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Reactive transport modeling of grout-rock interaction at the ONKALO site

Technical Report:

Abstract

Grouting of water-conducting fractures with low-alkali cement is foreseen for the potential future repository for spent nuclear fuel in Finland (ONKALO site). A possible consequence of the interaction between groundwater and grout is the formation of high pH solutions which will be able to react with the host rock (gneisses) and alter its mineralogy and porosity. A reactive transport modeling study of this possible alteration has been conducted. First, the hydration of the low-alkali cementitious grout has been modeled, using results from the literature as a guide. The hydrated cement is characterized by the absence of portlandite and the presence of a C-S-H gel with a Ca/Si ratio about 0.8 after tens of years (Ca/Si is about 1.7 in Ordinary Portland Cement). Afterwards, a one-dimensional system simulating the contact between a grouted section of a fracture and the gneiss has been studied. Diffusion is the only solute transport mechanism in this case. The results from the simulations show a very fast (days to tens of days) sealing of porosity at the rock-grout interface. The precipitation of C-S-H, and also ettringite in some cases, is responsible for this fast sealing of porosity. The mixing by diffusion of a high-pH Carich solution  More>>
Authors:
Soler, J M [1] 
  1. Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona (Spain)
Publication Date:
Oct 15, 2010
Product Type:
Technical Report
Report Number:
POSIVA-WR-10-73
Subject:
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; RADIOACTIVE WASTE DISPOSAL; UNDERGROUND DISPOSAL; GEOLOGIC FRACTURES; CEMENTS; INJECTION; SIMULATION; PH VALUE; LIQUID FLOW; GROUND WATER; GROUTING; DIFFUSION; POROSITY; ROCKS
OSTI ID:
1010732
Research Organizations:
Posiva Oy, Helsinki (Finland)
Country of Origin:
Finland
Language:
English
Other Identifying Numbers:
TRN: FI1104006
Availability:
Available in fulltext at http://www.posiva.fi/files/1480/WR_2010-73_web_rev.pdf or as a soft back edition from Posiva Oy, Olkiluoto, 27160 Eurajoki, Finland, tel. +358-2-837231
Submitting Site:
FIN
Size:
63 p. pages
Announcement Date:
Apr 11, 2011

Technical Report:

Citation Formats

Soler, J M. Reactive transport modeling of grout-rock interaction at the ONKALO site. Finland: N. p., 2010. Web.
Soler, J M. Reactive transport modeling of grout-rock interaction at the ONKALO site. Finland.
Soler, J M. 2010. "Reactive transport modeling of grout-rock interaction at the ONKALO site." Finland.
@misc{etde_1010732,
title = {Reactive transport modeling of grout-rock interaction at the ONKALO site}
author = {Soler, J M}
abstractNote = {Grouting of water-conducting fractures with low-alkali cement is foreseen for the potential future repository for spent nuclear fuel in Finland (ONKALO site). A possible consequence of the interaction between groundwater and grout is the formation of high pH solutions which will be able to react with the host rock (gneisses) and alter its mineralogy and porosity. A reactive transport modeling study of this possible alteration has been conducted. First, the hydration of the low-alkali cementitious grout has been modeled, using results from the literature as a guide. The hydrated cement is characterized by the absence of portlandite and the presence of a C-S-H gel with a Ca/Si ratio about 0.8 after tens of years (Ca/Si is about 1.7 in Ordinary Portland Cement). Afterwards, a one-dimensional system simulating the contact between a grouted section of a fracture and the gneiss has been studied. Diffusion is the only solute transport mechanism in this case. The results from the simulations show a very fast (days to tens of days) sealing of porosity at the rock-grout interface. The precipitation of C-S-H, and also ettringite in some cases, is responsible for this fast sealing of porosity. The mixing by diffusion of a high-pH Carich solution from the grout and a Si-rich solution from the rock (plagioclase dissolution) causes this precipitation. Finally, calculations have simulated the interaction between flowing water and grout and the formation of an alkalinity plume, which flows beyond the grouted section of the fracture. The calculations include the hydration and simultaneous leaching of the grout through diffusive exchange between the porewater in the grout and the flowing water in the fracture. The formation of an alkaline plume is extremely limited when the low-pH grout is used. Even when using a grout with a lower silica fume content, the extent and magnitude of the alkaline plume is rather minor. These results are in qualitative agreement with monitoring at ONKALO. (orig.)}
place = {Finland}
year = {2010}
month = {Oct}
}