Distribution of technetium-99 in UK coastal waters

The concentrations of 99Tc, discharged to the northeast Irish Sea from the nuclear reprocessing plant at Sellafield, have been measured in UK coastal waters. Temporal and spatial distributions of this radionuclide in surface seawater are provided prior to and post the authorized discharge of elevated quantities of 99Tc, arising from the operation of the Enhanced Actinide Removal Plant (EARP). Preceding the commissioning of EARP, concentrations of 99Tc in a large proportion of the Irish Sea were reasonably uniform (1–4 mBq l−1). Increased levels from most recent discharges were observed along the Cumbrian and southern Scottish coastline. However, 99Tc concentrations decreased rapidly away from the coastline and were dispersed in a parallel direction to the shore, consistent with residual surface currents. Following elevated discharge periods, a significant pulse of 99Tc was rapidly transported northwards parallel to the shore. Post-EARP surveys indicate that the most rapid migration of 99Tc from the outfall to the North Channel was less than 3 months and the mean transit time is estimated to be in the order of 6 months. Comparison of UK coastal surveys, prior to and post EARP, suggest that 99Tc had migrated to the northern North Sea within some 9 months following the initial elevated discharge.