Sorption of Radionuclides Onto Cement Materials Altered by Hydrothermal Reaction
- PDF / 455,041 Bytes
- 8 Pages / 386.64 x 620.1 pts Page_size
- 88 Downloads / 247 Views
D. SUGIYAMA and T. FUJITA Central Research Institute of Electric Power Industry (CRIEPI) 2-11-1, Iwado-Kita, Komae, Tokyo 201-8511, JAPAN
ABSTRACT
The sorption of radionuclides onto cement materials is a very important parameter when considering the release of radionuclides from radioactive wastes. Once the composition or crystallinity of the constituent minerals of a cement material is changed by alteration in the disposal environment, its sorption ability might be affected. In this study, the effect of hydrothermal alteration on the sorption properties of two cement grouts and Calcium Silicate Hydrogels (CSH-gels) is investigated by using the batch sorption technique. In the case of strontium (a model cation) sorption, the distribution ratio for Ordinary Portland Cement (OPC) and OPC/Blast Furnace Slag blended cement (OPC/BFS) decreased as the alteration temperature increased. This is mainly caused by the decrease of sorption onto CSH-gel which is a constituent of cement materials. In the case of selenium (selenite, a model anion) sorption, the distribution ratio decreased as the alteration temperature increased for OPC treated in both distilled water and groundwater, and for OPC/BFS in groundwater. This is attributed to the decomposition of ettringite which sorbs anions. The distribution ratio for OPC/BFS in distilled water increased as the alteration temperature increased, although ettringite decomposed. This is attributed to the formation of monosulphate which also sorbs anions. These results show that the hydrothermal alteration of cement mineral phases in a disposal environment may cause changes which could increase or decrease the sorption of radionuclides onto cements depending on the cement composition and radionuclide speciation. INTRODUCTION
Cement is a potential waste packaging and backfilling material for the disposal of radioactive waste. It is expected to provide both physical and chemical containment. In particular, the sorption of radionuclides onto cement materials is a very important parameter when considering the release of radionuclides from radioactive wastes [I]. For the long term, in the geological disposal environment, cement materials will be altered by, for example, dissolution, chemical reaction with ions in the groundwater, and hydrothermal reaction. Once the composition or crystallinity of the constituent minerals of cement has been changed by these processes, the sorption ability might be affected. However, the mechanisms of cement alteration and radionuclide sorption onto cements are not yet fully understood. In the present work, the sorption of radionuclides onto hydrothermally altered cements and Calcium Silicate Hydrogels (CSH-gels) is investigated. Hydrated Ordinary Portland Cement (OPC), OPC/Blast Furnace Slag blended cement (OPC/BFS) and CSH-gels were altered by heating at temperatures up to 70'C in distilled water or synthetic groundwater. The sorption of strontium (a model cation) and selenium (selenite, a model anion) onto these altered cements and minerals was then meas
Data Loading...
