Improvement of the dose assessment tools on the basis of dispersion of the 99Tc in the Nordic Seas and the Arctic Ocean

Compartment models are widely used for evaluation of radiological consequences to man and biota in marine environment with spatial and temporal scales of several thousand kilometres and millenniums, respectively (EC, 2003). The compartment modelling uses two rigid general assumptions for dispersion of radionuclides in oceanic space: (a) uniform and (b) instantaneous mixing in each compartment. The second assumption leads, in practical calculations, to instantaneous mixing in the whole ocean space and, therefore, inserts an additional systematic uncertainty into calculated results. The developed in Norwegian Radiation Protection Authority (NRPA) during last years model is based on a compartment modelling approach, which includes terms describing the radionuclide dispersion into oceanic space with time (noninstantaneous mixing in oceanic space). It showed that the modified approach provides more realistic results compared to traditional compartment modelling and this approach is more sensitive to processes near the sources of contamination and during the initial time of radionuclides dispersion (Iosjpe et al., 2002). Results between modified and traditional approaches can differ widely, especially for scenarios where redistribution of radionuclides between different marine areas was important (Iosjpe, 2006).