Environmental studies at pre-operational and operational stages of nuclear power plants in Italy: Chemical and radioanalytical implications

The Science of the Total Environment, 64 (1987) 191-209 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

191

E N V I R O N M E N T A L S T U D I E S AT P R E - O P E R A T I O N A L AND O P E R A T I O N A L S T A G E S OF NUCLEAR P O W E R P L A N T S IN ITALY: CHEMICAL AND RADIOANALYTICAL IMPLICATIONS

GIULIO QUEIRAZZA and LUIGI GUZZI

ENEL - - Thermal and Nuclear Research Centre, Via Rubattino 54, Milano 20134 (Italy) GIOVANNI CICERI and PAOLO FRIGIERI

C.I.S.E. S.p.A., Via Emilia 39, Segrate 20090 (MI) (Italy)

ABSTRACT The criteria currently adopted by the Italian Electricity Board (ENEL) to assess the capacity of the aquatic environment to receive radioactive liquid discharges from nuclear power plants are described. The behaviour of radionuclides and their stable isotopes in coastal seawater, in the presence of suspended matter, and sediments was studied at Montalto di Castro, where a nuclear power plant is being constructed. The environmental concentrations of dissolved elements that might be discharged by a reactor were determined. Large fractions of the total trace elements in seawater were found, by ultrafiltration techniques, to be associated with the finest particle fraction (m.m. < 1000). M o s t o f t h e e l e m e n t s c o u l d b e l e a c h e d f r o m t h e p a r t i c u l a t e s w i t h 0 . 3 M h y d r o c h l o r i c acid. This indicates that the leachable elements may become available to organisms. Distribution coefficients (particulate/water) were determined. Investigations of Cs-137 concentrations in various sediments showed Cs-137 to have a preference for sandy-clay. The concentrations of trace elements in pore water were also determined. Similar studies were carried out in the Po river system after scheduled releases of low-level radioactive liquid waste. Concentration factors for Co-60, Mn-54 and Zn-65 in fish, aquatic plants and molluscs are reported. The concentrations of radionuclides found in the sediments, the aquatic plants, and fish were low and in most cases indistinguishable from the background. The aim of these studies is to obtain adequate knowledge of the ability of the environment to accept radioactive liquid wastes without being harmed. INTRODUCTION

The ENEL (Italian Electricity Board) operates nuclear power plants at Trino Vercellese and Caorso on the Po river, and at Latina on the Tyrrhenian Sea. An additional plant is under construction at Montalto di Castro on the Tyrrhenian Sea (Fig. 1). The Thermal and Nuclear Research Centre of ENEL and CISE are involved in a large program investigating the biogeochemical cycles of elements that may be discharged by nuclear power plants into the aquatic environment. Publication 26 [1] of the International Commission on Radiological Protection (ICRP) recommends that the radiation dose shall be ~'as low as reasonably achievable" (ALARA). To achieve the recommended goal

0048-9697/87/$03.50

¢~ 1987 Elsevier Science Publishers B.V.

192

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a

Trino Vercellese (PWR, 270MVy.P~

Po R ~ r

O POWER PLANT IN OPERATION

• Montalto di

POWER PLANT IN CONSTRUCTION

Latina ( / ~ - - R , 153MWe)

Tyrrhenian Sea

Fig. 1. Location of Italian nuclear power plants. at an acceptable cost-benefit ratio, the most relevant, site-specific environmental parameters affected by nuclear waste discharges must be determined and used as the basis for action rather than the conservative, non-site-specific international guidelines [2-4]. The proper evaluation of the environmental effects of radioactive liquid discharges demands that the environmental compartments at risk be studied before and after a nuclear plant begins operation. The parameters such preoperational and operational investigations [5, 6] must consider are shown in Fig. 2. Once the concentrations of radionuclides are available, the doses reaching man can be calculated using existing computer codes based on dietary intake and factors characteristic of living habits. This paper presents the most significant results of studies of the behavior of radionuclides and other elements in riverine and marine ecosystems. PRE-OPERATIONAL STUDIES IN A COASTAL MARINE ECOSYSTEM The abiotic compartments of the coastal ecosystem at Montalto di Castro are under investigation to determine the distribution and the transfer rates of

