Determining the Transport Properties of Rock Specimens Using an Improved Laboratory Through-Diffusion Technique

Abstract

The safe disposal of radioactive nuclear wastes using multi-barrier systems requires a good understanding of their transport properties in geological materials. When groundwater flow is very slow, the most important mechanisms of transport and retardation are diffusion through and sorption onto geological materials, and an evaluation of relevant parameters, particularly the effective diffusion coefficient and rock capacity factor (or sorption coefficient), is of fundamental importance to any safety assessment. Although laboratory diffusion tests can be used to determine these two parameters, conventional through-diffusion testing has some limitations, such as the need for a relatively long test time, cumbersome test procedures and the possibility of errors due to differences between analytical assumptions and actual test conditions. In this paper, we offer a rigorous solution to the through-diffusion test. Boundary conditions are improved by taking into account concentration changes in both the source and the measurement cells. A companion approach for back-calculating the effective diffusion coefficient and rock capacity factor is also proposed. The effectiveness and advantages of this improved technique are demonstrated using experimental data derived from a sedimentary rock sample taken from a research site in Japan.

Diffusion and sorption of neptunium(V) in compacted montmorillonite: effects of carbonate and salinity

“…These curves were analyzed by the method proposed by Tachi et al [8], which is based on the analytical solution of Eq. (1) derived by Zhang et al [16] and multiple curve analysis. D e and α were determined by simultaneous fitting for two curves.…”

Matrix diffusion and sorption of Cs+, Na+, I– and HTO in granodiorite: Laboratory-scale results and their extrapolation to the in situ condition

“…The breakthrough curves in the outlet reservoir indicate a slower increase in concentration with time as sample thickness increases. Although the tracer depletion in the inlet reservoir was not significant, the tracer-depletion and breakthrough curves were fitted by a multiple curve analysis method Tachi et al, 2011) based on a rigorous analytical solution (Hsieh et al, 1981;Zhang et al, 2006). D e and α parameters were determined by simultaneous fitting of each of the two curves.…”

Diffusion and sorption of Cs+, I− and HTO in samples of the argillaceous Wakkanai Formation from the Horonobe URL, Japan: Clay-based modeling approach

“…Assuming linear sorption, Eq. (4) was first solved using the analytical solution derived by Zhang et al (2006) and Hsieh et al (1981) for through-diffusion experiments with variable tracer concentrations in the reservoirs. D e and a parameters were determined by simultaneous fitting for these two curves.…”