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

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TOCATTA status  planed tritium experiments

Séverine Le Dizès-Maurel

National Institute of Nuclear Safety (IRSN) Cadarache, France

13/09/11

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2/21

Why studying 14C and 3H? (1)

Carbon 14 and tritium are substantially released in the atmosphere

around:

Nuclear Power Plants (NPP);
Nuclear Recycling Plants (NRP).

TOCATTA status  planned tritium experiments

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Atmospheric releases

NRP NPP

4.00% 18.51% 77.49%

3H 14C Other

79.75% 20.20% 0.04%

3H 14C Other

85Kr = 99.97 %

TOCATTA status  planned tritium experiments

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4/21

Why studying 14C and 3H ? (2)

Still significant uncertainties on 14C and 3H:
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).

TOCATTA status  planned tritium experiments

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To estimate 14C and 3H 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).

The VATO project : VAlidation of the TOCATTA model

To study 14C and 3H transfers to cows and cowmilk as a function of

TOCATTA status  planned tritium experiments

In order to validate the TOCATTA model.

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14C  3H transfer modelling in TOCATTA (1)

 Main characteristics

▌Types of releases: atmospheric and / or liquid (spray irrigation)

TOCATTA status  planned tritium experiments

▌Main environmental media : agricultural systems (soil, plant and animals) ▌Multiple source term kinetics : normal and accidental modes ▌Physico-chemical forms of releases : 14CO2, HTO ▌Temporal scales:

Daily time step
Duration of simulation: ≥1 year(s)

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HTOvapor Source Foliar absorption Irrigation Root absorption

14C pathways 3H pathways 14C and 3H pathways

infiltration Biological depuration 14C and 3H: transfer processes in a rural ecosystem in TOCATTA Wet deposition

14CO2

Rain OBT OBT HTO translocation Diffusion HTO translocation Depuration Ingestion inhalation

metabolism

Biological growth Surface exchange HTOvap HTO Wet deposition

n plant

Wet deposition

n soil

Orga Organic nic14

14C

Litterfall Net primary production Decomposition +Translocation

14CO2

Volatilisation

14CO2 14CO2

Root exsudation

TOCATTA status  planned tritium experiments

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14C  3H 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

TOCATTA status  planned tritium experiments

▌Integrated in SYMBIOSE

Simple model, flexible, limited number of input parameters and compartments to be

used in an operational mode

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)

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

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The soil-plant system: conceptual model (3H)

SOURCE* CANOPY ATMOSPHERE

Surface exchange Wet Input (1-Captation) Net primary production Foliar absorption Wet Input Translocation

SOIL WATER

Root uptake Translocation Diffusion Migration

PLANT ORGANIC DRY MATERIAL

Rad. decay

Litterfall Grazing

PLANT WATER MATERIAL

Biol. decay
Rad. decay

Grazing Litterfall Root exudation

REST OF PLANT

Harvest

SINK

*Tritiated water (HTO) presents in the atmosphere (air or water droplets) or in irrigation water.

TOCATTA status  planned tritium experiments

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Mathematical model

▌Stock or concentration of stable or radioactive C within compartment i:

 First order differential equations  Conservation of mass within each compartment

Density (kg.m-2)

 

         

utput

m k p l k input m k p k j i i i

TC TC dt C d dt dA

 

 

  

1 ' , 1 ,

] [ 

Stock (mol.m-2) Mass transfer fluxes (mol.m-2.d-1)

(with Ai=0 à t=0)

Concentration (mol.kg-1)

TOCATTA status  planned tritium experiments

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VATO project: in situ lab

EXPERIMENTAL SITE "Atelier Nord"

AREVA LA HAGUE NRP

2 4 6 8 10 360 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340

"Atelier Nord": a well located experimental site, considering the most frequent wind directions Releases of 14C and 3H by the reprocessing plant induce greater concentrations than background levels France Wind rose at La Hague