193 STAGES Pro-operational

Operational

i Estimated characteristics of the release

Actual characteristics of the r e l e a s e

Hydrodynamic and

..4 geochemical ~.. data

Equilibrium concentrations in water

Observed concentrations in water

Concentration factors

-

Icr, x d l

I Observed

Equilibrium concentrations

concentrations

in e n v i r o n m e n t a l

in environmental

materials

materials

Dietary habits ~

survey

data

~

Specific rate of

Specific rate of

intake or e x p o s u r e

intake or e x p o s u r e Reference

primary standard

Authorized

Authorized input rate

input rate

%

/

Foroseable

%

Appropriate

/

Knowledge of the r e c e p t i v i t y of the e n v i r o n m e n t for radioactive waste

Fig. 2. A s s e s s m e n t o f e n v i r o n m e n t a l

r e c e p t i v i t y for l i q u i d r a d i o a c t i v e w a s t e s .

radionuclides. The biological compartments, although important with respect to radiological protection, are not considered, because they are not essential for the mass balance of radionuclides [7, 8]. The temporal and spatial changes in the concentrations of radionuclides in the aquatic coastal environment can be adequately described in terms of the interactions among the abiotic compartments. The behaviour of radionuclides is studied using as tracers stable isotopes [9] that are naturally present in the environment in very low concentrations. In this manner concentration factors are estimated, chemical species are identified, specific activities are computed, the effects of stable isotopes on the uptake of radionuclides are investigated, the fate of radionuclides is predicted, and the pathways from water to man are elucidated. The criteria of Golden and Whipple [10], based on the most probable constituents of liquid discharges from nuclear power plants, were used to select the most important elements. These elements, grouped according to decreasing differences between the concentrations in the primary coolant of boiling water reactors and the maximum permissible concentrations in the environment, are: group l: Ba, Ce, Co, Cr, I, Mn, Sr group 2: Cs, Fe, Zn group 3: Sb group 4: P

194 Thorium, an element of biogeochemical significance [11], calcium, yttrium, and lead were also studied. Elements with radionuclides having half-lives shorter than 3 days are not considered. Radioelements for which sufficient information is available from investigations of atmospheric fallout (Nb, Ru, Zr), radioelements of low environmental importance (Hf, Ag, S, Sn, W) and elements that are difficult to determine quantitatively (Nd, Ta, Te) were not included in the studies. Water

Generally, trace elements in uncomplexed forms (hydrated ions) are taken up by aquatic organisms from water more efficiently than complexes [12]. Lack of adequate analytical techniques makes it difficult to identify and quantitatively determine complexes formed between trace elements and naturally occurring ligands. Laminar ultrafiltration [13] of water samples, previously filtered through 0.4pm polycarbonate filters, and chromatography on Chelex-100 [14] were employed to obtain information about trace element species present in seawater. The concentrations of trace elements in coastal seawater at Montalto di Castro, determined by preconcentration techniques [15, 16] in samples filtered through 0.4 #m polycarbonate filters, are compared (Fig. 3) with the concentrations in the open ocean [17]. The concentrations of Th, Ce, Y, Pb and Mn are substantially higher in the coastal than in the open-sea water. The filtered

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Fig. 3. Concentrationsof soluble trace elements in seawater [17]and in Tyrrheniancoastal waters at Montalto di Castro.

195

EPement

Fe

Recovery96

Mn

35-41 6 6 - 8 i

Cr

Co

Cs

>5(

64-72

>9:

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1 2 3

1 2 3

Sr

Ca

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123

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Fig. 4. Association of trace elements with particulate fractions of molecular mass > 10 000 (fraction 1), between 1000 and 10000 (fraction 2), and < 1000 (fraction 3) determined by ultrafiltration. Samples collected during the winter of 1984 (A: 4km off-shore, B: 8 km off-shore) and summer 1984 (C: 4km off-shore).

seawater was subjected to ultrafiltration. At least 60% of each investigated element is associated with the finest particle fraction of molecular mass < 1000 (Fig. 4). These results agree with those obtained for Cu in estuarine waters [18]. The filtrates obtained by passing the samples through the ultrafilter (< 1000mol. mass) were chromatographed on Chelex-100 [14]. The column retained all Co, Cu, Fe, Mn, Pb and Zn present in the filtrates, even though they had not been irradiated with UV light and had not been treated with acid. These metal species in the filtrates must, therefore, be classified as labile and bioavailable according to the kinetic classification of Figura and McDuffie [14].

