Status of Tritium Model Intercomparison Exercise and TECDOC - - PowerPoint PPT Presentation

Vlad Korolevych Canadian Nuclear Laboratories Chalk River, K0J 1J0, Ontario, Canada E-mail: vlad.korolevych@cnl.ca

MODARIA TM-III, November 10, 2014, Vienna

MODARIA Working Group 7 (WG7): Harmonization and intercomparison of models for accidental tritium releases

Status of Tritium Model Intercomparison Exercise and TECDOC preparation

WG7 Objectives

Guidance on development and application of environmental tritium transfer models based on the updated Aiken list Analysis of the tritium transfer in terrestrial ecosystems Identification of knowledge gaps and assessment of their significance Inter-comparison of models on specific scenarios

WG7 Objectives

Guidance on development and application of environmental tritium transfer models based on the updated Aiken list Analysis of the tritium transfer in terrestrial ecosystems Identification of knowledge gaps and assessment of their significance Inter-comparison of models on specific scenarios

CRL’2008 Scenario (Canada): blind test model results will be presented and discussed – HTO in air (intermittent routine release) – HTO in soil and vegetation, OBT in vegetation and fruit IRSN’2013 Scenario (France): – HT and HTO in air, CO2 fluxes, soil water dynamics (lysimeters) – HTO and OBT in vegetation and soil CNSC’2012 Scenario (Canada): distributed to participants when ready. – HT and HTO in air – HTO in vegetation and soil and OBT in soil

Models Inter-comparison (3 scenarios)

CRL’2008 Scenario (Canada): blind test model results will be presented and discussed – HTO in air (intermittent routine release) – HTO in soil and vegetation, OBT in vegetation and fruit IRSN’2013 Scenario (France): – HT and HTO in air, CO2 fluxes, soil water dynamics (lysimeters) – HTO and OBT in vegetation and soil CNSC’2012 Scenario (Canada): distributed to participants when ready. – HT and HTO in air – HTO in vegetation and soil and OBT in soil

Models Inter-comparison (3 scenarios)

Data type Variable Units Time period Frequency

Meteorological Incoming Shortwave Radiation W/m2 15/4/08 - 08/12/08 30 mins Incoming Longwave Radiation W/m2 15/4/08 - 08/12/08 30 mins Precipitation rate mm/s 15/4/08 - 08/12/08 30 mins Temperature °C 15/4/08 - 08/12/08 30 mins Wind Speed m/s 15/4/08 - 08/12/08 30 mins Pressure Pa 15/4/08 - 08/12/08 30 mins Specific Humidity Kg/kg 15/4/08 - 08/12/08 30 mins

Scenario requirements (based on CRL data)

Data type Variable Units Time period Frequency

Source term Atmospheric HTO activity* Bq/L 15/4/08 - 08/12/08 30 mins (reconstr.) Rain HTO concentration** Bq/L 15/4/08 - 08/12/08 Monthly 30 mins (reconstr.) Tritium activity at the site Soil HTO at 0-35 cm Bq/L 30/7/08 – 23/10/08 On specific dates HTO in soil and vegetation Bq/L 30/6/08 – 20/10/08 On specific dates OBT*** in vegetation and fruit Bq/L 30/6/08 – 20/10/08 On specific dates * The atmospheric HTO activity is modelled based on Ar-41 high-frequency monitoring and atm dispersion modelling of HTO using the monitored source term. The reconstruction was QA checked by comparison against a number of half-hourly HTO measurements plus weekly HTO monitoring results (both HTO samplers are located in the immediate vicinity of the garden plot). ** The rain was measured monthly at ~7 km from the stack. We can deploy washout ratio approach for rain deposition in CRL Scenario with the washout coeff 0.2 (Rain_HTO_conc in Bq/L =0.2* atm._moisture_HTO in Bq/L). This is a bit unconventional, but the washout=0.2 provides reasonable fit to monthly observations of rain HTO concentration at the monitoring site at ~7km. *** Total not rinsed OBT (i.e. non-exch +exchOBT)

Scenario requirements (based on CRL data, cont.)

Participating models

• TOKATTA-CHI, IRSN, France
• SOLVEG-II, JAEA, Japan
• CLSS-TT, CNL, AECL, Canada
• CEA, France

500 1000 1500 2000 2500 3000 Concentration (Bq/L)

Plot 1 of 5: HTO in leaves

Modelled HTOlf L-Potato leaves HTO L-Tomato leaves HTO R-Potato leaves HTO R-Tomato leaves HTO L-Tomato HTO R-Tomato HTO Tomato DukeS HTO L-Tomato stem HTO R-Tomato stem HTO

SOLVEG-II

500 1000 1500 2000 2500 3000 Concentration (Bq/L)

Plot 1 of 5: HTO in leaves

Modelled HTOlf L-Potato leaves HTO L-Tomato leaves HTO R-Potato leaves HTO R-Tomato leaves HTO L-Tomato HTO R-Tomato HTO Tomato DukeS HTO L-Tomato stem HTO R-Tomato stem HTO

