Chemical speciation and environmental behaviour of 60Co discharged from a nuclear establishment

Abstract A radiochemical procedure has been developed which permits the separation and measurement of two different oxidation states of cobalt radionuclides (CoII and CoIII). The method has been applied to study the behaviour of 60 Co in authorized discharges from the Steam Generating Heavy Water Reactor at Winfrith (UK Atomic Energy Authority). Laboratory experiments suggested that 60 Co discharged in the form of 60 CoIII picolinate is not immediately reduced to the divalent species. Furthermore, although a significant fraction of both species was soluble in seawater, the particle reactivity tends to be more enhanced for 60 CoII than for 60 CoIII. Limited environmental investigations have so far indicated that both 60 CoII and 60 CoIII species are present and persist in seawater. Because of the relatively small difference in the solubility of the two forms insufficient evidence has, as yet, been obtained to confirm that the presence of the trivalent species significantly increases the mobility and dispersion of 60 Co arising from this discharge relative to sources such as Sellafield, which are assumed to discharge the radionuclide as 60 CoII. However, in the waters of Weymouth Bay and further afield there is a tendency for the proportion of 60 CoIII to increase with time and distance from the point of discharge.