A.V.Konoplev,*A.A.Bulg水ov,*V.Yu.V.Shvell(in,十

Abstract-The "Wash-ofP' scenario is designed to test modelsconcerned with the movement of trace contaminants fromterrestrial sources to bodies of water, specifically the contam.ination of surface water by wash-off of radionuclides initiallydeposited onto soils. Particular emphasis is placed on chemicalspeciation and on the geochemical and geophysical processesaffecting transfer of contaminants from soil to water. Thescenario gives descriptions of two experimental plots near theChernobyl power plant, one using heavy rain and one usingsnow melt, together with characteristics of the initial aerialdeposition of the radionuclides and data on topography, soiltype and characteristics, and time-varying precipitation. Pre-dictions are requested for (1) the vertical distribution ofconcentrations of exchangeable and nonexchangeable forms of137Cs and eosr in the soil of the experimental plots, (2)concentrations of 137Cs and eosr in runoff water from theexperimental plots, and (3) total amounts of 137Cs and eosr

removed by runoff from the experimental plots. Test data(field measurements) are available for all endpoints.Health Phys. 70(1):8-12; 1996

Key words: Chernobyl; environmental transport; contamina-tion, environmental; 137Cs

INTRODUCTION

Ttre "WASg-oFF' scenario is the first of a set of threemodel-testing scenarios developed by the Post ChernobylData Working Group of 'BIOMOVS II (BiosphericModel Validation Study, Phase II). Information on par-ticipating in the test exercises or obtaining the test datafor individual test scenarios is provided in an accompa-nying article (Hoffman et al. 1996).

This scenario offers an excellent opportunity to testmodels concerned with the movement of trace contami-

ン 増錨ンDive,Oak Ridge,TN 37830

Mα″″ざCrタレ確Cタルタ冴15れ,1994;″ッサs夕″″α″″sc/タテTCタルタ″31虹岱 1995,αoc?惚ダlA″

=パチ1995)

0017-9078/96浴 3.00/0

Copyright ⑥ 1996 Hcalth Physics SOciety

Aleksが rθttθ切 ち ,scPI・OJcc,Prof●郎冴

五sどrrrFe oFD,vまmmttF2F奴 2ど02Cどガr7

Fυ【gS,力И4口WTレ切照顕 y

7 Kanayagawa, Fukushima, 9601296, JapanPhone : + 81 - 24 - 504 - 2848Mobile : + 81 - 80 - 5844 - 0962h ttp : //w w. i e r.f u k u s hi ma- u, ac j p,/e-mail : 1701 @ipc.fu k us hi ma-u,a cjp

al exeikonoplev @ gma il,com

EXPERIMENTAL

E. Popov,x O. F. Popov,T A. V. Scherbak,tand F. O. Hoffman+

nants from terrestrial sources to water bodies. Theparticular objective is to take account of chemical spe-ciation, its effects on the transfer of contamination fromsoil to water, and the geochemical and geophysicalprocesses that affect such transfer. Although the presentscenario deals with the contamination of water subse-quent to aerial deposition of radionuclides following theChernobyl accident, the processes underlying the sce-nario may be adapted to many sources of contanrinationof surface and ground water.

Surface water runoff from contaminated land is oneof the main processes responsible for the contaminationof water bodies. Therefore it is very important to have areliable model for prediction of the contamination ofsurface water by natural runoff. The large area of landcontaminated by the Chernobyl accident has become acontinuing source of radionuclides entering natural wa-ters and the aquatic ecosystem. This has provided aunique opportunity to develop a data base suitable fortesting the predictive capability of mathematical modelsto assess radionuclide wash-off into rivers and lakes fromsoils contaminated by the deposition of fuel particles.

Overall, the scenario will provide the followingoppoftunities: (1) to evaluate the movement of contami-nants from soil to water; (2) to calculate the attenuationand migration of contaminants in soil over different timescales; and (3) to increase understanding of contaminanttransport at the process level.

The scenario examines the wash-off of eosr andtttcs from two experimental plots established in thevicinity of the Chernobyl reactor. Later phases of thescenario development will extend the calculations toaccount for wash-off on larger spatial scales, includingthe flood plain of the Pripyat River, which provides inputto the Kiev reservoir, and then the whole Dnieper Riverbasin, starting with the watershed processes and includ-ing consequent transpolt processes in the rirrer itself.

