Abstract:
Water flow is an essential factor in the sealability of any underground cavern,
including those for nuclear waste disposal, and is significantly affected by the
permeability of the rock. The permeability of rocks is affected by various
factors, including stress and temperature. The rock stress changes by excavating
a cavern, and rock temperature changes by decay heat from nuclear waste, and
the temperature change induces thermal stress. Therefore, water flow around
such caverns must be evaluated considering the effects of stress and
temperature. Numerical analyses of water migration around underground
nuclear waste disposal caverns have been carried out. However, studies
considering the stress and temperature-dependent permeability may not be
published yet. To demonstrate the necessity to consider the stress and
temperature-dependency in permeability, equations that represent the postfailure permeability as a function of average effective stress and temperature
were proposed. The water inflow was numerically calculated for a simple
underground nuclear waste disposal cavern with or without stress and
temperature dependency which showed the significance of the dependency.
Also, the importance of rock types was demonstrated by considering the three
rocks of granite, sandstone, and tuff for a full-scale underground radioactive
disposal site for the stress and temperature-dependent permeability. A high
sealability could be expected for granite and sandstone but not for the tuff.
Introducing the stress and temperature-dependent permeability could
contribute to the thoughtful design of an underground repository for
radioactive waste disposal considering rock types.
