PHOTOCHEMICAL DISSOLUTION OF RADIONUCLIDES FROM MARINE SEDIMENT

Laboratory experiments were carried out to assess the role of photoche mical reactions upon the dissolution of Pu-239+240 and Am-241 from mar ine sediment in seawater. Supplementary information was obtained by co mparing their behaviour with that of Mn-54 under similar experimental conditions. Irradiation from natural sunlight resulted in more than a ten-fold increase in the extent of Pu-239+240 desorption relative to t hat observed in the dark. Remobilisation of Mn-54 from sediment was al so enhanced by natural sunlight, albeit to a lesser extent than Pu-239 +240, whilst the behaviour of Am-241 was largely unaffected. Data for concentrations of dissolved Pu-239+240(IV) and Pu-239+240(V) species s howed that only the oxidised form was significantly affected by irradi ation, indicating remobilisation occurs as a result of photooxidation reactions. Further experiments were carried out using artificial light sources to establish the influence of wavelength. Data from these inv estigations indicated Pu-239+240 photooxidation (hence desorption) was a function of both light intensity and wavelength. Remobilisation dec reased concomitant with light intensity but increased as the wavelengt h decreased. Similar trends were observed for photoreduction of Mn-54, although differences were less pronounced than those observed for. Pu -239+240.