TOCATTA status  planned tritium experiments

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VATO project: monitoring system

Continuously Recording Field Monitor for krypton 85 10 m mast with sonic anemometer (turbulence) Weather station Lab Meteorological data acquisition CO2/H2O measurement acquisitions (LICOR 7000) Farm Grass, soil and groundwater (unsatured zone)

14C/ 3H trapping device

(bubbling) Groundwater sampling (satured zone)

TOCATTA status  planned tritium experiments

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14C concentration measurements in air, grass and soil

Great fluctuations of the signal in air and grass due to the wind direction and

the operation of the facility

200 400 600 800 1000 1200 1400 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 Concentration (Bq.kg-1 C) Air Herbe Sol Herbe bruit de fond

TOCATTA status  planned tritium experiments

No fluctuation in soil due to a poorly reactive pool of organic matter.

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14/21 200 400 600 800 1000 1200

Observations TOCATTA

O c t

b

e r

6

N

v

e m b e r

6

D e c e m b e r

6

J a n u a r y

7

F e b r u a r y

7

M a r c h

7

A p r i l

7

M a y

7

J u n e

7

J u l y

7

A u g u s t

7

S e p t e m b e r

7

O c t

b

e r

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N

v

e m b e r

7

D e c e m b e r

7

J a n u a r y

8

F e b r u a r y

8

M a r c h

8

A p r i l

8

M a y

8

J u n e

8

J u l y

8

Grass C-14 activity (Bq/kgC)

14C in grass: model versus measurements

Predicted values are lower (up to 40%) than measured concentrations
Variability between months is underestimated

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Why this model under-estimation?

The model is based on a daily isotopic equilibrium between the quantity
f newly created plant biomass and the surrounding air

TOCATTA status  planned tritium experiments

 collaboration between IRSN-INRA  Post-doctoral fellowship (C. Aulagnier, 01/2011- )

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)

It will take into account plant physiology and local meterology.
In particular, there is no difference whether a release occurs during the day or

during the night.

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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.

TOCATTA status  planned tritium experiments

In order to evaluate the concentration of 14C and 3H (HTO, OBT) in the

different compartments of rural ecosystem, from the atmosphere to the groundwater via grassland.

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200 400 600 800 1000 1200 6 6 6 7 7 7 7 8 8 O c t

b

e r

6

N

v

e m b e r

6

D e c e m b e r

6

J a n u a r y

7

F e b r u a r y

7

M a r c h

7

A p r i l

7

M a y

7

J u n e

7

J u l y

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A u g u s t

7

S e p t e m b e r

7

O c t

b

e r

7

N

v

e m b e r

7

D e c e m b e r

7

J a n u a r y

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F e b r u a r y

8

M a r c h

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A p r i l

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M a y

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J u n e

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J u l y

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Grass C-14 activity (Bq/kgC) PASIM (sap - 15d average) PASIM Observations TOCATTA

14C in grass: models versus measurements

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▌ Development of a new model (TOCATTA_) for the atmosphere-soil-

plant system

Intermediate level of complexity between TOCATTA and PASIM:

 Retains the “mechanistic” aspect of PASIM in modelling C cycle,

Accounts for the intra-day variability of 14C releases
Integrates the key physiological processes of PASIM (photosynthesis, growth)

at an hourly time-step

▌ Replacement of the TOCATTA model by TOCATTA_ in SYMBIOSE ??

 While being simpler and therefore more operational

TOCATTA status  planned tritium experiments

Conclusion/perspectives (2)

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Posters  publications

▌ S. Le Dizès, D. Maro, D. Hebert, M.-A. Gonze, C. Aulagnier. TOCATTA: a dynamic transfer

model of 14C from the atmosphere to soil-plant systems.

