Mo Modell llin ing and vali lidatio ion of f trit itiu ium - - PowerPoint PPT Presentation

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Mo Modell llin ing and vali lidatio ion of f trit itiu ium uptake, , re-emis issio sion and OBT BT fo formatio ion in in t tomato and potato pla lants at CR CRL

Environmental Technologies Branch, Nuclear Sciences Division, CRL, AECL

VY Korolevych and SB Kim

September 8, 2010, Aix-en-Provence

Objective

Modelling of airborne tritium in plants with emphasis on partitioning between

• rganically bound tritium (OBT) and

tissue free water tritium (HTO).

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Issue

Long term models consider Plant on SA grounds (OBT ~ HTO ~ Air HTO), while OBT/HTO ratios collected in numerous experiments span the range of 0.2-40.0 and are rarely seen = 1.0 (as SA concept would suggest). Predictions of short-term (dynamical) models start scattering far from observations in a long term. Uncertainties in modelling of Plant compartment directly affect total tritium dose.

__________________________________________ * IAEA EMRAS I, Tritium WG, S-Scenario

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Terrestrial Tritium Transfer: Key reasons for uncertainly

Assumptions behind modelling of HTO re-emission from plant and retained amount of HTO are not fully understood; Theory of OBT formation in plants and its validation is incomplete; Fractionation of OBT into exchangeable (like HTO) and non- exchangeable (like carbon) forms is important and needs more research; Further OBT translocation via roots and decomposition both in roots and within soil in the first place) is insufficiently studied.

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Tritium Pathways (this study)

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1500

2000 4000 6000 8000 10000 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 TBq/year Year

Gaseous Liquid

Source: CNSC

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Tritium Pathways (this study)

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Tritium Pathway via Plant Water and its Ambient Drivers (modelling)

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Credits:http://crew.iges.org

CLASS

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(D.L. Verseghy et al. Atmosphere-Ocean, V38, N1, 2000 Special Issue, 269 p.)

(Can. Land Surface Scheme) 2000 ~2007

CTEM (Can. Terrestrial Ecosystem Model)

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• V. Arora, 2007

CTEM+CLASS

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Source: CTEM manual v1.1

Tritium Translocation in CTEM+CLASS framework

AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL

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HTOSOL1 HTOSOL2 HTOSOL3 OBTRT2 OBTRT1 OBTSTEM OBTRT3 OBTLEAF HTOATM HTOLF

AECL Model

Diffusion (V

ex), Catm

Advection (E), Csoil Diffusion (V

ex), Cleaf

Advection (E), Cleaf Cleaf

UNRESTRICTED / ILLIMITÉ Catm is the HTO concentration in the atmospheric moisture (Bq/L), Catm is the weighted time-average of atmospheric HTO concentration (Bq/L), Cleaf is the HTO concentration in the plant water in leaf (Bq/L), M is the whole plant dry matter water equivalent (d.m.w.e. kg/m2), Mleaf is the mass of a leaf part of the plant per surface area, fresh water equivalent (f.w.e., kg/m2), Vex is exchange velocity in units converted to atmospheric water flux similar to that of ET (mm/s), Csoil is the HTO concentration in the soil moisture (Bq/L), E denotes ET (mm/s) and rw is the water density; IDp =0.8.

Plant tritium: Cleaf COBT

Csoil= g Catm

(1) (2)

AECL Model

Diffusion (V

ex), Catm

Advection (E), Csoil Diffusion (V

ex), Cleaf

Advection (E), Cleaf Cleaf

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Plant tritium Cleaf COBT

(1) (2)

ETMOD

Added to ETMOD formulation: (- ECleaf)

Off-line defined values:

V

ex, E, M, Catm, Csoil

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The HTO concentration in the leaf is determined by tritium diffusion from the air and mass transfer from the soil. These two processes are parameterized separately via V

ex and E

Aggregation of Catm driving Csoil is based on deposition (dry and wet) and “reference crop” evapotranspiration E in modified PM formulation, which is based on surface T and DTs in soil.

