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

MODARIA Working Group 7 (WG7): Harmonization and intercomparison of models for accidental tritium releases Status of Tritium Model Intercomparison Exercise and TECDOC preparation Vlad Korolevych Canadian Nuclear Laboratories Chalk River, K0J 1J0, Ontario, Canada E-mail: vlad.korolevych@cnl.ca MODARIA TM-III, November 10, 2014, Vienna

� 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

� 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, CO 2 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, CO 2 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

� Scenario requirements (based on CRL data) Data type Variable Units Time period Frequency W/m 2 Meteorological Incoming Shortwave 15/4/08 - 08/12/08 30 mins Radiation W/m 2 Incoming Longwave 15/4/08 - 08/12/08 30 mins Radiation 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, cont.) Data type Variable Units Time period Frequency Source term Atmospheric HTO Bq/L 15/4/08 - 08/12/08 30 mins (reconstr.) activity* Rain HTO Bq/L 15/4/08 - 08/12/08 Monthly concentration** 30 mins (reconstr.) Tritium activity Soil HTO at 0-35 cm Bq/L 30/7/08 – 23/10/08 On specific dates at the site HTO in soil and Bq/L 30/6/08 – 20/10/08 On specific dates vegetation OBT*** in vegetation Bq/L 30/6/08 – 20/10/08 On specific dates and fruit * 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)

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

SOLVEG-II 3000 Plot 1 of 5: HTO in leaves 2500 2000 Concentration (Bq/L) 1500 1000 500 0 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 3000 Plot 1 of 5: HTO in leaves 2500 2000 Concentration (Bq/L) 1500 1000 500 0 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 2500 2000 Concentration (Bq/L) 1500 1000 500 0 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 1600 Plot 2 of 5: HTO in soil 1400 1200 1000 Concentration (Bq/L) 800 600 400 200 0 HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

TOKATTA- 1600 Plot 2 of 5: HTO in soil χ 1400 1200 1000 Concentration (Bq/L) 800 600 400 200 0 HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

CLSS-TT 1600 Plot 2 of 5: HTO in soil 1400 1200 1000 Concentration (Bq/L) 800 600 400 200 0 HTOsol1 HTOsol2 HTOsol3 L-Soil HTO R-Soil HTO soil DukeS HTO L-Potato HTO R-Potato HTO Potato DukeS HTO

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 of 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.

� WG7 scope of work • 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: o During rainy weather o At night – Turnover of OBT in litter and soil (issues prioritized)

� 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 o Uptake of HTO o 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: o the need for quantification of EX-OBT DCF o The need of exclusion of EX-OBT form monitoring program