Bentonite has been considered as a candidate buffer
material for the disposal of HLW because of its low
permeability, high sorption capacity, self sealing characteristics, and durability in a natural environment
(Smith, 1980; Cho et al., 1999a). The highly compacted
bentonite blocks, which are applied in the deposition
holes, have a tremendous swelling potential due to the
low original water content of about 10 wt.%. The compacted
bentonite blocks will be saturated by drawing
moisture from the surrounding host rock although the
bentonite blocks will not be completely saturated within
a considered design life of the buffer. The saturated
bentonite possesses a high swelling pressure and it is not
initially in a mechanical equilibrium with the confining
rock and groundwater. The swelling of the bentonite
may also cause a penetration of the bentonite into open
rock fractures, which is hereafter called an intrusion.