Deposition of calcium-silicate-hydrate gel on rough surface of granite from calcium-rich highly alkaline plume

Yuichi Niibori, Kyo Komatsu, Hitoshi Mimura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Cement-based materials used in the construction of the repository for high/low level radioactive wastes may produce a highly alkaline calcium-rich groundwater (plume). The Ca ions react with soluble silicic acid, depositing calcium-silicate-hydrate (CSH) gel on the surfaces of the groundwater flow-paths and decreasing the permeability of the bedrock. Such a decrement of permeability may play a role in retarding the migration of radionuclides. In this study, the deposition behavior in a fracture was experimentally examined by using a micro flow-cell consisting of silicon plate (including a slit (60 mmx5 mm, or 60 mmx2 mm)) and granite-chip. The initial equivalent-aperture based on the square law was estimated in the range of 26 urn to 45 μn from the flow test of pure water. In the experiments, a Ca(OH)2 solution of 6.36 mM (pH: 12.2 to 12.5, including NaOH) was continuously injected into the flow system at a constant flow rate of 1 or 2 ml/h. The solution flowed on the surface of the granite-chip. In this study, we prepared two kinds of chips that differed in the treatment of the surface. One chip was roughly ground with #2000 sandpaper (hereinafter referred to as rough surface) and another was polished to mirror-like surface. As a result, on the rough surface the deposits of CSH gel appeared along flow-channels across mineral grain-boundaries, while the deposits on the mirror-like surface were relatively uniform. Furthermore, the permeability in the case of rough surface became smaller than that in the case of mirror-like surface, showing the repeats of rapid decrement and increment due to the relatively large roughness of the surface. In order to estimate the decrement degrees of permeability, a simple, one-dimensional mathematical model is proposed in this study.

Original languageEnglish
Title of host publicationScientific Basis for Nuclear Waste Management XXXV
Pages349-354
Number of pages6
DOIs
Publication statusPublished - 2012
Externally publishedYes
Event2012 MRS Spring Meeting - San Francisco, CA, United States
Duration: 2012 Apr 92012 Apr 13

Publication series

NameMaterials Research Society Symposium Proceedings
Volume1475
ISSN (Print)0272-9172

Other

Other2012 MRS Spring Meeting
CountryUnited States
CitySan Francisco, CA
Period12/4/912/4/13

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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