A distinguishing feature of radioactive contamina-tion due to a nuclear accident is the chemical speciationof the radionuclides present in atmospheric fallout anddeposited on the soil. When the Chernobyl accidentoccurred, nuclear fuel debris (UO2 + UO.), including

8

Paper一

酌IODEL TESTING USING C]I.WASH‐OFF OF9°Sr AND 137cs FRO酌質TWO

PLOTS ESTABLISHED IN THE VICINITY OFTHE CHERNOBYL REACTOR

Wash― off of 9° Sr and 137cs● A V ItoNOPLEV ET AL

fission products, was released into the environment.Some of the radionuclides were also deposited onto theground as aerosol particles that had been formed in theatmosphere due to condensation. These parlicles variedin size, chemical composition, and behavior in theenvironment.

Fuel particles have a radionuclide composition sim-ilar to that of inadiated fuel, but with varying proportionsof highly mobile and volatile decay products. The fuelparticles are of very low solubility in water and hence donot participate in exchange processes between soil andsoil-water solutions or in plant contamination via rootuptake from soil. However, as the fuel particles slowlydegrade, mobile fission products may be released. Thedegradation rate of the particles is dependent on the sizeand chemical composition of the particles; these are afunction of the distance from the Chernobyl NuclearPower Plant (NPP). The time scale of the particledegradation varies from 1 to 10 y for different points inthe 30-km zone around the nuclear power plant (Kono-plev and Bulgakov 1992; Konoplev et al. 1993),

In terms of predicting the migration of 137Cs and'"Sr in soil-water systems, it is reasonable to identify thefollowing chemical forms: (1) dissolved cations (Az); Q)exchangeable forms (Ar.), including radionuclides ab-sorbed onto soil or bottom sediments by ion-exchangemechanisms; and (3) non-exchangeable forms, includingradionuclides of nuclear fuel particles (Ar) and fixedradionuclides on mineral or organic components of soilor bottom sediments (A.). Over the course of time,

Fig. 1. Schematic representation of the transformation processes ofradionuclide chemical species. The chemical forms are representedas follows: Ar, radionuclides of nuclear fuel particles (non-exchangeable); Ar, dissolved cations; Ar., exchangeable forms,including radionuclides absorbed onto soil or bottom sediments byion exchange mechanisms; and A., non-exchangeable radionu-clides fixed on mineral or organic components of soil or bottomsediments. K is the constant for the ion-exchange equilibrium, and

\ is the rate constant for the process at issue (ij). The chemicalforms may be considered in units of either mass or activity. Theunits of the ion-exchange equilibrium constant K will depend onthe choice of concentration units for A, and Ar". Radioactivedecay has been omitted from the diagram because the time scale ofthe wash-off process being studied here is considerably smallerthan the halfJives for the radionuclides in question.

Table 1. Soil characteristics of the experimental plots.

Characteristic PIot HR Plot SM

General description

Effective water-holding capacity ofthe 0-10 cm layer of sotl, Vo

Hydraulic conductivity' (velocityof downward percolation ofwater in the soil profile), mmmtn -

Cation exchange capacity (CEC) ofthe upper 1 cm of soil, meq g-rdry weight

Alluvial acid sod Cultlvatcd sod

podzollc soll

45± 6 30± 3

034± 007 031 ± 003

015± 002 007± 001

'Hydraulic conductivity was calculated as the difference between rainfallintensity (mm min 1) and runoff intensity (mm min-r) during specialexperiments using artificial rain on I-m2 plots.

radionuclide chemical species undergo transformationprocesses (Fig. 1). The rate of migration processes issensitive to the chemical speciation of the radionuclidesin soil and other environmental media. A fraction A,moves into the dissolved state with retardation occurringthrough ion-exchange interaction with the solid phase.The solid-phase species .A.1, A2", and A. move only withthe particles in which they are incorporated.

EXPERIMENTAL DETAILS

Two experimental plots were constructed in areascontaminated by dry deposition resulting from the Cher-nobyl accident. Deposition (>957o) occurred between 26April and 10 May 1986. The contamination of the plotswas determined by taking randomly selected soil sam-ples; each sample was 180 cm' in arca and 10 cm indepth. Runoff samples were collected in plastic bottlesand filtered with a 0.45 p,m filter. The "'Cs content insoil samples, filters, and water samples was determinedthrough gamma spectrometry without preconcentrationsusing a Canberras gamma counter with a semiconductordetector (Makhonkb et al. 1985). The eosr content wasdetermined with a radiochemical analysis that usedcarbonates of precipitation (Sereda and Shulepko 1966).Al1 samples were processed at the Institute of Experi-mental Meteorology, SPA "Typhoon," in Obninsk, Rus-sia.

