Safe in salt

The geologic history of the 'Germanic Basin', in which saline sediments were piled up in different strata over a period of nearly 100 million years, and the formation of 'salt deposits' as a consequence of tectonic movements (strata bends, dislocations of strata) in the north-west german region are described. As compact rock being 'harnessed' in the ground, mineral salt is completely impermeable to gases and liquids. Its plasticity prevents any formation of pores or crevasses resp. eliminates existing ones. This impermeable quality has been used technically for a long time in order to use solution-mined caverns for the storage of petroleum or gas without containers. Furthermore, for storing radioactive substances it is of particular importance that mineral salt has the highest thermal conductivity of all sedimentary rocks, so that a local heat up will be distributed quickly. All considerations on a safe storage stem from the fact that all actions take place within rock-mechanically homogeneous mineral salt. Bands of different rocks lead to discontinuities and may render a mechanical calculation impossible in some cases. A careful exploration of the internal structure of salt deposits is therefore one of the most important prerequisites for a safe storage of substances to be separated from the biosphere. (RB)