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According to the German radioactive waste management concept, high level radioactive canisters are to be disposed of in boreholes in deep geological salt formations. Small amounts of luids (gases and water) are released from the salt into the boreholes because of heating and irradiation of the salt. For reasons of safety, the borehole seals are to be designed in such a manner that an unacceptable increase of the borehole gas pressure and an uncontrolled release of gases and radionclides into the repository are avoided. These requirements seem contradictory in principle but have to be considered during the development of borehole seals.
The conditions of state in and around a disposal borehole have been analysed in detail in order to quantify the requirements of a borehole seal. Additionally, the suitability of different sealing materials has been analysed.
Crushed salt was identified as the most suitable material and model calculations have been performed to analyse the compaction and permeability behaviour of that material. According to these calculations, the crushed salt in the annulus of HLW disposal boreholes reaches the properties of the surrounding undisturbed rock mass within very few years.
For the necessary validation of the used models, two time-scaled in situ experiments have been designed by thermomechanical and hydraulical model calculations. It could be shown that representative repository long term conditions can be achieved within a time period of approximately eighteen months. s.

Additional information

Authors: ROTHFUCHS T, GSF-Institut für Tieflagerung, Braunschweig (DE);KRÖHN K-P, GSF-Institut für Tieflagerung, Braunschweig (DE);WIECZOREK K, GSF-Institut für Tieflagerung, Braunschweig (DE);PRIJ J, ECN-Stichting Energieonderzoek Centrum, Petten (NL);VAN DEN HORN B A, ECN-Stichting Energieonderzoek Centrum, Petten (NL);KROHN K-P, GSF-Institut fur Tieflagerung, Braunschweig (DE)
Bibliographic Reference: EUR 16928 EN (1996) 67pp., FS, ECU 10
Availability: Available from the (2)
ISBN: ISBN 92-827-7465-1; ISSN
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