INPUT INFORMATION

Experimental plot for runoff following heavy rain(plot HR)

^The 625-m" experimental plot is located 7 km from

the Chernobyl Nuclear Power Plant, 0.6 km from thevillage of Benevka on the oxbow of the Pripyat River. Itis defined on three sides by dikes and on the lower partby a collection chute. The plot size is 25 m X 25 m; themean grade of the slope is 5Vo. The total aerial contam-

'uanberra lndustfles,Connecticut 06450.

Inc.. 800 Research Parkway, Meriden.

10 Health physics

ination in the experim.e^ntal plot was determined to be 1.4t 0.1 MBq m 'of '"Cs and 1.8 -f 0.4 MBq m-2 of"Sr 1* standard deviation (SD)1. Descriptions oithe soiland plot HR are given in Tables I, 2, and 3. Thevegetation on the experimental plot consisted primarilyof mixed grasses. The predominant wild plant speciesincluded Achillea millefolium, Ae godpodium pada[raria,Carex vulgaris, C. nigra, C. flacca, C. pilosa, Comarump alustre, D e schamp sia caespito sa, F ilip endula ulmaria,Leuc anthemum v ul g ar e, M e lampy rum ne mo r o s um, M en -tha arvensis, Myosotis palustris, Pedicularis palustris,P oly g onum li s to rta, P olytric hum c ommLlne, Ranunculusrepens, Trifulium repens, Veronica chamaedrus, andVaccinium myrtillus.

Table 2. Soil descriptions for the experimental plots.

Soil layer Depth (cm) pH

January 1996, Volume 70, Number 1

Intense artificial rain was used to simulate theformation of natural surface runoff on the two experi-mental plots. This was done for two main reasons. First,there was an urgent need at the time to predict thecontamination of water bodies due to runoff caused byrainfall, flooding, and snow melt from areas of contam-inated soil. However, there was a lack of rainfall durinsthe period immediately after the accident, and it was no-tpossible to wait until there was natural surface runoff.Second, in the 30-km zone there is poor surface runoffformation; the mean annual runoff coefficient is -ISVo.

The observations were carried out during an exper-iment conducted on 14 October 1986. The aftificialheavy rain was applied by pointing a fire hose up in theair and letting the water come down. A second artificialrainfall application was used to test the dependence ofradionuclide wash-off on initial conditions (i.e.. beforethe first rainfall application, the soil was dry; before thesecond application it was wet). A hydrograph of therunoff dynamics is given in Fig. 2. Chnacteristics of theartificial rain applications are given in Table 4. Thechemical composition of the artificial rain is not repre-sentative of the actual rain in the region, in that thearlificial rain contained more dissolved salts than actualrain would have contained. The intensitv of the artificialrain was representative of actual rain that can causesurface runoff. The applicability of data obtained withartificial rain to actual environmental conditions has beendiscussed by Bulgakov and Konoplev (1992) and Bulga-kov et al. (1992).

E-xperimental plot for runoff from snow melt (plotSM)

The 1,000-m2 experimental plot is located on anorth-facing slope near the town of Chernobyl. It isdefined on three sides by dikes and on the lowei part bya collection chute. The plot size is 50 m X 20 m; themean grade of the slope is 47o. The total aerial contam-ination in the experimental plot was determined to be 4g0+- 155 kBq m-' of "'Cs and 270 'r 48 kBq m-2 of eoSr

(* SD). The observations were carried out in winter and

Humuscontent

(Vo) Soil type

Plot HR

Root zone

Al HorizonB Homzon

0-8 51 8-12 sandy loam8 to 15-20 46-48 4-6 sandy loalll

15-20 to 40-50 46 1-2 sandy loal13

Plot SMI

Root zone

Plowld lay研

B Holttzon

一　

一　

一

5.8 4-5 sandy loam5.8 1-1.5 sandy loam

5.0-5.2 0.3-0.8 loamy sand-sand

Table 3. Characteristics of plot HR.

