Influence of Photochemical Reactions Upon the Redox Cycling of Pu Between the Solid and Liquid Phases in Seawater

摘要

Exchange processes at the sediment-water interface can significantly influence the migration and transport of radionuclides in aquatic environments. Laboratory experiments were carried out to assess the influence of photochemical reactions and temperature upon the dissolution of ~(239+240)Pu from, and uptake of ~(238)Pu(Ⅴ) tracer by, Irish Sea sediment in seawater. A low energy fluorescent tube with output of UV light was used to irradiate sample suspensions. Equilibrium of Pu(Ⅳ) species was rapidly attained (< 1 hour) between dissolved and particulate phases. Variations in temperature, within the range 4―25°C, did not appear to significantly effect the remobilisation of Pu(Ⅳ) species, although it is possible that light irradiation resulted in reduction of Pu(Ⅴ) to Pu(Ⅳ) in the dissolved phase. In contrast, the dissolution of Pu(Ⅴ) species from, and uptake of Pu(Ⅴ) species by, particulate material increased over the duration of these experiments. Furthermore, Pu(Ⅴ) remobilisation and Pu(Ⅴ) uptake increased concomitant with temperature and UV irradiation due to simultaneous promotion of oxidation and reduction reactions upon the surface of the suspended particles.