Effective diffusivity of the uranyl ion in a granite from Inada, Ibaraki, Japan

Abstract The effective diffusivity of uranium(VI) in Inada granite has been determined by through-diffusion. Experiments were performed at room temperature (20–25°C) in a 0.1 mol 1 −1 KCl solution where uranium is present predominantly as the poorly sorbing UO 2 2+ . An effective diffusivity ( D e ) of (3.6 ± 1.6) × 10 −14 m 2 s −1 was obtained, close to that for uranine (nonsorbing organic tracer), but one order of magnitude lower than those obtained for Sr 2+ and NpO 2 + , and two orders of magnitude lower than that obtained for I − . According to well established theory, a proportional relationship exists between D e and the diffusivity in the bulk of the solution ( D v ). The effective diffusivity obtained in granite was not proportional to D v . This agrees with results obtained for effective diffusivity in a Swedish granite. The ratio D e D v was found to be not constant but increased with D e or D v . This result suggests a limit to the application of the theory.