| Summary: | Background Technetium-99 (99Tc), produced in the fission of 235U, 238U and 239Pu, is a beta-emitter (Eβmax = 293keV) with a half-life (t) of 2x105 years. The main sources of 99Tc are global fallout from nuclear weapons testing and discharges from reprocessing plants for spent nuclear fuel in North-Western Europe [1]. Global fallout resulted in a 99Tc concentration in the North Atlantic of ~ 5 mBq m-3 [2]. Radioactive wastes have been discharged from the reprocessing plants Sellafield (Cumbria, UK) (Fig.1), into the Irish Sea and La Hague (France) into the English Channel since 1952 and 1966 respectively [3]. In seawater, 99Tc exists at the soluble pertechnetate ion, TcO4-, and is transported by ocean currents from Cumbria via the North Channel, across the North Sea to the coast of Norway, where it is carried northwards by the Norwegian Coastal Current. Between 1981 and 1993, discharges of 99Tc from Sellafield were below 7 TBq/a (BNFL, 1981-1996). In the first quarter of 1994 the discharges significantly increased with the opening of the new waste treatment plant Enhanced Actinide Removal Plant (EARP), and subsequent treatment of a backlog of radioactive wastes stored at the site [4;5]. According to BNFL, 72 TBq of
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