| dc.description.abstract | To assure the isolation of high level radioactive wastes from human environment, the multiple barrier deep geologic disposal is considered as the most suitable approach. The major barrier unit consists of waste package, buffer material, backfill material and host rock. The waste package in the disposal could deteriorate if in contact with underground water. The nuclides might release and endanger the environment. The capability in retardation and adsorption of the nuclides is one of critical elements when choosing buffer materials.
This research is to reckon the accuracy of the parameter in mass transport. The result shows that the slope of an effluent curve is the best method to figure out the dispersion coefficient(D) and the retardation factor(Rd). Zhisin clay was used as test material. A series of column tests were conducted, and the results are (1)before conducting a column test, a 14-day period of saturating and drip washing of the testing material is required; (2)under a high hydraulic gradient (285) the hydraulic conductivity was found to be 3.4×10-8 cm/s, which is judged to be low in permeation; (3)electrical conductivity testing system can be used effectively to monitor the near-field of deep geologic disposal site and to monitor the testing time of column test.
The column test was aimed at understanding the effects of the type of ion in solution, the concentration of the ion, and the dry intensity of Zhisin clay on the testing material in the mass transport process. It was found that: (1)the sodium ion’s dispersion coefficient is higher than calcium ion; and the calcium ion is easy to react with other low-affinity ion of the bentonites, which makes the retardation of the calcium ion more noticeable; (2) if the concentration is lower, the transport of calcium ion would be more noticeable; (3)there are more exchangeable calcium ion in Zhisin clay, thus exhibiting lower exchangeable rate for calcium. | en_US |