Novel method for analyzing transport parameters in through-diffusion tests

Abstract

Buffer materials such as bentonite are vital for absorbing radionuclide leakage and retarding migration from radioactive waste canisters. The diffusion coefficient and the retardation factor are the predominant properties controlling the diffusion-reaction process in a buffer material. Diffusion experiments combined with Crank's graphical method are a well-established process for determining asymptotic diffusion coefficients. However, the inaccuracy of the diffusion coefficient that results from the subjective judgement of the late-time linear part of the cumulative concentration data in Crank's graphical method will deteriorate the estimate of the retardation factor. A novel parameter identification process based on an iterative and analytical method (PIPIAM) is proposed here to obtain the diffusion coefficients and porosity of bentonite using concentration data. The results of PIPIAM and the graphical method are compared through an error analysis of concentration. The results show that PIPIAM outperforms the graphical method in terms of the error reduction of the concentration and the uncertainty decrease of the estimated parameters. The proposed method is thus a good alternative for acquiring transport parameters for use in safety assessments of nuclear waste repositories.

Keywords: Analytical solution; Diffusion coefficients; Iterative process; Parameter inversion; Through-diffusion test.