TOKATTA- χ

500 1000 1500 2000 2500 Concentration (Bq/L) Modelled HTOlf L-Potato leaves HTO L-Tomato leaves HTO R-Potato leaves HTO R-Tomato leaves HTO L-Tomato HTO R-Tomato HTO Tomato DukeS HTO L-Tomato stem HTO R-Tomato stem HTO

CLSS-TT

200 400 600 800 1000 1200 1400 1600 Concentration (Bq/L)

Plot 2 of 5: HTO in soil

HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

SOLVEG-II

200 400 600 800 1000 1200 1400 1600 Concentration (Bq/L)

Plot 2 of 5: HTO in soil

HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

TOKATTA- χ

200 400 600 800 1000 1200 1400 1600 Concentration (Bq/L)

Plot 2 of 5: HTO in soil

HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

CLSS-TT

Comments on OBT modelling

• All three models (SOLVEG-II, TOKATTA-chi, CLSS-

TT) predict quasi-stationary/constant NE-OBT within a narrow window, where CRL Scenario provides dynamically changing TOTAL OBT, which spikes up to 2000 Bq/L (i.e. up to HTO concentration in leaves).

• Predicted NE-OBT in all three models was

consistently in the range 170-220 Bq/L and also in certain correspondence with predicted HTO in second soil layer

Preliminary conclusions of CRL Scenario

• HTO modelling is correct
• NE-OBT is likely correct as it is consistent

between models

• Exchangeable OBT requires further

experimental investigation for proper parameterization of EX-OBT (and Total OBT) in the model

• Field data can differ significantly from results
• f controlled experiments

Preliminary conclusions of CRL Scenario (continued)

• HTO in vegetation (TFWT) and EX-OBT fluctuates with ambient air

HTO

• Monitoring of TFWT is only meaningful if all stages atmosphere-

vegetation exchange from plume deposition to subsequent re- emission are statistically representative (very large sample required)

• High OBT/HTO ratios do not indicate bioacumulation, but only

dynamical fluctuations in HTO

• NE-OBT in vegetation represents well the whole atmosphere-

vegetation-soil system and could be a basis of monitoring (infrequent sampling would be required)

• Alternatively soil HTO in rhizosphere could be a good indicator of

OBT and the whole system, including average source (air HTO)

Documenting future plans

Planned model enhancements Planned experiments Future development and experimental data need Specific experiments should be carried out for studying the following processes: isotopic fractionation of tritium in plants, formation of OBT during night time… Exchangeable OBT These topics will be adressed by IRSN in 2015-2016 based on hydroponic cultures

WG7 Objectives

Guidance on development and application of environmental tritium transfer models based on the updated Aiken list Analysis of the tritium transfer in terrestrial ecosystems Identification of knowledge gaps and assessment of their significance Inter-comparison of models on specific scenarios

Aiken List

1990 Workshop on Tritium, Aiken, SC,USA Raskob, W., and P. Barry. "Importance and variability in processes relevant to environmental tritium ingestion dose models." Journal of environmental radioactivity 36.2 (1997): 237-251.

• Path forward:

– Explicit modeling of proper parameterization of the uppermost soil layer (1-2 mm) interaction with atm. HTO – Wet deposition and re-emission (rain-time in-canopy processes); Include dewfall processes and dew-driven HTO deposition

• Extend Aiken List:

– Formation of OBT in dark reactions: interaction of so-formed OBT with HTO deposited onto leaves:

• During rainy weather
• At night

– Turnover of OBT in litter and soil (issues prioritized)

WG7 scope of work

WG7 scope of work (continued)

• Provide guidance on tritium land-atmosphere transfer:

– Foliar uptake and re-emission as an integral part of soil-plant- atmosphere complex – Turnover of OBT in litter and soil – Parameterization of vegetated and non-vegetated soil

• Uptake of HTO
• Re-emission of HTO
• Include discussion pertaining to regulatory prospective of WG7 results
• the role of simple “screening” models
• Possibility of shift of monitoring paradigm from HTO to OBT and

include discussion on:

• the need for quantification of EX-OBT DCF
• The need of exclusion of EX-OBT form monitoring program

MODARIA TM-III, WG7 Meeting results

• CRL Scenario is complete, pending analysis
• IRSN Scenario has been distributed to participants, results are

expected in February 2015, comparison of blind prediction distributed to participants and analysis completed before May 2015

• CNSC Scenario will be distributed to participants this coming
• December. Observations (to compare against blind predictions) will e

distributed in January, analysis is expected to be complete by May, 2015

• Contributions to theoretical part of TecDoc will be assembled in draft

report by February, 2015

• Interim Meeting of WG7 is planned in May, 2015, pending alignment

with other WG Meetings and individual WG7 participants schedule of

• work. The goal of Interim Meeting is assembly and finalization of

Draft TecDoc (theoretical part and three experimental scenarios analysis)

Thank you