Transcript IRSN - International Atomic Energy Agency

TOCATTA :
Transfer Of Carbon 14 And Tritium in Terrestrial and
Aquatic environments
Séverine Le Dizès
Environment and Emergency Operations Division
Department for the Study of Radionuclide Behavior in Ecosystems
Environmental Modelling Laboratory
Cadarache, St Paul-lez-Durance, France
September 28th, 2009
Plan
vPresentation of TOCATTA
ØConceptual model
ØMathematical model
vPresentation of VATO
vConclusions & perspectives
EMRAS II, Paris, 09/28/2009
Presentation of TOCATTA
C and H specificities
1. Integration of these radionuclides to living organic matter
2. Carbon14 and Tritium transfers within biotic compartments occur in the form of :
§ Organic matter and carbon dioxide (for 14C)
§ Organic matter and tritiated water (for tritium)
All these chemical forms are directly related to biomass (spatial and temporal growth), unlike other
radionuclides
Ø
14C
and 3H modeling (stocks, fluxes, residence time) does require dynamic models of biomass evolution (plant,
animal and/or microbial)
Ø More specifically, dynamic modeling of 14C and 3H in plants requires knowledge of plant growth dynamics
EMRAS II, Paris, 09/28/2009
Presentation of TOCATTA
Current 14C and 3H modeling in TOCATTA
§
Main environmental media : agricultural systems (soil, plant & animals)
§
Multiple source term kinetics : normal / accidental modes
§
Atmospheric and/or liquid releases
§
Temporal scales :
ü Daily time step
ü During one or several years
§
Dose man calculations through ingestion of contaminated foodstuffs (SYMBIOSE)
EMRAS II, Paris, 09/28/2009
Presentation of TOCATTA
Precipitation
HTOvapor
Source
14CO
2
Evapotranspiration
NetPrimaryProduction
HTO
14C
Foliar
absorption
HTO
Biological decay
organic
OBT
Diffusion 14CO2
Literfall
translocation
HTO
Microbial activity
14C
pathways
3H pathways
14C and 3H pathways
EMRAS II, Paris, 09/28/2009
Root absorption
Évaporation HTO
irrigation
infiltration
Presentation of TOCATTA
Conceptual model
Ø Carbon 14
Plant
(Organ)
Winter cereals
Spring cereals
Fruit vegetable
Root vegetables
Leaf vegetables
Grass
Ø Tritium
OrganicMatter
RadioactiveDecay
BiologicalGrowth
Grazing*
RestOfPlant
NetPrimaryProduction
Diffusion
RestOfWorld
Plant
(Organ)
Winter cereals
Spring cereals
Fruit vegetable
Root vegetables
Leaf vegetables
Grass
Water
RadioactiveDecay
BiologicalDecay
Grazing*
Grazing *
OrganicMatter
RadioactiveDecay
BiologicalGrowth
RestOfPlant
*For grass only
FoliarAbsorption
WetInputPlantTranslocation
RootUptakeTranslocation
NetPrimaryProduction
RestOfWorld
Presentation of TOCATTA
Mathematical model (1)
§
First order differential equations
§
Mass conservation balance of pollutant in each compartment
§
Example : Transfer of 14CO2 from Air to Grass :
d
1
Gra
Rad
[C _ 14C ]P.S 
 (TC14PNpp  TC14Diff

TC
14

TC
14
P. S
P
P )
dt
 P _ Om
Diffusion
NetPrimaryProduction
Plant dry density
Logistic or exponential model
EMRAS II, Paris, 09/28/2009
Grazing
RadioactiveDecay
Presentation of TOCATTA
Mathematical model (2)
Gro
TC14PNpp
 d P _ Om 