Suspended matter Radionuclides and trace elements in an aquatic system are sorbed by inorganic and organic particles and thus partition between the aqueous and solid phases. The distribution of an element between these phases is described by the distribution coefficient, Kd (Eqn (1)) [4]. K¢t -

amount of element per gram of particles amount of element dissolved in 1 ml water

(1)

Such distribution coefficients can be the same for radioactive and stable isotopes ("exchangeable" fraction) of an element [19]. To estimate the "exchangeable" fraction of each stable element considered, a sample of marine suspended matter ( ~ I g separated from 30001 of coastal seawater collected at Montalto di Castro) was subjected sequentially to acid leaching (fraction 1), acid-oxidative leaching (fraction 2), and total acid digestion (fraction 3). Preliminary experiments indicated a leaching time of 2h to be satisfactory. Fraction 1 was obtained by shaking 100 mg of suspended matter with 40 ml of 0.3 M HC1 for 2 h

196 at room temperature (20 + 2°C) and filtering the mixture through a 0.4pro preconditioned polycarbonate filter. Fraction 2 was obtained under the same conditions by shaking 100 mg of suspended matter with 40 ml of 0.3 M HC1 and 1 ml 30% H202. For the determination of total Fe, Zn, Mn, Co, Cs, Ba, Ca, Sr, Ce, Th and Y suspended matter was digested with a mixture of concentrated HNO3, HC104 and HF in Teflon vessels at a maximum temperature of 250°C. The digest was evaporated to dryness and the residue dissolved in 6 M HC1 containing 2% H3BO 3. For the determination of Sb and Cr the suspended matter was heated with a mixture of concentrated HNO3 and H2SO4 at temperatures not exceeding 250°C until SO3 fumes appeared. The mixtures were cooled and filtered through 0.4 #m polycarbonate filters. The digestion for the determination of Pb was carried out with a mixture of concentrated HNO3 and HC1 at a maximal temperature of 170°C. The digest was taken to dryness and the residue treated with 6 M HC1. Total element concentrations were determined with an atomic emission spectrometer (ICP-AES) for Fe, Mn, Zn, Ca, Ba, Sr, Ce, Y and Th; with a graphite furnace atomic absorption spectrometer (GFAAS) for Pb, Co, Cr and Cs; and by hydride generation/atomic absorption spectrometry for Sb. Effects of leaching time on the release of the elements from particulate matter to 0.3 M hydrochloric acid solutions are shown in Fig. 5A. For all of the elements investigated, with the exception of cobalt, the leaching time had little influence. Leaching of the particulate matter with 0.3 M hydrochloric acid dissolved > 50% of Ca, Cs, Mn, P, Pb, Sb, Sr, Y and Zn (Fig. 5B). Most of the iron and substantial amounts of Ba, Ca, Ce, Cr, Co and Th were released only after total digestion with acid. Only P, Cr and Pb were found in the solutions after leaching with 0.3 M hydrochloric acid/hydrogen peroxide (Fig. 5B). These results agree with those reported by Collier and Edmund [20] for the release of Fe, Mn and Zn from biogenic particulate matter to various leaching agents. Values for some distribution coefficients generated by the leaching studies are reported in Fig. 6. The averages of these coefficients are generally higher than those reported by IAEA [2], but are comparable to the maximum values of Onishi et al. [21]. The differences may be attributable to the experimental conditions. Whereas most distribution coefficients have been determined by mixing radionuclide tracers with seawater samples containing unrealistic, large amounts of sediments [22], the coefficients reported in Fig. 6 are based on the natural concentration of suspended matter in seawater. Sediments

Many properties of sediments (chemical composition, porosity, tortuosity, particle size, mineralogy) were determined to estimate their potential for sorption and release of radionuclides. A good correlation was found between chemical composition and particle size (Fig. 7) for 32 Tyrrhenian coastal sediments collected in the area shown in Fig. 8. The major and minor chemical

197

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Fig. 5. (A) Influence of leaching time on the release of elements to 0.3 M hydrochloric acid from suspended matter in relation to contact time. (B) Release of elements by particulate matter upon leaching with 0.3 M HC1 (fraction 1), 0.3 M HCl/hydrogen peroxide (fraction 2), and upon digestion with acid (fraction 3).

