Variability in the supply, distribution and transport of the transient tracer 99Tc in the NE Atlantic

In April 1994, a new waste treatment plant, the Enhanced Actinide Removal Plant (EARP), began operation at the nuclear reprocessing facilities at Sellafield in Cumbria, UK. EARP was introduced primarily to reduce the discharges of plutonium and americium, and does not remove technetium-99 (99Tc) from the effluents. An increased waste throughput from Sellafield since 1994 has resulted in increased discharges of 99Tc into the Irish Sea. Studies of the propagation of 99Tc from the Irish Sea into the North Sea post-EARP showed much more rapid transport than reported for other radionuclides prior to EARP. The purpose of the present study was fourfold: to extend the geographical range of sampling to allow the continuing spread of EARP-related 99Tc to be followed; to place the results in an appropriate oceanographic setting; to test whether the apparent initial rapid transport had been maintained; and to provide a dataset which could be used for model development and validation. Our results confirm that the EARP-related 99Tc contamination had reached Arctic waters by 2000. The 99Tc concentration was an order of magnitude higher than background levels in the Norwegian Coastal Current (NwCC) outside Tromsø in June/July 1999, and 6 times higher than background levels in the West Spitsbergen Current (WSC) in May/June 2000. Our results suggest that, following the initial rapid transport of 99Tc from the Irish Sea into the North Sea in 1994–1995, the transport rate from the North Sea and northwards with the NwCC and WSC slowed markedly, in apparent correspondence with variations in the North Atlantic Oscillation (NAO) winter index.