Porting the tritium dynamical model into soil moisture block of Canadian Land Surface scheme (CLASS) Environmental Technologies Branch, Nuclear Sciences Division, CRL, AECL VY Korolevych January 25, 2011, EMRAS II, WG7 Mtg., Vienna UNRESTRICTED / ILLIMITÉ
Objective Revision of dynamical interaction of plant and soil in the process of airborne tritium transfer. UNRESTRICTED / ILLIMITÉ 2
Issue Predictions of plant tritium in ETMOD deviate from observations in a long run (beyond ~72 hrs); soil tritium predictions of ETMOD is in error all the time. Enhancement of modelling of tritium in soil is implied by new Canadian regulations UNRESTRICTED / ILLIMITÉ 3
CNSC: Current regulations • 7,000 Bq/L is the current drinking water guideline in Canada • Where dose 7,000 Bq/L come from? • Radiation protection basis of the drinking water guideline is from ICRP • Effective dose limit for public is 1 mSv/y • Single exposure risk (1 mSv/y for one year) is estimated to be 7.3 x 10 -5 (ICRP, 1991) • Lifetime exposure risk (1 mSv/y for 70 years) is estimated to be 5 x 10 -3 (ICRP,1991) • Guideline for tritium in drinking water is 0.1 mSv/y of dose through consumption of drinking water (WHO) UNRESTRICTED / ILLIMITÉ 4
Guideline (GL) • GL = RDL/(DCF x Q) = (1 x 10 -4 Sv/y)/(730 L/y x 1.8 x 10 -11 Sv/Bq) • = 7,610 Bq/L • RDL = reference dose level, equal to 0.1 mSv/year • DCF = dose conversion factor for ingestion by • adults (Sv/Bq) Q = annual ingested volume of drinking water • UNRESTRICTED / ILLIMITÉ 5
Variation of the Final Criteria Country Final value Guideline calculation 7,610 Bq/L WHO 10,000 Bq/L Russia 7,700 Bq/L Canada 7,000 Bq/L UNRESTRICTED / ILLIMITÉ 6
Variation in Reference Dose Level Country RDL Drinking water guideline Australia 1 mSv/year 76,103 Bq/L Finland 0.5 mSv/year 30,000 Bq/L Unite State* 0.04 mSv/year 740 Bq/L Canada 0.1 mSv/year 7,000 Bq/L * US doesn't adapt ICRP UNRESTRICTED / ILLIMITÉ 7
CNSC: Tritium Study and new regulations • 100 Bq/L suggested new guideline (2010) • The decision of the European Parliament was cited wrt indicator of parametric value at 100 Bq/L on 13 May 1998 • Most EU members use the 100 Bq/L guideline for tritium only as a screening value • The risk at a lifetime exposure of 0.1 mSv/y is 6 x10 -4 (Health Canada, 1995) • Health Canada protocol for drinking water standard: lifetime risk is from 1 x 10 -5 to 1 x 10 -6 • “Essentially negligible” lifetime cancer risk of about 5 x 10 -6 • 100 Bq/L is reasonably practical and a planned action by early 2011 UNRESTRICTED / ILLIMITÉ 8
AECL Modelling capabilities • Present capabilities focussed at tritium atm. dispersion, deposition, transfer in plants and re-emission back to atmosphere: • ADDAM-IST (CAN CSA N288.2) • Various codes for Atmospheric Dispersion and Deposition • IMPACT (CAN CSA N288.1) • ETMOD-2 • UFOTRI • Primitive off-line TT model • CLASS 3.7 • CLASS+CTEM v1.1 • Under development: • CLASS+CTEM+TT (Stage 2: Soil module) UNRESTRICTED / ILLIMITÉ 9
ETMOD-2 overview UNRESTRICTED / ILLIMITÉ 10
ETMOD-2 overview Grid (1): UNRESTRICTED / ILLIMITÉ 11
ETMOD-2 overview Grid (2): UNRESTRICTED / ILLIMITÉ 12
ETMOD-2 (continued) UNRESTRICTED / ILLIMITÉ 13
ETMOD-2 (continued) Transport in soil (cont): UNRESTRICTED / ILLIMITÉ 14
ETMOD-2 (continued) Transport in soil (cont): HT: HT0: UNRESTRICTED / ILLIMITÉ 15
ETMOD-2 (continued) HTO transfer to/from vegetation: UNRESTRICTED / ILLIMITÉ 16
ETMOD-2 (continued) • Dry Matter Production • Gross photosynthesis rates are calculated using the CO 2 consumption model (Weir et al. 1984, Sellers 1985, Mitchell et al. 1991, Pinder et al. 1988) and depend on air temperature, the resistance to CO 2 uptake by the plant and the photosynthetically active radiation reaching the plant, which in turn depends on leaf area index. The production rate of dry matter is based on net photosynthesis taking into account both growth and maintenance respiration. Plant dry mass is updated using the dry matter produced in the time step. The wet vegetation mass is then calculated from the dry mass and the fractional water content, which is assumed to