Modelling the transport of actinide elements in the North-Eastern Irish sea

A model has been developed that appears to be able to simulate and predict the movement of isotopes from Sellafield within the north eastern inshore waters of the Irish Sea. The results confirm that the movement of isotopes within the off-shore mud patch may be simulated with simple diffusion constants, which simulate bioturbation down to a depth of 1.5 m. Moreover, the 'best' value of diffusion constant is 9.5 x 10-8 cm-2s-1 in the top few centimetres, reducing linearly to 0 at 1.5 m. There is a definite relationship between the top few (1-6) centimetres of the model mud patch profile and the depth profiles of the same isotopes at an inter-tidal site on the Esk estuary. This is strong evidence that the mechanism for the on-shore transport of radionuclides is on reactive particulates associated with the mud patch. There is a discrepancy in the model predicted activity peaks with depth at the inter-tidal site and the real data; the origin is unclear presently. The model has been used to estimate a discharge history for 244Cm. (orig.)