UFOTRI principles and regulatory body requirements; personal opinion - PowerPoint PPT Presentation

UFOTRI principles and regulatory body requirements; personal opinion on modelling Wolfgang Raskob Karlsruher Institut für Technologie (KIT) www.kit.edu KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)

Processes to be considered 2 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Key processes atmosphere Tritium released as gas (HT) or titiated water vapour (HTO) behaves like a gas Atmospheric transport and dispersion is similar as for other radionuclides except that HTO is re-emitted Equilibrium between air moisture and crop relatively fast during daytime but long lasting at night (stomata versus cuticula) Deposition to crops and soil is best described with resistance approaches 3 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Key processes soil Deposition to top millimetres of soil (HTO several mm; HT 20 mm) Only in case of rain deeper penetration Reemission is fast during the day and 50% of the HTO can be re-emitted during one day easily The Canadian HT release experiment has reported re-emission rates of average 33% during the half hour release time (Tächner et al. 1990) Root uptake small compared to direct uptake from atmosphere 4 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Contribution of pathways to the dose Typical contribution (%) of the exposure pathways to the maximum dose at 1 km distance for a release of tritium as HTO or HT, calculated with the accidental tritium assessment model UFOTRI (local production and consumption) Inhalation (plume passage) Ingestion HTO 20 80 HT < 0.1 > 90 5 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

‘Conventional’ modelling Concentration in crop is calculated as = • C in edible part C TF C p s with TF C p = concentration in crop C s = concentration in source TF = transfer factor C in soil / leaf TF is measured 6 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Tritium foodchain model Processes to be considered: phenological stages of crop development sowing, emergence, anthesis, harvest growth of crop based on photosynthesised organic matter photosynthesis rate respiration rate 7 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Schematic growth curve for rice 8 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Daily variation of growth curve 4.50 calculated 4.00 2 ) Photosynthesis rate (g/m 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 -0.50 1 6 11 16 21 Time of the day in hours 9 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Photosynthesis 10 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Photosynthesis (dependencies) Plant properties Plant development stage Photosynthetic active radiation (PAR) Leaf area index (LAI) Leaf temperature (air temperature) Opening of stomata radiation air humidity air temperature soil water content Photosynthesis highly dependent on the day of the year and the daytime 11 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Regulatory requirements for a model Relatively simple Transparent Easy to program Results should be conservative (but not too much) Deterministic calculations possible (worst case assessments) Probabilistic calculations possible (95% percentile as worst case) Is this possible for Tritium? 12 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Dependencies Dose from foodchain higher than dose from direct inhalation (re- emission of no concern for HTO releases) OBT is most important in this respect Green vegetables of no importance as no ingestion during the first day Physical dependencies important to define worst case scenario Stable atmospheric conditions High air concentration Low concentration in crops as this case appears mainly at night High turbulence Relatively low air concentration High initial concentration in crops High exchange with atmosphere (zero concentration after some time) and thus low concentration in organic material at harvest 13 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Dependencies cont Stable atmospheric conditions Low build-up of OBT as no photosynthesis only maintenance metabolism High turbulence High photosynthesis rate, but initial tritium in cop low Low concentration in organic material at harvest as initial tritium concentration in crops low Worst case scenario as defined for ITER Release in the morning at around 10 o’clock with Stability category E and low wind speed without rain during the linear growing phase of the edible part of the crop 14 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

BIOMOVS ( BIOsperic Model Validation Study) International study started 1986 First phase completed in 1990 Second phase covered the period from 1991 to 1996 Objective: Test of models designed to quantify the transfer and bioaccumulation of radionuclides and other trace substances in the environment Involves a number of working groups, one of which was the Special Radionuclides/Tritium Working Group The TWG had ~20 active members from 9 countries 15 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

BIOMOVS test of wheat exposure at day-time 'Day' exposure: TWT and OBT -1.2 2.1 Plant-OBT Plant-OBT -1.9 STAR H-3 (1) STAR H-3 (1) 1.7 -2.9 1.1 STAR H-3 (2) STAR H-3 (2) TWT -2.6 1.2 OBT UFOTRI UFOTRI -2.6 1.1 UFOTRI-AECL UFOTRI-AECL models excluding OBT formation during the night -2.8 ETMOD ETMOD 1.1 -2.7 TRICAROM TRICAROM -1.4 -5.3 1.1 TRIMOVS (1) TRIMOVS (1) 1.1 -1.1 TRIMOVS (2) TRIMOVS (2) 2 1 2 3 3 4 5 5 4 5 -4 -3 -2 -1 0 1 2 3 4 5 lower higher deviation from observation TWT in leaves after exposure, OBT at harvest 16 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

BIOMOVS test of wheat exposure at night-time 'Night' exposure: TWT and OBT -1.1 Plant-OBT Plant-OBT -1.2 1.4 -2.1 STAR H-3 (1) STAR H-3 (1) -3.1 1.0 STAR H-3 (2) STAR H-3 (2) TWT -2.5 OBT -3.1 UFOTRI UFOTRI -2.4 UFOTRI-AECL UFOTRI-AECL -2.4 >-100 models excluding OBT formation during the night ETMOD ETMOD -21 TRICAROM TRICAROM -9.1 -3.6 -4.0 TRIMOVS (1) TRIMOVS (1) -54 -4.0 -7.5 TRIMOVS (2) TRIMOVS (2) 5 4 1 3 2 2 4 3 -4 -3 -2 -1 0 1 2 3 4 5 lower higher deviation from observation TWT in leaves after exposure, OBT at harvest 17 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

OBT-FORMATION: rel. OBT grain at harvest, related toTWT in leaves at the end of exposure 1,0 0,9 0,8 grain OBTmes 0,7 grain OBT mod polynomial fit 0,6 % 0,5 0,4 0,3 0,2 mean 0.23 % 0,1 0,0 6 8 10 12 14 16 18 20 22 24 Time of day (h) at the beginning of exposure 18 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Status of modelling Processes which should be included in models and their status as defined in the early 90 th Ongoing work within the IAEA suported EMRAS II working programme: “Development of a state of the art tritium model” 19 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Conclusion - Vision Tritium is a very dynamic radionuclide which cannot be modelled with the same approaches as other radionuclides In the first days, tritium dynamics depend strongly on the environmental characteristics, therefore a simple compartment model might not be appropriate Definition of a worst case different, as physical dependencies should not be ignored – otherwise too conservative The way forward in Germany Take UFOTRI and compare it with the existing approach Define a set of calculations to derive the main dependencies If possible derive from the many calculations a simple process model (some key equations to calculate concentration of tritium in feed- and foodstuffs) that can be used in regulatory calculations 20 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview

Conclusion – Vision cont. Develop a new model Take an advanced dispersion model (particle model) Add subroutines for the key processes specific to tritium Dry and wet deposition Movement in soil Root uptake Behaviour in crops (transpiration) with OBT build up Secondary plume from reemission if HT is of interest Agree in the WG on these processes and the modelling approach Program these processes in subroutines that can be integrated into a dispersion model Derive from this a simple model for regulatory purposes 21 26.01.2010 Karlsruhe Institute of Technology (KIT-IKET) Tritium modelling overview