A natural cement analogue study to understand the long-term behaviour of cements in nuclear waste repositories: Maqarin (Jordan) |
| |
| Institution: | 1. Department of Earth Sciences, University of Toronto, Toronto M5S 3B1, Ontario, Canada;2. Department of Geography and Earth Science, Aberystwyth University, Wales SY23 3DB. UK;3. NASA Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91106, USA;4. Department of Geology, Anna University, Chennai, India;1. Portland State University, Geology, PO BOX 751, Portland, OR 97201, United States;2. Woods Hole Oceanographic Institution, Geology and Geophysics, 360 Woods Hole Rd., Woods Hole, MA 02543, United States;1. Applied Chemistry Department, Nuclear Research Center – Negev, P.O. Box 9001, Be''er Sheva 8419001, Israel;2. Geological & Environmental Sciences Department, Ben-Gurion University of the Negev, Be''er Sheva 653 84105, Israel;3. Geological Survey of Israel, 32 Yeshayahu Leibowitz St., Jerusalem 9371234, Israel;4. The Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235, USA |
| |
| Abstract: | The geological storage of nuclear waste includes multibarrier engineered systems where a large amount of cement-based material is used. Predicting the long term behaviour of cement is approached by reactive transport modelling, where some of the boundary conditions can be defined through studying natural cement analogues (e.g. at the Maqarin natural analogue site). At Maqarin, pyrometamorphism of clay biomicrites and siliceous chalks, caused by the in-situ combustion of organic matter, produced various clinker minerals. The interaction of infiltrating groundwater with these clinker phases resulted in a portlandite-buffered hyperalkaline leachate plume, which migrated into the adjacent biomicrite host rock, resulting in the precipitation of hydrated cement minerals.In this study, rock samples with different degrees of interaction with the hyperalkaline plume were investigated by various methods (mostly SEM-EDS). The observations have identified a paragenetic sequence of hydrous cement minerals, and reveal how the fractures and porosity in the biomicrite have become sequentially filled. In the alkaline disturbed zone, C-A-S-H (an unstoichiometric gel of Ca, Al, Si and OH) is observed to fill the pores of the biomicrite wallrock, as a consequence of reaction with a high pH Ca-rich fluid circulating in fractures. Porosity profiles indicate that in some cases the pores of the rock adjacent to the fractures became tightly sealed, whereas in the veins some porosity is preserved. Later pulses of sulphate-rich groundwater precipitated ettringite and occasionally thaumasite in the veins, whereas downstream in the lower pH distal regions of the hyperalkaline plume, zeolite was precipitated.Comparing our observations with the reactive transport modelling results reveals two major discrepancies: firstly, the models predict that ettringite is precipitated before C-A-S-H, whereas the C-A-S-H is observed as the earlier phase in Maqarin; and, secondly, the models predict that ettringite acts as the principal pore-filling phase in contrast to the C-A-S-H observed in the natural system. These discrepancies are related to the fact that our data were not available at the time the modelling studies were performed. However, all models succeeded in reproducing the porosity reduction observed at the fracture–rock interface in the natural analogue system. |
| |
| Keywords: | Natural analogue Nuclear waste repository Maqarin Cement Porosity Hyperalkaline plume Reactive transport model |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
