A Comparative Study of the Speciation and Behaviour of Plutonium in the Marine Environment of Two Reprocessing Plants

Abstract

New data are presented which highlight to the behaviour of Pu upon discharge into the open sea from nuclear reprocessing plants at Sellafield and Cap La Hague and Sellafield. Specifically, certain physico-chemical characteristics of Pu in sea water and sea-bed sediments are shown to be independent of both the source and near-field environmental conditions. For example, in filtered sea water the discharge-normalized Pu concentrations are similar at both sites (ca. 20-40μΒςΓ' per GBq discharged). The oxidation state distribution of Pu is also similar, with Pu(V,VI) predominating. A significant fraction of the Pu(III,IV) present in filtered water is associated with > 1 kDa colloids. In each zone, tide energy would appear to control the long-range dispersion of Pu in both the filtered and particulate fractions.

A process-based model for the partitioning of soluble, suspended particulate and bed sediment fractions of plutonium and caesium in the eastern Irish Sea

“…The Colloidal and Suspended load compartments represent the fractions of plutonium dispersed in the water column (presumably as Pu 4þ ) as colloids (nano-particles and macromolecules in the 1 nm to 1 mm size range) or particles in suspension (operationally defined as those removable by 0.45 mm pore size membrane filtration). Finally, the Far field compartment represents the plutonium that is removed from the Sellafield coastal area through the processes of advection and dispersion, based on knowledge of the mean residence time of the plutonium in the area (Boust et al, 1996).…”

“…This is a complex series of reactions which has been fully described in Vives i Batlle (1993) but which can be modelled simplistically as a simple two-way flow 'reaction', based on data from Boust et al (1996). From Seawater_Pu_III_IV, (a) removal to the far field, (b) chemical oxidation of Pu (III, IV) to Pu (V, VI), and physical adsorption onto (c) colloidal matter, (d) suspended load and (e) surface sediment.…”

“…The mean residence time of plutonium in seawater in the Sellafield area is 29 days (Boust et al, 1996).…”

“…Therefore, the partitioning of plutonium between particulate and filterable forms should not have changed to any large extent throughout the period of EARP commissioning. Boust et al (1996) studied the oxidation of Pu (IV) tracer in seawater over a 30-day period, during which an oxidised phase Pu (V, VI) began to form. To deduce the reaction rates for Pu (III, IV) 4 Pu (V, VI), Boust et al (1996) data (Figure 1 of that publication) were extracted and a simple two-way flow model between two compartments (oxidised and reduced) was found to fit well with this information (r 2 ¼ 0.986, p ¼ 0.006).…”

Diagenetic reactivity of the plutonium in marine anoxic sediments (Cumbrian mud patch - eastern Irish Sea)

“…Most of the so-called conservative radionuclides are advected northwards and leave the Irish Sea via the North Channel [2], with a smaller proportion being dispersed southwards to the English Channel approaches [3]. In contrast, radionuclides having a strong affinity for sediment particles are quickly removed from the water column by scavenging processes [4][5][6] onto suspended particulate matter, and accumulate in fine-grain deposits. In the eastern Irish Sea, muddy sediments are confined to the Cumbrian Mud Patch, a large offshore mudflat lying parallel to the Cumbrian coast, off Sellafield, which acts as a very efficient sink for particle-reactive radionuclides, such as transuranics.…”