CHEMICAL SPECIATION AND ENVIRONMENTAL BEHAVIOR OF CO-60 DISCHARGED FROM A NUCLEAR ESTABLISHMENT

A radiochemical procedure has been developed which permits the separat ion and measurement of two different oxidation states of cobalt radion uclides (CoII and CoIII). The method has been applied to study the beh aviour of Co-60 in authorized discharges from the Steam Generating Hea vy Water Reactor at Winfrith (UK Atomic Energy Authority). Laboratory experiments suggested that Co-60 discharged in the form of Co-60III pi colinate is not immediately reduced to the divalent species. Furthermo re, although a significant fraction of both species was soluble in sea water, the particle reactivity tends to be more enhanced for Co-60II t han for Co-60III. Limited environmental investigations have so far ind icated that both Co-60II and Co-60III species are present and persist in seawater. Because of the relatively small difference in the solubil ity of the two forms insufficient evidence has, as yet, been obtained to confirm that the presence of the trivalent species significantly in creases the mobility and dispersion of Co-60 arising from this dischar ge relative to sources such as Sellafield, which are assumed to discha rge the radionuclide as Co-60II. How-ever, in the waters of Weymouth B ay and further afield there is a tendency for the proportion of Co-60I II to increase with time and distance from the point of discharge.