The behaviour of ²³⁶U in the North Atlantic Ocean assessed from numerical modelling: A new evaluation of the input...

A numerical model, previously validated with other radionuclides, was applied to simulate the dispersion of ²³⁶U released from European nuclear fuel reprocessing plants in the North Atlantic and Shelf Seas using a published reconstruction of Sellafield and La Hague releases. Model results are in better agreement with observations if the lowest estimation of such releases are used. This implies that approximately 40kg of ²³⁶U has been discharged from Sellafield. It was found that adsorption of ²³⁶U on bed sediments of the shallow European Shelf Seas plays an essential role in its dispersion patterns. This contrasts strongly with the more conservative behaviour of ¹²⁹I in the same area. This has two important implications in the use of ²³⁶U as oceanographic tracer; i) special care must be taken in coastal areas, as sediments might act as sinks and sources of ²³⁶U; ii) the annual input function of ²³⁶U into the Arctic is not directly controlled by the annual discharges from Sellafield and La Hague, since sediments from the Irish, Celtic and North Sea modulate and smooth the signal. Only 52% of the total releases enter into the Arctic Ocean.