The safety studies actually consider - in the normal evolution scenario - that no preferential path for the migration of radionuclides through shafts and underground galleries will exist. For this reason horizontal and vertical plugs will have to be installed in the disposal architecture. These plugs should have special characteristics (low hydraulic conductivity, impermeabilty for gas,...)

The on-going program RESEAL (final results planned for March 2005) studies the installation and the performance of a vertical plug. At the end of the program the suitability of a mixture of FoCa - clay powder and pellets as material for the plug should be confirmed. However, an installation, testing and eventual dismantling of a horizontal plug (in order to seal main and disposal galleries) have not yet been performed. It is clear that this test is not depending on the reference architecture as a disposal system will always consist of underground galleries that need to be sealed/plugged.