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Published online by Cambridge University Press: 25 February 2011
This paper describes experiments and analyses conducted to determine the range of apparent diffusion coefficients of lead diffusing from an intentionally perforated lead-matrix titanium-shell container into a compacted 1:1 (by dry mass) silica-sand/sodium-bentonite buffer mixture saturated with Standard Canadian Shield Saline Solution at 363 K. Analysis of the experimental data using a single apparent diffusion coefficient could not explain the findings. A possible explanation of the behaviour is presented here. It uses a 2–D finite-element model with six lead species having six different apparent diffusion coefficients. The model can explain the data satisfactorily. Sixty-three percent of the source concentration consisted of slow-moving species, with an apparent diffusion coefficient of 10-15 m2 /s, whereas the fastest species, with an apparent diffusion coefficient of 10-10 m2 /s, constituted only three percent of the source concentration.