198

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199

First canonical correlation R-0.97 CHIM GRAN 2.0

¸

1.5 1.0 0.5 0.0

Fe 0.4234 Pb 0.5690 K 0,4351 Ti 0.6070 Cr 0.3189 Mn 0.5483 Ni 0.2858 Cu 0.6290 Zn 0.6508 Sr 0.3530 137Cs 0.6784

Medium Sand Fine Sand Silt Fine Silt Clay

0.1992 0,1114 0.2695 0.4460 0.8259 O

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n.-

-0.5 -1.0. -1.5 -2.0

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1

Fig. 7. First canonical correlation for sediments from the coastal area of Montalto di Castro. Plot of the first canonical variable (CHIM 1) of chemical data set and the first canonical variable (GRAN 1) of granulometric data set. The table gives the square multiple correlation between variables (CHIM or GRAN) and the first canonical variable (GRAN 1 or CHIM 1).

constituents were determined by X-ray fluorescence [23]. The particle size distribution was obtained by wet sieving. Sedimentary regions with homogenous physical and chemical properties are present in this area (Fig. 8). The distribution of Cs-137 from nuclear tests in the atmosphere among the Montalto di Castro sediments confirms this subzone classification (Fig. 8) and shows that radiocesium is preferentially associated with particles of sandy-clay.

~rz~_Fine sand

Ds,,y-sand

.........

.....

[] Si,l []

Sand

0Cs-137

7.5 Bq/Kg.w

Fig. 8. Sedimentary regions at Montalto di Castro and their Cs-]32 content and the area covered by the seaweed Posidonia oceanica.

200 The release of radionuclides and trace elements by the sediments to the water and biota is a major subject of environmental studies. The ability of a sediment to retain radionuclides is determined by its chemical composition. Therefore, experiments were carried out with sandy clay and sandy sediments from Montalto di Castro. Undisturbed cores were collected by a special device [24]. The cores were extruded under a nitrogen atmosphere and squeezed to obtain the pore water. The sequential extraction procedure ofTessier et al. [25] was used to determine the exchangeable elements (extraction with 1M magnesium chloride, pH 7), carbonate-bound elements (1 M sodium acetate/acetic acid, pH 5), elements bound to iron and manganese oxides (0.04 M hydroxylamine hydrochloride in 25% acetic acid), elements bound to organic matter (0.04 M nitric acid/30% hydrogen peroxide, pH 2), and residual elements (digestion with nitric, hydrofluoric/perchloric acid). Aliquots of the sediments were also leached with 0.3 M hydrochloric acid according to Malo's modified method [26], as described for the preparation of fraction 1 from suspended matter. Extraction with 0.3 M hydrochloric acid solubilized approximately the same amounts of elements (with the exception of phosphorus) as found in the exchangeable, carbonate-bound, iron and manganese oxide-bound and organically-bound fractions (Fig. 9). Approximately half of the calcium, phosphorus, manganese and strontium present in the sediments was extracted by 0.3M hydrochloric acid. The elements Ba, Fe, Cr and Cs are largely concentrated in the residual fraction. Strontium, Mn, Co, Zn, Ce and Y appear to a significant extent in the extractable fractions. Substantial amounts of Sr, Mn, Ce and Y appear to be carbonate-bound, suggesting that these elements are removed from the water as carbonates or hydroxides. Elements (Ce, Co, Cr, Fe, Mn, Y, Zn) that appear in the hydroxylamine extract (reducible fraction) can be mobilized under appropriate Eh-pH conditions. The differences in total metal concentrations and in metal concentrations in the various fractions between sandy-clay and sand are minor (Fig. 9). Cesium could not be determined by GFAAS in the exchangeable and carbonate-bound fractions because of severe interferences. Eighty to ninety percent of Sb and Th was not extractable from sandy-clay and sandy sediments with 0.3 M HC1. Elements and radionuclides observed in any fraction but the residual fraction may enter the aquatic food chains when ingested by benthic organisms. The flux of elements between sediments and seawater via the pore water is influenced by the ability of elements to desorb from the sediments and by the concentration gradient [27] from pore water to seawater. The distribution coefficients, Kd, for several elements between a sediment and its pore water are shown in Fig. 10B. Iron, cobalt, chromium and lead are almost completely retained by the sediment, whereas strontium is equally distributed between pore water and sediment. The enrichment factors (concentration in pore water/ concentration in overlying seawater), a measure of the concentration gradient between pore water and seawater, were found to be high for Fe, Mn, Co and Zn (Fig. 10A). These concentration differences can lead to significant fluxes from pore water to seawater.

