Influence of the arrangement of emplacement fields on the long-term safety of a salt dome repository

On the basis of concept A, representing combined borehole and gallery emplacement, the arrangement of the hot field bearing LWR fuel elements and of the cold field bearing intermediate-level radioactive wastes and HTR fuel elements were exchanged. In addition, the influence of the technical barrier ''dam'' on radionuclide release was studied. Using the reference values of the input parameters, no radionuclide release was recorded, irrespective of the arrangement of the emplacement fields. The variants with a higher dam permeability, however, show differences depending on the arrangement of the emplacement fields. If the hot field with LWR fuel elements is directly beside the central field, the driftway alongside this field is closed early by rock convergence, without any radiological consequences. If, however, the cold field with intermediate-level radioactive waste takes that place, brine penetrates into the emplacement sites. In the latter case, radionuclides are released entailing a dose commitment of 6.10-6 Sv/a. In general, it is more favourable, from the point of view of long-term safety, to arrange hot fields closer to the central field than cold fields. If the dams in the central field of the subsurface structures are neglected, in all studied cases radionuclide release was the consequence. Dose commitments here were in the range of 1.10-8 Sv/a to 6.10-5 Sv/a, with the high values being observed only when the values of dam permeability or the volume of limited brine inclusions were unfavourable. (orig./HP)