UFOTRI: Accident assessment model for tritium W. Raskob Presented by D Galeriu, with mandate from author

Tritium model UFOTRI

Content Introduction Modelling Applications Basic approaches Foodchain OBT formation Applications Tests of rice model Dose assessments

Modes of application of UFOTRI Deterministic (defined set of variables, e.g. predefined and constant weather) Probabilistic (assessment of all possible weather for a certain period) Near and/or far range Plant species considered in UFOTRI grass (fodder) leafy vegetables (continuously harvested) wheat potatoes rice

Endpoints of UFOTRI Concentration Organ doses Countermeasures Air concentration and deposition Time dependent concentration in air, soil and foodstuffs for selected points time dependent dose values for selected points Organ doses Short term effective doses long term effective doses Countermeasures Food restriction, areas and duration Coupling with COSYMA for further evaluation

Submodel short term (hourly time step) Transport and dispersion in the atmosphere primary plume by Gaussian trajectory model secondary plume by an area source model Exchange atmosphere - plant - soil deposition and reemission is expressed via resistance functions dependent on the prevailing meteorological conditions (for both tritium and water vapour) Exchange atmosphere - soil deposition of tritium to soil and evaporation of tritium and water is modelled via resistance functions Transport in soil water and tritium movement depends on the matrix forces Cycling through the foodchains

Submodel long term Compartment model for calculating the longer term behaviour of tritium in the foodchains transfer rates are means, valid for the vegetation period and derived from equilibrium conditions HTO and OBT are treated separately

Resistance approaches Atmospheric source Aerodynamic, Ra Boundary, Rb Stomatal, Rs Cuticular, Rct Ground, Rg for various surfaces Total Surface, Rc Aerodynamic resistance Ra depends on turbulence and wind speed Boundary layer resistance Rb depends on turbulence wind speed and surface properties Total surface resistance Rc can be split up into canopy and ground related resistance Canopy resistance depends on surface properties, temperature, photosynthetic active radiation, humidity, water content in soil

Stomata resistance- Jarvis approach r st,min = minimum stomata resistance Ip = incoming photosynthetic active radiation c = efficiency constant fl = weighting function for humidity ft = weighting function for temperature fw = weighting function for soil water content Canopy resistance Canopy resistance is the modified stomata resistance integrated over the leaf area index L

Actual evapotranspiration (Penman-Monteith) Ea = the actual evapotranspiration l = the latent heat of evaporation in J kg-1 d = the gradient of the vapour pressure curve at ambient temperature in J m-3 K-1 Ia = the incoming solar radiation in W m-2 rAV = the sum of the atmospheric and the boundary resistance cp = the specific heat of air at constant pressure in J kg-1 K-1 es = the actual saturation vapour pressure of air in N m-2 ea =the actual vapour pressure of air in N m-2 g = the psychrometer constant in J m-3 K-1 rx = the resistance of the surface Transpiration of plants (modification of Ia and rx = rc)

Tritium concentration in plant Basic assumptions: 100% saturation inside the stomata equilibrium conditions prevail with

Water movement in soil Simplified version of Darcey’s law is applied k = hydraulic conductivity S = suction tension V = Darcy velocity Z = vertical distance Simplified equation used in UFOTRI Gradient between two layers Equilibrium conditions with complete exchange of water between two adiiacent layers Soil resistance modeled using an effective diffusion and depth of dry soil layer

HT deposition velocity with the effective diffusivity D0 = the diffusion coefficient of HT in air (0.634 E-04 m2 s-1) zref = the reference depth in m (r = 23 mm) QS = the maximum water content QW = the water content at wilting point tort = the soil torture factor HTO deposition velocity The deposition velocity is the reciprocal of the sum of the three resistance: aerodynamic resistance boundary layer resistance soil resistance

Tritium food chain model Aim is to develop a model which calculates the cycling of tritium in both forms (tissue free water tritium, TWT and organically bound tritium, OBT) through the foodchain, based on plant physiological knowledge 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 Plant species considered in UFOTRI grass (fodder) leafy vegetables (continuously harvested) wheat Potatoes rice