201 5

I'

Ba

Sr

Fe

Mn

Method "A" • [] Method "S" • non-residual [ ] D

Cr

Co

Zn

Cs

Pb

Ce

Y

Ca

P

Element exchangeable with 0.3M HCI treatment Element non exchangeable with 0.3M HCI treatment Exchangeable (1M MgCI 2 ) Bound to carbonates (1M NaOAc buffer) Bound to iron and manganese oxides (O.04M NH2 OH + 25% HOAc)

[ ~ Bound to organic matter (O.02M HNO 3 ,H 202 30% ÷ 3.2M NH 40Ac, 20% HNO 3) []

Residual (HNO 3 ÷ HF + HCIO 4 )

Fig. 9. Results of sequential extractions of sandy clay and sand from Montalto di Castro. The height of a bar represents the logarithm of the total concentration of an element; the internal subdivision in a bar indicates the percent (linear scale) distribution of an element among different chemical fractions. OPERATIONAL STUDIES IN THE PO RIVER ECOSYSTEM T h e s t u d i e s in t h e Po R i v e r e c o s y s t e m w e r e p e r f o r m e d to c o l l e c t i n f o r m a t i o n a b o u t t h e f a t e of l i q u i d effluents from o p e r a t i n g n u c l e a r p o w e r p l a n t s a n d to t r a c e t h e m o v e m e n t of r a d i o n u c l i d e s a l o n g e x p o s u r e p a t h w a y s to man.

Transport of radionuclides R a d i o n u c l i d e s a r e t r a n s p o r t e d in w a t e r in a d s o r b e d a n d d i s s o l v e d forms. L a b o r a t o r y [28] a n d field s t u d i e s [29] w e r e u s e d to d e t e r m i n e t h e d i s t r i b u t i o n of r a d i o n u c l i d e s a n d t h e i r s t a b l e i s o t o p e s b e t w e e n t h e p a r t i c u l a t e a n d s o l u t i o n

2O2 Enrichment factor 10.000 1.oo0

iiiii-',i i!

lOO 10

Ba

L!ii

=:!N

Sr

Fe

Mn Co

Zn

Sr

Fe

Mn Co

Zn

@

Cr Ca

N n N Pb

Cs

P

Pb

Cs

P

Kd (mL/g) 10.000 1.000 1oo 10 .

.

.

Ba

.

.

Cr

Ca

Fig. 10. (A) Average enrichment factors for some elements between pore-water from coastal sediments collected at Montalto di Castro and the overlying seawater. (B) Average distribution coefficients (K~) between pore-water and the exchangeable fraction of elements in the sediments determined by leaching 100 mg of the sediments with 40 ml 0.3 M HC1 at room temperature for 2 h. phase. S c h e d u l e d d i s c h a r g e s f r o m the low a c t i v i t y w a s t e t a n k s of two n u c l e a r p o w e r p l a n t s [29] w e r e used to s t u d y the c h a n g e s in the d i s t r i b u t i o n coefficients as the d i s c h a r g e d w a s t e was diluted by the r i v e r w a t e r and the c h e m i c a l and p h y s i c a l forms of the r a d i o n u c l i d e s c h a n g e d c o n c o m i t a n t l y . The r e s u l t s (Fig. l l ) i n d i c a t e t h a t Cs-137 and Mn-54 are p r e d o m i n a n t l y in the c a t i o n i c form, and Co-60 in the a d s o r b e d f o r m in the u n d i l u t e d d i s c h a r g e from the T r i n o p o w e r station. T h e p a r t i c u l a t e s holding Co-60 were identified as a m i x t u r e of Fe and M n oxides. T h i r t y m i n u t e s a f t e r d i s c h a r g e a n d a 200-fold dilution by r i v e r water, the f r a c t i o n of Cs-137 sorbed by p a r t i c u l a t e s h a d i n c r e a s e d c o n s i d e r a b l y . M a n g a n e s e - 5 4 a n d Co-60 h a d not been affected. T h r e e h o u r s a f t e r d i s c h a r g e and a 140000-fold dilution, ~ 60% of Cs-137 and 30% of Mn-54 w e r e a s s o c i a t e d w i t h p a r t i c u l a t e m a t t e r . The d i s t r i b u t i o n of Co-60 h a d not changed. S i m i l a r r e s u l t s w e r e o b t a i n e d w i t h d i s c h a r g e s from the C a o r s o p o w e r p l a n t (Fig. 11). U l t r a f i l t r a t i o n of t h e s e s a m p l e s showed t h a t Cs-137 and n o n - r a d i o a c t i v e cesium are l a r g e l y a s s o c i a t e d with m a t e r i a l s of m o l e c u l a r m a s s < 1000 (Fig. 12). A p p r o x i m a t e l y 11% of the Coo60 in the w a s t e t a n k was a s s o c i a t e d with m a t e r i a l s of m o l e c u l a r m a s s b e t w e e n 1000 and 10000. U p o n m i x i n g with r i v e r w a t e r this p e r c e n t a g e d e c r e a s e d to 1.5, a p p r o x i m a t e l y the s a m e v a l u e c h a r a c t e r i s t i c of n o n - r a d i o a c t i v e cobalt. T h e f r a c t i o n of Co-60 a s s o c i a t e d with m a t e r i a l s of m o l e c u l a r m a s s > 10000 did not c h a n g e u p o n m i x i n g w i t h r i v e r w a t e r (Fig. 12). D i s t r i b u t i o n coefficients in the field e x p e r i m e n t s were c a l c u l a t e d from the c o n c e n t r a t i o n s of stable e l e m e n t s or r a d i o n u c l i d e s dissolved in the water, the " g r o s s " c o n c e n t r a t i o n s in the p a r t i c u l a t e s (after acid digestion), and the " a v a i l a b l e " c o n c e n t r a t i o n s in the p a r t i c u l a t e s (after e x t r a c t i o n with 0 . 3 M HC1). In the l a b o r a t o r y e x p e r i m e n t s w a t e r s a m p l e s from the Po R i v e r were spiked w i t h r a d i o n u c l i d e t r a c e r s and t h e n s h a k e n . T h e r e s u l t s are s u m m a r i z e d

