AU0019573 Tracing Discharges of Plutonium and Technetium from Nuclear Processing Plants by Ultra-sensitive Accelerator Mass Spectrometry. L.K. FIFIELD, P.A. HAUSLADEN, R.G. CRESSWELL and M.L. DI TADA Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia J.P. DAY and R.S. CARLING Department of Chemistry, University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom. D.H. OUGHTON Laboratory for Analytical Chemistry, Agricultural University of Norway, Oslo, Norway ABSTRACT Historical discharges of plutonium from the Russian nuclear processing plant at Mayak in the Urals have been traced in sediments, soils and river water using ultra-sensitive detection of plutonium isotopes by accelerator mass spectrometry (AMS). Significant advantages of AMS over other techniques are its very high sensitivity, which is presently ~106 atoms (1 uBq), and its ability to determine the 24OPu/239Pu ratio. The latter is a sensitive indicator of the source of the plutonium, being very low (1-2%) for weapons grade plutonium, and higher (~ 20%) for plutonium from civil reactors or fallout from nuclear weapons testing. Since this ratio has changed significantly over the years of discharges from Mayak, a measurement can provide important information about the source of plutonium at a particular location. Similar measurements have been performed on samples from the Kara Sea which contains a graveyard of nuclear submarines from the former Soviet Union. AMS techniques have also been developed for detection of "Tc down to levels of a few femtograms. This isotope is one of the most prolific fission products and has a very long half-life of 220 ka. Hundreds of kg have been discharged from the nuclear reprocessing plant at Sellafield in the UK. While there may be public health issues associated with these discharges which can be addressed with AMS, these discharges may also constitute a valuable oceanographic tracer experiment in this climatically-important region of the world's oceans. Applications to date have included a human uptake study to assess long-term retention of "Tc in the body, and a survey of seaweeds from northern Europe to establish a baseline for a future oceanographic study. 152.