Parent-daughter equilibria in ocean arising out of disposal of solid radioactive wastes on the sea bed

One dimension diffusion model, incorporating geochemical elimination and reflection at ocean boundaries, is employed to show the differences in spatial and temporal distribution of parent and daughter radionuclides, produced in situ, due to the discharge of solid radioactive wastes on to the sea bed. Concentration of daughter is generally lower than that of parent in deep waters. Short-lived daughters (relative to parent) reach spatial equilibrium with parent for finite periods whereas long-lived daughters attain only a fraction of the parent activity. However, when the dumping operation is assumed to be for infinite period, the relative ratio of concentration of daughter to parent would reach value > 1 in surface waters irrespective of the half-lives of the daughter and the magnitude of this ratio increases with increase in half-life of the daughter relative to the parent. This is the result of steep vertical gradient for the parent due to the small physical half-life and more or less uniform concentration of long-lived daughter. Geochemical elimination rate, when becomes significant in the overall removal processes, controls this differential spatial gradient of daughter and parent. However, the integrated activity of daughter over the entire depth is equal to or less than the parent activity. (author)