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 UNRESTRICTED / ILLIMITÉ
Objective Modelling of airborne tritium in plants with emphasis on partitioning between organically bound tritium (OBT) and tissue free water tritium (HTO). UNRESTRICTED / ILLIMITÉ 2
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 UNRESTRICTED / ILLIMITÉ 3
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. UNRESTRICTED / ILLIMITÉ 4
Tritium Pathways (this study) 10000 Gaseous Liquid 8000 TBq/year 6000 4000 2000 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 1500 Year Source: CNSC UNRESTRICTED / ILLIMITÉ UNRESTRICTED / ILLIMITÉ 5 5
Tritium Pathways (this study) UNRESTRICTED / ILLIMITÉ 6
Tritium Pathway via Plant Water and its Ambient Drivers (modelling) Credits:http://crew.iges.org UNRESTRICTED / ILLIMITÉ 7
CLASS (Can. Land Surface Scheme) 2000 ~2007 (D.L. Verseghy et al. Atmosphere-Ocean, V38, N1, 2000 Special Issue, 269 p.) UNRESTRICTED / ILLIMITÉ 8 8
CTEM (Can. Terrestrial Ecosystem Model) V. Arora, 2007 UNRESTRICTED / ILLIMITÉ 9
CTEM+CLASS Source: CTEM manual v1.1 UNRESTRICTED / ILLIMITÉ 10
Tritium Translocation in CTEM+CLASS framework HTOATM HTOLF OBTLEAF OBTSTEM HTOSOL1 OBTRT1 HTOSOL2 OBTRT2 HTOSOL3 OBTRT3 AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL 11
AECL Model Diffusion ( V ex ), C atm Diffusion ( V ex ), C leaf Plant tritium: C leaf C OBT Advection ( E ), C soil Advection ( E ), C leaf (1) C leaf (2) C soil = g C atm C atm is the HTO concentration in the atmospheric moisture (Bq/L), C atm is the weighted time-average of atmospheric HTO concentration (Bq/L), C leaf 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/m 2 ), M leaf is the mass of a leaf part of the plant per surface area, fresh water equivalent (f.w.e., kg/m 2 ), V ex is exchange velocity in units converted to atmospheric water flux similar to that of ET (mm/s), C soil is the HTO concentration in the soil moisture (Bq/L), E denotes ET (mm/s) and r w is the water density; ID p =0.8. UNRESTRICTED / ILLIMITÉ
AECL Model Diffusion ( V ex ), C atm Diffusion ( V ex ), C leaf Plant tritium C leaf C OBT Advection ( E ), C soil Advection ( E ), C leaf (1) C leaf ETMOD (2) Added to ETMOD formulation: (- E C leaf ) Off-line defined values: V ex , E , M, C atm , C soil UNRESTRICTED / ILLIMITÉ
AECL Model 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 C atm driving C soil is based on deposition (dry and wet) and “reference crop” evapotranspiration E in modified PM formulation, which is based on surface T and D T s in soil. UNRESTRICTED / ILLIMITÉ 14
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 UNRESTRICTED / ILLIMITÉ
CRL’2009 Details Fig.1 Acid Rain Site dedicated to Fig.2 Perch Lake Site dedicated atmospheric uptake of tritium (tarp- to re-emission of tritium and its covered clean soil) final retention in OBT form UNRESTRICTED / ILLIMITÉ
HTO and OBT Dynamics 5000 50 Concentration (Bq/m3) Concentration (Bq/L) HTO OBT Air 4000 40 30 3000 20 2000 1000 10 0 0 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 Date HTO and OBT measurements in tree leaves (B513): Deviation from SA-based CSA N288.1 Tritium DRL procedure on all aggregation intervals UNRESTRICTED / ILLIMITÉ
Available rates of HTO and OBT depuration Leaves 1.E+10 HTO Concentration (Bq/L) Vex for Simple Model has OBT 1.E+08 1.E+06 been has been measured 1.E+04 using in-house observations 1.E+02 of HTO and OBT dynamics. 1.E+00 0 0.5 3 8 15 22 37 41 56 Time after the end of exposure (days) Fruit 1.E+05 Concentration (Bq/L) 1.E+04 1.E+03 1.E+02 HTO OBT 1.E+01 1.E+00 15 22 28 37 41 69 76 90 Time after the end of exposure (days) UNRESTRICTED / ILLIMITÉ
High OBT/HTO ratio measured in parts of tomato and potato plants 11.5 L-Potato leaves 11 10.5 L-Potato 10 L-Tomato 9.5 L-Tomatoleaves 9 8.5 L-Tomatostem 8 R-Potato 7.5 R-Potatoleaves OBT/HTO ratio 7 6.5 R-Tomatoleaves 6 R-Tomato 5.5 TomatoDukeS 5 4.5 PotatoDukeS 4 R-Tomatostem 3.5 3 2.5 2 1.5 1 0.5 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 End of exposure: 06/30 07/30 07/31 08/05 08/11 08/14 08/15 09/26 09/30 10/20 sampling time, month and date Plume No plume UNRESTRICTED / ILLIMITÉ
Sampling approach: Drivers synchronization Gamma monitoring: Sampling period #2 35 2500 1 HTO in air 30 25 Air HTO active /L Bq/L 20 15 1000 10 sampling (bubbler): 5 94 0 0 20000 6 12 18 24 6 40000 60000 80000 100000 120000 12 hour Sampling period #2 3000 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 2500 Collection and 2000 1500 measuring HTO and 1000 OBT in plant tissues: 500 0 10:40 12:30 14:00 17:00 20:00 23:00 2:00 Sampling period #2 UNRESTRICTED / ILLIMITÉ 1
Is there a rapid OBT formation? 2500 L-Potato leaves HTO L-Potato leaves OBT L-Tomatoleaves HTO 2000 L-Tomatoleaves OBT 1500 Bq/L 1000 500 End of exposure: 0 10:40 12:30 14:00 17:00 20:00 23:00 2:00 Sampling time Plume (June 30 – 31, 2008) No plume UNRESTRICTED / ILLIMITÉ 21
Validation of Simple Model using OBT/HTO ratios collected worldwide model vs. ensemble 7 of 1976-2005 1:1 perfect fit field and laboratory OBT/HTO measurements: 6 QQ plot of ranked statistics 5 modelled OBT/HTO ratio 4 3 2 1 0 0 1 2 3 4 5 6 7 Observed OBT/HTO ratio UNRESTRICTED / ILLIMITÉ
Approach to on-going verification of tritium translocation in CTEM+CLASS UNRESTRICTED / ILLIMITÉ 23
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 observed 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. UNRESTRICTED / ILLIMITÉ 24
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 UNRESTRICTED / ILLIMITÉ 25
THANK YOU UNRESTRICTED / ILLIMITÉ 26
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