Won Jin Cho

Contribution of minerals to the sorption of U(VI) on granite

Summary Batch sorption experiments of U(VI) onto the surfaces of granite rock were carried out. The distribution of the sorbed U(VI) on crushed granite particles was investigated via a sequential chemical extraction method to quantify the amount of U(VI) sorbed on the mineral phases and by X-ray diffraction characterization of dried samples of the remaining minerals after each extraction step to determine the significant mineral phases that sorb U(VI). Chlorite among the constituent minerals, even though being present in a small amount, is assumed to contribute to the strong U(VI) sorption and most of the sorbed U(VI) was weakly bound to the granite surfaces. However, a discriminative amount of the sorbed U(VI) on granite particles was difficult to desorb, in particular, when sorption took place in the alkaline region. The distribution of the sorbed U(VI) both on the fresh intact surface and on the natural fracture surface was also investigated by a X-ray image mapping technique. The result shows that dominant minerals hosting the majority of the sorbed uranium are mica for the intact surface of granite and chlorite for the fracture surface of the granite.

Effect of Dry Density on Sr-90 Diffusion in a Compacted Ca-Bentonite for a Backfill of Radioactive Waste Repository

Abstract The transport of radionuclides in compacted bentonite is dominated by the diffusion process. The dry density is an important factor in the diffusion of radionuclides through the compacted bentonite. Through-diffusion tests were performed to investigate the effect of dry density on Sr-90 diffusion. In the diffusion tests the sample used was a bentonite taken from the southeastern area of Korea and the experimental solution was synthetic groundwater spiked with a tracer of Sr-90 (as 90 SrCl 2 ). The dry density was adjusted in the range of 1.0–1.7 Mg/m 3 . The distribution coefficient of Sr-90 in the compacted bentonite was much lower than that obtained by a batch test. The formation factor and porosity of the compacted bentonite were decreased with increasing dry density. The apparent and effective diffusion coefficients of Sr-90 were in the range of 1.14 × 10 −12 –1.20 × 10 −12 m 2 /s, 1.81 × 10 −11 –1.11 × 10 −11 m 2 /s, respectively, and decreased with increasing dry density of compacted bentonite. It was found for Sr-90 that the higher the dry density increases, the more significant the surface diffusion, as compared with the pore diffusion. The results obtained will be used as basic data for the safety assessment of a repository.