DISTRIBUTION OF TC-99 IN UK COASTAL WATERS

The concentrations of Tc-99, discharged to the northeast Irish Sea fro m the nuclear reprocessing plant at Sellafield, have been measured in UK coastal waters. Temporal and spatial distributions of this radionuc lide in surface seawater are provided prior to and post the authorized discharge of elevated quantities of Tc-99, arising from the operation of the Enhanced Actinide Removal Plant (EARP). Preceding the commissi oning of EARP, concentrations of Tc-99 in a large proportion of the Ir ish 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, Tc-99 concentrations decreased rapidly aw ay from the coastline and were dispersed in a parallel direction to th e shore, consistent with residual surface currents. Following elevated discharge periods, a significant pulse of Tc-99 was rapidly transport ed northwards parallel to the shore. Post-EARP surveys indicate that t he mast rapid migration of Tc-99 from the outfall to the North Channel was less than 3 months and the mean transit time is estimated to be i n the order of 6 months. Comparison of UK coastal surveys, prior to an d post EARP, suggest that Tc-99 had migrated to the northern North Sea within some 9 months following the initial elevated discharge. Crown copyright (C) 1997 Published by Elsevier Science Ltd.