2003 Fiscal Year Final Research Report Summary
Effects of cement and iron corrosion products on the durability of buffer material in geological disposal of HLW
| Project/Area Number |
13680584
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Nuclear engineering
|
|---|
| Research Institution | Hokkaido University |
|---|
Principal Investigator |
SATO Seichi Hokkaido University, Graduate School of Eng., Professor, 大学院・工学研究科, 教授 (40117122)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
KOZAKI Tamotsu Hokkaido University, Graduate School of Eng., Assoc.Prof., 大学院・工学研究科, 助教授 (60234746)
|
|---|
| Project Period (FY) |
2001 – 2003
|
| Keywords | radioactive waste / cement / bentonite / iron corrosion products / geological disposal / diffusion |
|---|
| Research Abstract |
For the safety assessment of the geological disposal of high-level radioactive waste, a fundamental study on the long-term durability of bentonite buffer was made from the viewpoint of the alterations of Na-bentonite that would occur after disposal.
Fe-bentonite is one of alteration products caused by the corrosion of overpack. In this study, Fe-bentonite was prepared from Na-bentonite in an oxygen-free glove-box by contacting Na-bentonite with FeCl_2 solution, and characterized by various analytical methods such as selective dissolution method, mossbauer spectroscopy and X-ray diffraction method. An oxidized Fe-bentonite sample was prepared by exposing Fe-bentonite to air, and also characterized in the same way. It was found that divalent cations, Fe^<2+>, were the predominant exchangeable cations in Fe-bentonite, and they were gradually oxidized when the sample was exposed to air. In batch sorption experiments, the higher sorption coefficients of Se(IV) and Se(VI) were obtained for Fe-bentonite and oxidized Fe-bentonite than for Na-type.
Another alteration product is Ca-bentonite that would be generated by Ca^<2+> ions from the dissolution of cement materials in a waste repository. In this study, apparent diffusion coefficients of Na^+ and Ca^<2+> were determined for the mixture samples of Na-and Ca-bentonite at various diffusion temperatures. The salinity effect on the diffusion coefficient of Na^+ ions was also studied for Na-bentonite. It was indicated that the effects of Ca-bentonite and salinity on the apparent diffusion were not remarkable. However, significant effects of the salinity on the activation energy for diffusion were found. The change in the activation energy can be explained by the diffusion model in which the predominant diffusion process is considered to change as the salinity increases.
|
