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surface. The reference repository is situated 540 m below the cap-rock. A diagram of the repository
structure for HLW and MLW is shown in Figure II.32. After closure, the repository structure will be
filled-up with brine contained by dams with permeabilities of 7×10 -16 m 2 . In the German concept of
radioactive waste disposal, heat producing waste will be disposed of in bore holes, and non-heating
wastes in chambers. About 58 000 canisters HLW (10 454 m 3 ) corresponding to a nominal initial
quantity of 73 000 tHM spent fuel will be disposed of. Feed sludges and cladding wastes totalling
80 000 m 3 will accompany the HLW in the repository structure. The most important safety feature is the
convergence of the salt towards the cavities created for the emplacement of the waste.
Figure II.32 Reference repository in salt formations in the Gorleben salt dome
In the framework of the EVEREST project [194], several scenarios have been investigated:
the convection-diffusion scenario, the cavern convection scenario and the uplift scenario.
The calculations show that the maximum dose generated according to the convection-diffusion
scenario does not exceed 0.7 µSv/year after 20 000 years. The following nuclides are responsible for the
bulk of the radiological burden: 79 Se, 129 I, 135 Cs, 237 Np and its daughter products. The peak in annual
dose ranges from 6 000 years for 129 I through 30 000 years for 79 Se to 100 000 years for 237 Np and
finally to 200 000 years for 99 Tc and 135 Cs. The highest annual dose due to 237 Np amounts to
0.12 µSv/year at the peak release. The parameter uncertainties involved in the calculations are
predominantly related to the geophysical conditions (sorption, permeability-porosity) prevailing during
the elapsed time period. Figure II.33 shows the evolution of the dose rates for the most significant
radionuclides.
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