Plutonium from European reprocessing operations — Its behaviour in the marine environment

Controlled releases of low-level liquid wastes from European nuclear fuel reprocessing operations have resulted in a significant addition to the total inventory of plutonium in the seas of the northern hemisphere. The principal source has been the Sellafield (Windscale) site in the U.K. discharging into the Irish Sea (590 TBq 239,240Pu since 1952). This has provided a unique opportunity to investigate the behaviour of plutonium in a dynamic coastal environment, taking advantage of environmental concentrations several orders of magnitude higher than those resulting from global fallout; it has, for exampled, allowed oxidation state, colloidal and chemical associations to be studied. A small fraction of these particle-reactive radionuclides can be traced for over 2500 km from the source. However, most of the plutonium (not, vert, similar90%) resides in the seabed and intertidal sediments of the eastern Irish Sea. Here it is subject to a complex interaction of physical, chemical and biological processes, covering a wide range of space-and time-scales. Substantial reductions in the discharge rate have occurred within the past decade. In many cases, this has been accompanied by reductions in environmental concentrations. But previous, much higher discharges 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.