High-level reprocessing waste package requirements for a deep borehole disposal facility to be mined in a salt dome

The ultimate disposal of high-level waste may entail waste package requirements that differ from or complement those originally specified for the immobilization process. Waste package requirements are presented for a disposal concept based on the use of deep boreholes, as in a Netherlands concept for a facility to be mined in a salt dome. Most attention is given to the rather stringent rock salt temperature limitations that were formulated in anticipation of the presence within the repository area of minor bands of K and/or Mg salts. For three different canister diameters a review is given of the variations in the high-level waste and the disposal-geometry parameters as calculated to be consistent with the predetermined maximum rock salt temperatures. Until another dry-drilling technique can be developed for drilling deep boreholes with a diameter larger than 35 cm, currently available dry-drilling technique limits the diameter of the canisters to about 30 cm. The canister construction and its wall thickness are discussed in relation to the stacking load and the rock pressure build-up around the emplaced canisters due to borehole convergence and a subsequent temporary excess of rock pressure due to thermal loading. Finally, it is argued that carefully developed deep borehole disposal in a salt dome involves no additional waste package requirements deriving from the generic safety assessment other than that the waste form should be solid. (author)