dt


Gro
TOBTPNpp
 d P _ Om 


dt


 [C _ 12C ]P 
[C _ 14C ] Air
[C _ 12C ] Air
pHTO  [C _ 3H ] Air  FDPf  DI P
 [ H ]P 
[ H ]Air
Assumptions :
1.
Use of a daily time step (current version)
2.
Isotopic equilibrium between newly created plant biomass and surrounding air, at each time step
3.
Growth curves are logistics (cereals) or exponential (grass, leaf-, fruit- or root vegetables)
4.
Isotopic discrimination factor for tritium entering plant organic matter
EMRAS II, Paris, 09/28/2009
Presentation of VATO
VATO
VAlidation of TOcatta
Séverine Le Dizès1, Denis Maro2 & Didier Hébert2
1IRSN/DEI/Environmental
Modelling Laboratory/Cadarache, St-Paul-lez-Durance
2IRSN/Laboratory of Continental Radioecology/Cherbourg-Octeville
EMRAS II, Paris, 09/28/2009
Presentation of VATO
Goals
v Estimate fluxes of 14C and 3H in a grassland ecosystem (Raygrass), in relation with :
- 14C and 3H concentrations in air,
- Climate conditions,
- Land use (grazing, maïze silage and hay).
v Study transferts of 14C and 3H to cows and cowmilk in function of the alimentary diet.
In order to validate the TOCATTA model
EMRAS II, Paris, 09/28/2009
Presentation of VATO
Agenda
Carbon 14
2007-2009 : Transfers between air, grass and soil
2009-2010 : Transfers to cow
2008-2009 : Model-measures comparisons
2010 : Publication
Tritium
2010 : Measurement (speciation of 3H releases in air)
2010-2011 : Transfers between air, rain water, grass and soil
2012 : Transfers to cow
2011-2012 : Model-measures comparison
2012 : Publication
EMRAS II, Paris, 09/28/2009
Presentation of VATO
Site location
Important releases of 14C and 3H by the
AREVA NC La Hague reprocessing plant
Important concentrations
environment
in
the
Wind conditions 2008 - "Omonville La Petite".
Wind speed (m.s-1) and Direction (°)
340
360
10
20
8
320
EXPERIMENTAL SITE
 Ateli er Nord 
40
6
300
60
fréq dir (%)
4
2
280
80
0
260
100
240
120
220
AREVA LA HAGUE
140
200
160
180
« Atelier Nord » : a well located experimental site, considering the most frequent wind directions
EMRAS II, Paris, 09/28/2009
Presentation of VATO
Experimental design
10 m mast with sonic anemometer (turbulence)
Meteorological data acquisition
Lab
Grass (Raygrass)
Weather station
14C
CO2 measurement acquisition (LICOR 7000)
Fram
Continuously Recording Field Monitor for Krypton-85
trapping device (bubbe gas through soda)
Presentation of VATO
Main assumptions of the plant submodel
1.
Use of a daily time step
2.
Grass growth is linear based on monthly dry weight data
Estimation of a daily growth rate
Ø
3.
Air concentration data are measured each month
Ø
Daily air concentration inputs are assumed to be constant over the month
EMRAS II, Paris, 09/28/2009
Presentation of VATO
Comparison of measured and calculated 14C specific activities
1300
Air
1200
Measured Grass Zones1&2
1100
Measured Soil Zones1&2
Uncontaminated Soil
1000
Uncontaminated Grass
900
Simulated Grass Zones1&2
Bq/kg C
800
700
600
500
400
300
200
100
0
01/08/06
09/11/06
17/02/07
28/05/07
05/09/07
Measured Grass 14C activities > Measured Air 14C activities
> Simulated Grass 14C activities
EMRAS II, Paris 09/28/2009
14/12/07
23/03/08
01/07/08
Presentation of VATO
Two ways of improving the comparison between modeled/measured activities :
1.
Regarding the model itself : the specific activity concept is adapted for chronic releases
Need to improve the model in terms of kinetics to adapt it to time varying releases and meteorology
Use of an hourly-based growth model for grass in function of local meteorological data
2.
Regarding the 14C releases : the atmospheric 14C concentrations are measured on a monthly basis
Need to improve the calculations in terms of kinetics (e.g. every hour)
Use of the hourly 85Kr data
EMRAS II, Paris 09/28/2009
Presentation of VATO
A model of grass growth
Johnson et al. (1983) A model of Grass Growth, Ann. Bot. 51, 599-609.
Johnson and Thornley (1983) Vegetative crop growth model incorporating leaf area expansion and senescence, and applied to grass, Plant, Cell and
Environment 6, 721-729.
§ A compartmental model based on an hourly time step
Light interception
Photosynthesis
 dWS 
 dt   P  G / Y  Rm


Root growth and
maintenance
Maintenance respiration,
Rm
Storage dry weight, WS
Growth, G
Growth respiration, Rg
Structural dry weight, WG
Senescence
EMRAS II, Paris 09/28/2009
 dWG 
 dt   G  S


 dL

 dt

  G  S

  m(1  W / Ws )
Presentation of VATO
Calculation of atmospheric 14C on an hourly basis
Krypton 85 : a good indicator of 14C atmospheric dispersion over a short periodicity
Hourly 14C atmospheric concentration
EMRAS II, Paris 09/28/2009
Presentation of VATO
Comparison of measured and calculated aboveground dry matter
EMRAS II, Paris 09/28/2009
Presentation of VATO
Comparison of measured and calculated 14C specific activities
EMRAS II, Paris 09/28/2009
Presentation of VATO
Conclusions
§ To adapt the model to time varying releases and meteorology, an hourly time-step is required :
Ø To estimate 14C air concentration inputs to the model, based on hourly 85Kr data
Ø To simulate photosynthesis and plant growth dynamics
§ The VATO projects supports the approach to use plant physiological parameters within 14C (and tritium) models
EMRAS II, Paris 09/28/2009
Presentation of VATO
Perspectives
§
To adress dynamic modeling of 14C and 3H in plants, ongoing effort should be addressed to improve the modelling
of photosynthesis and dry matter production
§
Concerning 3H modelling in case of time varying releases and meteorology, it is also necessary to consider
most of the relevant water transfer processes with a dynamic approach based on a short time step.
§
Use of PASIM*, a biogeochemical grassland ecosystem model that simulates fluxes of C, N, water and energy at
the soil-plant atmosphere interface.
A collaboration starts in October with INRA (Clermont-Ferrand).
*Riédo et a., 1998. A Pasture Simulation Model for dry matter production, and fluxed of carbon, nitrogen, water and energy. Ecol. Model. 105,
141-183.
EMRAS II, Paris 09/28/2009
Compartment models (1)
Advantages
ü Simple structure (e.g. Model of Johnson, 2 compartments)
ü Generic, flexible : can be used to test scenarios
ü Simple ordinary differential equations
ü A simplification of the mathematical model (variables are represented as singli scalars instead of spatially
distributed fields)
EMRAS II, Paris, 09/28/2009
Compartment models (2)
Drawbacks
ü Can not be spatially explicit (e.g.PaSim : no spatial heterogeneity)
ü The model parameters are less likely to be physiological (constant coefficients)
EMRAS II, Paris, 09/28/2009
Thank you for your attention !