203 TRINO VERCELLESE

CAORSO

10 Km Down Stream

Low Rad Waste Tank

Dil. Factor 204 Cone. 2634 Bq/I 13 s./,

145.000 2 lsq/.~

28B,/I

27.000 1.04sQ/~'

Dil. Factor Conc. 1055Bq/I

134.000 7.92Sq/n~ 22Bq/,

16.000 1.41Bg/m3

Element

Low Rad Waste

Tank

Dil. Factor

Step

187 5 Bq/I

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Canal

CO

Anior~c O

Discharge

200 144.000 23.000 78BQ/, 0.39Bq/I 0.54aq/m~ 14SQ/, 0.61BQ/~

Conc.

Q

First Mixing

Dil. Factor Conc.

Non Ionic

20 Bq/I

22.000 0.61 Bq/m3

Fig. 11. Distribution of Cs-137, Co-60 and Mn-54 among particulate, cationic, anionic and non-ionic forms in low radiation waste tanks and in discharges diluted with river water. WASTE TANK

FIRSTMIXING STEP

FIRST MIXING STEP 98

Cs

137Cs

~ 4 ' . 6

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~

84

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98

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~ < I 0 '

Fig. 12. Association of Cs-137, Co-60 and their stable isotopes with materials of molecular mass < 1000, between 1000 and 10000 and > 10000 in the low radiation waste tank and after 200-fold dilution with river water.

in Table 1. The distribution coefficients found in the field studies (gross) for Fe, Sr and Zn are comparable to those obtained in the laboratory. The coefficients for Mn, Co and Cs differ by one order of magnitude. The IAEA coefficients for freshwater [2] agree with the Po River field values only for Co and Sr. The

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2o5 methods used for the determination of distribution coefficients seem to infiuence the results.

Radioactivity in the Po River system During 1978-1982, sediments, aquatic plants and fish were collected from the Po River [30] and their radioactivity determined to obtain information about the temporal and spatial changes of contamination. The averages and the ranges of the concentrations of Ag-110m, Cs-137, Co-60, Co-58 and Mn-54 are displayed in Fig. 13. As expected, the radioactivity is highest in the sediments and lowest in the fish. Even the highest radioactivity found in sediments (Co-60, 740 Bq kg 1 dry weight) is insignificant with respect to protection from radionuclides. The Casale Monferrato and Isola Serafini dams play a critical role in the accumulation of radionuclides. However, only upstream of the Casale Monferrato dam were significant mean annual concentrations of Cs-137 detected in sediments and detritus-feeding fish (Fig. 14).

