Photochemical dissolution of radionuclides from marine sediment

Laboratory experiments were carried out to assess the role of photochemical reactions upon the dissolution of ^{239 + 240}pu and ²⁴¹Am from marine sediment in sea water. Supplementary information was obtained by comparing their behaviour with that of ⁵⁴Mn under similar experimental conditions. Irradiation from natural sunlight resulted in more than a ten-fold increase in the extent of ^{239 + 240}Pu desorption relative to that observed in the dark. Remobilisation of ⁵⁴Mn from sediment was also enhanced by natural sunlight, albeit to a lesser extent than ^{239 + 240}Pu, whilst the behaviour of ²⁴¹Am was largely unaffected. Data for concentrations of dissolved ^{239 + 240}Pu(IV) and ^{239 + 240}Pu(V) species showed that only the oxidised form was significantly affected by irradiation, 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 investigations indicated ^{239 + 240}Pu photooxidation (hence desorption) was a function of both light intensity and wavelength. Remobilisation decreased concomitant with light intensity but increased as the wavelength decreased. Similar trends were observed for photoreduction of ⁵⁴Mn, although differences were less pronounced than those observed for ^{239 + 240}Pu.