 Accepted to the J. Env. Radioact. (Sept 6th, 2011)

▌ C. Aulagnier, S. Le Dizès, D. Maro, D. Hebert, R. lardy, R.Martin, M.-A. Gonze. Modelling

chronic and accidental releases of 14C to the environment : A case study in a grass field near AREVA-NC La Hague.

 Submitted to the J. Env. Radioact. (Sept. 1st, 2011)

▌ C. Aulagnier, S. Le Dizès, D. Maro, D. Hebert, R. lardy, R.Martin, M.-A. Gonze. New TOCATTA

model developments for accidental release scenarios.

 To be submitted (end of year 2011)

▌ 2 posters: “Proceedings ICRER 2011, 19-24 June, Hamilton (Canada)”:

Maro et al.: Modelling and validating 14C transfer in terrestrial environments in response to 14C

releases

Le Dizès et al.: Modelling 14C transfer in terrestrial environments in response to chronic and

accidental 14C releases

TOCATTA status  planned tritium experiments

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Measurements in air, grass and soil Measurements in air, rain water, grass, soil, soil unsaturated zone, and ground water Measurements in cow milk Model-measures comparison

▌ Carbon 14 ▌ Tritium

2014 2013 2012 2011

Measurements in cow milk Model-measures comparison

Agenda

2012 2011 2010 2009 2008 2007 2006

Model adjustment and publications Model adjustment and publications

TOCATTA status  planned tritium experiments

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Planned 3H studies

▌Probably a collaboration of IRSN with the Canadian Nuclear Safety Commission (CNSC, Ottawa) that will be discussed and validated in November ▌“Transfer of tritium in a grassland ecosystem”: main characteristics:

A 4-year project
Comparison of materials and sampling and measurement techniques in

vegetation, soil and groundwater

Study and comparison of mass balance and fluxes of water and tritium in two

grassland ecosystems

Model analysis and comparison
Other aspects/uncertainties :

atmospheric dispersion of the plume, chemical forms of 3H release (HTO/HT) in the atmosphere quantification of wet and dry deposition quantification of OBT …

TOCATTA status  planned tritium experiments

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SYMBIOSE: A Modeling and Simulation Platform for Environmental Radiological Risk Assessments (1/2)

Purpose: Risk assessment calculations
fate and transport of radionuclides in ecosystems;
dose to man.
Flexible approach to deal with a wide range of situations
multiple

radioactive releases (atmospheric, fluvial, and/or marine) from nuclear facilities under normal, incidental or accidental conditions;

multi-media (atmospheric, terrestrial, freshwater and marine)

and interfaces;

multiple exposure routes (external, inhalation, ingestion…).

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Calculations
reference data bank with generic versus site-specific data;
dynamical (physically-based) and spatially-distributed modeling;
including daughters (radioactive decay chains);
specific models to deal with hydrogen, carbon and chlorine.

SYMBIOSE: A Modeling and Simulation Platform for Environmental Radiological Risk Assessments (2/2)

TOCATTA model

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Grazing litterfall Biological growth Plant dry density Plant dry density Predefined growth model

r empirical growth data

▌Example : Transfer of tritium from atmosphere to vegetation

(organic pool) :

       dt d t

P P Gro P

   1 ) (

Relative growth rate (d-1)

Mathematical model: the plant module (1)

Radioactive decay NetPrimaryProduction

TOCATTA status  planned tritium experiments

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▌Hypothesis:

Daily time-step (current version)
Isotopic equilibrium between the quantity of newly created plant biomass

and the surrounding air, at each time step (i.e. 1 day)

Logistic growth curves (cereals), exponential (prairie) or linear (leafy

vegetables, fruit vegetables, root vegetables), or empirical data, if available

Isotopic discrimination of tritium when entering vegetation

Air

] [ ] 3 _ [ ] [ ) 1 ( H DI H C p H f f TOBT

P Air HTO P Gro P S P S P Npp P

       

Relative growth rate (d-1)

Mathematical model: the plant module (2)

TOCATTA status  planned tritium experiments