Published online by Cambridge University Press: 21 March 2011
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.