Affiliation(s)
Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Sendai 9808579, Japan
ABSTRACT
Na-type bentonite is
commonly used as a tunnel backfilling material to prevent groundwater and
radionuclide migration during the construction of a geological disposal system
for high-level radioactive waste in Japan. However, host rock fractures with
strong water flow can develop groundwater paths in the backfilling material.
Especially, the alteration to Ca-type bentonite causes degradation of the
barrier performance and accelerates the development of groundwater paths.
Additionally, using cementitious materials gradually changes pH between 13 and
8. High alkaline groundwater results in high solubility of silicic acid;
therefore, silicic acid is eluted from the host rock. Downstream, in the low
alkaline area, the groundwater becomes supersaturated in silicic acid. This
acid is deposited on Ca-type bentonite, thus leading to the clogging of the
groundwater paths. In the present study, we investigate the silicic acid
deposition rate on Ca-type bentonite under 288-323 K for depths greater or
equal to 500 m. The results indicate that temperature does not affect the
silicic acid deposition rate up to 323 K. However, in this temperature range,
the deposition of silicic acid on Ca-type bentonite in backfilled tunnels
results in clogging of the flow paths.
KEYWORDS
Supersaturated
silicic acid, Ca-type bentonite, backfilling material, apparent deposition rate
constant, geological disposal system, flow paths.
Cite this paper
References