OrtecGammaVision. Before measuring, samples weredehydrated, homogenized, sieved and put inMarinelli vessels for the measurement. Each samplewas measured with a long counting time (12-24 h)to allow the detection of small amounts of activity.From the analysis of the resulting spectrum, the Cs, Co (if present) were considered and thenatural K was considered as a comparison term.The extraction of U and Pu from sample wasperformed by means the chemical proceduresschematically described in Figure 4. Before, thesample was dried in an oven at 110°C andhomogenized.The ultra-sensitive actinides measurements werecarried out by the AMS facility at the CIRCE,aiming to the determination of concentrations andisotopic abundances of U down to natural level andof Pu at ultra trace-level. The 3 MV CIRCEtandem accelerator is of Pelletron type. Since theinstallation of CIRCE in 2005, the measuringcapabilities of the original system, which was thenintended mainly for C dating, have been extendedto allow U and Pu isotopes detection (De Cesare etal., 2013). ResultsFigure 5 shows synoptically the comparison of thespecific activity values (in logarithmic scale) of theγ-emitter radionuclides and actinides, grouped foreach environmental matrix and coded with differentcolour and symbols: Co (blue),
Cs (dark green), K (red),
U (cyan),
U (violet),
Pu (orange)and
Pu (light green).It is possible to see that the specific activity valuesof K are, on average, one order of magnitudegreater than those of
U, which is one order ofmagnitude greater of the anthropogenic
Cs. Otherradionuclide have in general lower specific activitiesvalues. The values of
U ranges from 10 -6 to 10 -9 Bq/g. It also emerges that the values of specific activitiesof soils, river sediments and plants are generallycomparable among them, but higher than those ofwater samples, due to the low density of bulkmaterial in water. Figure 6 shows the maps of the distributions ofsome actinide isotopes ( U, U and
Pu) and ofthe
Cs in the Garigliano plain (in logarithmiccolour scale, except for Caesium). There is no areashowing particularly high concentrations. Inparticular, no increase of any radionuclidesconcentration is seen in the area surrounding theNPP. Nevertheless, individual cases of extremevalues can be seen, due to statistical distribution ofthese isotopes, which is expected to be log-normal.The comparison of
Cs specific activity values ofsoil samples collected in the Sele plain, 130 kmsouthern from the plain under study, gives nosignificant differences, confirming the hypothesis ofa global fallout origin of the anthropogeniccontamination (Figure 7).Discussion and ConclusionsThe samples collected around the GNPP have beenprepared and measured for radiological signaturewith high sensitivity techniques. The results showvalues in agreement with the average of otherenvironments not affected by nuclear power plantsactivities. The whole analyses show no significantalterations in the radiological characteristics of thearea surroundings the plant, with an overallradioactivity depending mainly from the globalfallout and natural sources; in particular, fallout ofthe Chernobyl accident plays a cardinal role(Alexakhin et al., 2007). Therefore, the values ofanthropogenic radionuclides do not show anyincrease in concentrations in the plant area andhave consistent values with the environmentalcontamination due to the fallout, in accordancewith other studies (Quinto et al., 2009) and withthe environmental campaigns previously carriedFigure 7. Distribution of the specific activities of
Cs in soil samples collected in the Garigliano andSele plains.ut. This thesis is further confirmed by themapping of the
U and
U specific activity.Indeed, the total specific quantity of
U in thesamples varies in a range of about two orders ofmagnitude (except for an outlier). This variabilitydepends on the nature of soil. Similarly, theinspection of the
U gives values coherent withglobal fallout. Alexakhin, R.M., Sanzharova, N.I., Fesenko, S.V., Spiridonov, S.I., Panov, A.V., 2007. Chernobyl radionuclide distribution, migration, and environmental and agricultural impacts. Health Phys. 93, 418–426. doi:10.1097/01.HP.0000285093.63814.b7De Cesare, M., Fifield, L.K., Sabbarese, C., Tims, S.G., De Cesare, N., D’Onofrio, A., D’Arco, A., Esposito, A.M., Petraglia, A., Roca, V., Terrasi, F., 2013. Actinides AMS at CIRCE and 236U and Pu measurements of structural and environmental samples from in and around a mothballed nuclear power plant. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry, Wellington, New Zealand, 20-25 March 2011 294, 152–159. doi:10.1016/j.nimb.2012.05.020Jones, D.G., Roberts, P.D., Strutt, M.H., Higgo, J.J., Davis, J.R., 1999. Distribution of 137Cs and inventories of 238Pu, 239/240Pu, 241Am and 137Cs in Irish Sea intertidal sediments. J. Environ. Radioact. 44, 159–189. doi:10.1016/S0265-931X(98)00133-7Petraglia, A., Sabbarese, C., De Cesare, M., De Cesare, N., Quinto, F., Terrasi, F., D’onofrio, A., Steier, P., Fifield, L.K., Esposito, A.M., 2012. Assessment of the radiological impact of a decommissioned nuclear power plant in Italy. Radioprotection 47, 285. doi:10.1051/radiopro/2012010Quinto, F., Steier, P., Wallner, G., Wallner, A., Srncik, M., Bichler, M., Kutschera, W., Terrasi, F., Petraglia, A., Sabbarese, C., 2009. The first use of 236 U in the general environment and near a shutdown nuclear power plant. Appl. Radiat. Isot. 67, 1775–1780.Sabbarese, C., Esposito, A.M., Visciano, L., D’Onofrio, A., Lubritto, C., Terrasi, F., Roca, V., Alfieri, S., Migliore, G., 2005. A monitoring network of the radioactive releases due to Garigliano nuclear power plant decommissioning. Radioprotection 40, 797–802. doi:10.1051/radiopro:2005s1-117Steier, P., Bichler, M., Fifield, L.K., Golser, R., Kutschera, W., Priller, A., Quinto, F., Richter, S., Srncik, M., Terrasi, F., Wacker, L., Wallner, A., Wallner, G., Wilcken, K.M., Wild, E.M., 2008. Natural and anthropogenic 236U in environmental samples. Nucl Instrum Methods B 266, 2246–2250.This is the preprint of the paper published in theProceedings of the 4 thth