Investigations concerning the mechanical load on waste packages in vertical repository boreholes

The current concept for the planned Gorleben repository provides for the final disposal of high activity waste and intermediate level waste of the upper activity category according to the borehole technique (Barnet, 1994). For this purpose, the packages are lowred from the floor of drifts at 800 m depth into 300 m deep boreholes. Any cavities left between the packgages and the borehole wall are backfilled with crushed salt so that the packages are completely embedded in and covered by crushed salt. This type of emplacement constitutes the current reference concept for the borehole technique in which crushed salt has to fulfil the following functions. Embedding of the waste packgages in crushed salt limits the stacking forces acting on the packages owing to load diversion to the borehole wall. Complete backfilling with crushed salt of the remaining cavities prevents uncontrolled dispersion of radiolytic hydrogen and 85Kr by convection into the upper borehole section not yet filled. The danger of propagating flame fronts due to radiolytically formed hydrogen in the presence of local ignition sources in prevented since crushed salt acts as a flame barrier