Determining the Transport Properties of Rock Specimens Using an Improved Laboratory Through-Diffusion Technique
- PDF / 140,106 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 154 Views
Determining the Transport Properties of Rock Specimens Using an Improved Laboratory Through-Diffusion Technique M. Zhang*, M. Takeda and H. Nakajima Research Center for Deep Geological Environments National Institute of Advanced Industrial Science and Technology Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan *[email protected]
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.
INTRODUCTION The safe disposal of radioactive nuclear wastes using natural and/or engineering barriers, i.e., multi-barrier systems, requires a good understanding of their transport properties in geological materials. Diffusion through and sorption onto geological materials are the most important mechanisms of transport and retardation when groundwater flow is very low [1,2], and an evaluation of relevant parameters, in particular the effective diffusion coefficient and rock capacity factor (or sorption coefficient), is of crucial significance for the safety assessment. Laboratory diffusion testing is a well-established and widely adopted technique for characterizing the transport properties of geological materials. Although there are several types of diffusion test, such as the in-diffusion test, the out-diffusion test, the reservoir depletion test and the through-diffusion test, currently available, the through-diffusion test is the one that has been most extensively used for testing rock samples in relation to the geological disposal of radioactive nuclear wastes [1,3,4]. This may be due to the fact that 1) the effective diffusion coefficient rather than the apparent diffusion coefficient can be directly obtained from a through-diffusion test, and that 2) it is not necessary to section or slice the specimen, a relatively cumbersome procedure that entails grindin
Data Loading...
