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Séverine Le Dizès Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ec

TOCATTA : T ransfer O f C arbon 14 A nd T ritium in T errestrial and A quatic environments. Séverine Le Dizès Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ecosystems Environmental Modelling Laboratory

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Séverine Le Dizès Environment and Emergency Operations Division Department for the Study of Radionuclide Behavior in Ec

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  1. 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

  2. Plan • Presentation of TOCATTA • Conceptual model • Mathematical model • Presentation of VATO • Conclusions & perspectives EMRAS II, Paris, 09/28/2009

  3. Presentation of TOCATTA C and H specificities • Integration of these radionuclides to living organic matter • 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 • 14C and 3Hmodeling (stocks, fluxes, residence time) does require dynamic models of biomass evolution (plant, animal and/or microbial) • More specifically, dynamic modeling of 14C and 3H in plants requires knowledge of plant growth dynamics EMRAS II, Paris, 09/28/2009

  4. 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 : • Daily time step • During one or several years • Dose man calculations through ingestion of contaminated foodstuffs (SYMBIOSE) EMRAS II, Paris, 09/28/2009

  5. Presentation of TOCATTA HTOvapor 14CO2 Evapotranspiration HTO HTO Biological decay Literfall translocation HTO Source Precipitation NetPrimaryProduction Foliar absorption 14Corganic OBT Diffusion 14CO2 Évaporation HTO irrigation Microbial activity infiltration 14C pathways 3H pathways 14C and 3H pathways Root absorption EMRAS II, Paris, 09/28/2009

  6. Presentation of TOCATTA • Winter cereals • Spring cereals • Fruit vegetable • Root vegetables • Leaf vegetables • Grass • Winter cereals • Spring cereals • Fruit vegetable • Root vegetables • Leaf vegetables • Grass Conceptual model • Carbon 14 • Tritium *For grass only

  7. Presentation of TOCATTA Logistic or exponential model Mathematical model (1) • First order differential equations • Mass conservation balance of pollutant in each compartment • Example : Transfer of 14CO2 from Air to Grass : Diffusion Grazing RadioactiveDecay NetPrimaryProduction Plant dry density EMRAS II, Paris, 09/28/2009

  8. Presentation of TOCATTA Mathematical model (2) Assumptions : • Use of a daily time step (current version) Isotopic equilibriumbetween newly created plant biomass and surrounding air, at each time step Growth curves are logistics(cereals) or exponential (grass, leaf-, fruit- or root vegetables) • Isotopic discrimination factor for tritium entering plant organic matter EMRAS II, Paris, 09/28/2009

  9. Presentation of VATO VATO VAlidationof 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

  10. Presentation of VATO In order to validatethe TOCATTA model Goals • Estimate fluxes of 14C and3H in a grassland ecosystem (Raygrass), in relation with : • - 14C and 3H concentrations in air, • - Climate conditions, • - Land use (grazing, maïze silage and hay). • Study transferts of 14C and 3H to cows and cowmilk in function of the alimentary diet. EMRAS II, Paris, 09/28/2009

  11. 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

  12. Presentation of VATO Important concentrations in the environment EXPERIMENTAL SITE « Ateli er Nord » AREVA LA HAGUE EMRAS II, Paris, 09/28/2009 Site location Important releases of 14C and 3H by the AREVA NC La Hague reprocessing plant « Atelier Nord » : a well located experimental site, considering the most frequent wind directions

  13. Presentation of VATO Experimental design 10 m mast with sonic anemometer (turbulence) Meteorological data acquisition Lab Grass (Raygrass) Weather station 14C trapping device (bubbe gas through soda) CO2 measurement acquisition (LICOR 7000) Fram Continuously Recording Field Monitor for Krypton-85

  14. Presentation of VATO Main assumptions of the plant submodel Use of a daily time step • Grass growth is linear based on monthly dry weight data • Estimation of a daily growth rate • Air concentration data are measured each month • Daily air concentration inputs are assumed to be constant over the month EMRAS II, Paris, 09/28/2009

  15. Presentation of VATO Comparison of measured and calculated 14C specific activities Measured Grass 14C activities > Measured Air 14C activities > Simulated Grass 14C activities EMRAS II, Paris 09/28/2009

  16. Presentation of VATO Two ways of improving the comparison between modeled/measured activities : 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 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

  17. Presentation of VATO Light interception Photosynthesis Root growth and maintenance Maintenance respiration, Rm Storage dry weight, WS Growth, G Growth respiration, Rg Structural dry weight, WG Senescence A model of grass growthJohnson 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 EMRAS II, Paris 09/28/2009

  18. Presentation of VATO Calculation of atmospheric 14C on an hourly basisKrypton 85 : a good indicator of 14C atmospheric dispersion over a short periodicity Hourly 14C atmospheric concentration EMRAS II, Paris 09/28/2009

  19. Presentation of VATO Comparison of measured and calculated aboveground dry matter EMRAS II, Paris 09/28/2009

  20. Presentation of VATO Comparison of measured and calculated 14C specific activities EMRAS II, Paris 09/28/2009

  21. Presentation of VATO Conclusions • To adapt the model to time varying releases and meteorology, an hourly time-step is required : • To estimate 14C air concentration inputs to the model, based on hourly 85Kr data • 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

  22. 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

  23. Compartment models (1) Advantages • Simple structure (e.g. Model of Johnson, 2 compartments) • Generic, flexible : can be used to test scenarios • Simple ordinary differential equations • A simplification of the mathematical model (variables are represented as singli scalars instead of spatially distributed fields) EMRAS II, Paris, 09/28/2009

  24. Compartment models (2) Drawbacks • Can not be spatially explicit (e.g.PaSim : no spatial heterogeneity) • The model parameters are less likely to be physiological (constant coefficients) EMRAS II, Paris, 09/28/2009

  25. Thank you for your attention !

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