Research project MAW and HTR fuel element test storage in boreholes (MHV project). Emplacement and borehole sealing techniques (EBT part-project). Final report on project phase October 1, 1989 - December 31, 1992

The paper documents the working results of the third project phase from 1.10.89 to 31.12.92. At the beginning, the atmosphere in the repository borehole during the operational and post-operational phase is described. The borehole atmosphere is decisively influenced by gas and humidity releases from the waste forms and the solid rock salt, by the propagation of gases in the unfilled part of the borehole and in the part backfilled with salt grit, and by the permiabilities of the borehole lock and the solid bedrock. Hydrogen gas may be oxidized by an addition agent. The reference concept of borehole storage is the embedding of the waste forms in salt grit. The salt grit backfill required therefore is characterized, and pressure distribution in the backfill during storing of the forms in the borehole is modelled. Finally the flame extinguishing effect of salt grit is described. Safety considerations and a draft concept of a borehole backfill container complete the work of this project phase. (orig./HP)