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

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UFOTRI principles and regulatory body requirements; personal opinion on modelling

Wolfgang Raskob Karlsruher Institut für Technologie (KIT)

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 2

Processes to be considered

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 3

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 4

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 5

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 6

‘Conventional’ modelling

Concentration in crop is calculated as

with Cp = concentration in crop Cs = concentration in source TF = transfer factor

TF is measured

s p

C TF C

• =

TF C in edible part C in soil / leaf

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 7

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 8

Schematic growth curve for rice

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 9

Daily variation of growth curve

• 0.50

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 1 6 11 16 21 Time of the day in hours Photosynthesis rate (g/m

2)

calculated

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 10

Photosynthesis

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 11

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 12

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?

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 13

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 14

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

• f the edible part of the crop

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 15

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 16

BIOMOVS test of wheat exposure at day-time

TRIMOVS (2) TRIMOVS (1) TRICAROM ETMOD UFOTRI-AECL UFOTRI STAR H-3 (2) STAR H-3 (1) Plant-OBT

• 4
• 3
• 2
• 1

deviation from observation TRIMOVS (2) TRIMOVS (1) TRICAROM ETMOD UFOTRI-AECL UFOTRI STAR H-3 (2) STAR H-3 (1) Plant-OBT 'Day' exposure: TWT and OBT TWT OBT 2 3

4 1 2 3 4

models excluding OBT formation during the night

lower higher 2.1

• 1.9
• 2.9
• 2.6
• 2.6
• 2.8
• 2.7
• 1.4
• 5.3
• 1.1

1.7 1.1 1.2 1.1 1.1 1.1 1.1

• 1.2

5

TWT in leaves after exposure, OBT at harvest

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 17

BIOMOVS test of wheat exposure at night-time

TRIMOVS (2) TRIMOVS (1) TRICAROM ETMOD UFOTRI-AECL UFOTRI STAR H-3 (2) STAR H-3 (1) Plant-OBT

• 4
• 3
• 2
• 1

deviation from observation TRIMOVS (2) TRIMOVS (1) TRICAROM ETMOD UFOTRI-AECL UFOTRI STAR H-3 (2) STAR H-3 (1) Plant-OBT 'Night' exposure: TWT and OBT TWT OBT

models excluding OBT formation during the night

1 2 3 4 5 2 3 4 higher lower

• 2.1
• 3.1
• 2.5
• 3.1
• 2.4
• 2.4

>-100

• 21
• 9.1
• 3.6
• 4.0
• 54
• 4.0
• 7.5
• 1.2
• 1.1

1.4 1.0

TWT in leaves after exposure, OBT at harvest

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 18

OBT-FORMATION: rel. OBTgrain at harvest, related toTWT in leaves at the end of exposure

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 6 8 10 12 14 16 18 20 22 24

Time of day (h) at the beginning of exposure %

grain OBTmes grain OBT mod polynomial fit

mean 0.23 %

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 19

Status of modelling

Processes which should be included in models and their status as defined in the early 90th Ongoing work within the IAEA suported EMRAS II working programme: “Development of a state of the art tritium model”

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 20

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

Tritium modelling overview

Karlsruhe Institute of Technology (KIT-IKET)

26.01.2010 21

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