Photosynthesis

Photosynthesis rate (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

Schematic growth curve for rice

Daily variation of growth curve

1. Photosynthesis rate without any limitation, based on CO2 assimilation Ppot = potential CO2 assimilation rate in g CO2 per m-2 h-1 Pm = maximum CO2 assimilation rate in CO2 per m-2 h-1 H = absorbed photosynthetically active radiation in W per m-2 e = initial light use efficiency in g CO2 per W m-2 h-1 R = respiration rate in g CO2 per m-2 h-1 2.Analytical solution of the basic equation with integration of the leaf area over the canopy height Iabs = radiation flux absorbed by the canopy In0 = incoming photosynthetically active radiation L = leaf area in m-2/m-2, ranging from zero to the total leaf area index k = extinction coefficient (0.69)

3. Temperature dependency of the maximum photosynthesis rate DH1, DH2 = activation and denaturation energies for the electron transport, respectively, in cal C0 = value for the formation of organic matter in mg CO2 per m-2 h-1 R = gas constant in cal/Kelvin per mol DS = entropy change on denaturation of the electron transport system in cal/Kelvin per mol T = air/leaf temperature in Kelvin 4. Respiration rate, expressed in CO2 equivalents R = photorespiration + maintenance respiration C1p Pc = photorespiration, dependent on the photosynthesis rate C2m Wd = maintenance respiration, dependent on the plant weight C1p C2m = constants

Dry matter production and OBT build-up COA = conversion factor CO2 to dry matter f(sr) = weighting function for the stomata opening Radiation, temperature, humidity soil water content Tact = OBT build-up in Bq/h Pact = organic matter build-up g/h BM = basic metabolism CTWT = mean TWT concentration in crop in Bq/g fg = partitioning in the growing phase after anthesis dis = distribution parameter (set to 2)

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)

Winter what Germany Ratio modelled / measured 14 experiments have been carried out in the years 1995 and 1996 The exposure of the wheat plants took place mostly in the linear growing phase after anthesis; Exposure times were distributed all over the day; this includes exposure in the morning, at mid-day, in the evening and during the night Samples were taken in most cases 1h, 3h, 12 h, 24 h, 7 d, 14 d and at harvest time. U-UFOTRI; P- PLANT OBT (trial model)

HTO reemission experiments from soil

RICE-Comparison of measured and calculated concentration ratios (Korea experiments)

Rice experiments performed in Japan Potted rice plants were exposed with deuterium under daytime and night-time conditions 8 hours exposure Half of the potted rice plants were flooded Continuous measurements of air, leaf, stem and seed concentrations

Applications Assessment calculations for the potential European fusion sites Cadarache (France), Studsvik (Sweden), one site in Italy and Greifswald (Germany) Application in the ITER (International Thermonuclear Experimental Reactor) study to define the release limits for a generic site Assessment calculation in the frame of the SEAFP (Safety and Environmental Aspects of Fusion Power) study

Deterministic release scenarios (ITER) Three different release heights (ground level, stack and high speed exhaust from roof) Two different dispersion parameter sets Three different sets of weather conditions for accidental releases (‚average‘, ‚worst case‘ and ‚rain‘) Four types of doses (plume dose, early dose, EDE without ingestion, EDE with ingestion)

Probabilistic calculations (Greifswald) 144 weather sequences describing the meteorological situation for one vegetation period Ground level and stack releases (100 m) Early (7 d) and chronic doses Large initial areas of food interdiction when applying the EC-CFILs (activity concentration intervention levels in human foodstuffs) were estimated

Summary UFOTRI considers most of the relevant transfer processes with dynamical approaches UFOTRI is widely accepted in the frame of ITER UFOTRI was applied for generic assessments and also site specific assessments in Europe Future effort should be addressed to improve the modelling of formation and translocation of OBT as well as the reemission from soil Tests for the generic rice model supports the approach to use plant physiological parameters within tritium models