remain constant as the plant grows. • OBT Formation • The dry matter produced at a given time is assumed to have a T/H ratio equal to 0.6 times the T/H ratio in the plant water that takes part in the photosynthesis at that time. OBT concentrations following exposure decrease due to dilution with new uncontaminated dry matter. ETMOD does not account for the slow conversion of OBT to HTO in plants due to metabolic processes. OBT concentrations calculated in this way are assumed to apply to all dry matter in the plant. The rate of OBT concentration ( C OBT (t) , Bq/L) accumulation follows the biomass growth: d(M C OBT )/dt = ID p dM/dt C HTO, ID p – isotopic discrimination factor, and M(t) is a dry matter water equivalent of biomass (combustible water, kg/m 2 ). UNRESTRICTED / ILLIMITÉ 17
ETMOD-2 Face Validity Tests UNRESTRICTED / ILLIMITÉ 18
ETMOD-2 Tests (continued) UNRESTRICTED / ILLIMITÉ 19
ETMOD-2 Tests (continued) Soybean Scenario Report: C pw is the HTO concentration per unit mass of plant water (Bq kg -1 ), where • V ex is an exchange velocity (m s -1 ), • M w is the mass of plant water per unit ground surface area (kg m -2 ), • C a is the HTO concentration in air (Bq m -3 ), • is the ratio of the vapour pressure of HTO to H 2 O (0.91), and • h is the saturation humidity at leaf temperature (assumed equal to air temperature) • (kg m -3 ). • • Exchange velocities calculated by ETMOD fluctuate according to the current meteorological conditions, with most values lying between 2 x 10-3 and 8 x 10-3 m/s • ETMOD overpredicts in the initial period and underpredicts after 3 days (72 hrs) UNRESTRICTED / ILLIMITÉ 20
New Development Stage 2: Soil module of CLASS+CTEM+TT Stage 2 of Tritium Transfer implementation in CTEM+CLASS: Porting the tritium dynamical model into soil moisture block of Canadian Land Surface scheme (CLASS) Validation of the modelling system against surface flux measurements and meteorological observations at Perch Lake tower at CRL and at experimental garden plots in the Perch Lake tower vicinity. On going work: Analysis of gaps in available inputs and assembly of datasets to run the model at different sites: • Point flux measurements • Gridded inputs UNRESTRICTED / ILLIMITÉ 21
CLASS (Can. Land Surface Scheme) (D.L. Verseghy et al. Atmosphere-Ocean, V38, N1, 2000 Special Issue, 269 p.) UNRESTRICTED / ILLIMITÉ 22 22
Components of CLASS CO2 Energy Fluxes Fluxes Water Radiation Fluxes Fluxes UNRESTRICTED / ILLIMITÉ 23
Can. Terrestrial Ecosystem Model (CTEM), V. Arora’2007 ) Carbon assimilation, allocation and dissimilation (5 pools) UNRESTRICTED / ILLIMITÉ 24
CTEM+CLASS Source: CTEM manual v1.1 UNRESTRICTED / ILLIMITÉ 25
Tritium Transfer in CTEM+CLASS framework HTOATM HTOLF OBTLEAF OBTSTEM HTOSOL1 OBTRT1 HTOSOL2 OBTRT2 HTOSOL3 OBTRT3 AECL - OFFICIAL USE ONLY / À USAGE EXCLUSIF - EACL 26
Tritium Transfer in CTEM Leaf compartment TFWT: M L = (C L + A -R gL -R mL -D L )/(0.45 0.19) Stem compartment HTO activity : M s C HTO,s (t+ t) = I 1 [(A stem - R gL - R mL -D L ) C HTO,leaf - ( R gs -R ms –D s ) C HTO,s (t) ] . . M s (t+ t) = . M s (t) + M s (0.45 0.19) -1 (C s +A stem -R gs -R ms -D s ) OBT activity: M s C OBT,s (t+ t) = I dmwe [( C OBT,leaf A stem - C OBT ,s (t) (R gs -R ms -D s )] Roots: HTO activity C HTO,R = C HTO,sr1 OBT activity: M s C OBT,R (t+ t) = I dmwe [C OBT,leaf A R - - C OBT,R (t) (R gR +R mR -D R )] Root zone ( HTO activity in soil layer 1): M SR1 C HTO,sr1 = I dmwe f r1 C OBT,root (R gR +R mR +D R ) - C HTO,sr1 (E bs + a 12 ) - a 21 C HTO,sr2 , … UNRESTRICTED / ILLIMITÉ 27
Tritium Transfer in CTEM Leaf compartment Updates in mass of 5 compartments results in OBT and HTO translocation M L = I 1 (C L + A - - R gL - R mL -D L ) Stem compartment : M HTO,s = I 1 [(A stem - R gL - R mL Exported: -D L ) C HTO,leaf - A stem , A roots ,D L - ( R gs -R ms –D s ) C HTO,s ] ..... C OBT =C HTO,leaf Roots : M R = I st (C R + + A roots -R gR -R mR ) HTO Released into soil layer 1 : f r1 M R C OBT,R = f r1 I st (A R + +R gR +R mR ) C OBT,R UNRESTRICTED / ILLIMITÉ 28
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