Radioecological indicators and concentration factors The concentrations of radionuclides in living and non-living matter that might take part in transporting radionuclides to man are generally indistinguishable from the background and are, in some materials, below the detection limits. To identify and select radioecological indicators, the bioaccumulation of stable isotopes of radionuclides by aquatic organisms (macrophytes and animals) was studied [31] in a section of the Po River with low hydrodynamic energy.

÷ PO Sediments

= '3~Cs too-~!i I

RIVER ~.....m..H.H.M.~

(1978-1983) Aquatic

plants

L............... ~F i s h e s

6°Co I '~'Cs I ~'°Ag ~ ~Co ~4Mn '-74o-.-~; i _ ~! I

Fig. 13. Averages and ranges of the concentrations of Ag-ll0m, Co-60, Co-58, Cs-137, Cs-134 and Mn-54 in sediments (Bqkg-1 wet weight), aquatic plants and fish (Bq kg 1wet weight) of the Po River.

206 0.5-

_12.5 I

Sediments

0.4

_10.0 Fishes

-5

0.3

.

5.0

.

2.5

Vercellese Power

Trino

{~r

!D!

~

~:~o >

Kin-20

0

L

Caorso

Plant

Power

Plant

(~ Dam

Dam

20

I

40

J

F i g . 14. D i s t r i b u t i o n

~ 0-o

I

60 ~ I

80

100

I

I

120

140

]

I

~ :=

160 I

0 '7Nm

180

200

]

I

220 ]

o f Cs-137 i n s e d i m e n t s a n d f i s h a l o n g t h e P o R i v e r .

For example, the bioconcentration ability, BA, of the filter-feeding mollusc

Unio elongatulus was compared with that of the macrophyte Potamogeton crispus on the basis of the following ratio relationship between element concentrations [X] and [Y] (Eqn (2)): BA -

[X]u/[Y]u [Z]p/[Y]p

(2)

The data obtained (Table 2) indicate that Co is preferentially bioaccumulated by Potamogeton crispus and Zn by Unio elongatulus, whereas no significant preference exists for Cr, Mn and Fe. TABLE 2 Normalized

values

Lamellibranch) Zn Co Cr Mn Fe

and

of the trace

element

concentration

Potamogeton crispus

(aquatic plant)

ratios ~ in

Unio elongatulus

(mollusc,

-95 - 28 -3 - 30

+ 95 -+ 4 +28 + 3

+ 28 - 4 -+9 1

+ 3 -~ 28 - 9 -- 9

+ 30 - 3 1 +9 --

Zn

Co

Cr

Mn

Fe

~Positive values indicate a preferential bioaccumulation preferential bioaccumulation by the aquatic plant.

by the mollusc, a negative

value

a

207

With the help of these data biological indicators can be selected and used to detect low level environmental concentrations of specific radionuclides. Because the concentration factors reported for some radionuclides in the literature [32] may differ by several orders of magnitude, a study was carried out to obtain site-specific data for molluscs and macrophytes (Po River), and fish and molluscs (discharge canal of the Caorso power plant). Fish and molluscs were kept in the discharge canal in submerged cages. The concentration factors calculated from concentrations in the organisms and in the water, were determined for radionuclides and their stable isotopes. A summary of the data obtained over several years is presented in Fig. 15. The radionuclides Co-60, Mn-54 and Zn-65 have lower concentration factors than their stable isotopes. The recently discharged radionuclides have probably not yet been converted completely to the physicochemical forms in which the stable isotopes are present in the river. The forms in which the stable isotopes appear seem to be more efficiently taken up by organisms than the forms characteristic of the radionuclides. PO RIVER

10000 i 1000

[] un~oe. 1 [] Potamogeton c. [] Miriophyllum s:

]

r

co 100 g o o

10

~Co

Co

S,Mn

Mn DISCHARGE CANAL

10000[ [][] AlburnUSuni e. alborella o

I

! [] Cyprinus _carpio g 1coo.L-cO

:i

o

:

:::

o:t2L

o

1

~°Co

Co

5'Mn

Mn

"6;Zn

Zn

Fig. 15. Concentration factors for radioactive and stable Co, Mn and Zn in organisms of the Po River and the discharge canal of the Caorso nuclear power plant.

208 ACKNOWLEDGEMENT We thank

Professor

S. M e l o n i ,

sita di Pavia, for critical

Department

discussions

concerning

of General

Chemistry,

Univer-

the manuscript.

REFERENCES 1

2

3

4

5 6

7

8

9 10

11

12

13 14

15

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