Characteristic Value

Water table depth (m)

Standing water depth duringartificial rain appl icatior.(mm)

Measured natural plecipitation atrunoff plot during 1986 (mm)

MayJuneJulyAugustSeptemberOctober

Biomass densitywet weight (g - ')dry weight (g m-')

Vertical distribution of soil densityin experimental plot HR

Layer (cm)

Voiumetric density (g cm-3 dryweight)

Porosity (Eo, cm3/cm3)Chemical forms of radionuclides

in the soil of plo{ HR prior toartificial rain application

Radionuclide

Mobile fomu (7o)

Non-exchangeable form (7o)

0.5-5(yearly average, 1.5)

5-10

20.5(cstmatcd)

39.5

19560144.6

264

510± 200130± 40

0-5 5-10

ｒと一Ｅ

ＥＥ

び中軍

ｃ鳩】

100

495

9°Sr

149

426

137cs

0 10 20 00 40 50 60 70 80 90

Hme,lnnin

Fig.2.Hydrograph of thc runoff dyna■ lics For plot i=R.

Ｊ

ｌ。

u Amount in solution and exfacted in 1 N ammonium aeetate solution.

Table 4. Characteristics of the artificial rain applied to plot HR.

Characteristic Valuc

Wash― ofC of 9° Sr alld 137cs● A V KoNOPLEV ET AL

Table 5. Characteristics of plot SM.

Characteristic Value

pH

Ionic composition of water (mg L-t)c*+K+Na+Mg"HCO3-

Start of rain application

Duration (nin)Rain amount (mm)Rainfall intensity (mm min-')Soil moisture content before rain

(Vo, gH2O g-r soil wet weight)

72

55

5

17

12

170

16:29 17:22

Soil density (0*10 cm)Soil porosity (0-10 cm)Snow storage in the snow melt

periodDepth of freezing (January and

February)pH of snow waterCation composition of snow water

(mg L-t)c**K+Na*NHo*Mg'*

155 g cm~3位 y、veight

375%(cm3 pcr Cm3)2351111n

60-100 cm

53

151.3

19144.4

16

218137

spring in the snow melt period of 1988 (March). Ahydrograph of the runoff dynamics is given in Fig. 3,Descriptions of the soil and of the snow water are givenin Tables I,2, 5, 6,7, 8, and 9.

ASSESSMENT TASKS

Predictions for experimental plot HR

Midpoint. Calculate the vertical distribution of thetotal amounts (Bq g-' dry weight) qld the percentage ofexchangeable forms of "'Cs and ""Sr in soil immedi-ately prior to rain application on 14 October 1986.Include the 957o confidence intervals about the bestestimates of the mean concentrations. Suggested soillayers are 0-0.5 cm, 0.5-1.0 cm, 1.0-2.0 cm,2.0-3.0cm. 3.0-5.0 cm. and 5.0-10.0 cm.

Endpoints.

1. Calculate the total concentrations (Bq L*1; of 137Cs

and eosr in surface runoff during the experiment,

18 19 20 21 22 23 24 25 26 27

date and iime,March 1988

Fig。 3.Hydl・ograph of thc mnoff dynamics for plot SM.

Table 6. Chemical forms of the radionuclides deposited withatmospheric fallout.^

RadionuclideWIobilc folib

%Non-exchangeable

fonn 7o

9°Sr137cs

a Samplcs wctt talcen dおly ttom fallout collcctors begl■ ning on 26 April

1986,consげ vcd by a spccial lncthod and storcd Tllc chcmical foms、 vere

deterlmned in the laboratory duttng 1988 Sal■lplcs、 vere dded and storcd

in scalcd contalners to e■ sure dlat the chellllcal forms measured、 verc thc

samc as、vtte depOsited Thc valucs arc intcgrated estmates bascd on the

total actvity rcccivcd by tlc plot over the entre tmc of initial depositionb AInount in soluion and exttactcd、 vith ammonium acetate

Table 7.Chelnical radionuclidc forms in thc soll of plot SM at thc

cnd ofthc cxpcimcnt(5 Ap五 11988).

Radlo■uclldc

Moblle forma

%Non-exchangeable

forlr' Vo

9°Sr137cs

' Water-soiuble * exchangeable,

together with the percentages in dissolved and partic-ulate (i.e., associated with suspended particles) forms.Include the 95Vo confidence intervals about the bestestimates of the mean concentrations.

2. Calculate the amounts (Bq) of t37Cs and eosr lostfrom the HR experimental plot in the 24 h sinceapplication began. Include the 957o confidence inter-vals about the best estimates of the mean values.

Predictions for experimental plot SM

Midpoint. Calculate the verlical distribution of totalamounts (Bq g-' dry weight) and the percentage ofexchangeable forms of "'Cs and "St in soil as of 15

March 1988. Include Ihe 957o confidence intervals aboutthe best estimates of the mean concentrations. Suggestedsoil layers are 0-0.5 cm, 0.5-1.0 cm, 1.0-2.0 cm,2.0-3.0 cm, 3.0-5.0 cm, and 5.0*10.0 cm.

