TOCATTA status planed tritium experiments Sverine Le Dizs-Maurel - PowerPoint PPT Presentation

TOCATTA status  planed tritium experiments Séverine Le Dizès-Maurel National Institute of Nuclear Safety (IRSN) Cadarache, France 13/09/11

Why studying 14 C and 3 H? (1)  Carbon 14 and tritium are substantially released in the atmosphere around:  Nuclear Power Plants (NPP);  Nuclear Recycling Plants (NRP). 2/21 TOCATTA status  planned tritium experiments

Atmospheric releases NRP NPP 85 Kr = 99.97 % 4.00% 0.04% 20.20% 18.51% 77.49% 79.75% 3H 14C Other 3H 14C Other 3/21 TOCATTA status  planned tritium experiments

Why studying 14 C and 3 H ? (2)  Still significant uncertainties on 14 C and 3 H :  sampling and measurement;  evolution of the chemical form in the atmosphere, vegetation, soil and groundwater;  quantification of dry and wet deposition;  quantification of Organically Bound Tritium (OBT). 4/21 TOCATTA status  planned tritium experiments

The VATO project : VAlidation of the TOCATTA model  To estimate 14 C and 3 H fluxes in a grassland ecosystem ( raygrass sp ., soil and groundwater in both saturated and unsaturated zones), in relation with:  evolution of air concentrations (day versus night);  weather conditions;  land use (grazing, maïze silage and hay).  To study 14 C and 3 H transfers to cows and cowmilk as a function of In order to validate the TOCATTA model. 5/21 TOCATTA status  planned tritium experiments

14 C  3 H transfer modelling in TOCATTA (1)  Main characteristics ▌ Types of releases: atmospheric and / or liquid (spray irrigation) ▌ Main environmental media : agricultural systems (soil, plant and animals) ▌ Multiple source term kinetics : normal and accidental modes ▌ Physico-chemical forms of releases : 14 CO 2 , HTO ▌ Temporal scales:  Daily time step  Duration of simulation: ≥ 1 year(s) 6/21 TOCATTA status  planned tritium experiments

14 C and 3 H: transfer processes in a rural ecosystem in TOCATTA HTO vapor Source Rain 14 CO 2 Irrigation Ingestion Foliar inhalation absorption metabolism Wet deposition Net primary production Depuration OBT OBT 14 CO 2 Biological Wet deposition nic 14 14 C Organic Orga depuration on plant translocation HTO Biological HTO Volatilisation growth Wet deposition HTO vap on soil Litterfall translocation Surface exchange Decomposition Root absorption 14 CO 2 HTO 14 CO 2 +Translocation 14 C pathways 3 H pathways infiltration Diffusion Root 14 C and 3 H pathways exsudation 7/21 TOCATTA status  planned tritium experiments

14 C  3 H transfer modelling in TOCATTA (2)  Other characteristics ▌ A dynamic model  Based on plant biomass growth whose curves are either predefined or derived from experimental data  Based on the assumption of isotopic equilibrium between the quantity of newly created plant biomass and the surrounding air, at each time step (i.e. 1 day) ▌ Integrated in SYMBIOSE  Simple model, flexible, limited number of input parameters and compartments to be used in an operational mode  Model parameterized for various types of agricultural plants, broken down into three groups : annual crops, vegetable crops and pasture grass. Two categories of soils considered by default: sandy soil and clayey soil.  Conceptual (interaction matrix) and mathematical models (mass balance)  Dose man calculations through ingestion of contaminated foodstuffs 8/21 TOCATTA status  planned tritium experiments

The soil-plant system: conceptual model ( 3 H) SOURCE* Surface Net primary Foliar absorption CANOPY exchange production ATMOSPHERE Wet Input  Wet Input  Translocation (1-Captation) Root uptake Diffusion SOIL WATER  Translocation Migration Rad. decay Litterfall PLANT ORGANIC Grazing DRY MATERIAL Biol. decay Grazing PLANT WATER Rad. decay MATERIAL Litterfall Harvest REST OF Root exudation PLANT SINK *Tritiated water (HTO) presents in the atmosphere (air or water droplets) or in irrigation water. 9/21 TOCATTA status  planned tritium experiments

Mathematical model  First order differential equations  Conservation of mass within each compartment ▌ Stock or concentration of stable or radioactive C within compartment i: Stock Concentration (mol.m -2 ) (mol.kg -1 )    m m dA d [ C ]      p p ' i i i TC TC j , k k , l dt dt             k 1 k 1 input output Density Mass transfer fluxes (kg.m -2 ) (mol.m -2 .d -1 ) (with A i =0 à t=0) 10/21 TOCATTA status  planned tritium experiments

