PLUTONIUM FROM EUROPEAN REPROCESSING OPERATIONS - ITS BEHAVIOR IN THEMARINE-ENVIRONMENT

Controlled releases of low-level liquid wastes from European nuclear f uel reprocessing operations have resulted in a significant addition to the total inventory of plutonium in the seas of the northern hemisphe re. The principal source has been the Sellafield (Windscale) site in t he U.K. discharging into the Irish Sea (590 TBq Pu-239.240 since 1952) . This has provided a unique opportunity to investigate the behaviour of plutonium in a dynamic coastal environment, taking advantage of env ironmental concentrations several orders of magnitude higher than thos e resulting from global fallout; ir has, for example, allowed oxidatio n state, colloidal and chemical associations to be studied. A small fr action of these particle-reactive radionuclides can be traced for over 2500 km from the source. However, most of the plutonium (similar to 9 0%) resides in the seabed and intertidal sediments of the eastern Iris h Sea. Here it is subject to a complex interaction of physical, chemic al and biological processes, covering a wide range of space-and time-s cales. Substantial reductions in the discharge rate have occurred with in the past decade. In many cases, this has been accompanied by reduct ions in environmental concentrations. But previous, much higher discha rges represent an important legacy-at some sites sediment inventories are still increasing-and the ultimate ''sink'' for Sellafield-derived plutonium cannot be predicted with confidence.