ｒｂ

一、ぁ

〓のＣＯ中Ｌ一羊ＯＣっ、

12 Health Physics

Table 8. Air and soil temperature for plot SM during the snowmelt period of 1988.

Air temperature, 'CSoil temperature

(0-2 cm), 'C

■me ■meMarch1988 9:00 15:00 21:00 9,00 15,00 21:00

January 1996, Volume 70, Number 1

Acknowledgmenrs-This scenario was developed by A. V. Konoplev(Institute of Experimental Meteorology, SPA "Typhoon," Obninsk, Rus-sia) and F. O. Hoffman (SENES Oak Ridge, U.S.A.) on the basis ofexperiments carried out in the 30-km zone of the Chernobyl Nuclear PowerPlant by scientists from the Institute of Experimental Meteorology, SPA"Typhoon," Obninsk, Russia, and the Ukainian HydrometeorologicalInstitute, Kiev, Ukraine. We are grateful to SENES Oak Ridge, Inc., andpersonally to K. M. Thiessen and J. S. Hammonds for very helpfulcomments and valuable help in preparation of this manuscript for publi-cation.

REFERENCES

Bulgakov, A. A.; Konoplev, A. V. The role of chemicalspeciations of radionuclides in soils in their transfer tosurface runoff. In: Proceedings of the Interxational Sympo-sium on Radioecology, Chemical Speciation-Hot Parti-cles. Znojmo: Society of Czechoslovak Radioecologists12-16 October; 1992: 17 20.

Bulgakov. A. A.;_Konoplev, A. V.; Popov, V. E. Predictionof '"Sr and "'Cs behavior in soil-water system after theChernobyl accident. In: Ecological and geophysical aspectsof nuclear accidents. Moscow: Gidrometeoizdat', 1992:2l-42 (in Russian).

Hoffman, F. O.; Thiessen, K. M.;Watkins, B. Opportunities forthe testing of environmental transport models using dataobtained following the Chernobyl accident. Health Phys.70:5-7; 1996.

Konoplev, A. V.; Bulgakov, A. A. Behavior of the Chernobyl-origin hot particles in the environment. In: Proceedings ofthe International Symposium on Radioecology, ChemicalSpeciation-Hot Particles. Znojmo: Society of Czechoslo-vak Radioecologists 12-16 October, 1992: 56-60.

Konoplev, A. V.; Viktorova, N. V.; Virchenko, E. P., Popov,V. E.; Bulgakov, A. A.; Desmet, G. M. Influence ofagricultural countefineasures on the ratio of different chem-ical forms ofradionuclides in soil and soil solution. ScienceTotal Environ. 137:147-162; 1993.

Makhonko, K. P.; Silantiev, A. N.; Shkuratova, L G. Monitor-ing of environmental radioactivity in the vicinity of nuclearpower plants. Moscow: Gidrometeoizdat; 1985 (in Rus-sian).

Sereda, G. A.; Shulepko, Z. S. Methods of determination ofradioactivity of the environment. Vol. 2. Moscow: Gidrom-eteoizdat; 1966 (in Russian).

■ ■

Date

15

16

17

18

19

2021

22

23

24

25a

-65-36372.3

-25-25-4.6

10192.1

08

13041184115294.4

25454.4

75

-1,7

051.0

-08-20-0.5-050311162.5

-06 -373.9 -2.869 130.5 0.3

-14 -0714 -10

-2.1 -2.214 028 1139 146 0

a Rtlnoff ceased after 25 MIarch 1988.

Table 9.Variations in attnosphcdc prccipitaton at plot SM during

tllc s■ o■7 1nelt poビ lod of MIttch 1988.

Date 15■ 21 22 23 24 25 26 27 28-31

Precipitation, mm

Endpoints

1. Calculate the total concentrations (Bq L-i; of 137Cs

and eosr in surface runoff at the following timeperiods, together with the percentages in dissolvedand particulate (i.e., associated with suspended parti-cles) forms:a) at peak flow for 18 March 1988,20 March 1988,

and24 March 1988; andb) at the minimum flow on the night of 20 - 2I

March 1988.

Include Ihe 957o confidence intervals about the bestestimates of the mean concentrations.

2. Calculate the total amounts (Bq) of t3tcs and eosr

lost from the experimental plot as of 31 March 1988.Include the 957o confidence intervals about the bestestimates of the mean values.