Development dynamic compartment modelsto predict behavior of radionuclides

in rice paddy field

Tomoyuki TAKAHASHI

Kyoto University Research Reactor InstituteOsaka, Japan

My main experiences on development of dynamic compartment models

BIOMOVS II uranium mill tailings scenario (U-238 chain) with Dr. Homma and Dr. Togawa (JAEA)

Transfer of tritium by river network at Toki site with Dr. Yamanishi (NIFS) Dr. Momoshima and Dr. Sugihara (Kyushu Univ.)

Behavior of radionuclides in rice paddy field - Iodine, Cesium and Strontium - Carbon-14 (EMRAS I) with Dr. Uchida, Dr. Tagami, Dr. Ishii and Dr. Takeda (NIRS) Dr. Yamamoto (Y first Inc.) Dr. Tomita and Dr. Hayashi (V.I.C. Inc.)

BIOMOVS II uranium mill tailings scenario (U-238 chain)

Source term: - Groundwater release (leaching from tailings pile) - Atmospheric release (dust and gas from tailings pile)

Dynamic compartment: Vegetable land and pasture land

Deterministic analysis -Time dependent annual total dose (each nuclides and total)Probabilistic analysis - Cumulative distribution functions of peak total dose - Time dependent 90% confidence interval - Statistical coefficients between variable parameters and peak

total dose

River and sampling points of river waters in Toki area

Meeting point

B-1B-1

BasinB-3

A-1A-2

A-3

C-2

BasinC-1

F-1F-3

F-2

Basin

Downstream

Network of rivers assumed in the analysis

Ikuta river Tsumaki river

Toki river

Surface flow River water River water

of downstream

Groundwater Infiltration

Rainfall

Evaporation

(a) Basin

River water

River water of upstream

River water of downstream

River water of upstream

(b) Meeting point

Compartment models for basin and meeting point

A migration prediction code "MOGRA" was used

0.0

1.0

2.0

3.0

4.0

5.0

1982 1984 1986 1988 1990 1992

Calender year

Con

cent

ratio

n of

triti

um in

wat

er (

Bq

L-1

)

Measured concentration in groundwater

Estimated concentration in groundwater at B-1 point

Estimated concentration in river water at B-1 point

Measured concentration at B-3 point

Measured concentration at B-1 point

Measured concentration at B-2 point

Measured and estimated tritium concentration in river water and groundwater

Behavior of radionuclides in rice paddy field Background and objectives

Appropriate estimation of internal dose by the pathway of ingestion of rice which is a staple food in Asian countries

Reasonable dose assessment caused by nuclear facilities

Prediction of behavior of radionuclides in rice paddy field

Development of dynamic compartment models for some

important radionuclides

Hull Bran Rice

Deeper zone

Water

Leaf & stem

Sorption & desorptionSorption & desorption

Ear

TranslocationTranslocation

AirRain

Outside

Outside

OutflowOutflow

InfiltrationInfiltration

　　　　　　　　　　　　 Surface water　　　　　　　　　　　

ChangeChange

Leaf & stemthrough

Soil (slow)

VolatilizationVolatilization

HarvestHarvest

WeatheringWeathering

Leaf & steminternal

Outside

Root uptakeRoot uptake

Soil (fast)

Leaf & stemsurface

IrrigationIrrigation

DepositionDeposition

PlowingPlowing

PlowingPlowing

TranslocationTranslocation

Sorption & desorptionSorption & desorption

InfiltrationInfiltration

Structure of compartment model for I, Cs and Sr

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80 100 120

Days after planting (days)

Nor

mar

ized

wei

ght(

-)

Growing curve of rice plant

Estimated parameters

g(0))g(T

g(0)-g(t)WW(t)

Hmax

)T-K(t

)T-K(t

1/2

1/2

101

10g(t)

K(d-1) T1/2(d) Wmax(g)

Total 0.06 54 12.3

Ear 0.09 66 7.1

Leaf & stem = Total - Ear

Ishizuka & Tanaka (1953)

WLeaf =WTotal-WEar

Leaf & stem

WEar

Ear

WTotal

Total

Growing curve

14C is one of the most critical radionuclide for the safety assessment - Nuclear fuel reprocessing plant - Radioactive waste disposal plant

Developed a dynamic compartment model to predict 14C behavior in rice paddy field and its concentration in rice grains

Development of a Dynamic Compartment Model for Prediction of Transfer of Carbon-14 to Rice Grains

First stepThe source term was considered as 14CO2

released into the atmosphere

Second stepThe source term was considered as 14C

with the irrigation water

Leaf & stemorganic

Earorganic

Plant inorganic

Soil

Air

Inflow

Outflow

Respiration

Respiration

Photosynthesis

Translocation

Translocation

Translocation

AbsorptionPhotosynthesis

Uptake Release

Structure of compartment model for 14Cfrom the atmosphere

Exchange

Revise to more appropriate parameter values

Leaf & stem organic Ear organic

Plant inorganic

Soil 1

Air nearbyrice plant

Respiration

PhotosynthesisTranslocation

Exchange

Exchange

Photosynthesis

Uptake Release

Scheme of compartment model for 14Cfrom the irrigation water

Soil 2

Sink

Irrigated water

Respiration

Exchange

Infiltration

Source Sink

OutflowIrrigationExchange

Absorption

Root uptake

Air

InfiltrationMixture

Outside

Exchange ExchangeVolatilization

Mixture

Leaf & stem organic Ear organic

Plant inorganic

Soil 1

Air nearbyrice plant

Respiration

PhotosynthesisTranslocation

Exchange

Exchange

Photosynthesis

Uptake Release

Scheme of compartment model for 14Cfrom the irrigation water

Soil 2

Sink

Irrigated water

Respiration

Exchange

Infiltration

Source Sink

OutflowIrrigationExchange

Absorption

Root uptake

InfiltrationMixture

Outside

Exchange ExchangeVolatilization

Estimation of parameter values from batch experiment with Dr. Uchida, Dr. Tagami, Dr. Ishii and Dr. Yamamoto

Important pathway

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8 9 10

日数

各相

の存

在割

合

0

20

40

60

80

100

120

140

160

180

200

(ml/

g)固

液分

配比

ai rwatersoi l固液分配比

GasWaterSoil Soil/water

Con

c. in

soi

l / C

onc.

in w

ater

(m

L/g

)

Dis

trib

utio

n in

eac

h ph

ase

(%)

days

Estimation of transfer parameters between soil, water and air