VATO project: in situ lab Releases of 14 C and 3 H by the reprocessing plant induce greater concentrations than background levels France EXPERIMENTAL SITE "Atelier Nord" 360 10 340 20 8 320 40 6 300 60 4 2 280 80 0 AREVA LA HAGUE NRP 260 100 240 120 220 140 200 160 180 Wind rose at La Hague "Atelier Nord": a well located experimental site, considering the most frequent wind directions 11/21 TOCATTA status  planned tritium experiments

VATO project: monitoring system 10 m mast with sonic anemometer (turbulence) Meteorological data acquisition Lab Grass, soil and groundwater (unsatured zone) Weather station 14 C/ 3 H trapping device (bubbling) CO 2 /H 2 O measurement acquisitions (LICOR 7000) Farm Groundwater Continuously Recording Field Monitor for sampling krypton 85 (satured zone) 12/21 TOCATTA status  planned tritium experiments

14 C concentration measurements in air, grass and soil 1400 Air Herbe 1200 Sol Herbe bruit de fond Concentration (Bq.kg -1 C) 1000 800 600 400 200 0 01/08/2006 29/11/2006 29/03/2007 27/07/2007 24/11/2007 23/03/2008 21/07/2008 18/11/2008 Date  Great fluctuations of the signal in air and grass due to the wind direction and the operation of the facility  No fluctuation in soil due to a poorly reactive pool of organic matter. 13/21 TOCATTA status  planned tritium experiments

14 C in grass: model versus measurements Grass C-14 activity (Bq/kgC) Observations TOCATTA 1200  Predicted values are lower (up to 40%) than measured concentrations 1000  Variability between months is underestimated 800 600 400 200 6 7 6 7 7 7 8 6 7 7 7 7 8 8 8 7 7 7 7 8 8 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 - - - - - - - - r - - r - r - - - - - r r - - - - r y y - r y y - e h e e h e e l y y t e e l y y e e r r i s r r i b r n b r n b c a l b b c a l b a a u b a a u p u p m m r M u m m m r M u u u u u o a A J g o a A J J J t e n r M u t e n r M e e e b b c c a a v c A v c O t O e e p o J o J e e F F 14/21 e N N D D S

Why this model under-estimation?  The model is based on a daily isotopic equilibrium between the quantity of newly created plant biomass and the surrounding air  In particular, there is no difference whether a release occurs during the day or during the night.  In other words, the model is better adapted for chronic releases than for accidental releases .  A new model is being built based on the PASIM* model. * Grassland ecosystem odel simulating the flow of carbon, nitrogen, water and energy at the soil-plant- atmosphere interface (Riédo et al., 1998; Vuichard, 1997)  collaboration between IRSN-INRA  Post-doctoral fellowship (C. Aulagnier, 01/2011- )  It will take into account plant physiology and local meterology. 15/21 TOCATTA status  planned tritium experiments

Conclusion (1)  The new model still needs further adaptations to take into account the acute variations in radionuclide releases and weather fluctuations. An hourly time-step is required:  to simulate photosynthesis: carbon 14 cycling;  to simulate water exchange: tritium cycling.  In order to evaluate the concentration of 14 C and 3 H (HTO, OBT) in the different compartments of rural ecosystem, from the atmosphere to the groundwater via grassland. 16/21 TOCATTA status  planned tritium experiments

14 C in grass: models versus measurements Grass C-14 activity (Bq/kgC) PASIM (sap - 15d average) 1200 PASIM Observations TOCATTA 1000 800 600 400 200 6 6 7 7 6 6 7 7 7 7 7 7 8 8 6 6 7 7 7 8 8 8 7 7 7 7 7 8 8 8 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 - - - - - - r - - - r - - r - - - - - r - - - - y y - r y y - r e h e r e h e e l y y t e e l y y e e r r i s r r i b b b c r a n l b b c r a n l b a a b a a p u u p u m m r M u m m m r M u u u u u o a A J g o a A J J J t n r M t n r M e e u e e e b b c c a a v A v O c t O c e e p o J o J e e F F e N N D D S 17/21

Conclusion/perspectives (2) ▌ Development of a new model ( TOCATTA_  ) for the atmosphere-soil- plant system  Integrates the key physiological processes of PASIM (photosynthesis, growth) at an hourly time-step  Intermediate level of complexity between TOCATTA and PASIM:  Retains the “mechanistic” aspect of PASIM in modelling C cycle,  While being simpler and therefore more operational  Accounts for the intra-day variability of 14 C releases ▌ Replacement of the TOCATTA model by TOCATTA_  in SYMBIOSE ?? 18/21 TOCATTA status  planned tritium experiments