AECL Model

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HTO Night Exposure Experiments

Germany, 1996. Wheat, open field + exposure chamber Korea,1998. Rice pots, exposure chamber Canada

• CRL, Perch Lake 2001. Tomato pots, open field
• CRL, 2004. Tomato, Radish and Lettuce pots,

exposure chamber

• CRL, 2009. Tomato and potato, open field

Fig.1 Acid Rain Site dedicated to atmospheric uptake of tritium (tarp- covered clean soil) Fig.2 Perch Lake Site dedicated to re-emission of tritium and its final retention in OBT form

CRL’2009 Details

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HTO and OBT Dynamics

10 20 30 40 50

1000 2000 3000 4000 5000 1 8 15 22 29 5 12 19 26 3 10 17 24 31 7 14 21 28 4 11 18 25 2 9 16 May June July Aug Sep Oct Concentration (Bq/m3)

Concentration (Bq/L) Date

HTO OBT Air

HTO and OBT measurements in tree leaves (B513): Deviation from SA-based CSA N288.1 Tritium DRL procedure on all aggregation intervals

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Available rates of HTO and OBT depuration

1.E+00 1.E+02 1.E+04 1.E+06 1.E+08 1.E+10 0.5 3 8 15 22 37 41 56

Concentration (Bq/L) Time after the end of exposure (days) Leaves

HTO OBT

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 15 22 28 37 41 69 76 90

Concentration (Bq/L) Time after the end of exposure (days)

Fruit

HTO OBT

Vex for Simple Model has been has been measured using in-house observations

• f HTO and OBT dynamics.

High OBT/HTO ratio measured in parts of tomato and potato plants

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0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5

17:40 10:40 11:10 11:30 12:30 13:10 13:30 23:00 24:00:00 1:00 2:00 3:00 4:00 9:10 13:10 15:00 15:25 15:50 8:15 9:00 8:10 8:25 8:10 14:00 14:30 14:50 16:00 14:35 16:15 16:30 8:30 14:15 14:00 14:45 16:00 8:05 8:10 06/30 07/30 07/31 08/05 08/11 08/14 08/15 09/26 09/30 10/20

OBT/HTO ratio sampling time, month and date L-Potato leaves L-Potato L-Tomato L-Tomatoleaves L-Tomatostem R-Potato R-Potatoleaves R-Tomatoleaves R-Tomato TomatoDukeS PotatoDukeS R-Tomatostem

End of exposure: Plume No plume

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Sampling approach: Drivers synchronization

500 1000 1500 2000 2500 3000 10:40 12:30 14:00 17:00 20:00 23:00 2:00 L-Potato leaves HTO L-Potato leaves OBT L-Tomatoleaves HTO L-Tomatoleaves OBT R-Potatoleaves HTO R-Potatoleaves OBT R-Tomatoleaves HTO R-Tomatoleaves OBT 5 10 15 20 25 30 35 20000 40000 60000 80000 100000 120000

2500 94 Bq/L /L 1000

hour

HTO in air

Gamma monitoring: Air HTO active sampling (bubbler): Collection and measuring HTO and OBT in plant tissues:

Sampling period #2

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Is there a rapid OBT formation?

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500 1000 1500 2000 2500 10:40 12:30 14:00 17:00 20:00 23:00 2:00 L-Potato leaves HTO L-Potato leaves OBT L-Tomatoleaves HTO L-Tomatoleaves OBT

Bq/L

End of exposure: Plume No plume

Sampling time (June 30 – 31, 2008)

Validation of Simple Model using OBT/HTO ratios collected worldwide

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1 2 3 4 5 6 7 1 2 3 4 5 6 7 modelled OBT/HTO ratio Observed OBT/HTO ratio 1:1 perfect fit OBT/HTO

model vs. ensemble

• f 1976-2005

field and laboratory measurements: QQ plot of ranked statistics

Approach to on-going verification of tritium translocation in CTEM+CLASS

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SUMMARY

• Model update by inclusion of ambient drivers into the Simple Plant Tritium

Model (through E) works reasonably well – explains most of the range of

• bserved OBT/HTO ratios.
• OBT is probably formed much more rapidly (~minutes) in plant, than it has

been suggested before. Investigation of this possibility and general quantification of maintenance sugars with their decomposition in “dark” reactions require targeted experiments.

• Elaborate process-based models are sensitive to tritium parameterization –

accuracy in parameters definition is required.

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Future prospects

• Implement seasonal (dynamical) adjustments

in the CSA N288.1-08 tritium procedures

• Complete simple OBT formation model
• Assess the role of Soil compartment

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THANK YOU