Dynamic modelling of grass-cow-milk exposure pathway accounting for multible season sequences

Dynamic compartment models have been developed for caesium and iodine to model the activity transfer after accidental release and deposition. The models take into account the inhalation of initially airborne activity, direct deposition on grass, forage, root uptake as well as transfer of contaminated soil together with grass consumed by cow. Seasonal variations caused by deposition during spring, summer, autumn or housed season of cattle are accounted for. The temporal behaviour of activity content in milk can be followed during multiple season sequences. The derivation of input parameters and comparisons to experimental observations have been carried out in close co-operation with the Finnish Centre for Radiation and Nuclear Safety. The dynamic simulations applying the DETRA computer code have been made for a model accident. The computer code ARANO has been employed for the calculation of integrated airborne concentration and deposition at different downwind distances from the release point. The model prediction confirms that deposition occuring in the summer season causes the greatest time integrated specific activity content of milk and further doses by consumption of contaminate milk.